Metals

17 pages, 3795 KiB

Open AccessArticle

Temperature Effects on Tensile Deformation Behavior of a Medium Manganese TRIP Steel and a Quenched and Partitioned Steel

by Whitney A. Poling, Emmanuel De Moor, John G. Speer and Kip O. Findley

Metals 2021, 11(2), 375; https://doi.org/10.3390/met11020375 - 23 Feb 2021

Cited by 18 | Viewed by 3109

Abstract

Third-generation advanced high-strength steels (AHSS) containing metastable retained austenite are being developed for the structural components of vehicles to reduce vehicle weight and improve crash performance. The goal of this work was to compare the effect of temperature on austenite stability and tensile [...] Read more.

Third-generation advanced high-strength steels (AHSS) containing metastable retained austenite are being developed for the structural components of vehicles to reduce vehicle weight and improve crash performance. The goal of this work was to compare the effect of temperature on austenite stability and tensile mechanical properties of two steels, a quenched and partitioned (Q&P) steel with a martensite and retained austenite microstructure, and a medium manganese transformation-induced plasticity (TRIP) steel with a ferrite and retained austenite microstructure. Quasi-static tensile tests were performed at temperatures between −10 and 85 °C for the Q&P steel (0.28C-2.56Mn-1.56Si in wt.%), and between −10 and 115 °C for the medium manganese TRIP steel (0.14C-7.14Mn-0.23Si in wt.%). X-ray diffraction measurements as a function of strain were performed from interrupted tensile tests at all test temperatures. For the medium manganese TRIP steel, austenite stability increased significantly, serrated flow behavior changed, and tensile strength and elongation changed significantly with increasing temperature. For the Q&P steel, flow stress was mostly insensitive to temperature, uniform elongation decreased with increasing temperature, and austenite stability increased with increasing temperature. The Olson–Cohen model for the austenite-to-martensite transformation as a function of strain showed good agreement for the medium manganese TRIP steel data and fit most of the Q&P steel data above 1% strain. Full article

(This article belongs to the Special Issue Recent Developments in Medium and High Manganese Steels)

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13 pages, 8216 KiB

Open AccessArticle

Large Eddy Simulation of Multi-Phase Flow and Slag Entrapment in Molds with Different Widths

by Xianjiu Zhao, Xianglong Li and Jieyu Zhang

Metals 2021, 11(2), 374; https://doi.org/10.3390/met11020374 - 23 Feb 2021

Cited by 6 | Viewed by 2196

Abstract

Slag entrapment is a critical problem that affects the quality of steel. In this work, a three-dimensional model is established to simulate the slag entrapment phenomenon, mainly focusing on the slag entrapment phenomenon at the interface between slag and steel in molds with [...] Read more.

Slag entrapment is a critical problem that affects the quality of steel. In this work, a three-dimensional model is established to simulate the slag entrapment phenomenon, mainly focusing on the slag entrapment phenomenon at the interface between slag and steel in molds with different widths. The large eddy simulation (LES) model and discrete particle model (DPM) are used to simulate the movements of bubbles. The interactions between phases involve two-way coupling. The accuracy of our mathematical model is validated by comparing slag–metal interface fluctuations with practical measurements. The results reveal that the average interface velocity and transverse velocity decrease as the mold width increases, however, they cannot represent the severity of slag entrapment at the interface between slag and steel. Due to the influence of bubble motion behavior, the maximum interface velocity increases with mold width and causes slag entrapment readily, which can reflect the severity of slag entrapment. On this basis, by monitoring the change of impact depths in different molds, a new dimensionless number “C” is found to reveal the severity of slag entrapment at the interface between slag and steel. The results show that the criterion number C increases with mold width, which is consistent with the results of flaw detection. Therefore, criterion number C can be used to reflect the severity of slag entrapment in different molds. Full article

(This article belongs to the Section Metal Casting, Forming and Heat Treatment)

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24 pages, 6886 KiB

Open AccessArticle

Failure Pressure Prediction of High Toughness Pipeline with a Single Corrosion Defect Subjected to Combined Loadings Using Artificial Neural Network (ANN)

by Suria Devi Vijaya Kumar, Saravanan Karuppanan and Mark Ovinis

Metals 2021, 11(2), 373; https://doi.org/10.3390/met11020373 - 23 Feb 2021

Cited by 36 | Viewed by 2873

Abstract

Conventional pipeline corrosion assessment methods result in failure pressure predictions that are conservative, especially for pipelines that are subjected to internal pressure and axial compressive stress. Alternatively, numerical methods may be used. However, they are computationally expensive. This paper proposes an analytical equation [...] Read more.

Conventional pipeline corrosion assessment methods result in failure pressure predictions that are conservative, especially for pipelines that are subjected to internal pressure and axial compressive stress. Alternatively, numerical methods may be used. However, they are computationally expensive. This paper proposes an analytical equation based on finite element analysis (FEA) for the failure pressure prediction of a high toughness corroded pipeline with a single corrosion defect subjected to internal pressure and axial compressive stress. The equation was developed based on the weights and biases of an Artificial Neural Network (ANN) model trained with failure pressure from finite element analysis (FEA) of a high toughness pipeline for various defect depths, defect lengths, and axial compressive stresses. The proposed model was validated against actual burst test results for high toughness materials and was found to be capable of making accurate predictions with a coefficient of determination (R²) of 0.99. An extensive parametric study using the proposed model was subsequently conducted to determine the effects of defect length, defect depth, and axial compressive stress on the failure pressure of a corroded pipe with a single defect. The application of ANN together with FEA has shown promising results in the development of an empirical solution for the failure pressure prediction of pipes with a single corrosion defect subjected to internal pressure and axial compressive stress. Full article

(This article belongs to the Section Metal Failure Analysis)

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17 pages, 5030 KiB

Open AccessArticle

Combining Differential Scanning Calorimetry and Cooling-Heating Curve Thermal Analysis to Study the Melting and Solidification Behavior of Al-Ce Binary Alloys

by Marta Aniolek, Tyler Smith and Frank Czerwinski

Metals 2021, 11(2), 372; https://doi.org/10.3390/met11020372 - 23 Feb 2021

Cited by 7 | Viewed by 4094

Abstract

Two common techniques of thermal analysis, Differential Scanning Calorimetry (DSC) and Cooling/Heating Curve Thermal Analysis (CCTA), based on different signal collected and utilizing samples with a weight difference of three orders of magnitude, were used to assess the solidification and melting behavior of [...] Read more.

Two common techniques of thermal analysis, Differential Scanning Calorimetry (DSC) and Cooling/Heating Curve Thermal Analysis (CCTA), based on different signal collected and utilizing samples with a weight difference of three orders of magnitude, were used to assess the solidification and melting behavior of Al-Ce binary alloys, containing from 5 to 20 wt. % Ce. Thermal analysis was accompanied by microscopic observations of solidified structures. For heating/cooling rates of 0.2–0.4 °C/s, temperatures of eutectic transformation L ↔ Al + Al₁₁Ce₃ in the Al-10Ce alloy along with additional proeutectic reactions L ↔ Al in the Al-5Ce hypoeutectic alloy and L ↔ Al₁₁Ce₃ in Al-15Ce and Al-20Ce hypereutectic alloys, were determined. Although there was a general agreement in major transformations, registered by DSC and CCTA during melting and solidification, differences in the reaction temperature determined exceeded the typical measurement errors for each technique. In addition, DSC and CCTA exhibited differences in detecting some proeutectic reactions and minor non-equilibrium effects, accompanying the eutectic transformation. Some factors that could contribute to differences observed and their implications for engineering practice were discussed. Full article

(This article belongs to the Special Issue Phase Transformations in Lightweight Alloys)

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18 pages, 9482 KiB

Open AccessArticle

Hydrometallurgical Leaching of Copper Flash Furnace Electrostatic Precipitator Dust for the Separation of Copper from Bismuth and Arsenic

by Michael Caplan, Joseph Trouba, Corby Anderson and Shijie Wang

Metals 2021, 11(2), 371; https://doi.org/10.3390/met11020371 - 23 Feb 2021

Cited by 9 | Viewed by 3450

Abstract

Flash furnace electrostatic precipitator dust (FF-ESP dust) is a recycle stream in some primary copper production facilities. This dust contains high amounts of copper. In some cases, the FF-ESP dust contains elevated levels of bismuth and arsenic, both of which cause problems during [...] Read more.

Flash furnace electrostatic precipitator dust (FF-ESP dust) is a recycle stream in some primary copper production facilities. This dust contains high amounts of copper. In some cases, the FF-ESP dust contains elevated levels of bismuth and arsenic, both of which cause problems during the electrorefining stages of copper production. Because of this, methods for separation of copper from bismuth and arsenic in FF-ESP dust are necessary. Hydrometallurgical leaching using a number of lixiviants, including sulfuric acid, sulfurous acid, sodium hydroxide, and water, were explored. Pourbaix diagrams of copper, bismuth, and arsenic were used to determine sets of conditions which would thermodynamically separate copper from bismuth and arsenic. The data indicate that water provides the best overall separation between copper and both bismuth and arsenic. Sodium hydroxide provided a separation between copper and arsenic. Sulfurous acid provided a separation between copper and bismuth. Sulfuric acid did not provide any separations between copper and bismuth or copper and arsenic. Full article

(This article belongs to the Special Issue Recovery and Recycling of Valuable Metals)

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7 pages, 384 KiB

Open AccessFeature PaperReview

Heuristic Design of Advanced Martensitic Steels That Are Highly Resistant to Hydrogen Embrittlement by ε-Carbide

by Michio Shimotomai

Metals 2021, 11(2), 370; https://doi.org/10.3390/met11020370 - 23 Feb 2021

Cited by 6 | Viewed by 2493

Abstract

Many advanced steels are based on tempered martensitic microstructures. Their mechanical strength is characterized by fine sub-grain structures with a high density of free dislocations and metallic carbides and/or nitrides. However, the strength for practical use has been limited mostly to below 1400 [...] Read more.

Many advanced steels are based on tempered martensitic microstructures. Their mechanical strength is characterized by fine sub-grain structures with a high density of free dislocations and metallic carbides and/or nitrides. However, the strength for practical use has been limited mostly to below 1400 MPa, owing to delayed fractures that are caused by hydrogen. A literature survey suggests that ε-carbide in the tempered martensite is effective for strengthening. A preliminary experimental survey of the hydrogen absorption and hydrogen embrittlement of a tempered martensitic steel with ε-carbide precipitates suggested that the proper use of carbides in steels can promote a high resistance to hydrogen embrittlement. Based on the surveys, martensitic steels that are highly resistant to hydrogen embrittlement and that have high strength and toughness are proposed. The heuristic design of the steels includes alloying elements necessary to stabilize the ε-carbide and procedures to introduce inoculants for the controlled nucleation of ε-carbide. Full article

(This article belongs to the Special Issue Heat Treatment of Steels)

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21 pages, 50867 KiB

Open AccessArticle

Effect of Side Blowing on Fluid Flow and Mixing Phenomenon in Gas-Stirred Ladle

by Rong Cheng, Liangjin Zhang, Yanbin Yin and Jiongming Zhang

Metals 2021, 11(2), 369; https://doi.org/10.3390/met11020369 - 23 Feb 2021

Cited by 16 | Viewed by 2678

Abstract

To investigate the gas agitation characteristics of side blowing, the fluid flow and mixing phenomenon in a 1:3 scale model ladle of a 150 t industrial gas-stirred ladle with bottom and side plugs were studied by using physical and numerical modelings together. Side [...] Read more.

To investigate the gas agitation characteristics of side blowing, the fluid flow and mixing phenomenon in a 1:3 scale model ladle of a 150 t industrial gas-stirred ladle with bottom and side plugs were studied by using physical and numerical modelings together. Side blowing enhanced the horizontal flow of water in the model ladle. Compared with bottom blowing, side blowing that is close to the ladle bottom with more than two plugs increases the average velocity of water, which represents the agitation power, improves the uniformity of water velocity distribution, reduces the stagnant region rate, and shortens the mixing time. The mixing time of dual bottom plugs is almost 1.5 times of that of four side plugs at 116 mm under the same flow rate. The mixing time is not only influenced by the agitation power but also by the uniformity of water velocity distribution. Although the agitation power of four side plugs at 450 mm under the flow rate of 1.8 m³/h is about 1.5 times of that at 116 mm with 0.6 m³/h. The mixing time of the 1.8 m³/h flow rate is about 1.2 times of that of the 0.6 m³/h because of the different water velocity distributions. Full article

(This article belongs to the Special Issue Experimental and Numerical Simulation of Metallic Materials)

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14 pages, 9311 KiB

Open AccessArticle

Microstructure and Properties of a Novel Al-Mg-Si Alloy AA 6086

by Franc Zupanič, Matej Steinacher, Sandi Žist and Tonica Bončina

Metals 2021, 11(2), 368; https://doi.org/10.3390/met11020368 - 23 Feb 2021

Cited by 28 | Viewed by 4787

Abstract

In this work, we investigated a novel Al-Mg-Si alloy, which was developed from an AA 6082, in order to considerably improve the yield and tensile strengths whilst retain excellent ductility. The new alloy possesses a higher content of Si than specified by AA [...] Read more.

In this work, we investigated a novel Al-Mg-Si alloy, which was developed from an AA 6082, in order to considerably improve the yield and tensile strengths whilst retain excellent ductility. The new alloy possesses a higher content of Si than specified by AA 6082, and, in addition, it contains copper and zirconium. The alloy was characterized in the as-cast condition, after homogenization, extrusion, and T6 heat treatment using light microscopy, scanning and transmission electron microscopy with energy dispersive spectrometry, X-ray diffraction, differential thermal analysis and tensile testing. After T6 temper, tensile strengths were around 490 MPa with more than 10% elongation at fracture. The microstructure consisted of small-grained Al-rich matrix with α-AlMnSi and Al₃Zr dispersoids, and Q′-AlCuMgSi and β-Mg₂Si-type precipitates. Full article

(This article belongs to the Special Issue Structure and Properties of Aluminium Alloys)

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20 pages, 7164 KiB

Open AccessArticle

Laser Surface Modification in Ti-xNb-yMo Alloys Prepared by Powder Metallurgy

by Inmaculada Tendero, Mariana Correa Rossi, Mauricio Viera, José Manuel Amado, María José Tobar, Ángel Vicente, Armando Yañez and Vicente Amigó

Metals 2021, 11(2), 367; https://doi.org/10.3390/met11020367 - 22 Feb 2021

Cited by 9 | Viewed by 2453

Abstract

The main objective was to study the effect of surface modification by laser on Ti-Nb-Mo powder metallurgical alloys to improve their mechano-chemical behavior and their application as a biomedical implant. The used powder mixtures were produced in an inert atmosphere. Uniaxial compaction took [...] Read more.

The main objective was to study the effect of surface modification by laser on Ti-Nb-Mo powder metallurgical alloys to improve their mechano-chemical behavior and their application as a biomedical implant. The used powder mixtures were produced in an inert atmosphere. Uniaxial compaction took place at 600 MPa with high-vacuum sintering at 1250 °C for 3 h. The specimens for the three-point flexure test were prepared and their mechanical properties determined. Microstructural characterization was performed by scanning electron microscopy (SEM) and X-ray diffraction (XRD) to obtain the distribution of phases, porosity, size, and shape of the grains of each alloy. Corrosion behavior was evaluated by electrochemical tests using an artificial saliva electrolyte modified from Fusayama at 37 °C. Chemical characterization was completed by analyzing the ionic release by Inductively coupled plasma atomic emission spectroscopy (ICP-EOS) after immersion for 730 h in Fusayama solution modified with NaF at 37 °C to simulate a 20-year life span based on a daily 2-min cycle of three toothbrushes. Corrosion behavior confirmed promising possibilities for the biomedicine field. The surface porosity of the samples not submitted to surface treatment deteriorated properties against corrosion and ion release. The obtained phase was β, with a low α”-martensite percentage. The maximum resistance to bending was greater after surface fusion. Plastic deformations were above 7% under some conditions. Microhardness came close to 300 HV in heat-affected zone (HAZ) and 350 HV in fusion zone (FZ) (under the determined condition. The elastic modulus lowered by around 10%. The corrosion rate was lower in Ti-27Nb-8Mo and Ti-35Nb-6Mo. Niobium release was significant, but below the physiological limit. Full article

(This article belongs to the Special Issue Laser Treatment of Metallic Materials)

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9 pages, 11170 KiB

Open AccessArticle

Application of Active-Screen Plasma Nitriding to an Austenitic Stainless Steel Small-Diameter Thin Pipe

by Kenzo Sumiya, Shinkichi Tokuyama, Akio Nishimoto, Junichi Fukui and Atsushi Nishiyama

Metals 2021, 11(2), 366; https://doi.org/10.3390/met11020366 - 22 Feb 2021

Cited by 17 | Viewed by 2707

Abstract

Low-temperature active-screen plasma nitriding (ASPN) was applied in this study to improve the bending rigidity and corrosion resistance of a small-diameter thin pipe composed of austenitic stainless steel (SUS 304). The inner and outer diameters of the pipe were ϕ0.3 and ϕ0.4 mm, [...] Read more.

Low-temperature active-screen plasma nitriding (ASPN) was applied in this study to improve the bending rigidity and corrosion resistance of a small-diameter thin pipe composed of austenitic stainless steel (SUS 304). The inner and outer diameters of the pipe were ϕ0.3 and ϕ0.4 mm, respectively, and the pipe length was 50 mm. The jig temperature was measured using a thermocouple and was adopted as the nitriding temperature because measuring the temperature of a small-diameter pipe is difficult. The nitriding temperature was varied from 578 to 638 K to investigate the effect of temperature on the nitriding layer and mechanical property. The nitriding layer thickness increased with an increase in nitriding temperature, reaching 15 μm at 638 K. The existence of expanded austenite (S phase) in this nitriding layer was revealed using the X-ray diffraction pattern. Moreover, the surface hardness increased with the nitriding temperature and took a maximum value of 1100 HV above 598 K. The bending load increased with an increase in the nitriding temperature in relation to the thicker nitriding layer and increased surface hardness. The nitrided samples did not corrode near the center, and corrosion was noted only near the tip at high nitriding temperatures of 618 and 638 K in a salt spray test. These results indicated that the bending rigidity of the small-diameter thin pipe composed of austenitic stainless steel was successfully improved using low-temperature ASPN while ensuring corrosion resistance. Full article

(This article belongs to the Special Issue Active Screen Plasma Treatment)

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22 pages, 6742 KiB

Open AccessArticle

Fatigue Models Based on Real Load Spectra and Corrected S-N Curve for Estimating the Residual Service Life of the Remanufactured Excavator Beam

by Gang Zhao, Junsong Xiao and Qi Zhou

Metals 2021, 11(2), 365; https://doi.org/10.3390/met11020365 - 22 Feb 2021

Cited by 3 | Viewed by 2718

Abstract

To more accurately predict the residual fatigue cycles and estimate the service life of the remanufactured excavator, the fatigue models integrating the corrected S-N curve, the RFC algorithm, the FEA model, and the mechanism dynamic model are established depending on the real load [...] Read more.

To more accurately predict the residual fatigue cycles and estimate the service life of the remanufactured excavator, the fatigue models integrating the corrected S-N curve, the RFC algorithm, the FEA model, and the mechanism dynamic model are established depending on the real load spectra under experimental working conditions and the corrected S-N curve of the beam metal remanufactured with the welding process. Depending on the test data of the unidirectional stress history and the servo displacements of the major cylinders, the mechanism dynamic model was first established to illustrate the real load spectra applied on the pivots of the working beam. The load spectra are further used in the finite element analysis (FEA) model to obtain the stress contours of the beam relevant to the sampling time, which is the stress spectra at any nodes on the beam in theory. Subsequently, the rain flow counting (RFC) algorithm based on the dual parameters of the cyclic stress amplitude and mean is established to provide the frequency spectra in the longevity region on the beam. Furthermore, due to the fatigue property changes of the beam metal remanufactured with the welding process, its S-N curve is corrected based on the detail fatigue rating (DFR) method to compute the stress cycles at each stress level on the crisis nodes. Finally, the total stress cycles that can be burdened by the remanufactured beam is computed under the Miner’s linear fatigue cumulative criterion. The total number of stress cycles is eventually converted to the fatigue and service life depending on the proportion of the sampling time under relevant working conditions. The results show that integrated fatigue models provide a practical approach to enhancing the accuracy of the estimation on the residual service life of the remanufactured excavator beam. It is significant for improving the reliability and safety of the remanufactured excavator. Full article

(This article belongs to the Special Issue Fatigue Life Prediction of Metallic Materials)

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25 pages, 5258 KiB

Open AccessReview

Low Melting Temperature Sn-Bi Solder: Effect of Alloying and Nanoparticle Addition on the Microstructural, Thermal, Interfacial Bonding, and Mechanical Characteristics

by Hyejun Kang, Sri Harini Rajendran and Jae Pil Jung

Metals 2021, 11(2), 364; https://doi.org/10.3390/met11020364 - 22 Feb 2021

Cited by 65 | Viewed by 13741

Abstract

Sn-based lead-free solders such as Sn-Ag-Cu, Sn-Cu, and Sn-Bi have been used extensively for a long time in the electronic packaging field. Recently, low-temperature Sn-Bi solder alloys attract much attention from industries for flexible printed circuit board (FPCB) applications. Low melting temperatures of [...] Read more.

Sn-based lead-free solders such as Sn-Ag-Cu, Sn-Cu, and Sn-Bi have been used extensively for a long time in the electronic packaging field. Recently, low-temperature Sn-Bi solder alloys attract much attention from industries for flexible printed circuit board (FPCB) applications. Low melting temperatures of Sn-Bi solders avoid warpage wherein printed circuit board and electronic parts deform or deviate from the initial state due to their thermal mismatch during soldering. However, the addition of alloying elements and nanoparticles Sn-Bi solders improves the melting temperature, wettability, microstructure, and mechanical properties. Improving the brittleness of the eutectic Sn-58wt%Bi solder alloy by grain refinement of the Bi-phase becomes a hot topic. In this paper, literature studies about melting temperature, microstructure, inter-metallic thickness, and mechanical properties of Sn-Bi solder alloys upon alloying and nanoparticle addition are reviewed. Full article

(This article belongs to the Special Issue Emerging Interconnection Technology and Pb-Free Solder Materials for Advanced Microelectronic Packaging)

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19 pages, 6685 KiB

Open AccessEditor’s ChoiceArticle

Improved Corrosion Behavior of AZ31 Alloy through ECAP Processing

by A. I. Alateyah, Talal A. Aljohani, Majed O. Alawad, H. Abd El-Hafez, A. N. Almutairi, E. S. Alharbi, R. Alhamada, B. W. El-Garaihy and W. H. El-Garaihy

Metals 2021, 11(2), 363; https://doi.org/10.3390/met11020363 - 21 Feb 2021

Cited by 37 | Viewed by 3840

Abstract

This study aims to establish the effects of equal channel angular pressing (ECAP) processing on the corrosion behavior and hardness values of the AZ31 Mg alloy. The AZ31 billets were processed through ECAP successfully at 250 °C and their microstructural evolution was studied [...] Read more.

This study aims to establish the effects of equal channel angular pressing (ECAP) processing on the corrosion behavior and hardness values of the AZ31 Mg alloy. The AZ31 billets were processed through ECAP successfully at 250 °C and their microstructural evolution was studied using optical and field emission scanning electron microscopy. The corrosion resistance of the AZ31 alloy was studied before and after processing through ECAP. The homogeneity of the hardness distribution was studied using both sections cut parallel and perpendicular to the extrusion direction. ECAP processing resulted in highly deformed central regions with elongated grains aligned parallel to the extrusion direction, whereas the peripheral regions showed an ultra-fine-grain recrystallized structure. After processing, small ultra-fine secondary particles were found to be homogeneously dispersed alongside the grain boundaries of the α-Mg matrix. Regarding the corrosion properties, measurements showed that ECAP processing through 1-P and 2-Bc resulted in decreasing their corrosion rate to 67.7% and 78.3%, respectively, of their as-annealed counterpart’s. The corrosion resistance of the ECAPed Mg alloy increased with the number of processing passes. This was due to the refinement of the grain size of the α-Mg matrix and secondary phases till ultra-fine size, caused by the accumulation of strain during processing. On the other hand, ECAP processing through 2-Bc resulted in increasing the Vickers hardness values by 132% and 71.8% at the peripheral and central areas, respectively, compared to the as-annealed counterpart. Full article

(This article belongs to the Special Issue Surface Chemistry and Corrosion of Light Alloys)

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12 pages, 2753 KiB

Open AccessFeature PaperArticle

Experimental and Simulation Analysis of Effects of Laser Bending on Microstructures Applied to Advanced Metallic Alloys

by Esteban Ramos-Moore, Joaquín Hoffmann, Rafael H. M. Siqueira, Sheila Medeiros de Carvalho, Milton S. Fernandes de Lima and Diego J. Celentano

Metals 2021, 11(2), 362; https://doi.org/10.3390/met11020362 - 21 Feb 2021

Cited by 1 | Viewed by 2447

Abstract

The aim of this work is the analysis of laser beam forming (LBF) in the bending of two relevant materials used in the transportation industry—interstitial-free (IF) steel and AA6013 high-strength aluminum alloy. Our experiments and numerical simulations consider two different operating scenarios achieved [...] Read more.

The aim of this work is the analysis of laser beam forming (LBF) in the bending of two relevant materials used in the transportation industry—interstitial-free (IF) steel and AA6013 high-strength aluminum alloy. Our experiments and numerical simulations consider two different operating scenarios achieved by varying the laser beam scanning velocity using linear paths. The material behavior during this process is described via a coupled thermomechanical-plasticity-based formulation that allows prediction of temperature profiles and bending angles. Metallography, glow discharge optical emission spectroscopy, and X-ray diffraction are used for microstructure characterization. In addition, microstress analyses are performed in order to study the stress behavior of the irradiated zones. It is found that LBF mainly induces grain growth and melting in the case of high surface temperatures. Before melting, the materials developed compressive stresses that could be useful in preventing cracking failures. The resulting bending angles are predicted and experimentally validated, indicating the robustness of the model to estimate LBF effects on advanced alloys. The present analysis relating bending angles together with temperature and microstructure profiles along the thickness of the sheets is the main original contribution of this work, highlighting the need for further modeling refinement of the effects of LBF on advanced alloys to include more microstructural properties, such as grain boundary diffusion and surface roughness. Full article

(This article belongs to the Special Issue Laser Processing of Metals and Alloys)

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12 pages, 1079 KiB

Open AccessArticle

Study Regarding the Micro Filler Effect of Sludge Resulting from Steel Pickling

by Claudiu Aciu, Daniela Lucia Manea and Dana-Adriana Iluţiu-Varvara

Metals 2021, 11(2), 361; https://doi.org/10.3390/met11020361 - 21 Feb 2021

Cited by 1 | Viewed by 2226

Abstract

The management of waste, resulting in high amounts from different production processes, often raises special problems. This is also the case for sludge, generated in increasing amounts from the chemical pickling of steel pipes. This article presents the results of laboratory experiments regarding [...] Read more.

The management of waste, resulting in high amounts from different production processes, often raises special problems. This is also the case for sludge, generated in increasing amounts from the chemical pickling of steel pipes. This article presents the results of laboratory experiments regarding the micro filler effect of sludge generated by chemical pickling of steel pipes and analyzes its capacity to be a pozzolanic material. The study involved the performance of mechanical tests (specific surface of the powder; compressive mechanical strengths) and chemical tests (determination of the general chemical composition of cement and sludge using the X-ray fluorescence (XRF) method; determination of oxides in the chemical composition of sludge by Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES); X-ray diffraction (XRD) analysis of the sludge and cement used). This topic was addressed because recycling of sludge, by using it for the manufacture of new building materials, takes advantage of the waste resulting from the pickling of steel pipes that-until now-has generated large volumes without a specific use. Full article

(This article belongs to the Special Issue Sustainable Metallurgical Processes for Metallic Waste Valorization)

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17 pages, 9333 KiB

Open AccessArticle

Hot Deformation Characteristics and Processing Parameter Optimization of Al–6.32Zn–2.10Mg Alloy Using Constitutive Equation and Processing Map

by Zhengbing Xiao, Qiang Wang, Yuanchun Huang, Jiawei Hu and Ming Li

Metals 2021, 11(2), 360; https://doi.org/10.3390/met11020360 - 20 Feb 2021

Cited by 11 | Viewed by 2203

Abstract

Hot compression tests over the temperature range from 350 °C to 500 °C and strain rates range from 0.001 s⁻¹ to 1 s⁻¹ for homogenized Al–6.32Zn–2.10Mg alloy were carried out on a Gleeble-3800 thermal simulation machine to characterize its hot deformation [...] Read more.

Hot compression tests over the temperature range from 350 °C to 500 °C and strain rates range from 0.001 s⁻¹ to 1 s⁻¹ for homogenized Al–6.32Zn–2.10Mg alloy were carried out on a Gleeble-3800 thermal simulation machine to characterize its hot deformation behavior. At the same time, a modified Arrhenius constitutive equation was established to describe the flow behavior of the alloy, whose average absolute error is 2.89%, which proved to have an excellent predictive effect on the flow stress of the alloy. The hot processing map of the alloy was established, and the stability processing parameters were 460–500 °C and 0.01–0.08 s⁻¹. Then, the Z parameter processing map and activation energy processing (AEP) maps were established for further optimization. Eventually, the optimal processing parameters of the alloy was 460–500 °C (0.03–0.08 s⁻¹). Then, the microstructure of specimens was observed using electron backscatter diffraction. Based on the findings the reasonability of the AEP map and Z parameter map was verified. Finally, electron backscatter diffraction (EBSD) techniques were used to analyze the evolution of the grain structure during the deformation process. It was found that dynamic recovery (DRV) was the main softening mechanism of Al–6.32Zn–2.10Mg. Continuous dynamic recrystallization (CDRX) and discontinuous dynamic recrystallization (DDRX) operated together with the increase of strain, but CDRX was confirmed as the dominant DRX mechanism. Full article

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14 pages, 8784 KiB

Open AccessArticle

Investigation of the Dynamic Recovery and Recrystallization of Near-β Titanium Alloy Ti-55511 during Two-Pass Hot Compression

by Hande Wang, Jinyang Ge, Xiaoyong Zhang, Chao Chen and Kechao Zhou

Metals 2021, 11(2), 359; https://doi.org/10.3390/met11020359 - 20 Feb 2021

Cited by 8 | Viewed by 2388

Abstract

The two-pass thermal compression behavior of near-β Ti-55511 alloy was investigated. The first-pass restoration mechanisms changed from dynamic recrystallization (DRX) to dynamic recovery (DRV) as the first-pass deformation temperature increased from 700 °C to 850 °C. The occurrence of recrystallization reduced the dislocation [...] Read more.

The two-pass thermal compression behavior of near-β Ti-55511 alloy was investigated. The first-pass restoration mechanisms changed from dynamic recrystallization (DRX) to dynamic recovery (DRV) as the first-pass deformation temperature increased from 700 °C to 850 °C. The occurrence of recrystallization reduced the dislocation density, resulting in a slower grain growth rate in the subsequent process. Because of the static recrystallization (SRX) and β grain growth, the β grain size increased and the morphology became less uniform during the subsequent β holding process, which also changed the restoration mechanism during second-pass compression. The level of continuous dynamic recrystallization (CDRX) and discontinuous dynamic recrystallization (DDRX) become weaker during second-pass deformation. The changes in the restoration mechanism and the microstructures slightly increased the peak stress during the second-pass deformation. Full article

(This article belongs to the Special Issue Microstructure and Mechanical Properties of Titanium Alloys)

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23 pages, 7539 KiB

Open AccessFeature PaperReview

Hydrogen Embrittlement of Medium Mn Steels

by Lawrence Cho, Yuran Kong, John G. Speer and Kip O. Findley

Metals 2021, 11(2), 358; https://doi.org/10.3390/met11020358 - 20 Feb 2021

Cited by 21 | Viewed by 5583

Abstract

Recent research efforts to develop advanced–/ultrahigh–strength medium-Mn steels have led to the development of a variety of alloying concepts, thermo-mechanical processing routes, and microstructural variants for these steel grades. However, certain grades of advanced–/ultrahigh–strength steels (A/UHSS) are known to be highly susceptible to [...] Read more.

Recent research efforts to develop advanced–/ultrahigh–strength medium-Mn steels have led to the development of a variety of alloying concepts, thermo-mechanical processing routes, and microstructural variants for these steel grades. However, certain grades of advanced–/ultrahigh–strength steels (A/UHSS) are known to be highly susceptible to hydrogen embrittlement, due to their high strength levels. Hydrogen embrittlement characteristics of medium–Mn steels are less understood compared to other classes of A/UHSS, such as high Mn twinning–induced plasticity steel, because of the relatively short history of the development of this steel class and the complex nature of multiphase, fine-grained microstructures that are present in medium–Mn steels. The motivation of this paper is to review the current understanding of the hydrogen embrittlement characteristics of medium or intermediate Mn (4 to 15 wt pct) multiphase steels and to address various alloying and processing strategies that are available to enhance the hydrogen-resistance of these steel grades. Full article

(This article belongs to the Special Issue Recent Developments in Medium and High Manganese Steels)

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12 pages, 4413 KiB

Open AccessArticle

Effect of Transition Metal Elements on High-Temperature Properties of Al–Si–Cu–Mg Alloys

by Chao Gao, Lingkun Zhang and Bingrong Zhang

Metals 2021, 11(2), 357; https://doi.org/10.3390/met11020357 - 20 Feb 2021

Cited by 5 | Viewed by 1963

Abstract

In the present work, we studied the effects of transition metal elements on microstructure evolution and high-temperature mechanical properties via the preparation of new modified alloys with micro-additions of Cr, Ti, V, Zr, Mo, and Mn to address the poor high-temperature performance of [...] Read more.

In the present work, we studied the effects of transition metal elements on microstructure evolution and high-temperature mechanical properties via the preparation of new modified alloys with micro-additions of Cr, Ti, V, Zr, Mo, and Mn to address the poor high-temperature performance of Al–Si–Cu–Mg alloys for automotive engines. The results show that the addition of transition metal elements formed a variety of new intermetallic phases that were stable at high temperatures, such as (AlSi)₃(TiVZr), (AlSi)₃Ti, (AlSi)₃(CrVTi), Al₇₄Si₆Mn₄Cr₂Fe, Al₈₅Si₅Mn₂Mo₂CrFe, Al_0.78Fe_4.8Mn_0.27Mo_4.15Si₂, (AlSi)₂(CrVTi)Mo, and Al₁₃(MoCrVTi)₄Si₄, and these phases evidently improved the ultimate high-temperature tensile strength and yield strength. The ultimate tensile strength and yield strength of the modified alloy increased by 17.49% and 31.65% when the test temperature increased to 240 °C, respectively, and by 71.28% and 74.73% when the test temperature increased to 300 °C, respectively. The fundamental reason for this change is that the intermetallic phase hinders the expansion of cracks, which can exist stably at high temperatures. When a crack extends to the intermetallic phases, it will break along with the intermetallic phases or propagate along the morphological edge of the intermetallic phases. Full article

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18 pages, 15513 KiB

Open AccessArticle

Effect of Processing Parameters on Mechanical Properties of Deformed and Partitioned (D&P) Medium Mn Steels

by Chengpeng Huang and Mingxin Huang

Metals 2021, 11(2), 356; https://doi.org/10.3390/met11020356 - 20 Feb 2021

Cited by 7 | Viewed by 2751

Abstract

Deformed and partitioned (D&P) medium Mn steels exhibiting high strength, large ductility, and excellent fracture toughness have been developed recently. The ultra-high dislocation density and transformation-induced plasticity (TRIP) effect are the main mechanisms for their exceptional mechanical properties. The simple processing route to [...] Read more.

Deformed and partitioned (D&P) medium Mn steels exhibiting high strength, large ductility, and excellent fracture toughness have been developed recently. The ultra-high dislocation density and transformation-induced plasticity (TRIP) effect are the main mechanisms for their exceptional mechanical properties. The simple processing route to manufacturing D&P steel makes it promising for large-scale industrial applications. However, the exact effect of each processing step on the final mechanical properties of D&P steel is not yet fully understood. In the present work, the effects of processing parameters on the mechanical properties of D&P steels are systematically investigated. The evolution of microstructure, tensile behavior and austenite fraction of warm rolled samples and D&P samples are revealed. Two D&P steels, with and without the intercritical annealing process, are both produced for comparison. It is revealed that the intercritical annealing process plays an insignificant role to the mechanical properties of D&P steel. The partitioning process is extremely important for obtaining large uniform elongation via slow but sustaining strain hardening by the TRIP effect in the partitioned austenite. The cold rolling process is also significant for acquiring high strength, and the cold rolling thickness reduction (CRTR) is extremely critical for the strength–ductility synergy of D&P steels. Full article

(This article belongs to the Special Issue Recent Developments in Medium and High Manganese Steels)

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11 pages, 4447 KiB

Open AccessArticle

Tribological Performance of CoCrMo Alloys with Boron Additions in As-Cast and Heat-Treated Conditions

by Marco A. L. Hernandez-Rodriguez, Diego E. Lozano, Gabriela M. Martinez-Cazares and Yaneth Bedolla-Gil

Metals 2021, 11(2), 355; https://doi.org/10.3390/met11020355 - 19 Feb 2021

Cited by 3 | Viewed by 2279

Abstract

The present study evaluates the effect of boron additions on the tribological performance of CoCrMo alloys. The alloys were prepared with boron ranging from 0.06 to 1 wt%. The materials were characterized using metallographic techniques, scanning electronic microscopy, and roughness and hardness tests. [...] Read more.

The present study evaluates the effect of boron additions on the tribological performance of CoCrMo alloys. The alloys were prepared with boron ranging from 0.06 to 1 wt%. The materials were characterized using metallographic techniques, scanning electronic microscopy, and roughness and hardness tests. Tribological evaluation was made by means of ball-on-disc tests for sliding distances of 4, 8 and 12 km. The samples were in the as-cast condition and after a heat treatment at 1200 °C for 1 h, finished by water quenching. The results showed that wear resistance was influenced by the microstructure and the number of secondary phases. The volume loss decreased as the boron content increased. Due to hard phases, abrasion wear was observed. Delamination fatigue was also detected after long sliding distances. Both wear mechanisms diminished in higher boron content alloys. Full article

(This article belongs to the Special Issue Manufacture, Mechanical Properties and Metallurgy of Metallic Biomaterials)

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14 pages, 13282 KiB

Open AccessFeature PaperArticle

Effect of Mn Addition on Hot-Working Behavior and Microstructure of Hot-Rolled Medium-Mn Steels

by Adam Skowronek, Dariusz Woźniak and Adam Grajcar

Metals 2021, 11(2), 354; https://doi.org/10.3390/met11020354 - 19 Feb 2021

Cited by 3 | Viewed by 2268

Abstract

Hot plastic working behavior and microstructure evolution were investigated during a production process of four medium-Mn steels, which differed in Mn (3 and 5%) and Nb contents. The production process started with casting, followed by hot forging, rough hot-rolling and concluded with final [...] Read more.

Hot plastic working behavior and microstructure evolution were investigated during a production process of four medium-Mn steels, which differed in Mn (3 and 5%) and Nb contents. The production process started with casting, followed by hot forging, rough hot-rolling and concluded with final thermomechanical processing, which was performed to obtain multiphase bainite-based alloys with some fractions of retained austenite. The rough rolling was composed of four passes with total true strain of 0.99 and finishing rolling temperature of 850 °C, whereas thermomechanical processing contained five passes and total true strain of 0.95 at a finishing rolling temperature of 750 °C. During the process, the force parameters were recorded, which showed that the rolling forces for steels containing 3% Mn are higher compared to the 5% Mn alloys. There was no significant influence of Nb on the rolling parameters. The produced as-cast microstructures were composed of dendritic bainitic-martensitic phases. A positive effect of Nb micro-addition on a refinement of the as-cast structure was noticed. The thermomechanical processed steels showed fine multiphase microstructures with some fractions of retained austenite, the fraction of which depended on the Mn content in steel. The steels containing 3% Mn generated higher forces both during rough and thermomechanical rolling, which is related to slower recrystallization softening in these alloys compared to the steels containing 5% Mn. Full article

(This article belongs to the Special Issue Advanced Multiphase Steels)

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18 pages, 4755 KiB

Open AccessReview

Preventing Evaporation Products for High-Quality Metal Film in Directed Energy Deposition: A Review

by Kang-Hyung Kim, Chan-Hyun Jung, Dae-Yong Jeong and Soong-Keun Hyun

Metals 2021, 11(2), 353; https://doi.org/10.3390/met11020353 - 19 Feb 2021

Cited by 6 | Viewed by 3604

Abstract

Directed energy deposition (DED), a type of additive manufacturing (AM) is a process that enables high-speed deposition using laser technology. The application of DED extends not only to 3D printing, but also to the 2D surface modification by direct laser-deposition dissimilar materials with [...] Read more.

Directed energy deposition (DED), a type of additive manufacturing (AM) is a process that enables high-speed deposition using laser technology. The application of DED extends not only to 3D printing, but also to the 2D surface modification by direct laser-deposition dissimilar materials with a sub-millimeter thickness. One of the reasons why DED has not been widely applied in the industry is the low velocity with a few m/min, but thin-DED has been developed to the extent that it can be over 100 m/min in roller deposition. The remaining task is to improve quality by reducing defects. Thus far, defect studies on AM, including DED, have focused mostly on preventing pores and crack defects that reduce fatigue strength. However, evaporation products, fumes, and spatters, were often neglected despite being one of the main causes of porosity and defects. In high-quality metal deposition, the problems caused by evaporation products are difficult to solve, but they have not yet caught the attention of metallurgists and physicists. This review examines the effect of the laser, material, and process parameters on the evaporation products to help obtain a high-quality metal film layer in thin-DED. Full article

(This article belongs to the Special Issue Directed Energy Deposition of Metal Alloys)

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28 pages, 10342 KiB

Open AccessFeature PaperArticle

Increasing Low-Temperature Toughness of 09Mn2Si Steel through Lamellar Structuring by Helical Rolling

by Sergey Panin, Ilya Vlasov, Dmitry Moiseenko, Pavel Maksimov, Pavlo Maruschak, Alexander Yakovlev, Julia Gomorova, Ivan Mishin and Siegfried Schmauder

Metals 2021, 11(2), 352; https://doi.org/10.3390/met11020352 - 19 Feb 2021

Cited by 6 | Viewed by 2753

Abstract

The aim of the paper was to investigate the helical rolling parameters (a number of passes) for the microstructural modification and the low-temperature impact toughness improvement of the 09Mn2Si High Strength Low-Alloyed (HSLA) steel. In order to achieve this purpose, work spent to [...] Read more.

The aim of the paper was to investigate the helical rolling parameters (a number of passes) for the microstructural modification and the low-temperature impact toughness improvement of the 09Mn2Si High Strength Low-Alloyed (HSLA) steel. In order to achieve this purpose, work spent to crack initiation and propagation was analyzed and compared with patterns of fracture surfaces. The microstructure and impact toughness values were presented in the temperature range from +20 to –70°C. Also, the fracture mechanisms in individual regions on the fracture surfaces were discussed. In addition, a methodology for computer simulation of the process was developed and implemented within the framework of the excitable cellular automata method and its integration with the kinetic theory of fracture. Finally, a theoretical analysis of the effect of grain shapes and orientations on the strain response patterns of a certain meso-volume simulating the material after the helical rolling was carried out. Full article

(This article belongs to the Special Issue Thermo-Mechanical Processing and Additive Manufacturing of Steels)

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12 pages, 5932 KiB

Open AccessArticle

The Weld Microstructure and Mechanical Properties of the Alloy 52 and Its Variants with Applied Electromagnetic Stirring during Welding

by Tai-Jung Wu, Sheng-Long Jeng and Junn-Yuan Huang

Metals 2021, 11(2), 351; https://doi.org/10.3390/met11020351 - 19 Feb 2021

Cited by 4 | Viewed by 1880

Abstract

This study investigated the impact of electromagnetic stirring (EMS) on nickel-base alloy welds prepared with the gas tungsten arc welding process. Alloy 52 and its variants, Alloy 52M and Alloy 52MSS, were carefully evaluated with their weld microstructure and mechanical properties. The results [...] Read more.

This study investigated the impact of electromagnetic stirring (EMS) on nickel-base alloy welds prepared with the gas tungsten arc welding process. Alloy 52 and its variants, Alloy 52M and Alloy 52MSS, were carefully evaluated with their weld microstructure and mechanical properties. The results showed that the welds exhibited a typical microstructure of dendrites, and that the dendrites could be refined by electromagnetic stirring. Meanwhile, with an application of EMS, the precipitates became smaller and more evenly distributed in the inter-dendritic areas. Ti(N,C)s, Nb/(Nb,Si)Cs, and large-scale Laves phase with (Nb,Mo,Ti)Cs were the precipitates present in the Alloy 52, Alloy 52M, and Alloy 52MSS welds, respectively. With the refined microstructure, both Alloy 52 and Alloy 52M welds were observed to have an increase in their tensile strength, with a decrease in their elongations. Comparatively, for the Alloy 52MSS weld, the tensile strength was enhanced along with a slight increase in elongation. Deep and dense dimples were a dominant feature of low-Nb-additions welds, and dendrite-like features were found prevalent among the Alloy 52MSS welds. With EMS, the dimples of Alloy 52 welds and the dendrite-like features of Alloy 52MSS welds became finer, while the dimples of Alloy 52M welds grew coarser. Full article

(This article belongs to the Section Metal Casting, Forming and Heat Treatment)

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16 pages, 22940 KiB

Open AccessArticle

Inhibition Effect of Fluoride Ion on Corrosion of 304 Stainless Steel in Occluded Cell Corrosion Stage in the Presence of Chloride Ion

by Zhengwei Luo, Jie Zuo, Hui Jiang, Wenhua Geng, Yongzhang Zhou, Zhouyang Lian and Wuji Wei

Metals 2021, 11(2), 350; https://doi.org/10.3390/met11020350 - 19 Feb 2021

Cited by 9 | Viewed by 4880

Abstract

The role of F⁻ in the corrosion of stainless steel at the stage of occluded cell corrosion in a mixture of chloride, fluoride, and sulfate ions was investigated. A simulated occluded corrosion cell was designed using an elaborate simulated rust layer. Composite [...] Read more.

The role of F⁻ in the corrosion of stainless steel at the stage of occluded cell corrosion in a mixture of chloride, fluoride, and sulfate ions was investigated. A simulated occluded corrosion cell was designed using an elaborate simulated rust layer. Composite electrodes were used to monitor the variation of the concentration of ions, pH, and dissolved oxygen of the occluded solution. The results show that the influence of F⁻ on the corrosion of 304 stainless steel, in the occluded cell corrosion stage, is concentration dependent. When the F⁻/Cl⁻ ratio is higher than 2, the corrosion can be significantly suppressed. Analyses showed that the corrosion inhibition effect could be attributed to the migration of F⁻ to the occluded cell, which can reduce the migration of Cl⁻, dampen the decrease in pH, and react with metal ions to form semi-soluble products. Meanwhile, the influence of F⁻ on the corrosion process was also verified using drilled stainless steel specimens, demonstrating the practicality and validity of the simulated occluded cell corrosion model. Full article

(This article belongs to the Special Issue Corrosion and Inhibition Processes)

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14 pages, 4318 KiB

Open AccessArticle

Control-Oriented Characterization of Product Properties during Hot Hole-Flanging of X46Cr13 Sheet Material in a Progressive-Die

by Juri Martschin, Rickmer Meya, Daniel Klöser, Thomas Meurer and A. Erman Tekkaya

Metals 2021, 11(2), 349; https://doi.org/10.3390/met11020349 - 19 Feb 2021

Cited by 2 | Viewed by 3577

Abstract

Robust and versatile production is enabled by a closed-loop control of product properties. This essentially relies on the characterization of the interaction between properties and available degrees of freedom to control the process. In particular, this work examines the setting of collar height, [...] Read more.

Robust and versatile production is enabled by a closed-loop control of product properties. This essentially relies on the characterization of the interaction between properties and available degrees of freedom to control the process. In particular, this work examines the setting of collar height, thinning, curvature, and hardness during hot hole-flanging of X46Cr13 sheet material with simultaneous heat treatment to identify approaches for a closed-loop property control in hot hole-flanging during multi-stage hot sheet metal forming. To scrutinize the adjustability of the hardness of X46Cr13 sheet material by heat treatment with rapid heating and short dwell times, quenching tests with austenitizing temperatures from 900 to 1100 °C and dwell times from 1 to 300 s were carried out. A hardness between 317 and 680 HV10 was measured. By analyzing the force-displacement curve and the contact situation between tools and blank during hot hole-flanging, an understanding for the process was established. To determine the adjustability of geometrical collar properties and the hardness of the collar, collars were formed at punch speeds between 5 and 100 mm/s and at different temperatures. Here, a dependency of the geometry of the collar on temperature and punch speed as well as setting of the hardness was demonstrated. Full article

(This article belongs to the Special Issue Challenges and Achievements in Metal Forming)

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10 pages, 3085 KiB

Open AccessArticle

Failure Mechanism of Gun Barrel Caused by Peeling of Cr Layer and Softening of Bore Matrix

by Zi-meng Wang, Chun-dong Hu, Yang-xin Wang, Heng-chang Lu, Jun-song Li and Han Dong

Metals 2021, 11(2), 348; https://doi.org/10.3390/met11020348 - 19 Feb 2021

Cited by 12 | Viewed by 4933

Abstract

Research on failure mechanism is essential for the prolonging of gun barrel lifetime. To explore the gun barrel failure mechanism, the damage characteristics of a machine gun barrel were characterized. The results show that the failure of the gun barrel is correlated with [...] Read more.

Research on failure mechanism is essential for the prolonging of gun barrel lifetime. To explore the gun barrel failure mechanism, the damage characteristics of a machine gun barrel were characterized. The results show that the failure of the gun barrel is correlated with the peeling of the Cr layer on the bore surface and the softening of the bore matrix. The damage of the Cr layer varies along the axial direction. From the gun tail to the muzzle, the damage mode of the Cr layer changes from peeling to wearing. The damage rate in both the tail and the muzzle is higher than that in the middle of the barrel. The matrix close to the bore surface is softened due to the high temperatures caused by stress–relief–annealing and shooting. The gun tail suffers from higher temperatures, thus being softened more seriously than the other parts. The softened matrix results in an increase in the tendency of plastic deformation of the bore surface and an increment in the bore diameter, which leads to a decrease in the firing accuracy. Full article

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14 pages, 19059 KiB

Open AccessArticle

Hot Processing Map of an Al–4.30 Mg Alloy under High One-Pass Deformation

by Yanjun Zhao, Haochen Ding, Yunfei Cao, Peilin Chen, Zhiliu Hu, Jingrui Zhang and Lingxiao Li

Metals 2021, 11(2), 347; https://doi.org/10.3390/met11020347 - 19 Feb 2021

Cited by 5 | Viewed by 2309

Abstract

The high one-pass deformation behaviors of mass-produced Al–4.30Mg alloy are investigated in the temperature ranging of 350 °C–500 °C, the strain rate ranging of 0.01 s⁻¹–1 s⁻¹ and the reduction ranging of 50–75%. 3D processing maps are constructed by the [...] Read more.

The high one-pass deformation behaviors of mass-produced Al–4.30Mg alloy are investigated in the temperature ranging of 350 °C–500 °C, the strain rate ranging of 0.01 s⁻¹–1 s⁻¹ and the reduction ranging of 50–75%. 3D processing maps are constructed by the superimposition of the instability map and the power dissipation map at the true strain of 0.69, 0.92, 1.20 and 1.38. When the true strain increases from 0.69 to 1.38, the average apparent activation energy (Q) decreases from 140.3 kJ/mol to 112.7 kJ/mol, indicating the reduction of the hot deformation energy barrier. The heating caused by a large strain of 1.38 greatly reduces the Q and improves processing efficiency. The instability regions at the strain of 0.69 appear at two domains, namely 350 °C/1.0 s⁻¹ and 450 °C/1.0 s⁻¹; whereas, the instability regions disappear at the strain of 1.38. The maximum efficiency of power dissipation is about 48%, which occurs at both domains of 440–480 °C/0.01 s⁻¹/0.69 true strain and 470–500 °C/1.0 s⁻¹/1.20 true strain. High-efficiency domains represent the optimized deformation conditions which are verified by stress-strain curves and microstructure characterization, in which the local dynamic recrystallization is observed and the power dissipates mainly by dynamic recrystallization during deformation. Full article

(This article belongs to the Section Metal Casting, Forming and Heat Treatment)

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14 pages, 4155 KiB

Open AccessArticle

Effects of Heat Treatments on Microstructures and Mechanical Properties of Ti6Al4V Alloy Produced by Laser Solid Forming

by Fei Li, Bojin Qi, Yongxin Zhang, Wei Guo, Peng Peng, Hepeng Zhang, Guangzhi He, Dezhi Zhu and Jianfeng Yan

Metals 2021, 11(2), 346; https://doi.org/10.3390/met11020346 - 19 Feb 2021

Cited by 13 | Viewed by 2763

Abstract

The steep thermal gradient and complicated thermal cycle occur in the fabrication of Ti6Al4V alloy during laser solid forming (LSF). That leads to obvious anisotropic mechanical properties and requires essential heat treatments to improve its performance. In this work, different heat treatment strategies [...] Read more.

The steep thermal gradient and complicated thermal cycle occur in the fabrication of Ti6Al4V alloy during laser solid forming (LSF). That leads to obvious anisotropic mechanical properties and requires essential heat treatments to improve its performance. In this work, different heat treatment strategies under vacuum condition were used to study the evolution of microstructures and mechanical properties of Ti6Al4V alloy produced by LSF. The results show that transformation from α phase into lamellar α + β dual-phases structure is introduced at low temperature (550 °C), and the α phase is broken and refined at higher temperature (800 °C). Tensile tests present the increase of elongations in the horizontal and vertical directions by 12.4% and 13.2% for specimens treated by two-step heat treatment (750 °C × 4 h + 500 °C × 1 h). Fatigue crack growth (FCG) lives of LSFed Ti6Al4V alloy after different heat treatments were improved due to the elimination of residual tensile stress and the transformation of α phase into α + β dual-phase structure. Specimens treated at 800 °C for 4 h exhibit a higher fatigue life among those heat-treated alloys. The low sensitivities of the FCG behavior in the Paris-zone to different heat treatments under vacuum condition are explored in the FCG testing of Ti6Al4V alloy. Full article

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