Metals

2979 KiB

Open AccessArticle

Effect of Process and Post-Process Conditions on the Mechanical Properties of an A357 Alloy Produced via Laser Powder Bed Fusion

by Alberta Aversa, Massimo Lorusso, Francesco Trevisan, Elisa Paola Ambrosio, Flaviana Calignano, Diego Manfredi, Sara Biamino, Paolo Fino, Mariangela Lombardi and Matteo Pavese

Metals 2017, 7(2), 68; https://doi.org/10.3390/met7020068 - 22 Feb 2017

Cited by 80 | Viewed by 7597

Abstract

A357 samples were realized by laser powder bed fusion (LPBF) on building platforms heated up to different temperatures. The effect of the preheating temperature and of the post processing heat treatment on the microstructure and the mechanical properties of the samples was studied. [...] Read more.

A357 samples were realized by laser powder bed fusion (LPBF) on building platforms heated up to different temperatures. The effect of the preheating temperature and of the post processing heat treatment on the microstructure and the mechanical properties of the samples was studied. It was demonstrated that building platform heating can act as an in situ ageing heat treatment following the fast cooling that arises during laser scanning. A 17% higher ultimate tensile strength was achieved by the selection of the optimum building platform temperature. Moreover, the possibility to further increase the mechanical properties by means of a direct ageing heat treatment was investigated. Full article

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5299 KiB

Open AccessFeature PaperArticle

Titanium Powder Sintering in a Graphite Furnace and Mechanical Properties of Sintered Parts

by Changzhou Yu, Peng Cao and Mark Ian Jones

Metals 2017, 7(2), 67; https://doi.org/10.3390/met7020067 - 22 Feb 2017

Cited by 20 | Viewed by 9540

Abstract

Recent accreditation of titanium powder products for commercial aircraft applications marks a milestone in titanium powder metallurgy. Currently, powder metallurgical titanium production primarily relies on vacuum sintering. This work reported on the feasibility of powder sintering in a non-vacuum furnace and the tensile [...] Read more.

Recent accreditation of titanium powder products for commercial aircraft applications marks a milestone in titanium powder metallurgy. Currently, powder metallurgical titanium production primarily relies on vacuum sintering. This work reported on the feasibility of powder sintering in a non-vacuum furnace and the tensile properties of the as-sintered Ti. Specifically, we investigated atmospheric sintering of commercially pure (C.P.) titanium in a graphite furnace backfilled with argon and studied the effects of common contaminants (C, O, N) on sintering densification of titanium. It is found that on the surface of the as-sintered titanium, a severely contaminated porous scale was formed and identified as titanium oxycarbonitride. Despite the porous surface, the sintered density in the sample interiors increased with increasing sintering temperature and holding time. Tensile specimens cut from different positions within a large sintered cylinder reveal different tensile properties, strongly dependent on the impurity level mainly carbon and oxygen. Depending on where the specimen is taken from the sintered compact, ultimate tensile strength varied from 300 to 580 MPa. An average tensile elongation of 5% to 7% was observed. Largely depending on the interstitial contents, the fracture modes from typical brittle intergranular fracture to typical ductile fracture. Full article

(This article belongs to the Special Issue Titanium Alloys 2017)

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6321 KiB

Open AccessArticle

Evolution of Metal Surface Topography during Fatigue

by Darong Zhu, Lu Xu, Fangbin Wang, Tao Liu and Ke Lu

Metals 2017, 7(2), 66; https://doi.org/10.3390/met7020066 - 22 Feb 2017

Cited by 6 | Viewed by 4615

Abstract

Changes in surface topography reflect the state of fatigue damage. In this paper, a new method to characterize metal surface topography during fatigue has been proposed. Firstly, we acquired surface topography images based on machine vision and separated them into roughness, waviness, and [...] Read more.

Changes in surface topography reflect the state of fatigue damage. In this paper, a new method to characterize metal surface topography during fatigue has been proposed. Firstly, we acquired surface topography images based on machine vision and separated them into roughness, waviness, and form error images through a shearlet transform. Secondly, we constructed gray co-occurrence matrixes of the obtained surface topography images and calculated the characteristic parameters, such as contrast, correlation coefficient, energy, and entropy for all the original and separated images. Then, taking a Q235 steel specimen as an example for testing, the experimental results and theoretical analysis demonstrate that the parameter contrast increases while energy, correlation coefficient and entropy decrease gradually with number of loading circles, which reach their maximum and minimums before fracture, respectively. Full article

(This article belongs to the Special Issue Non-Destructive Metallic Materials Testing—Recent Research and Future Perspectives)

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5419 KiB

Open AccessArticle

Evaluating Strengthening and Impact Toughness Mechanisms for Ferritic and Bainitic Microstructures in Nb, Nb-Mo and Ti-Mo Microalloyed Steels

by Gorka Larzabal, Nerea Isasti, Jose M. Rodriguez-Ibabe and Pello Uranga

Metals 2017, 7(2), 65; https://doi.org/10.3390/met7020065 - 22 Feb 2017

Cited by 39 | Viewed by 7374

Abstract

Low carbon microalloyed steels show interesting commercial possibilities by combining different “micro”-alloying elements when high strength and low temperature toughness properties are required. Depending on the elements chosen for the chemistry design, the mechanisms controlling the strengths and toughness may differ. In this [...] Read more.

Low carbon microalloyed steels show interesting commercial possibilities by combining different “micro”-alloying elements when high strength and low temperature toughness properties are required. Depending on the elements chosen for the chemistry design, the mechanisms controlling the strengths and toughness may differ. In this paper, a detailed characterization of the microstructural features of three different microalloyed steels, Nb, Nb-Mo and Ti-Mo, is described using mainly the electron backscattered diffraction technique (EBSD) as well as transmission electron microscopy (TEM). The contribution of different strengthening mechanisms to yield strength and impact toughness is evaluated, and its relative weight is computed for different coiling temperatures. Grain refinement is shown to be the most effective mechanism for controlling both mechanical properties. As yield strength increases, the relative contribution of precipitation strengthening increases, and this factor is especially important in the Ti-Mo microalloyed steel where different combinations of interphase and random precipitation are detected depending on the coiling temperature. In addition to average grain size values, microstructural heterogeneity is considered in order to propose a new equation for predicting ductile–brittle transition temperature (DBTT). This equation considers the wide range of microstructures analyzed as well as the increase in the transition temperature related to precipitation strengthening. Full article

(This article belongs to the Special Issue Bainite and Martensite: Developments and Challenges)

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4009 KiB

Open AccessArticle

Synthesis, Characterization, and Toxicity Evaluation of Dextran-Coated Iron Oxide Nanoparticles

by Mihaela Balas, Carmen Steluta Ciobanu, Carmen Burtea, Miruna Silvia Stan, Eugenia Bezirtzoglou, Daniela Predoi and Anca Dinischiotu

Metals 2017, 7(2), 63; https://doi.org/10.3390/met7020063 - 21 Feb 2017

Cited by 25 | Viewed by 7259

Abstract

We report the synthesis of dextran-coated iron oxide magnetic nanoparticles (DIO-NPs) with spherical shape and uniform size distribution as well as their accumulation and toxic effects on Jurkat cells up to 72 h. The characterization of dextran-coated maghemite nanoparticles was done by X-ray [...] Read more.

We report the synthesis of dextran-coated iron oxide magnetic nanoparticles (DIO-NPs) with spherical shape and uniform size distribution as well as their accumulation and toxic effects on Jurkat cells up to 72 h. The characterization of dextran-coated maghemite nanoparticles was done by X-ray diffraction and dynamic light scattering analyses, transmission electron microscopy imaging, attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy, magnetic hysteresis, and relaxometry measurements. The quantification of DIO-NPs intracellular uptake showed a progressive accumulation of iron as a function of time and dose accompanied by additional lysosome formation and an increasing darkening exhibited by a magnetic resonance imaging (MRI) scanner. The cytotoxicity assays revealed a decrease of cell viability and a loss of membrane integrity in a time- and dose-dependent manner. Exposure to DIO-NPs determined an increase in reactive oxygen species level up to 72 h. In the first two days of exposure, the level of reduced glutathione decreased and the amount of malondyaldehyde increased, but at the end of the experiment, their concentrations returned to control values. These nanoparticles could be used as contrast agents for MRI but several parameters concerning their interaction with the cells should be taken into consideration for a safe utilization. Full article

(This article belongs to the Special Issue Metallic and Metal Oxide Nanoparticles: Novel Approaches)

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4243 KiB

Open AccessArticle

Investigation on Porosity and Microhardness of 316L Stainless Steel Fabricated by Selective Laser Melting

by Shahir Mohd Yusuf, Yifei Chen, Richard Boardman, Shoufeng Yang and Nong Gao

Metals 2017, 7(2), 64; https://doi.org/10.3390/met7020064 - 20 Feb 2017

Cited by 159 | Viewed by 14325

Abstract

This study investigates the porosity and microhardness of 316L stainless steel samples fabricated by selective laser melting (SLM). The porosity content was measured using the Archimedes method and the advanced X-ray computed tomography (XCT) scan. High densification level (≥99%) with a low average [...] Read more.

This study investigates the porosity and microhardness of 316L stainless steel samples fabricated by selective laser melting (SLM). The porosity content was measured using the Archimedes method and the advanced X-ray computed tomography (XCT) scan. High densification level (≥99%) with a low average porosity content (~0.82%) were obtained from the Archimedes method. The highest porosity content in the XCT-scanned sample was ~0.61. However, the pores in the SLM samples for both cases (optical microscopy and XCT) were not uniformly distributed. The higher average microhardness values in the SLM samples compared to the wrought manufactured counterpart are attributed to the fine microstructures from the localised melting and rapid solidification rate of the SLM process. Full article

(This article belongs to the Special Issue 3D Printing of Metals)

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5661 KiB

Open AccessArticle

Surface Characteristics and Fatigue Behavior of Gradient Nano-Structured Magnesium Alloy

by Xiaohui Zhao, Yanjun Zhang and Yu Liu

Metals 2017, 7(2), 62; https://doi.org/10.3390/met7020062 - 20 Feb 2017

Cited by 12 | Viewed by 4993

Abstract

High-frequency impacting and rolling was applied on AZ31B magnesium alloy to obtain a gradient nano-structured surface. Surface characteristics were experimentally investigated, and the nanocrystallization mechanism is discussed in detail. Results showed that the gradient nano-structure with the characteristics of work hardening, compressive residual [...] Read more.

High-frequency impacting and rolling was applied on AZ31B magnesium alloy to obtain a gradient nano-structured surface. Surface characteristics were experimentally investigated, and the nanocrystallization mechanism is discussed in detail. Results showed that the gradient nano-structure with the characteristics of work hardening, compressive residual stress and a smooth surface was induced on the treated surface. Grains on the top surface were generally refined to around 20 nm. Twins, dislocations and dynamic recrystallization dominated the grain refinement process. Fatigue strength of the treated specimens corresponding to 10⁷ cycles was increased by 28.6% compared to that of the as-received specimens. The work hardened layer induced by high-frequency impacting and rolling is the major reason to improve fatigue life. Full article

(This article belongs to the Special Issue Fatigue Damage)

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4066 KiB

Open AccessArticle

DFT Investigation of the Effects of Coexisting Cations and Complexing Reagents on Ni(II) Adsorption by a Polyvinylidene Fluoride-Type Chelating Membrane Bearing Poly(Amino Phosphonic Acid) Groups

by Xiuli Wang, Laizhou Song, Caili Tian, Jun He, Shuaijie Wang, Jinbo Wang and Chunyu Li

Metals 2017, 7(2), 61; https://doi.org/10.3390/met7020061 - 17 Feb 2017

Cited by 11 | Viewed by 4834

Abstract

A polyvinylidene fluoride (PVDF)-type chelating membrane bearing poly(amino phosphonic acid) groups, denoted as ethylenediamine tetra(methylene phosphonic acid) (EDTMPA)-tetrabutyl orthotitanate (TBOT)/PVDF, was employed to remove Ni(II) from the aqueous solution. The effects of coexisting Ca(II), Pb(II), citrate, nitrilotriacetic acid (NTA) and ethylenediaminetetraacetic acid (EDTA) [...] Read more.

A polyvinylidene fluoride (PVDF)-type chelating membrane bearing poly(amino phosphonic acid) groups, denoted as ethylenediamine tetra(methylene phosphonic acid) (EDTMPA)-tetrabutyl orthotitanate (TBOT)/PVDF, was employed to remove Ni(II) from the aqueous solution. The effects of coexisting Ca(II), Pb(II), citrate, nitrilotriacetic acid (NTA) and ethylenediaminetetraacetic acid (EDTA) on the Ni(II) adsorption by this chelating membrane were revealed using density functional theory (DFT) calculations. Pb(II) showed a more detrimental effect than Ca(II) on the Ni(II) uptake; EDTA interfered with the capture of Ni(II) more remarkably than citrate and NTA. The results derived from DFT calculations were consistent with the experimental data. Ni(II) and Pb(II) showed more excellent affinity to the EDTMPA-TBOT/PVDF membrane than Ca(II). The stabilities between Ni(II) and the [EDTMPA-TBOT]7− chelating ligand of the membrane and those between Ni(II) and the three aforementioned complexing reagents followed the sequence: [Ni(II)-(EDTMPA-TBOT)]5− > Ni(II)-EDTA > Ni(II)-NTA > Ni(II)-citrate. The complexation between Ni(II) and the chelating membrane was prominent with the presence of citrate, NTA and EDTA. Full article

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6789 KiB

Open AccessArticle

Role of Microstructure Heterogeneity on Fatigue Crack Propagation of Low-Alloyed PM Steels in the As-Sintered Condition

by Saba Mousavinasab and Carl Blais

Metals 2017, 7(2), 60; https://doi.org/10.3390/met7020060 - 17 Feb 2017

Cited by 7 | Viewed by 6404

Abstract

Due to their lower production costs, powder metallurgy (PM) steels are increasingly being considered for replacing wrought counterparts. Nevertheless, the presence of a non-negligible volume fraction of porosity in typical PM steels makes their use difficult, especially in applications where cyclic loading is [...] Read more.

Due to their lower production costs, powder metallurgy (PM) steels are increasingly being considered for replacing wrought counterparts. Nevertheless, the presence of a non-negligible volume fraction of porosity in typical PM steels makes their use difficult, especially in applications where cyclic loading is involved. On the other hand, PM offers the possibility of obtaining steel microstructures that cannot be found in wrought. Indeed, by adequately using alloying strategies based on admixing, pre-alloying, diffusion bonding or combinations of those, it is possible to tailor the final microstructure to obtain a distribution of phases that could possibly increase the fatigue resistance of PM steel components. Therefore, a detailed study of the effect of different microstructural phases on fatigue crack propagation in PM steels was performed using admixed nickel PM steels (FN0208) as well as pre-alloyed PM steels (FL5208). Specimens were pressed and sintered to a density of 7.3 g/cm³ in order to specifically investigate the effect of matrix microstructure on fatigue properties. Fatigue crack growth rates were measured at four different R-ratios, 0.1, 0.3, 0.5 and 0.7 for both PM steels. The negative effect of increasing the R-ratio on fatigue properties was observed for both alloys. The crack propagation path was characterized using quantitative image analysis of fracture surfaces. Measurements of roughness profile and volume fractions of each phase along the crack path were made to determine the preferred crack path. Weak Ni-rich ferritic rings in the FN0208 series (heterogeneous microstructure) caused a larger crack deflection compared to the more homogeneous microstructure of the FL5208 series. It was determined that, contrary to results reported in literature, crack propagation does not pass through retained austenite areas even though fatigue cracks propagated predominantly along prior particle boundaries, i.e., intergranular fracture. Full article

(This article belongs to the Special Issue Fatigue Damage)

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3419 KiB

Open AccessArticle

Microstructure and Oxidation Behavior of CrAl Laser-Coated Zircaloy-4 Alloy

by Jeong-Min Kim, Tae-Hyung Ha, Il-Hyun Kim and Hyun-Gil Kim

Metals 2017, 7(2), 59; https://doi.org/10.3390/met7020059 - 15 Feb 2017

Cited by 51 | Viewed by 5861

Abstract

Laser coating of a CrAl layer on Zircaloy-4 alloy was carried out for the surface protection of the Zr substrate at high temperatures, and its microstructural and thermal stability were investigated. Significant mixing of CrAl coating metal with the Zr substrate occurred during [...] Read more.

Laser coating of a CrAl layer on Zircaloy-4 alloy was carried out for the surface protection of the Zr substrate at high temperatures, and its microstructural and thermal stability were investigated. Significant mixing of CrAl coating metal with the Zr substrate occurred during the laser surface treatment, and a rapidly solidified microstructure was obtained. A considerable degree of diffusion of solute atoms and some intermetallic compounds were observed to occur when the coated specimen was heated at a high temperature. Oxidation appears to proceed more preferentially at Zr-rich region than Cr-rich region, and the incorporation of Zr into the CrAl coating layer deteriorates the oxidation resistance because of the formation of thermally unstable Zr oxides. Full article

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4899 KiB

Open AccessArticle

Effect of Low-Temperature Sensitization on Hydrogen Embrittlement of 301 Stainless Steel

by Chieh Yu, Ren-Kae Shiue, Chun Chen and Leu-Wen Tsay

Metals 2017, 7(2), 58; https://doi.org/10.3390/met7020058 - 15 Feb 2017

Cited by 6 | Viewed by 5364

Abstract

The effect of metastable austenite on the hydrogen embrittlement (HE) of cold-rolled (30% reduction in thickness) 301 stainless steel (SS) was investigated. Cold-rolled (CR) specimens were hydrogen-charged in an autoclave at 300 or 450 °C under a pressure of 10 MPa for 160 [...] Read more.

The effect of metastable austenite on the hydrogen embrittlement (HE) of cold-rolled (30% reduction in thickness) 301 stainless steel (SS) was investigated. Cold-rolled (CR) specimens were hydrogen-charged in an autoclave at 300 or 450 °C under a pressure of 10 MPa for 160 h before tensile tests. Both ordinary and notched tensile tests were performed in air to measure the tensile properties of the non-charged and charged specimens. The results indicated that cold rolling caused the transformation of austenite into α′ and ε-martensite in the 301 SS. Aging at 450 °C enhanced the precipitation of M₂₃C₆ carbides, G, and σ phases in the cold-rolled specimen. In addition, the formation of α′ martensite and M₂₃C₆ carbides along the grain boundaries increased the HE susceptibility and low-temperature sensitization of the 450 °C-aged 301 SS. In contrast, the grain boundary α′-martensite and M₂₃C₆ carbides were not observed in the as-rolled and 300 °C-aged specimens. Full article

(This article belongs to the Special Issue Alloy Steels)

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3678 KiB

Open AccessArticle

The BCC/B2 Morphologies in Al_xNiCoFeCr High-Entropy Alloys

by Yue Ma, Beibei Jiang, Chunling Li, Qing Wang, Chuang Dong, Peter K. Liaw, Fen Xu and Lixian Sun

Metals 2017, 7(2), 57; https://doi.org/10.3390/met7020057 - 15 Feb 2017

Cited by 146 | Viewed by 13801

Abstract

The present work primarily investigates the morphological evolution of the body-centered-cubic (BCC)/B2 phases in Al_xNiCoFeCr high-entropy alloys (HEAs) with increasing Al content. It is found that the BCC/B2 coherent morphology is closely related to the lattice misfit between these two phases, [...] Read more.

The present work primarily investigates the morphological evolution of the body-centered-cubic (BCC)/B2 phases in Al_xNiCoFeCr high-entropy alloys (HEAs) with increasing Al content. It is found that the BCC/B2 coherent morphology is closely related to the lattice misfit between these two phases, which is sensitive to Al. There are two types of microscopic BCC/B2 morphologies in this HEA series: one is the weave-like morphology induced by the spinodal decomposition, and the other is the microstructure of a spherical disordered BCC precipitation on the ordered B2 matrix that appears in HEAs with a much higher Al content. The mechanical properties, including the compressive yielding strength and microhardness of the Al_xNiCoFeCr HEAs, are also discussed in light of the concept of the valence electron concentration (VEC). Full article

(This article belongs to the Special Issue High-Entropy Alloys (HEAs))

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5430 KiB

Open AccessArticle

Effect of Preparation Parameter on Microstructure and Grain Refining Behavior of In Situ AlN-TiN-TiB₂/Al Composite Inoculants on Pure Aluminum

by Qian Wang, Chunxiang Cui, Xin Wang, Lichen Zhao, Nuo Li and Shuiqing Liu

Metals 2017, 7(2), 56; https://doi.org/10.3390/met7020056 - 15 Feb 2017

Cited by 4 | Viewed by 5436

Abstract

The formation of in situ AlN-TiN-TiB₂/Al composite inoculants, which contain multi-phase refiner particles including AlN, TiN, TiB₂, Al₃Ti, and α-Al, was investigated using nitrogen gas injection. The effects of the main preparation parameters such as nitriding temperature, [...] Read more.

The formation of in situ AlN-TiN-TiB₂/Al composite inoculants, which contain multi-phase refiner particles including AlN, TiN, TiB₂, Al₃Ti, and α-Al, was investigated using nitrogen gas injection. The effects of the main preparation parameters such as nitriding temperature, nitriding time, Ti content in melts, on the microstructure and grain refinement of in situ AlN-TiN-TiB₂/Al composite inoculants were studied. The shape, content and size of different ceramic particles in the inoculants can be tuned by controlling the nitriding temperature and time, inducing excellent refining and reinforcing effects on pure aluminum. As a result, the average grain size of pure aluminum can be reduced to about 122 ± 22 μm from original 1010 ± 80 μm by adding 0.3 wt % inoculants. The mechanical properties including the tensile strength, yield strength and microhardness of the refined as-cast pure aluminum are also improved. Full article

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3109 KiB

Open AccessArticle

Urban Mining and Electrochemistry: Cyclic Voltammetry Study of Acidic Solutions from Electronic Wastes (Printed Circuit Boards) for Recovery of Cu, Zn, and Ni

by Ma. Isabel Reyes‐Valderrama, Eleazar Salinas‐Rodríguez, J. Fabian Montiel‐Hernández, Isauro Rivera‐Landero, Eduardo Cerecedo‐Sáenz, Juan Hernándezvila and Alberto Arenas‐Flores

Metals 2017, 7(2), 55; https://doi.org/10.3390/met7020055 - 13 Feb 2017

Cited by 11 | Viewed by 6324

Abstract

We report potentiodynamic studies to characterize copper, nickel and zinc leaching solutions from electronic waste. The metals were leached using oxygen and sulfuric acid (pH = 1.5). As is known, reduction potentials are determined using thermodynamics laws, and metal recovery strategies from electronic [...] Read more.

We report potentiodynamic studies to characterize copper, nickel and zinc leaching solutions from electronic waste. The metals were leached using oxygen and sulfuric acid (pH = 1.5). As is known, reduction potentials are determined using thermodynamics laws, and metal recovery strategies from electronic waste are usually considered according these thermodynamic values. Pourbaix‐type diagrams are not appropriate to plan strategies in electrochemical processing. Therefore, knowledge of electrode potentials for the metal deposit/dissolution process is the basis for the selective recovery planning. For this reason, potentiodynamic studies, specifically cyclic voltammetry, are revealed as a good way to decide the best conditions for the process of electrochemical recovery of metals from electronic waste, which is also cost‐efficient and has no interference from strange ions, such as lead, in this case. Full article

(This article belongs to the Special Issue Valuable Metal Recycling)

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3475 KiB

Open AccessArticle

Effect of Strain Range on the Low Cycle Fatigue in Alloy 617 at High Temperature

by Rando Tungga Dewa, Seon Jin Kim, Woo Gon Kim and Eung Seon Kim

Metals 2017, 7(2), 54; https://doi.org/10.3390/met7020054 - 10 Feb 2017

Cited by 18 | Viewed by 5343

Abstract

The aim of this study is to investigate the fully‐reversed low cycle fatigue properties of Alloy 617 in the air at 950 °C; these tests were conducted at total strain ranges from 0.9% to 1.5% with a constant strain rate of 10−3/s. The [...] Read more.

The aim of this study is to investigate the fully‐reversed low cycle fatigue properties of Alloy 617 in the air at 950 °C; these tests were conducted at total strain ranges from 0.9% to 1.5% with a constant strain rate of 10−3/s. The result of the fatigue tests showed a decrease in fatigue resistance with an increasing total strain range. The reduction of fatigue resistance was due to the effect of the total strain range and microstructure evolution during high temperature, such as brittle oxides cracking. At all testing conditions, the cyclic softening mechanism was observed as a function of the total strain range in the current high temperature condition. An analysis of low cycle fatigue resistance was performed using the Coffin–Manson relationship and the total strain energy density; it was found that Alloy 617 followed these relationships well. In addition, this study compared well with previous work reported in the literature for a similar testing condition. Post‐fracture analysis on the fracture surfaces of failed specimens revealed a more severe damage cracking at the periphery of specimens due to the increase in the total strain range. The surface connected grain boundary cracks induced by oxidation were obvious at low strain range. Thus, the primary crack propagation occurred in transgranular mode from persistent slip bands. Full article

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2720 KiB

Open AccessArticle

Study on Pores in Ultrasonic‐Assisted TIG Weld of Aluminum Alloy

by Qihao Chen, Hongliang Ge, Chunli Yang, Sanbao Lin and Chenglei Fan

Metals 2017, 7(2), 53; https://doi.org/10.3390/met7020053 - 10 Feb 2017

Cited by 43 | Viewed by 5989

Abstract

Ultrasonic‐assisted tungsten inert gas welding was carried out on a thin plate of 2195 Al‐Li alloy, and the characteristics of the weld pores were analyzed in terms of their size and porosity. The effects of welding speed and ultrasonic power on the porosity [...] Read more.

Ultrasonic‐assisted tungsten inert gas welding was carried out on a thin plate of 2195 Al‐Li alloy, and the characteristics of the weld pores were analyzed in terms of their size and porosity. The effects of welding speed and ultrasonic power on the porosity and size of the pores were investigated. The pores were found to occur primarily adjacent to the surface of the weld. The porosity decreased and the size increased with a decrease in welding speed. The effect of ultrasonic power on the characteristics of the pores was different from that of the welding speed. The porosity and size of the pores decreased and then increased with an increase in ultrasonic power. A relationship was found between the transient cavitation intensity and the characteristics of pores. An increasing transient cavitation intensity results in a decrease in the porosity and size of pores when the transient cavitation intensity is lower. However, it can result in an increase in the porosity and pore size when the transient cavitation intensity further increases. Finally, the influencing mechanism of cavitation on welding pores was discussed. Full article

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2968 KiB

Open AccessArticle

XPS and AFM Investigations of Ti-Al-N Coatings Fabricated Using DC Magnetron Sputtering at Various Nitrogen Flow Rates and Deposition Temperatures

by Aleksei Obrosov, Roman Gulyaev, Markus Ratzke, Alex A. Volinsky, Sebastian Bolz, Muhammad Naveed and Sabine Weiß

Metals 2017, 7(2), 52; https://doi.org/10.3390/met7020052 - 10 Feb 2017

Cited by 40 | Viewed by 9838

Abstract

Ti-Al-N coatings were deposited by direct current magnetron sputtering (DCMS) onto IN 718 at different nitrogen flow rates and deposition temperatures. The coatings’ properties were characterized using atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) as well as nanoindentation. It was found that [...] Read more.

Ti-Al-N coatings were deposited by direct current magnetron sputtering (DCMS) onto IN 718 at different nitrogen flow rates and deposition temperatures. The coatings’ properties were characterized using atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) as well as nanoindentation. It was found that higher deposition temperature leads to higher surface roughness and nitrogen flux influences the shape of grains. According to XPS, the bonding structure of all coatings exhibited the (Ti,Al)N phase. Mechanical properties depend on the Al content within the films. The coating with the best mechanical properties (deposited at 500 °C and 20 standard cubic centimeters per minute (sccm)) was further deposited onto tungsten carbide (WC) cutting tools for cylindrical turning experiments. A quasi-constant flank wear was observed until a machining volume of 23,500 mm³. Full article

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2763 KiB

Open AccessArticle

Effect of Batch Annealing Temperature on Microstructure and Resistance to Fish Scaling of Ultra-Low Carbon Enamel Steel

by Zaiwang Liu, Yonglin Kang, Zhimin Zhang and Xiaojing Shao

Metals 2017, 7(2), 51; https://doi.org/10.3390/met7020051 - 9 Feb 2017

Cited by 3 | Viewed by 5890

Abstract

In the present work, an ultra-low carbon enamel steel was batch annealed at different temperatures, and the effect of the batch annealing temperature on the microstructure and resistance to fish scaling was investigated by optical microscopy, transmission electron microscopy, and a hydrogen permeation [...] Read more.

In the present work, an ultra-low carbon enamel steel was batch annealed at different temperatures, and the effect of the batch annealing temperature on the microstructure and resistance to fish scaling was investigated by optical microscopy, transmission electron microscopy, and a hydrogen permeation test. The results show that the main precipitates in experimental steel are fine TiC and coarse Ti4C2S2 particles. The average sizes of both TiC and Ti4C2S2 increase with increasing the batch annealing temperature. The resistance to fish scaling decreases with increasing the annealing temperature, which is caused by the growth of ferrite grain and the coarsening of the TiC and Ti4C2S2 particles Full article

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9886 KiB

Open AccessArticle

Hot Deformation Behavior of As-Cast 30Cr2Ni4MoV Steel Using Processing Maps

by Peng Zhou, Qingxian Ma and Jianbin Luo

Metals 2017, 7(2), 50; https://doi.org/10.3390/met7020050 - 9 Feb 2017

Cited by 10 | Viewed by 5025

Abstract

The hot deformation behavior of as-cast 30Cr2Ni4MoV steel was characterized using processing maps in the temperature range 850 to 1200 °C and strain rate range 0.01 to 10 s⁻¹. Based on the obtained flow curves, the power dissipation maps at different [...] Read more.

The hot deformation behavior of as-cast 30Cr2Ni4MoV steel was characterized using processing maps in the temperature range 850 to 1200 °C and strain rate range 0.01 to 10 s⁻¹. Based on the obtained flow curves, the power dissipation maps at different strains were developed and the effect of the strain on the efficiency of power dissipation was discussed in detail. The processing maps at different strains were obtained by superimposing the instability maps on the power dissipation maps. According to the processing map and the metallographic observation, the optimum domain of hot deformation was in the temperature range of 950–1200 °C and strain rate range of 0.03–0.5 s⁻¹, with a peak efficiency of 0.41 at 1100 °C and 0.25 s⁻¹ which were the optimum hot working parameters. Full article

(This article belongs to the Special Issue Advances in Plastic Forming of Metals)

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2488 KiB

Open AccessArticle

Microstructures and Tensile Properties of Al–Cu Matrix Composites Reinforced with Nano-Sized SiCp Fabricated by Semisolid Stirring Process

by Feng Qiu, Xiang Gao, Jian Tang, Yu-Yang Gao, Shi-Li Shu, Xue Han, Qiang Li and Qi-Chuan Jiang

Metals 2017, 7(2), 49; https://doi.org/10.3390/met7020049 - 8 Feb 2017

Cited by 29 | Viewed by 6960

Abstract

The nano-sized SiCp/Al–Cu composites were successfully fabricated by combining semisolid stirring with ball milling technology. Microstructures were examined by an olympus optical microscope (OM), field emission scanning electron microscope (FESEM) and transmission electron microscope (TEM). Tensile properties were studied at room temperature. The [...] Read more.

The nano-sized SiCp/Al–Cu composites were successfully fabricated by combining semisolid stirring with ball milling technology. Microstructures were examined by an olympus optical microscope (OM), field emission scanning electron microscope (FESEM) and transmission electron microscope (TEM). Tensile properties were studied at room temperature. The results show that the α-Al dendrites of the composites were strongly refined, especially in the composite with 3 wt. % nano-sized SiCp, of which the morphology of the α-Al changes from 200 μm dendritic crystal to 90 μm much finer equiaxial grain. The strength and ductility of the composites are improved synchronously with the addition of nano-sized SiCp particles. The as-cast 3 wt. % nano-sized SiCp/Al–Cu composite displays the best tensile properties, i.e., the yield strength, ultimate tensile strength (UTS) and fracture strain increase from 175 MPa, 310 MPa and 4.1% of the as-cast Al–Cu alloy to 220 MPa, 410 MPa and 6.3%, respectively. The significant improvement in the tensile properties of the composites is mainly due to the refinement of the α-Al dendrites, nano-sized SiCp strengthening, and good interface combination between the SiCp and Al–Cu alloys. Full article

(This article belongs to the Special Issue Metal Matrix Composites)

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10712 KiB

Open AccessArticle

Effect of the Welding Speed on the Macrostructure, Microstructure and Mechanical Properties of AA6061-T6 Friction Stir Butt Welds

by Firouz Fadaeifard, Khamirul Amin Matori, Sidek Abd Aziz, Liyana Zolkarnain and Mohd Aliff Zairie Bin Abdul Rahim

Metals 2017, 7(2), 48; https://doi.org/10.3390/met7020048 - 8 Feb 2017

Cited by 24 | Viewed by 7628

Abstract

Friction stir welding of aluminum alloys has been progressively used in different industries on the ground of higher welding quality in comparison to fusion welding. In this article, friction stir welding of 6061-T6 aluminum alloy with 9.6 mm thickness was carried out by [...] Read more.

Friction stir welding of aluminum alloys has been progressively used in different industries on the ground of higher welding quality in comparison to fusion welding. In this article, friction stir welding of 6061-T6 aluminum alloy with 9.6 mm thickness was carried out by using three different welding speeds (63, 89 and 110 mm/min). The effect of welding speed on macro- and microstructure, micro hardness, tensile properties and kissing bond was investigated. Results show that the Low Hardness Zone was moved toward the weld center by increasing the welding speed. The average micro hardness in the weld nugget zone increased from 60.1 to 67.6 HV with the raise of welding speed from 63 to 110 mm/min. Thermo Mechanical Affected Zone was clearly revealed using Electron backscatter diffraction (EBSD). The kissing bond was studied by Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray (EDX) mapping. It was proven that the damaging effect of kissing bond was linked to location of this discontinuity, although the growth of kissing bond was linked to higher welding speed. The maximum value of Ultimate Tensile Strength (UTS) (159 MPa) was obtained at 110 mm/min, whereas the Yield Strength (YS) in the sample at 89 and 110 mm/min welding speed exhibit the same trend with 137 MPa and 134 MPa respectively. Full article

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5259 KiB

Open AccessArticle

Discussion on the Local Magnetic Force between Reversely Magnetized Micro Metal Particles in the Microwave Sintering Process

by Yu Xiao, Feng Xu, Bo Dong, Wenchao Liu and Xiaofang Hu

Metals 2017, 7(2), 47; https://doi.org/10.3390/met7020047 - 8 Feb 2017

Cited by 8 | Viewed by 4035

Abstract

Synchrotron radiation computed tomography was applied to investigate Cu–Fe mixture microwave sintering in situ and to examine the magnetic force between reversely magnetized micro-metal particles in microwave sintering. Results revealed that the growth rate of the sintering necks between Cu–Fe particles and Cu–Cu [...] Read more.

Synchrotron radiation computed tomography was applied to investigate Cu–Fe mixture microwave sintering in situ and to examine the magnetic force between reversely magnetized micro-metal particles in microwave sintering. Results revealed that the growth rate of the sintering necks between Cu–Fe particles and Cu–Cu particles around the iron particles distributed in a vertical direction was faster than that of the sintering necks in the horizontal direction. These phenomena were consistent with the possible influence caused by the magnetic force between metal particles, as shown in our simple particle model. The kinetic curves of sintering neck growth along the vertical and horizontal directions quantitatively revealed the difference in growth rates. The contributing factors of magnetic force in microwave sintering were subsequently discussed. The volume of iron particles was proportional to the influence of magnetic force, and their shape elicited a remarkable influence based on demagnetization effects. This study provided a useful basis for microwave sintering mechanisms and anisotropic material preparation. Full article

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5716 KiB

Open AccessArticle

Nanoporous Microtubes via Oxidation and Reduction of Cu–Ni Commercial Wires

by Emanuele Francesco Marano, Alberto Castellero and Marcello Baricco

Metals 2017, 7(2), 46; https://doi.org/10.3390/met7020046 - 7 Feb 2017

Cited by 1 | Viewed by 4461

Abstract

Metallic porous microtubes were obtained from commercial wires (200–250 µm diameter) of Cu-65Ni-2Fe, Cu-44Ni-1Mn and Cu-23Ni, alloys (wt. %) by surface oxidation at 1173 K in air, removal of the unoxidized core by chemical etching, and reduction in annealing in the hydrogen atmosphere. [...] Read more.

Metallic porous microtubes were obtained from commercial wires (200–250 µm diameter) of Cu-65Ni-2Fe, Cu-44Ni-1Mn and Cu-23Ni, alloys (wt. %) by surface oxidation at 1173 K in air, removal of the unoxidized core by chemical etching, and reduction in annealing in the hydrogen atmosphere. Transversal sections of the partially oxidized wires show a porous layered structure, with an external shell of CuO (about 10 μm thick) and an inner layer of NiO (70–80 μm thick). In partially oxidized Cu-44Ni-1Mn and Cu-23Ni, Cu₂O is dispersed in NiO because the maximum solubility of Cu in NiO is exceeded, whereas in Cu-65Ni-2Fe, a Cu₂O shell is present between CuO and NiO layers. Chemical etching removed the unoxidized metallic core and Cu₂O with formation of porous oxide microtubes. Porosity increases with Cu content because of the larger amount of Cu₂O in the partially oxidized wire. After reduction, the transversal sections of the metallic porous microtubes show a series of f.c.c.-(Cu,Ni) solid solutions with different compositions, due to the segregation of CuO and NiO during oxidation caused by the different diffusion coefficients of Ni and Cu in the respective oxides. Pore formation occurs at each step of the process because of the Kirkendall effect, selective phase removal and volume contraction. Full article

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2814 KiB

Open AccessArticle

Theoretical and Experimental Nucleation and Growth of Precipitates in a Medium Carbon–Vanadium Steel

by Sebastián F. Medina, Inigo Ruiz-Bustinza, José Robla and Jessica Calvo

Metals 2017, 7(2), 45; https://doi.org/10.3390/met7020045 - 7 Feb 2017

Cited by 4 | Viewed by 4283

Abstract

Using the general theory of nucleation, the nucleation period, critical radius, and growth of particles were determined for a medium carbon V-steel. Several parameters were calculated, which have allowed the plotting of nucleation critical time vs. temperature and precipitate critical radius vs. temperature. [...] Read more.

Using the general theory of nucleation, the nucleation period, critical radius, and growth of particles were determined for a medium carbon V-steel. Several parameters were calculated, which have allowed the plotting of nucleation critical time vs. temperature and precipitate critical radius vs. temperature. Meanwhile, an experimental study was performed and it was found that the growth of precipitates during precipitation obeys a quadratic growth equation and not a cubic coalescence equation. The experimentally determined growth rate coincides with the theoretically predicted growth rate. Full article

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3446 KiB

Open AccessArticle

The Corrosion Inhibition Effect of Triazinedithiol Inhibitors for Aluminum Alloy in a 1 M HCl Solution

by Qian Zhao, Tiantian Tang, Peilin Dang, Zhiyi Zhang and Fang Wang

Metals 2017, 7(2), 44; https://doi.org/10.3390/met7020044 - 5 Feb 2017

Cited by 24 | Viewed by 6545

Abstract

Two environmental friendly triazinedithiol inhibitors 6-diallylamino-1,3,5-triazine-2,4-dithiol monosodium (DAN) and 6-dibutylamino-1,3,5-triazine-2,4-dithiol monosodium (DBN) were synthesized and their corrosion inhibition for aluminum alloy in a 1 M HCl solution was studied using weight loss methods, electrochemical measurements, and scanning electron microscopy (SEM) techniques. The inhibition [...] Read more.

Two environmental friendly triazinedithiol inhibitors 6-diallylamino-1,3,5-triazine-2,4-dithiol monosodium (DAN) and 6-dibutylamino-1,3,5-triazine-2,4-dithiol monosodium (DBN) were synthesized and their corrosion inhibition for aluminum alloy in a 1 M HCl solution was studied using weight loss methods, electrochemical measurements, and scanning electron microscopy (SEM) techniques. The inhibition efficiency of both DAN and DBN improved with increases in inhibitor concentration but decreased with increases in temperature. Results from potentiodynamic polarization and EIS showed that the corrosion inhibition efficiency of DAN and DBN was excellent. The adsorption of inhibitors on the aluminum alloy surface followed Langmuir adsorption isotherms. Morphology observation revealed that the aluminum alloy was greatly protected by these triazinedithiol inhibitors. Further, density functional theory (DFT) was used to investigate the relationships between molecular structural and inhibition efficiency. Full article

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2256 KiB

Open AccessFeature PaperReview

Corrosion-Resistant High-Entropy Alloys: A Review

by Yunzhu Shi, Bin Yang and Peter K. Liaw

Metals 2017, 7(2), 43; https://doi.org/10.3390/met7020043 - 5 Feb 2017

Cited by 688 | Viewed by 33568

Abstract

Corrosion destroys more than three percent of the world’s gross domestic product. Therefore, the design of highly corrosion-resistant materials is urgently needed. By breaking the classical alloy-design philosophy, high-entropy alloys (HEAs) possess unique microstructures, which are solid solutions with random arrangements of multiple [...] Read more.

Corrosion destroys more than three percent of the world’s gross domestic product. Therefore, the design of highly corrosion-resistant materials is urgently needed. By breaking the classical alloy-design philosophy, high-entropy alloys (HEAs) possess unique microstructures, which are solid solutions with random arrangements of multiple elements. The particular locally-disordered chemical environment is expected to lead to unique corrosion-resistant properties. In this review, the studies of the corrosion-resistant HEAs during the last decade are summarized. The corrosion-resistant properties of HEAs in various aqueous environments and the corrosion behavior of HEA coatings are presented. The effects of environments, alloying elements, and processing methods on the corrosion resistance are analyzed in detail. Furthermore, the possible directions of future work regarding the corrosion behavior of HEAs are suggested. Full article

(This article belongs to the Special Issue High-Entropy Alloys (HEAs))

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4742 KiB

Open AccessCommunication

Friction Stir Welding of Dissimilar Materials Aluminum AL6061-T6 to Ultra Low Carbon Steel

by Zakaria Boumerzoug and Yazid Helal

Metals 2017, 7(2), 42; https://doi.org/10.3390/met7020042 - 3 Feb 2017

Cited by 25 | Viewed by 7874

Abstract

In this study, the microstructure and strength properties of friction stir welded 6061-T6 aluminum alloy to ultra-low carbon steel have been investigated using different advancing speeds of 100, 200, and 400 mm·min⁻¹ at constant rotation rate. Microstructure observations have been conducted by [...] Read more.

In this study, the microstructure and strength properties of friction stir welded 6061-T6 aluminum alloy to ultra-low carbon steel have been investigated using different advancing speeds of 100, 200, and 400 mm·min⁻¹ at constant rotation rate. Microstructure observations have been conducted by optical and scanning electron microscopy. The joint strength was evaluated on a tensile testing machine. The effect of advancing speed on the shear load of a joint has been found, as well as a relationship between microstructures and mechanical properties. Full article

(This article belongs to the Special Issue Selected Papers from ICWET16)

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6424 KiB

Open AccessArticle

The 2D Finite Element Microstructure Evaluation of V-Shaped Arc Welding of AISI 1045 Steel

by Omer Eyercioglu, Ahmed Samir Anwar, Kursat Gov and Necip Fazil Yilmaz

Metals 2017, 7(2), 41; https://doi.org/10.3390/met7020041 - 3 Feb 2017

Cited by 5 | Viewed by 5782

Abstract

In the present study, V-shaped arc welding of the AISI 1045 steel is modeled by using 2D Finite Element Model (FEM). The temperature distribution, microstructure, grain growth, and the hardness of the heat-affected zone (HAZ) of the welding are simulated. The experimental work [...] Read more.

In the present study, V-shaped arc welding of the AISI 1045 steel is modeled by using 2D Finite Element Model (FEM). The temperature distribution, microstructure, grain growth, and the hardness of the heat-affected zone (HAZ) of the welding are simulated. The experimental work is carried out to validate the FE model. The very close agreement between the simulation and experimental results show that the FE model is very effective for predicting the microstructure, the phase transformation, the grain growth and the hardness. The effect of preheat temperature on the martensite formation is analysed, and it is shown that 225 °C preheating completely eliminates the martensite formations for the 12 mm thick plate. Full article

(This article belongs to the Special Issue Selected Papers from ICWET16)

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10119 KiB

Open AccessArticle

The Effects of Cr and Al Addition on Transformation and Properties in Low‐Carbon Bainitic Steels

by Junyu Tian, Guang Xu, Mingxing Zhou, Haijiang Hu and Xiangliang Wan

Metals 2017, 7(2), 40; https://doi.org/10.3390/met7020040 - 31 Jan 2017

Cited by 45 | Viewed by 7134

Abstract

Three low‐carbon bainitic steels were designed to investigate the effects of Cr and Al addition on bainitic transformation, microstructures, and properties by metallographic method and dilatometry. The results show that compared with the base steel without Cr and Al addition, only Cr addition [...] Read more.

Three low‐carbon bainitic steels were designed to investigate the effects of Cr and Al addition on bainitic transformation, microstructures, and properties by metallographic method and dilatometry. The results show that compared with the base steel without Cr and Al addition, only Cr addition is effective for improving the strength of low‐carbon bainitic steel by increasing the amount of bainite. However, compared with the base steel, combined addition of Cr and Al has no significant effect on bainitic transformation and properties. In Cr‐bearing steel, Al addition accelerates initial bainitic transformation, but meanwhile reduces the final amount of bainitic transformation due to the formation of a high‐temperature transformation product such as ferrite. Consequently, the composite strengthening effect of Cr and Al addition is not effective compared with individual addition of Cr in low‐carbon bainitic steels. Therefore, in contrast to high‐carbon steels, bainitic transformation in Cr‐bearing low‐carbon bainitic steels can be finished in a short time, and Al should not be added because Al addition would result in lower mechanical properties. Full article

(This article belongs to the Special Issue Alloy Steels)

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2644 KiB

Open AccessReview

Effects of Heat Input on Microstructure, Corrosion and Mechanical Characteristics of Welded Austenitic and Duplex Stainless Steels: A Review

by Ghusoon Ridha Mohammed, Mahadzir Ishak, Syarifah N. Aqida and Hassan A. Abdulhadi

Metals 2017, 7(2), 39; https://doi.org/10.3390/met7020039 - 30 Jan 2017

Cited by 110 | Viewed by 14563

Abstract

The effects of input heat of different welding processes on the microstructure, corrosion, and mechanical characteristics of welded duplex stainless steel (DSS) are reviewed. Austenitic stainless steel (ASS) is welded using low-heat inputs. However, owing to differences in the physical metallurgy between ASS [...] Read more.

The effects of input heat of different welding processes on the microstructure, corrosion, and mechanical characteristics of welded duplex stainless steel (DSS) are reviewed. Austenitic stainless steel (ASS) is welded using low-heat inputs. However, owing to differences in the physical metallurgy between ASS and DSS, low-heat inputs should be avoided for DSS. This review highlights the differences in solidification mode and transformation characteristics between ASS and DSS with regard to the heat input in welding processes. Specifically, many studies about the effects of heat energy input in welding process on the pitting corrosion, intergranular stress, stresscorrosion cracking, and mechanical properties of weldments of DSS are reviewed. Full article

(This article belongs to the Special Issue Alloy Steels)

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Metals, Volume 7, Issue 2 (February 2017) – 37 articles

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