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7 pages, 1167 KiB

Open AccessEditorial

Failure Mechanisms in Alloys

by George A. Pantazopoulos

Metals 2020, 10(1), 117; https://doi.org/10.3390/met10010117 - 13 Jan 2020

Cited by 3 | Viewed by 3739

Abstract

The era of lean production and excellence in manufacturing, while advancing with sustainable development, demands the rational utilization of raw materials and energy resources, adopting cleaner and environmentally friendly industrial processes [...] Full article

(This article belongs to the Special Issue Failure Mechanisms in Alloys)

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Research

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25 pages, 16251 KiB

Open AccessArticle

Research of Tribological Properties of 34CrNiMo6 Steel in the Production of a Newly Designed Self-Equalizing Thrust Bearing

by Marek Urban and Katarina Monkova

Metals 2020, 10(1), 84; https://doi.org/10.3390/met10010084 - 3 Jan 2020

Cited by 7 | Viewed by 4521

Abstract

There are many cases when in large power equipment (such as a turbine or compressor) asymmetrically loading on bearings due to thermal deformations, production inaccuracies, or simple deflection of the shaft occurs. This asymmetrically loading means misalignment of rotor against stator in angle [...] Read more.

There are many cases when in large power equipment (such as a turbine or compressor) asymmetrically loading on bearings due to thermal deformations, production inaccuracies, or simple deflection of the shaft occurs. This asymmetrically loading means misalignment of rotor against stator in angle more than several tenths of a degree and it has an influence on a journal and thrust bearings. Over the last few years, thanks to increasingly precise manufacturing, solutions that can eliminate this phenomenon have been revealed. In the case of the thrust bearing, it is a system of very precise manufactured levers, which are in close contact each to other, so they have to be not only properly designed from the geometrical point of view but the important role plays a quality of the functional surfaces of these levers. The article deals with the surface treatment effect on tribological properties of 34CrNiMo6 steel used for the production of bearing levers, which are the critical parts of a newly developing self-equalizing thrust bearing. The samples with cylindrical and plate shapes were produced from 34CrNiMo6 steel as representatives of the most suitable geometries for contact surfaces. All samples were heat-treated. The surfaces of some samples were treated by electroless nickel plating or nitriding, some of the samples were treated by tumbling. Gradually, the surface roughness, microhardness, metallographic analysis and the influence of selected types of surface treatments on the wear for individual samples were evaluated within the research presented in the article. As the testing methods for evaluation of tribological properties were selected Pin-on-disc test and frequency tribological test. The results showed that the best tribological properties achieved samples treated by electroless nickel plating compared with the nitrided or only heat-treated samples. Full article

(This article belongs to the Special Issue Failure Mechanisms in Alloys)

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25 pages, 21350 KiB

Open AccessArticle

Examination of Formability Properties of 6063 Alloy Extruded Profiles for the Automotive Industry

by Athanasios Vazdirvanidis, Ioannis Pressas, Sofia Papadopoulou, Anagnostis Toulfatzis, Andreas Rikos, Marianna Katsivarda, Grigoris Symeonidis and George Pantazopoulos

Metals 2019, 9(10), 1080; https://doi.org/10.3390/met9101080 - 7 Oct 2019

Cited by 6 | Viewed by 3929

Abstract

Bendability is a crucial property of automotive parts, which describes the ability of extruded profiles to be formed to shape, without the appearance of discontinuities that will have an adverse effect on the mechanical properties and their energy absorption capacity (crashworthiness). Anisotropic behavior [...] Read more.

Bendability is a crucial property of automotive parts, which describes the ability of extruded profiles to be formed to shape, without the appearance of discontinuities that will have an adverse effect on the mechanical properties and their energy absorption capacity (crashworthiness). Anisotropic behavior exhibited by Al alloy extrusions has been documented due to the nature of the hot working process. In the present article an attempt is made in order to determine the main factors influencing bending properties in longitudinal and transverse to extrusion direction, which are also related with anisotropic behavior. Mechanical testing, microscopic examination and finite element analysis were applied in the frame of the current investigation. The findings were indicative that grain morphology and orientation (texture), especially on the surface zone of the extruded profiles, as well as morphology and distribution of the constituent particles are strongly related with formability. Full article

(This article belongs to the Special Issue Failure Mechanisms in Alloys)

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20 pages, 5236 KiB

Open AccessArticle

Finite Element Analysis of Forward Slip in Micro Flexible Rolling of Thin Aluminium Strips

by Feijun Qu, Jianzhong Xu and Zhengyi Jiang

Metals 2019, 9(10), 1062; https://doi.org/10.3390/met9101062 - 29 Sep 2019

Cited by 3 | Viewed by 2925

Abstract

This study delineates a novel finite element model to consider a pattern of process parameters affecting the forward slip in micro flexible rolling, which focuses on the thickness transition area of the rolled strip with thickness in the micrometre range. According to the [...] Read more.

This study delineates a novel finite element model to consider a pattern of process parameters affecting the forward slip in micro flexible rolling, which focuses on the thickness transition area of the rolled strip with thickness in the micrometre range. According to the strip marking method, the forward slip is obtained by comparison between the distance of the bumped ridges on the roll and that of the markings indented by the ridges, which not only simplifies the calculation process, but also maintains the accuracy as compared with theoretical estimates. The simulation results identify the qualitative and quantitative variations of forward slip with regard to the variations in the reduction, rolling speed, estimated friction coefficient and the ratio of strip thickness to grain size, respectively, which also locate the cases wherein the relative sliding happens between the strip and the roll. The developed grain-based finite element model featuring 3D Voronoi tessellations allows for the investigation of the scatter effect of forward slip, which gets strengthened by the enhanced effect of every single grain attributed to the dispersion of fewer grains in a thinner strip with respect to constant grain size. The multilinear regression analysis is performed to establish a statistical model based upon the simulation results, which has been proven to be accurate in quantitatively describing the relationship between the forward slip and the aforementioned process parameters by considering both correlation and error analyses. The magnitudes of each process parameter affecting forward slip are also determined by variance analysis. Full article

(This article belongs to the Special Issue Failure Mechanisms in Alloys)

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8 pages, 6129 KiB

Open AccessArticle

Creep Failure of Reformer Tubes in a Petrochemical Plant

by Abbas Bahrami and Peyman Taheri

Metals 2019, 9(10), 1026; https://doi.org/10.3390/met9101026 - 21 Sep 2019

Cited by 14 | Viewed by 7784

Abstract

This paper investigates a failure in HP-Mod radiant tubes in a petrochemical plant. Tubes fail after 90,000 h of working at 950 °C. Observed failure is in the form of excessive bulging and longitudinal cracking in reformer tubes. Cracks are also largely branched. [...] Read more.

This paper investigates a failure in HP-Mod radiant tubes in a petrochemical plant. Tubes fail after 90,000 h of working at 950 °C. Observed failure is in the form of excessive bulging and longitudinal cracking in reformer tubes. Cracks are also largely branched. The microstructure of service-exposed tubes was evaluated using optical and scanning electron microscopes (SEM). Energy-dispersive X-ray spectroscopy (EDS) was used to analyze and characterize different phases in the microstructure. The results of this study showed that carbides are coarsened at both the inner and the outer surface due to the long exposure to a carburizing environment. Metallography examinations also revealed that there are many creep voids that are nucleated on carbide phases and scattered in between dendrites. Cracks appeared to form as a result of creep void coalescence. Failure is therefore attributed to creep due to a long exposure to a high temperature. Full article

(This article belongs to the Special Issue Failure Mechanisms in Alloys)

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12 pages, 2054 KiB

Open AccessArticle

Prediction of Bake Hardening Behavior of Selected Advanced High Strength Automotive Steels and Hailstone Failure Discussion

by Mária Mihaliková, Kristína Zgodavová, Peter Bober and Andrea Sütőová

Metals 2019, 9(9), 1016; https://doi.org/10.3390/met9091016 - 18 Sep 2019

Cited by 10 | Viewed by 4200

Abstract

The purpose of the present study is three-fold. Firstly, it attempts to describe the bake hardening (BH) behavior of selected interstitial free (IF) and dual phase (DP) steels. Secondly, it predicts the BH behavior of the IF DX 51D and DP 500 HCT [...] Read more.

The purpose of the present study is three-fold. Firstly, it attempts to describe the bake hardening (BH) behavior of selected interstitial free (IF) and dual phase (DP) steels. Secondly, it predicts the BH behavior of the IF DX 51D and DP 500 HCT 590X plates of steel, and thirdly studies material failure prevention in scholarly sources. The research is aimed at investigating the increasing steel strength during the BH of these two high-strength sheets of steel used for outer vehicle body parts. Samples of steel were pre-strained to 1%, 2%, and 5% and then baked at 140–220 °C for 10 to 30 min. The BH effect was determined from three factors: pre-strain, baking temperature, and baking time. Research has shown that increasing the yield strength by the BH effect is predictable. Therefore, the number of experiments could be reduced for the investigation of BH effect for other kinds of IF and DP steels. The literature study of the hailstone failure reveals that the knowledge of BH steels behavior helps to calculate the steel supplier´s failure mode effect analysis (FMEA) risk priority number. Full article

(This article belongs to the Special Issue Failure Mechanisms in Alloys)

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7 pages, 2173 KiB

Open AccessArticle

A Study on the Failure of AISI 304 Stainless Steel Tubes in a Gas Heater Unit

by Abbas Bahrami and Peyman Taheri

Metals 2019, 9(9), 969; https://doi.org/10.3390/met9090969 - 3 Sep 2019

Cited by 26 | Viewed by 4651

Abstract

This paper investigates a failure in convection section tubes of a gas heater unit in a petrochemical plant. Tubes are made of AISI 304 stainless steel. The failure is reported after 5 years of service at working temperature 500 °C. The failure is [...] Read more.

This paper investigates a failure in convection section tubes of a gas heater unit in a petrochemical plant. Tubes are made of AISI 304 stainless steel. The failure is reported after 5 years of service at working temperature 500 °C. The failure is in the form of circumferential cracks in the vicinity of the weld. Various characterization techniques, including optical and electron microscopes as well as energy-dispersive X-ray spectroscopy (EDS), were used to study the failure. Results showed that that the damage has initiated in the heat affected zone (HAZ) area parallel to the weld/base metal interface. Cracks have propagated alongside grain boundaries, resulting in an intergranular fracture. The main cause of failure was concluded to be attributable to the grain boundary sensitization and intergranular grain boundary attack due to improper welding and long time exposure of tubes to high temperature. Possible mitigation strategies to minimize similar failures will be discussed. Full article

(This article belongs to the Special Issue Failure Mechanisms in Alloys)

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27 pages, 37541 KiB

Open AccessArticle

Research on Chip Shear Angle and Built-Up Edge of Slow-Rate Machining EN C45 and EN 16MnCr5 Steels

by Katarina Monkova, Peter Pavol Monka, Adriana Sekerakova, Jozef Tkac, Martin Bednarik, Juraj Kovac and Andrej Jahnatek

Metals 2019, 9(9), 956; https://doi.org/10.3390/met9090956 - 30 Aug 2019

Cited by 7 | Viewed by 5117

Abstract

One of the phenomena that accompanies metal cutting is extensive plastic deformation and fracture. The excess material is plastically deformed, fractured, and removed from the workpiece in the form of chips, the formation of which depends on the type of crack and their [...] Read more.

One of the phenomena that accompanies metal cutting is extensive plastic deformation and fracture. The excess material is plastically deformed, fractured, and removed from the workpiece in the form of chips, the formation of which depends on the type of crack and their propagation. Even in case of the so-called ‘continuous’ chip formation there still has to be a fracture, as the cutting process involves the separation of a chip from the workpiece. Controlling the chip separation and its patterning in a suitable form is the most important problem of the current industrial processes, which should be highly automated to achieve maximal production efficiency. The article deals with the chip root evaluation of two EN C45 and EN 16MnCr5 steels, focusing on the shear angle measuring and built-up edge observation as important factors influencing the machining process, because a repeated formation and dislodgement of built-up edge unfavorably affects changes in the rake angle, causing fluctuation in cutting forces, and thus inducing vibration, which is harmful to the cutting tool. Consequently, this leads to surface finish deterioration. The planing was selected as a slow-rate machining operation, within which orthogonal and oblique cutting has been used for the comparative chips’ root study. The planned experiment was implemented at three levels (lower, basic, and upper) for the test preparation and the statistical method, and regression function was used for the data evaluation. The mutual connections among the four considered factors (cutting speed, cutting depth, tool cutting edge inclination, and rake angle) and investigated by the shear angle were plotted in the form of graphical dependencies. Finally, chips obtained from both steels types and within both cutting methods were systematically processed from the microscopic (chip root) and macroscopic (chip pattern) points of view. Full article

(This article belongs to the Special Issue Failure Mechanisms in Alloys)

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14 pages, 2203 KiB

Open AccessArticle

Validation of a New Quality Assessment Procedure for Ductile Irons Production Based on Strain Hardening Analysis

by Giuliano Angella and Franco Zanardi

Metals 2019, 9(8), 837; https://doi.org/10.3390/met9080837 - 27 Jul 2019

Cited by 9 | Viewed by 3033

Abstract

A mathematical procedure based on the analysis of tensile flow curves has been proposed to assess the microstructure quality of several ductile irons (DIs). The procedure consists of a first diagram for the assessment of the ideal microstructure of DIs, that is, the [...] Read more.

A mathematical procedure based on the analysis of tensile flow curves has been proposed to assess the microstructure quality of several ductile irons (DIs). The procedure consists of a first diagram for the assessment of the ideal microstructure of DIs, that is, the matrix where mobile dislocations move, and a second diagram for the assessment of the casting integrity because of potential metallurgical discontinuities and defects in DIs. Both diagrams are based on the dislocation-density-related constitutive Voce equation that is used for modeling the tensile plastic behavior of DIs. The procedure stands on the fundamental assumption that the strain hardening behavior of DIs is not affected by the nature and the density of the potential metallurgical discontinuities and defects, which are expected to affect only the elongations to fracture. However, this fundamental assumption is not obvious, and so its validity was evaluated through tensile testing Isothermed Ductile Irons (IDIs) 800, showing a wide scatter of elongations to rupture. The analysis of the strain hardening behaviors supported by strain energy density calculations of IDIs tensile tests proved that the fundamental assumption was valid and the quality assessment procedure could be applied to IDIs. A modified Voce equation was also introduced to improve the fitting of the experimental tensile flow curves and the strain energy density calculations. Full article

(This article belongs to the Special Issue Failure Mechanisms in Alloys)

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12 pages, 4226 KiB

Open AccessArticle

Failure-Analysis Based Redesign of Furnace Conveyor System Components: A Case Study

by Beatriz González-Ciordia, Borja Fernández, Garikoitz Artola, Maider Muro, Ángel Sanz and Luis Norberto López de Lacalle

Metals 2019, 9(8), 816; https://doi.org/10.3390/met9080816 - 25 Jul 2019

Cited by 15 | Viewed by 4249

Abstract

Any manufacturing equipment designed from scratch requires a detailed follow-up of the performance for the first units placed in service during the production ramp-up, so that lessons learned are immediately implemented in next deliveries and running equipment is accordingly updated. Component failure analysis [...] Read more.

Any manufacturing equipment designed from scratch requires a detailed follow-up of the performance for the first units placed in service during the production ramp-up, so that lessons learned are immediately implemented in next deliveries and running equipment is accordingly updated. Component failure analysis is one of the most valuable sources of improvement among these lessons. In this context, a failure-assessment based design revision of the conveying system of a newly developed press hardening furnace is presented. The proposed method starts with a forensic metallurgical analysis of the failed components, followed by an investigation of the working conditions to ensure they match the forensic observations. The results of this approach evidenced an initially unforeseen thermo-mechanical damage produced by a combination of thermal distortions, material ageing, and mechanical fatigue. Once the cause–effect relationship for the failure is backed up by evidence, an improved design is proposed. As a conclusion, a new standard design for the furnace entrance set of rollers in hot stamping lines was established for roller hearth furnaces. The solution can be extended to similar applications, ensuring the same issues will not arise thanks to the lessons learned. Full article

(This article belongs to the Special Issue Failure Mechanisms in Alloys)

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10 pages, 5467 KiB

Open AccessFeature PaperArticle

Aging Phenomena during In-Service Creep Exposure of Heat-Resistant Steels

by G. N. Haidemenopoulos, K. Polychronopoulou, A. D. Zervaki, H. Kamoutsi, S. I. Alkhoori, S. Jaffar, P. Cho and H. Mavros

Metals 2019, 9(7), 800; https://doi.org/10.3390/met9070800 - 19 Jul 2019

Cited by 9 | Viewed by 3877

Abstract

An investigation of aging phenomena during creep exposure has been conducted for HP-Nb cast reformer tubes for several exposure conditions. Aging was manifested by carbide precipitation, carbide coarsening, and carbide transformation. The transformation of primary M₇C₃ to the more stable [...] Read more.

An investigation of aging phenomena during creep exposure has been conducted for HP-Nb cast reformer tubes for several exposure conditions. Aging was manifested by carbide precipitation, carbide coarsening, and carbide transformation. The transformation of primary M₇C₃ to the more stable M₂₃C₆ carbide takes place at high exposure temperature (910 °C and above). The primary MC carbides transform to the Ni-Nb silicide or G-phase during creep exposure. The presence of Ti in the steel prevented the transformation of MC carbides to the G-phase. Morphological changes like needle to globular transitions, rounding of carbide edges, and carbide coarsening take place during creep exposure. The room-temperature tensile elongation and ultimate tensile strength are significantly reduced during creep exposure. The above aging phenomena are precursors to creep damage. Full article

(This article belongs to the Special Issue Failure Mechanisms in Alloys)

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22 pages, 6054 KiB

Open AccessFeature PaperArticle

Comparative Study of Chip Formation in Orthogonal and Oblique Slow-Rate Machining of EN 16MnCr5 Steel

by Katarina Monkova, Peter Pavol Monka, Adriana Sekerakova, Lumir Hruzik, Adam Burecek and Marek Urban

Metals 2019, 9(6), 698; https://doi.org/10.3390/met9060698 - 20 Jun 2019

Cited by 8 | Viewed by 5444

Abstract

In today’s unmanned productions systems, it is very important that the manufacturing processes are carried out efficiently and smoothly. Therefore, controlling chip formation becomes an essential issue to be dealt with. It can be said that the material removal from a workpiece using [...] Read more.

In today’s unmanned productions systems, it is very important that the manufacturing processes are carried out efficiently and smoothly. Therefore, controlling chip formation becomes an essential issue to be dealt with. It can be said that the material removal from a workpiece using machining is based on the degradation of material cohesion made in a controlled manner. The aim of the study was to understand the chip formation mechanisms that can, during uncontrolled processes, result in the formation and propagation of microcracks on the machined surface and, as such, cause failure of a component during its operation. This article addresses some aspects of chip formation in the orthogonal and oblique slow-rate machining of EN 16MnCr5 steel. In order to avoid chip root deformation and its thermal influence on sample acquisition, that could cause the changes in the microstructure of material, a new reliable method for sample acquisition has been developed in this research. The results of the experiments have been statistically processed. The obtained dependencies have uncovered how the cutting tool geometry and cutting conditions influence a chip shape, temperature in cutting area, or microhardness according to Vickers in the area of shear angle. Full article

(This article belongs to the Special Issue Failure Mechanisms in Alloys)

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11 pages, 6589 KiB

Open AccessArticle

Enhanced Ductility of a W-30Cu Composite by Improving Microstructure Homogeneity

by Zehui Hao, Jinxu Liu, Jin Cao, Shukui Li, Xingwei Liu, Chuan He and Xinying Xue

Metals 2019, 9(6), 646; https://doi.org/10.3390/met9060646 - 3 Jun 2019

Cited by 12 | Viewed by 3135

Abstract

Due to its negligible solubility, it is difficult to obtain a W-30Cu composite with a homogenous microstructure. However, with a selected W skeleton, a homogeneous phase distribution was achieved for a W-30Cu composite in the present study. By detailed characterization of the mechanical [...] Read more.

Due to its negligible solubility, it is difficult to obtain a W-30Cu composite with a homogenous microstructure. However, with a selected W skeleton, a homogeneous phase distribution was achieved for a W-30Cu composite in the present study. By detailed characterization of the mechanical performance and microstructure of the W-30Cu composite, as well as the stress distribution state under a loading condition, the effects of microstructure homogeneity on the mechanical properties and failure mechanisms are identified. The mechanisms by which the ductility and strength depend on microstructure homogeneity contain the effects on plastic deformation and stress coordination of the Cu phase network. The dominant factors for the high ductility and strength of W-30Cu composites are proposed. Full article

(This article belongs to the Special Issue Failure Mechanisms in Alloys)

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14 pages, 3001 KiB

Open AccessArticle

A Macroscopic Strength Criterion for Isotropic Metals Based on the Concept of Fracture Plane

by Jiefei Gu, Puhui Chen, Ke Li and Lei Su

Metals 2019, 9(6), 634; https://doi.org/10.3390/met9060634 - 31 May 2019

Cited by 3 | Viewed by 3182

Abstract

Although the linear Mohr–Coulomb criterion is frequently applied to predict the failure of brittle materials such as cast iron, it can be used for ductile metals too. However, the criterion has some significant deficiencies which limit its predictive ability. In the present study, [...] Read more.

Although the linear Mohr–Coulomb criterion is frequently applied to predict the failure of brittle materials such as cast iron, it can be used for ductile metals too. However, the criterion has some significant deficiencies which limit its predictive ability. In the present study, the underlying failure hypotheses of the linear Mohr–Coulomb criterion were thoroughly discussed. Based on Mohr’s physically meaningful concept of fracture plane, a macroscopic strength criterion was developed to explain the failure mechanism of isotropic metals. The failure function was expressed as a polynomial expansion in terms of the stresses acting on the fracture plane, and the quadratic approximation was employed to describe the non-linear behavior of the failure envelope. With an in-depth understanding of Mohr’s fracture plane concept, the failure angle was regarded as a generalized strength parameter in addition to the failure stress (i.e., the conventional basic strength). The undetermined coefficients of the non-linear failure function were calibrated by the strength parameters obtained from the common uniaxial tension and compression tests. Theoretical and experimental assessment for different types of isotropic metals validated the effectiveness of the proposed criterion in predicting material failure. Full article

(This article belongs to the Special Issue Failure Mechanisms in Alloys)

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16 pages, 10691 KiB

Open AccessArticle

An Extended Iterative Identification Method for the GISSMO Model

by Yue Xiao and Yumei Hu

Metals 2019, 9(5), 568; https://doi.org/10.3390/met9050568 - 15 May 2019

Cited by 17 | Viewed by 5161

Abstract

This study examines an extended method to obtain the parameters in the Generalized Incremental Stress State Dependent Damage (GISSMO) model. This method is based on an iterative Finite Element Method (FEM) method aiming at predicting the fracture behavior considering softening and failure. A [...] Read more.

This study examines an extended method to obtain the parameters in the Generalized Incremental Stress State Dependent Damage (GISSMO) model. This method is based on an iterative Finite Element Method (FEM) method aiming at predicting the fracture behavior considering softening and failure. A large number of experimental tests have been conducted on four different alloys (7003 aluminum alloy, ADC12 aluminum alloy, ZK60 magnesium alloy and 20CrMnTiH Steel), here considering tests that span a wide range of stress triaxiality. The proposed method is compared with the two existing methods. Results show that the new extended Iterative FEM method gives the good estimate of the fracture behaviors for all four alloys considered. Full article

(This article belongs to the Special Issue Failure Mechanisms in Alloys)

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15 pages, 5117 KiB

Open AccessFeature PaperArticle

Modeling of Ti6Al4V Alloy Orthogonal Cutting with Smooth Particle Hydrodynamics: A Parametric Analysis on Formulation and Particle Density

by Adam D. Lampropoulos, Angelos P. Markopoulos and Dimitrios E. Manolakos

Metals 2019, 9(4), 388; https://doi.org/10.3390/met9040388 - 28 Mar 2019

Cited by 8 | Viewed by 3429

Abstract

Computational modeling is a widely used method for simulation and analysis of machining processes. Smooth particle hydrodynamics (SPH) is a comparatively recently developed method that is used for the simulation of processes where high strains and fragmentation occur. The purpose of this work [...] Read more.

Computational modeling is a widely used method for simulation and analysis of machining processes. Smooth particle hydrodynamics (SPH) is a comparatively recently developed method that is used for the simulation of processes where high strains and fragmentation occur. The purpose of this work is the application of the SPH method for the prediction of cutting forces and chip formation mechanism in orthogonal cutting of Ti6Al4V alloy. In addition, it is examined how the final results of the simulation are influenced by the choice of the particular formulation of the SPH method, as well as by the density of the particles. Full article

(This article belongs to the Special Issue Failure Mechanisms in Alloys)

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9 pages, 5386 KiB

Open AccessArticle

In Situ Observation of the Deformation and Fracture Behaviors of Long-Term Thermally Aged Cast Duplex Stainless Steels

by Shilei Li, Yanli Wang and Xitao Wang

Metals 2019, 9(2), 258; https://doi.org/10.3390/met9020258 - 21 Feb 2019

Cited by 10 | Viewed by 3336

Abstract

Cast duplex stainless steel (CDSS) components suffer embrittlement after long-term thermal aging. The deformation and fracture behaviors of un-aged and thermally aged (at 400 °C for 20,000 h) CDSS were investigated using in situ scanning electron microscopy (SEM). The tensile strength of CDSS [...] Read more.

Cast duplex stainless steel (CDSS) components suffer embrittlement after long-term thermal aging. The deformation and fracture behaviors of un-aged and thermally aged (at 400 °C for 20,000 h) CDSS were investigated using in situ scanning electron microscopy (SEM). The tensile strength of CDSS had a small increase, and the tensile fracture changed from ductile to brittle after thermal aging. Observations using in situ SEM indicated that the initial cracks appeared in the ferrite perpendicular to the loading direction after the macroscopic stress exceeded a critical value. The premature fracture of ferrite grains caused stress on the phase boundaries, leading the cracks to grow into austenite. The cleavage fracture of ferrite accelerated the shearing of austenite and reduced the plasticity of the thermally aged CDSS. Full article

(This article belongs to the Special Issue Failure Mechanisms in Alloys)

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17 pages, 4253 KiB

Open AccessArticle

Numerical Computation of Material Properties of Nanocrystalline Materials Utilizing Three-Dimensional Voronoi Models

by Panagiotis Bazios, Konstantinos Tserpes and Spiros Pantelakis

Metals 2019, 9(2), 202; https://doi.org/10.3390/met9020202 - 8 Feb 2019

Cited by 6 | Viewed by 4217

Abstract

Nanocrystalline metals have been the cause of substantial intrigue over the past two decades due to their high strength, which is highly sensitive to their microstructure. The aim of the present project is to develop a finite element two-phase model that is able [...] Read more.

Nanocrystalline metals have been the cause of substantial intrigue over the past two decades due to their high strength, which is highly sensitive to their microstructure. The aim of the present project is to develop a finite element two-phase model that is able to predict the elastic moduli and the yield strength of nanostructured material as functions of their microstructure. The numerical methodology uses representative volume elements (RVEs) in which the material microstructure, i.e., the grains and grain boundaries, is presented utilizing the three-dimensional (3D) Voronoi algorithm. The implementation of the 3D Voronoi particles was performed on the nanostructure investigation of ultrafine materials by SEM and TEM. Proper material properties for the grain interiors (GI) and grain boundaries (GB) were computed using the Hall-Petch equation and a dislocation-based analytical approach, respectively. The numerical outcomes show that the Young’s Modulus of nanostructured copper increased by increasing the crystallite volume fraction, while the yield strength increased by decreasing the grain size. The numerical predictions were strongly confirmed in opposition to finite element outcomes, experimental results from the open literature, and predictions from the rule of mixtures and the Mori-Tanaka analytical models. Full article

(This article belongs to the Special Issue Failure Mechanisms in Alloys)

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14 pages, 4274 KiB

Open AccessArticle

Improving the Reliability of Mechanical Components That Have Failed in the Field Due to Repetitive Stress

by Seongwoo Woo and Dennis L. O’Neal

Metals 2019, 9(1), 38; https://doi.org/10.3390/met9010038 - 4 Jan 2019

Cited by 3 | Viewed by 3023

Abstract

To improve the reliability of mechanical parts that have failed in the field, a reliability methodology for parametric accelerated life testing (ALT) is proposed. It consists of: (1) a parametric ALT plan, (2) a load analysis, (3) a tailored series of parametric ALTs [...] Read more.

To improve the reliability of mechanical parts that have failed in the field, a reliability methodology for parametric accelerated life testing (ALT) is proposed. It consists of: (1) a parametric ALT plan, (2) a load analysis, (3) a tailored series of parametric ALTs with action plans, and (4) an evaluation of the final designs to ensure the design requirements are satisfied. This parametric ALT should help an engineer reproduce the fractured or failed parts in a product subjectedto repetitive loading and correct the faulty designs. As a test case, the helix upper dispenser of a refrigerator ice-maker fractured in field was studied. Using a load analysis, we discerned that the helix upper dispenser fracture was due to repetitive loads and a faulty design with a 2 mm gap between the blade dispenser and the helix upper dispenser. During the first and second ALTs, the fracture in the helix upper dispenser was reproduced. The failure modes and mechanisms found were similar to those of the failed sample in field. As an action plan, the design of the helix upper dispenser was modified by eliminating the 2 mm gap and adding enforced ribs. In the third ALT there were no problems. After three rounds of parametric ALTs, the reliability of the helix upper dispenser was guaranteed as a 10-year life with an accumulated failure rate of 1%. Full article

(This article belongs to the Special Issue Failure Mechanisms in Alloys)

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15 pages, 3478 KiB

Open AccessArticle

Evaluation Study on Iterative Inverse Modeling Procedure for Determining Post-Necking Hardening Behavior of Sheet Metal at Elevated Temperature

by Han Mei, Lihui Lang, Kangning Liu and Xiaoguang Yang

Metals 2018, 8(12), 1044; https://doi.org/10.3390/met8121044 - 10 Dec 2018

Cited by 12 | Viewed by 3933

Abstract

The identification of the post-necking strain hardening behavior of metal sheet is important for finite element analysis procedures of sheet metal forming process. The inverse modeling method is a practical way to determine the hardening curve to large strains. This study is thus [...] Read more.

The identification of the post-necking strain hardening behavior of metal sheet is important for finite element analysis procedures of sheet metal forming process. The inverse modeling method is a practical way to determine the hardening curve to large strains. This study is thus focused on the evaluation of the inverse modeling method using a novel material performance test. In this article, hot uniaxial tensile test of a commercially pure titanium sheet with rectangular section was first conducted. Utilizing the raw data from the tensile test, the post-necking hardening behavior of the material is determined by a FE-based inverse modeling procedure. Then the inverse method is compared with some classical hardening models. In order to further evaluate the applicability of the inverse method, biaxial tensile test at elevated temperatures was performed using a special designed cruciform specimen. The cruciform specimen could guarantee that the maximum equi-biaxial deformation occurs in the center section. By using the inverse modeling procedure, the hardening curves under biaxial stress state are able to be extracted. Finally the stress-strain curves obtained from the two experiments are compared and analysis studies are provided. Full article

(This article belongs to the Special Issue Failure Mechanisms in Alloys)

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19 pages, 4616 KiB

Open AccessArticle

A Comprehensive CFD Model for Dual-Phase Brass Indirect Extrusion Based on Constitutive Laws: Assessment of Hot-Zone Formation and Failure Prognosis

by George Pashos, George A. Pantazopoulos and Ioannis Contopoulos

Metals 2018, 8(12), 1043; https://doi.org/10.3390/met8121043 - 8 Dec 2018

Cited by 3 | Viewed by 3989

Abstract

A numerical method for the precise calculation of temperature, velocity and pressure profiles of the α-β brass indirect hot extrusion process is presented. The method solves the Navier–Stokes equations for non-Newtonian liquids with strain-rate and temperature-dependent viscosity that is formulated using established constitutive [...] Read more.

A numerical method for the precise calculation of temperature, velocity and pressure profiles of the α-β brass indirect hot extrusion process is presented. The method solves the Navier–Stokes equations for non-Newtonian liquids with strain-rate and temperature-dependent viscosity that is formulated using established constitutive laws based on the Zener–Hollomon type equation for plastic flow stress. The method can be implemented with standard computational fluid dynamics (CFD) software, has relatively low computational cost, and avoids the numerical artifacts associated with other methods commonly used for such processes. A response surface technique is also implemented, and it is thus possible to build a reduced order model that approximately maps the process with respect to all combinations of its parameters, including the extrusion speed and brass phase constitution. The reduced order model can be a very useful tool for production, because it instantaneously provides important quantities, such as the average pressure or the temperature of hot-spots that are formed due to the combined effect of die/billet friction and the generation of heat from plastic deformation (adiabatic shear deformation heating). This approach can assist in the preliminary evaluation of the metal flow pattern, and in the prediction and prevention of critical extrusion failures, thus leading to subsequent process and product quality improvements. Full article

(This article belongs to the Special Issue Failure Mechanisms in Alloys)

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14 pages, 5038 KiB

Open AccessArticle

Electrochemical Investigation of Corrosion of X80 Steel under Elastic and Plastic Tensile Stress in CO₂ Environment

by Wei Wu, Hailong Yin, Hao Zhang, Jia Kang, Yun Li and Yong Dan

Metals 2018, 8(11), 949; https://doi.org/10.3390/met8110949 - 14 Nov 2018

Cited by 15 | Viewed by 4880

Abstract

An investigation into the electrochemical corrosion behavior of X80 pipeline steel under different elastic and plastic tensile stress in a CO₂-saturated NaCl solution has been carried out by using open-circuit potential, potentiodynamic polarization, electrochemical impedance spectroscopy, and surface analysis techniques. The [...] Read more.

An investigation into the electrochemical corrosion behavior of X80 pipeline steel under different elastic and plastic tensile stress in a CO₂-saturated NaCl solution has been carried out by using open-circuit potential, potentiodynamic polarization, electrochemical impedance spectroscopy, and surface analysis techniques. The results show that the corrosion rate of X80 steel first increases and then slightly decreases with the increase of elastic tensile stress, whereas the corrosion rate sharply increases with the increase of plastic tensile stress. Both elastic and plastic tensile stress can enhance steel corrosion by improving the electrochemical activity of both anodic and cathodic reactions. Moreover, compared with elastic tensile stress, plastic tensile stress has a more significant effect. Furthermore, electrochemical reactions for CO₂ corrosion and mechanoelectrochemical effect are used to reasonably explain the corrosion behavior of stressed X80 steel in CO₂ environment. Full article

(This article belongs to the Special Issue Failure Mechanisms in Alloys)

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15 pages, 7236 KiB

Open AccessArticle

Improvement of Strength and Impact Toughness for Cold-Worked Austenitic Stainless Steels Using a Surface-Cracking Technique

by Kwangyoon Kim, Minha Park, Jaeho Jang, Hyoung Chan Kim, Hyoung-Seok Moon, Dong-Ha Lim, Jong Bae Jeon, Se-Hun Kwon, Hyunmyung Kim and Byung Jun Kim

Metals 2018, 8(11), 932; https://doi.org/10.3390/met8110932 - 12 Nov 2018

Cited by 10 | Viewed by 6367

Abstract

For cryogenic applications, materials must be cautiously selected because of a drastic degradation in the mechanical properties of materials when they are exposed to very low temperatures. We have developed a new technique using a cold-working and surface-cracking process to overcome such degradation [...] Read more.

For cryogenic applications, materials must be cautiously selected because of a drastic degradation in the mechanical properties of materials when they are exposed to very low temperatures. We have developed a new technique using a cold-working and surface-cracking process to overcome such degradation of mechanical properties at low temperatures. This technique intentionally induced surface-cracks in cold-worked austenitic stainless steels and resulted in a significant increase in both strength and fracture at low temperatures. According to the microstructure observations, dissipation of the crack propagation energy with surface-cracks enhanced the impact toughness, showing a ductile fracture mode in even the cryogenic temperature region. In particular, we obtained the high strength and toughness materials by a surface-cracking technique at 5% cold-worked specimen with surface-cracks. Full article

(This article belongs to the Special Issue Failure Mechanisms in Alloys)

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16 pages, 7249 KiB

Open AccessArticle

Investigation of Stress-Oriented Hydrogen-Induced Cracking (SOHIC) in an Amine Absorber Column of an Oil Refinery

by Gregory N. Haidemenopoulos, Helen Kamoutsi, Kyriaki Polychronopoulou, Panagiotis Papageorgiou, Ioannis Altanis, Panagiotis Dimitriadis and Michael Stiakakis

Metals 2018, 8(9), 663; https://doi.org/10.3390/met8090663 - 24 Aug 2018

Cited by 5 | Viewed by 7185

Abstract

Stress-oriented hydrogen-induced cracking (SOHIC) of an amine absorber column made of a Hydrogen Induced Cracking (HIC) resistant steel and operating under wet H₂S service was investigated. SOHIC was not related to welds in the column and evolved in two steps: initiation [...] Read more.

Stress-oriented hydrogen-induced cracking (SOHIC) of an amine absorber column made of a Hydrogen Induced Cracking (HIC) resistant steel and operating under wet H₂S service was investigated. SOHIC was not related to welds in the column and evolved in two steps: initiation of HIC cracks in the rolling plane and through-thickness linking of the HIC cracks. Both the original HIC cracks as well as the linking cracks propagated with a cleavage mechanism. The key factors identified were periods with high hydrogen charging conditions, manifested by high H₂S/amine ratio, and stress triaxiality, imposed by the relatively large thickness of the plate. In addition, the mechanical properties of the steel away from cracked regions were unaffected, indicating the localized nature of SOHIC. Full article

(This article belongs to the Special Issue Failure Mechanisms in Alloys)

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32 pages, 7509 KiB

Open AccessArticle

Crack Propagation Mechanisms for Creep Fatigue: A Consolidated Explanation of Fundamental Behaviours from Initiation to Failure

by Dan Liu and Dirk John Pons

Metals 2018, 8(8), 623; https://doi.org/10.3390/met8080623 - 8 Aug 2018

Cited by 36 | Viewed by 15275

Abstract

Background—Creep-fatigue damage is generally identified as the combined effect of fatigue and creep. This behaviour is macroscopically described by crack growth, wherein fatigue and creep follow different principles. Need—Although the literature contains many studies that explore the crack-growth path, there is [...] Read more.

Background—Creep-fatigue damage is generally identified as the combined effect of fatigue and creep. This behaviour is macroscopically described by crack growth, wherein fatigue and creep follow different principles. Need—Although the literature contains many studies that explore the crack-growth path, there is a lack of clear models to link these disparate findings and to explain the possible mechanisms at a grain-based level for crack growth from crack initiation, through the steady stage (this is particularly challenging), ending in structural failure. Method—Finite element (FE) methods were used to provide a quantitative validation of the grain-size effect and the failure principles for fatigue and creep. Thereafter, a microstructural conceptual framework for the three stages of crack growth was developed by integrating existing crack-growth microstructural observations for fatigue and creep. Specifically, the crack propagation is based on existing mechanisms of plastic blunting and diffusion creep. Results—Fatigue and creep effects are treated separately due to their different damage principles. The possible grain-boundary behaviours, such as the mismatch behaviour at grain boundary due to creep deformation, are included. The framework illustrates the possible situations for crack propagation at a grain-based level, particularly the situation in which the crack encounters the grain boundary. Originality—The framework is consistent with the various creep and fatigue microstructure observations in the literature, but goes further by integrating these together into a logically consistent framework that describes the overall failure process at the microstructural level. Full article

(This article belongs to the Special Issue Failure Mechanisms in Alloys)

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15 pages, 8890 KiB

Open AccessArticle

The Effect of Impingement Velocity and Angle Variation on the Erosion Corrosion Performance of API 5L-X65 Carbon Steel in a Flow Loop

by Ihsan UlHaq Toor, Hafiz Muzammil Irshad, Hassan Mohamed Badr and Mohammed Abdul Samad

Metals 2018, 8(6), 402; https://doi.org/10.3390/met8060402 - 31 May 2018

Cited by 23 | Viewed by 6014

Abstract

Erosion corrosion performance of API 5L-X65 carbon steel was investigated at three different impingement velocities (3, 6 & 12 m/s), five different angles (15, 30, 45, 60, & 90°), and with/without solid particles (average particle size of 314 µm). The experiments were conducted [...] Read more.

Erosion corrosion performance of API 5L-X65 carbon steel was investigated at three different impingement velocities (3, 6 & 12 m/s), five different angles (15, 30, 45, 60, & 90°), and with/without solid particles (average particle size of 314 µm). The experiments were conducted in 0.2 M NaCl solution at room temperature for a duration of 24 h and the results showed that the maximum erosion corrosion rate was observed at 45° irrespective of the velocity. The highest erosion corrosion rate at 45° was due to the balance between the shear and normal impact stress at this angle. Ploughing, deep craters, and micro-forging/plastic deformation were found to be the main erosion corrosion mechanisms. The maximum wear scar depth measured using optical profilometery was found to be 51 µm (average) at an impingement angle of 45°. Full article

(This article belongs to the Special Issue Failure Mechanisms in Alloys)

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17 pages, 12410 KiB

Open AccessFeature PaperReview

An Introduction to Wear Degradation Mechanisms of Surface-Protected Metallic Components

by Pandora P. Psyllaki

Metals 2019, 9(10), 1057; https://doi.org/10.3390/met9101057 - 28 Sep 2019

Cited by 4 | Viewed by 3126

Abstract

Despite the fact that ceramics and polymers have found numerous applications in several mechanical systems, metals and metallic alloys still remain the main materials family for manufacturing the bulk of parts and components of engineering assemblies. However, in cases of components that are [...] Read more.

Despite the fact that ceramics and polymers have found numerous applications in several mechanical systems, metals and metallic alloys still remain the main materials family for manufacturing the bulk of parts and components of engineering assemblies. However, in cases of components that are serving as parts of a tribosystem, the application of surface modification techniques is required to ensure their unhampered function during operation. After a short introduction on fundamental aspects of tribology, this review article delves further into four representative case studies, where the inappropriate application of wear protection techniques has led to acceleration of the degradation of the quasi-protected metallic material. The first deals with the effects of the deficient lubrication of rolling bearings designed to function under oil lubrication conditions; the second is focused on the effects of overloading on sliding bearing surfaces, wear-protected via nitrocarburizing; the third concerns the application of welding techniques for producing hardfacing overlayers intended for the wear protection of heavily loaded, non-lubricated surfaces; the fourth deals with the degradation of thermal-sprayed ceramic coatings, commonly used as wear-resistant layers. Full article

(This article belongs to the Special Issue Failure Mechanisms in Alloys)

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20 pages, 4047 KiB

Open AccessReview

A Short Review on Fracture Mechanisms of Mechanical Components Operated under Industrial Process Conditions: Fractographic Analysis and Selected Prevention Strategies

by George A. Pantazopoulos

Metals 2019, 9(2), 148; https://doi.org/10.3390/met9020148 - 29 Jan 2019

Cited by 79 | Viewed by 15539

Abstract

An insight of the dominant fracture mechanisms occurring in mechanical metallic components during industrial service conditions is offered through this short overview. Emphasis is given on the phenomenological aspects of fracture and their relationships with the emergent fracture mode(s) with respect to the [...] Read more.

An insight of the dominant fracture mechanisms occurring in mechanical metallic components during industrial service conditions is offered through this short overview. Emphasis is given on the phenomenological aspects of fracture and their relationships with the emergent fracture mode(s) with respect to the prevailed operating parameters and loading conditions. This presentation is basically fulfilled by embracing and reviewing industrial case histories addressed from a technical expert viewpoint. The referenced case histories reflected mainly the author’s team expertise in failure analysis investigation. As a secondary perspective of the current study, selected failure investigation and prevention methodological approaches are briefly summarized and discussed, aiming to provide a holistic overview of the specific frameworks and systems in place, which could assist the organization of risk minimization and quality enhancement. Full article

(This article belongs to the Special Issue Failure Mechanisms in Alloys)

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