scholarly journals High-Temperature Deformation Behaviors of the C-Doped and N-Doped High Entropy Alloys

Metals ◽  
2021 ◽  
Vol 11 (10) ◽  
pp. 1517
Author(s):  
Hailong Yi ◽  
Yifan Zhang ◽  
Renyi Xie ◽  
Mengyuan Bi ◽  
Daixiu Wei
Keyword(s):  
High Temperature ◽  
Strain Rate ◽  
Flow Behavior ◽  
Temperature Deformation ◽  
Cubic Phase ◽  
High Entropy Alloys ◽  
Face Centered Cubic ◽  
High Entropy ◽  
Recrystallization Mechanism ◽  
Low Strain Rate

High entropy alloys (HEAs) containing multi-principal metallic constituents have attracted much attention. A good understanding of their hot-deformation behavior and recrystallization mechanism is the prerequisite for microstructures tuning and for optimizing mechanical performance. Here, the flow behavior and recrystallization mechanism of the N-doped and C-doped face-centered cubic phase HEAs are produced at high temperatures by hot-compression at 1123–1273 K, with strain rates of 0.1–0.001 s−1. Constitutive equations were successfully constructed to reveal flow behavior, and stress-strain curves were predicted using strain compensated polynomial functions. Discontinuous and continuous dynamic recrystallization proceeded concurrently when compressed at a low temperature and high strain rate, whereas discontinuous recrystallization, which occurs at primary grain boundaries, became predominant at a high temperature and low strain rate, significantly contributing to the refinement and homogenization of the grains. For this reason, a relatively high temperature and a low strain rate, in which the recrystallized grains exhibit equiaxed morphology and very weak texture, are more suitable for refining grains. The average size of the grains was approximately 10 μm. This study sheds light on grain optimization and mechanical properties through thermomechanical processing.

scholarly journals A Review of the Serrated-Flow Phenomenon and Its Role in the Deformation Behavior of High-Entropy Alloys

Metals ◽  
2020 ◽  
Vol 10 (8) ◽  
pp. 1101 ◽  
Author(s):  
Jamieson Brechtl ◽  
Shuying Chen ◽  
Chanho Lee ◽  
Yunzhu Shi ◽  
Rui Feng ◽  
...  
Keyword(s):  
Strain Rate ◽  
Complexity Analysis ◽  
Flow Behavior ◽  
Dynamical Behavior ◽  
Future Research ◽  
High Entropy Alloys ◽  
Material System ◽  
Experimental Conditions ◽  
Serrated Flow ◽  
High Entropy

High-entropy alloys (HEAs) are a novel class of alloys that have many desirable properties. The serrated flow that occurs in high-entropy alloys during mechanical deformation is an important phenomenon since it can lead to significant changes in the microstructure of the alloy. In this article, we review the recent findings on the serration behavior in a variety of high-entropy alloys. Relationships among the serrated flow behavior, composition, microstructure, and testing condition are explored. Importantly, the mechanical-testing type (compression/tension), testing temperature, applied strain rate, and serration type for certain high-entropy alloys are summarized. The literature reveals that the serrated flow can be affected by experimental conditions such as the strain rate and test temperature. Furthermore, this type of phenomenon has been successfully modeled and analyzed, using several different types of analytical methods, including the mean-field theory formalism and the complexity-analysis technique. Importantly, the results of the analyses show that the serrated flow in HEAs consists of complex dynamical behavior. It is anticipated that this review will provide some useful and clarifying information regarding the serrated-flow mechanisms in this material system. Finally, suggestions for future research directions in this field are proposed, such as the effects of irradiation, additives (such as C and Al), the presence of nanoparticles, and twinning on the serrated flow behavior in HEAs.

High-temperature plasticity of cubic bismuth oxide

1996 ◽  
Vol 11 (6) ◽  
pp. 1433-1439 ◽  
Author(s):  
Anne Vilette ◽  
S. L. Kampe
Keyword(s):  
High Temperature ◽  
Strain Rate ◽  
Bismuth Oxide ◽  
Rate Sensitivity ◽  
High Temperature Deformation ◽  
Temperature Deformation ◽  
Cubic Phase ◽  
Superplastic Behavior ◽  
Wide Range

Cubic (δ) bismuth oxide (Bi2O3) has been subjected to high temperature deformation over a wide range of temperatures and strain rates. Results indicate that bismuth oxide is essentially incapable of plastic deformation at temperatures below the monoclithic to cubic phase transformation which occurs at approximately 730 °C. Above the transformation temperature, however, Bi2O3 is extensively deformable. The variability of flow stress to temperature and strain rate has been quantified through the determination of phenomenological-based constitutive equations to describe its behavior at these high temperatures. Analysis of the so-determined deformation constants indicate an extremely strong sensitivity to strain rate and temperature, with values of the strain-rate sensitivity approaching values commonly cited as indicative of superplastic behavior.

High-Temperature Deformation Behavior of the γ Alloy Ti-48Ai-2Cr-2Nb

1990 ◽  
Vol 213 ◽  
Author(s):  
Donald S. Shih ◽  
Gary K. Scarr
Keyword(s):  
High Temperature ◽  
Strain Rate ◽  
True Strain ◽  
High Temperature Deformation ◽  
Temperature Deformation ◽  
Strain Rates ◽  
Compression Tests ◽  
Uniform Deformation ◽  
Good Workability ◽  
Low Strain Rate

ABSTRACTThe hot-workability of a two-phase (γ+α2) alloy, Ti-48A1-2Cr-2Nb, has been studied by conducting isothermal compression tests to 0.8 true strain over the temperature range of 975–1200°C at strain rates between 1×l0−1 and 3×10−3s−1. A deformation map showing temperature, strain rate, soundness of deformation, and isostress contours was constructed. Good workability is found from the low temperature/low strain rate regime to combinations of high temperature and either high or low strain rate. The upper-limit flow stress for good workability is between 450 and 500 MPa. Deformation induced softening occurs at all conditions. SEM and TEM examinations of the deformed specimens reveal that non-uniform deformation takes place at all strain rates, but cracking occurs mostly at high strain rates (e.g. 1×10−1s−1), especially combined with low temperatures. The cracking appears to progress primarily along γ/α2interfaces. It is thought that non-uniform deformation develops channels of shear bands, which in turn promote localized recrystallization, thus accommodating higher strains.

Hot Deformation Behavior of the 30%Mo/Cu-Al2O3 Composite Prepared by Vacuum Hot-Pressed Sintering

2011 ◽  
Vol 117-119 ◽  
pp. 893-896
Author(s):  
Yong Liu ◽  
Yong Wei Sun ◽  
Bao Hong Tian ◽  
Jiang Feng ◽  
Yi Zhang
Keyword(s):  
High Temperature ◽  
Strain Rate ◽  
Hot Deformation ◽  
Deformation Behavior ◽  
Flow Behavior ◽  
Peak Stress ◽  
High Temperature Deformation ◽  
Temperature Deformation ◽  
Compression Tests ◽  
Hot Deformation Behavior

Hot deformation behavior of the 30%Mo/Cu-Al2O3 composite was investigated by hot compression tests on Gleeble-1500D thermal simulator in the temperature ranges of 450~750°C and the strain rate ranges of 0.01~5s-1, as the total strain is 0.7. The results show that the peak stress increases with the decreased deformation temperature or the increased strain rate. Based on the true stress-strain curves, the established constitutive equation represents the high-temperature flow behavior of the composite, and the calculated flow stresses are in good agreement with the high- temperature deformation experimental results.

scholarly journals Plasma-Nitriding Properties of CoCrFeMnNi High-Entropy Alloys Produced by Spark Plasma Sintering

Metals ◽  
2020 ◽  
Vol 10 (6) ◽  
pp. 761
Author(s):  
Takato Karimoto ◽  
Akio Nishimoto
Keyword(s):  
Wear Resistance ◽  
Spark Plasma Sintering ◽  
Plasma Nitriding ◽  
Cubic Phase ◽  
High Entropy Alloys ◽  
Face Centered Cubic ◽  
Surface Plasma ◽  
High Entropy ◽  
Plasma Sintering ◽  
Spark Plasma

High-entropy alloys (HEAs) were fabricated by powder metallurgy using gas-atomized powder and spark plasma sintering (SPS) followed by surface modification (plasma nitriding) of the sintered sample. Plasma nitriding forms nitride and induces solid-soluting of N; it enables the diffusion of N atoms by removing the passive film formed on the surface of alloys such as stainless steel, Al alloys, and Ti alloys, via the sputtering of cations during glow discharge. Therefore, plasma nitriding has the potential to process HEAs that contain strong oxidizing elements such as Cr, Al, and Ti. In this work, a sintered CoCrFeMnNi HEA was plasma-nitrided and its properties were subsequently evaluated. A uniform microstructure without segregation was obtained in the SPS sample, and its hardness and wear resistance were found to have improved. Analysis of the sample surface after nitriding revealed that an expanded face-centered cubic phase formed on the surface plasma-nitrided at 673 K and that a CrN phase formed on the surface plasma-nitrided at temperatures greater than 723 K. The surface hardness of the plasma-nitrided sample was 1200 HV or greater, and the wear resistance and pitting corrosion resistance were improved compared with those of the untreated sample.

High Temperature Flow Behavior and Microstructure of Al-Cu/Mg2Si Metal Matrix Composite

2015 ◽  
Vol 137 (2) ◽  
Author(s):  
A. H. Shafieizad ◽  
A. Zarei-Hanzaki ◽  
M. Ghambari ◽  
A. Abbasi-Bani
Keyword(s):  
High Temperature ◽  
Strain Rate ◽  
Metal Matrix Composite ◽  
Matrix Composite ◽  
Metal Matrix ◽  
Flow Behavior ◽  
Temperature Deformation ◽  
Type Model ◽  
Second Phase ◽  
Wide Range

The present work deals with the high temperature flow behavior and the microstructure of the Al-Cu/Mg2Si metal matrix composite. Toward this end, a set of hot compression tests was performed in a wide range of temperature (573–773 K) and strain rate (0.001–0.1 s−1). The results indicated that the temperature and strain rate have a significant effect on the flow softening and hardening behavior of the material. The work hardening rate may be offset due to the occurrence of the restoration processes, the dynamic coarsening, and spheroidization of the second phase particles. In this regard, two phenomenological constitutive models, Johnson–Cook (JC) and Arrhenius-type equations, were employed to describe the high temperature deformation behavior of the composite. The JC equation diverged from experimental curves mainly in conditions which are far from its reference temperature and reference strain rate. This was justified considering the fact that JC model considers thermal softening, strain rate hardening, and strain hardening as three independent phenomena. In contrast, the Arrhenius-type model was more accurate in modeling of the flow behavior in wide range of temperature and strain rate. The minor deviation at some specified conditions was attributed to the negative strain rate sensitivity of the alloys at low temperature deformation regime.

scholarly journals A strategy of designing high-entropy alloys with high-temperature shape memory effect

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Je In Lee ◽  
Koichi Tsuchiya ◽  
Wataru Tasaki ◽  
Hyun Seok Oh ◽  
Takahiro Sawaguchi ◽  
...  
Keyword(s):  
High Temperature ◽  
Shape Memory ◽  
Shape Memory Effect ◽  
Memory Effect ◽  
Noble Metals ◽  
Alloy System ◽  
Equilibrium Temperature ◽  
High Entropy Alloys ◽  
Face Centered Cubic ◽  
High Entropy

Abstract Shape memory effect, the ability to recover a pre-deformed shape on heating, results from a reversible martensitic transformation between austenite and martensite phases. Here, we demonstrate a strategy of designing high-entropy alloys (HEAs) with high-temperature shape memory effect in the CrMnFeCoNi alloy system. First, we calculate the difference in Gibbs free energy between face-centered-cubic (FCC) and hexagonal-close-packed (HCP) phases, and find a substantial increase in thermodynamic equilibrium temperature between the FCC and HCP phases through composition tuning, leading to thermally- and stress-induced martensitic transformations. As a consequence, the shape recovery temperature in non-equiatomic CrMnFeCoNi alloys can be increased to 698 K, which is much higher than that of conventional shape memory alloys (SMAs) and comparable to that of B2-based multi-component SMAs containing noble metals (Pd, Pt, etc.) or refractory metals (Zr, Hf, etc.). This result opens a vast field of applications of HEAs as a novel class of cost-effective high-temperature SMAs.

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