Jaiveer Singh

Bio: Jaiveer Singh is an academic researcher from Sunchon National University. The author has contributed to research in topics: Electron backscatter diffraction & Crystal twinning. The author has an hindex of 10, co-authored 23 publications receiving 230 citations. Previous affiliations of Jaiveer Singh include Indian Institute of Technology Bombay & Indian Institute of Technology, Jodhpur.

The effect of initial texture on micromechanical deformation behaviors in Mg alloys under a mini-V-bending test

Abstract: Micromechanical deformation behaviors of E-form fine grain (EFG), E-form coarse grain (ECG), and AZ31 magnesium (Mg) alloys were investigated and compared using a mini-V-bending test. EFG and ECG Mg alloys with a weaker texture showed better bendability compared with AZ31 alloy that has a stronger texture. The evolution of the microstructure and microtexture during the mini-V-bending process was experimentally analyzed via an electron back-scattered diffraction (EBSD) technique. This study was focused on the effect that deformation twinning exerts on the strain localization and crack initiation. The twin bands (TBs) developed in the tension zone of bent specimens found to be closely related to the strain localization and crack initiation during the mini-V-bending process. A resolved shear stress (RSS) criterion and microstructure based crystal plasticity finite element method (CPFEM) were used to theoretically predict the activation of { 10 1 ¯ 2 } tension (TTW) and { 10 1 ¯ 1 } compression (CTW) twins in Mg alloys under a mini-V-bending process. RSS analysis indicated that EFG and ECG Mg alloys are more favorable for the activity of TTW and less favorable for the activity of CTW when compared with AZ31 Mg alloy during a mini-V-bending process. However, RSS analysis was not effective in quantitatively predicting twin development. The relative activities of six deformation modes, accumulated twin fractions, and accumulated plastic strains were simulated via microstructure-based CPFEM modeling. Compared with RSS analysis, CPFEM precisely explained the twin behavior that has been experimentally observed in ECG and AZ31 Mg alloys.

Effect of strain rate on twinning in a Zr alloy

Abstract: Zr–1Nb alloy uniaxially compressed at room temperature at 10−2 and 103 s−1 exhibited twinning and a three-stage strain-hardening behavior. At 103 s−1 the twin fraction initially increased to 0.3, decreasing to 0.02 at higher strains. Despite the difference in texture at intermediate strains, the final texture was similar at both strain rates. The increasing strain-hardening rate in the second stage was attributed to strengthening from grain boundaries and dislocations, and softening from reorientation due to twinning.

Deformation mechanisms and texture evolution in high entropy alloy during cold rolling

Abstract: In the present study, equiatomic CoCrFeMnNi high entropy alloy (HEA) was subjected to thickness reductions of 20, 40, and 60% during cold rolling in order to thoroughly investigate the evolutions of both the microstructure and the deformation texture. Important aspects of deformed microstructures such as the activation of multiple twin variants and the formation of shear bands in the matrix were captured using electron backscatter diffraction (EBSD) and electron channeling contrast imaging (ECCI) techniques. Twin trace analysis (TTA) was performed in conjunction with resolved shear stress (RSS) analysis for the identification of active twin variants. The RSS ratio, which is a ratio of the maximum RSS values for corresponding twin and slip systems, was used to reveal the orientation dependence of deformation twinning. Visco-plastic self-consistent (VPSC) simulations were carried out to predict the evolution of the crystallographic texture, the transition routes of ideal orientations subjected to multiple deformation twinning, and the role that deformation modes play in the rotation of orientation. Experimental and simulation results substantiated the key finding of the deformation twinning of a Brass orientation, which established new perspectives concerning the evolution of microstructure and texture. One twin variant of the Copper orientation was moved to a Goss orientation by dislocation slip while the other two variants were rotated towards Brass and S orientations. Meanwhile, twin variants of the S and Brass orientations primarily transitioned to a Brass orientation. The Goss orientation showed great resistance to the twinning mode. Furthermore, dislocation slip and the formation of shear bands contributed to the evolution of a strong texture while deformation twinning had the opposite effect.

Effect of initial microstructure on the deformation heterogeneities of 316L stainless steels fabricated by selective laser melting processing

Abstract: The selective laser melting (SLM) is a popular additive manufacturing (AM) technique used for the fabrication of metal parts In the present study, two 316L stainless steel specimens (SLM-I and SLM-II) with different microstructures were fabricated with different levels of energy density by changing the laser power and scanning speed, which are the main SLM process conditions The deformation and fracture behavior of miniature SLM specimens under uniaxial tension were experimentally measured via optical microscopy (OM), field emission scanning microscopy (FE-SEM), and an electron back-scattered diffraction (EBSD) technique In order to analyze the deformation heterogeneities under uniaxial tension, the inverse pole figure (IPF) map, kernel average misorientation (KAM) map, Taylor factor (TF) map, grain boundaries (GBs), Σ3 twin boundaries (TBs), and melt pool boundaries (MPBs) developed in deformed SLM specimens were analyzed at different strain levels The effect of microstructural factors on the deformation heterogeneities of SLM specimens was explained by the evolution of KAM, GBs, MPBs, and Σ3 TBs The initial microstructures of the SLM specimens significantly influenced the generation and propagation of cracks under uniaxial tension

The effect of strain heterogeneity on the deformation and failure behaviors of E-form Mg alloy sheets during a mini-V-bending test

Abstract: Deformation and failure behaviors of E-form magnesium (Mg) alloy sheets were investigated using a mini-V-bending test. The evolution of the microstructure and microtexture of the deformed E-form Mg alloy sheets (before and after failure) was analyzed via an electron back-scattered diffraction (EBSD) technique. Finite element analysis (FEA) was used to capture the heterogeneous distribution of longitudinal-strain components through the thickness direction under mini-V-bending at different punch strokes. The relationships between punch stroke, bending radius and longitudinal-strain at the tension and compression zones were established. EBSD analysis revealed that shear localization by dislocation slip along with compression and double twins were the main deformation mechanisms in the tension zone while tensile twins were a main deformation mechanism in the compression zone in E-form Mg alloy sheets during mini-V-bending. The effect that deformation twinning had on the crack propagation sites in E-form Mg alloy sheets was also investigated. The networks of compression { 10 1 ¯ 1 } and double { 10 1 ¯ 1 } − { 10 1 ¯ 2 } twins in the tension zone of E-form Mg alloy sheets were closely related to the crack propagation during mini-V-bending at near room temperature (RT).

I and i

Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

Strain rate dependence of deformation-induced transformation and twinning in a metastable titanium alloy

Abstract: A metastable β Ti–10V–3Fe–3Al–0.27O (wt.%) alloy was subjected to thermo-mechanical processing to induce α and ω phase formation, so that the alloy can exhibit the features responsible for both transformation induced plasticity (TRIP) and twinning induced plasticity (TWIP) behaviour during deformation. The alloy thereafter was deformed at different strain rates (10−3, 10−1, 101, 102 s−1) at ambient temperature. At slow strain rate (≤10−3 s−1), in addition to slip the alloy displayed a dominant deformation mechanism with α′′ martensite formation, where mechanical {332}〈113〉β twinning and deformation-induced ω phase were also activated. At an intermediate strain rate, 10−1 s−1, there was a competition between stress-induced phase transformations and stress-induced twinning deformation mechanisms. With increasing strain rate to 101 s−1 or higher; it was found that the dominant deformation mode was twinning. These results have been correlated with the β phase stability of the samples.

Friction Stir Processing of a High Entropy Alloy Al0.1CoCrFeNi

Abstract: High entropy alloys are a new class of metallic materials with a potential for use in structural applications. However, most of the studies have focused on microhardness and compressive strength measurements for mechanical properties determination. This study presents the tensile deformation behavior of a single-phase, face-centered cubic Al0.1CoCrFeNi high entropy alloy (HEA). Friction stir processing was carried out to refine the grain size. Scanning electron microscopy and electron backscatter diffraction were carried out for microstructural examination. The grain size of the alloy was on the order of millimeters in the as-received condition. The average grain size after friction stir processing of the alloy was 14 ± 10 micrometers. The mechanical properties were determined through microhardness measurement and mini-tensile tests. The friction stir processed alloy showed a total elongation of ~75% for the mini-tensile sample used and yield strength of 315 MPa. It is an exceptional combination of strength and ductility. Friction stress was determined to be 174 MPa and the Hall–Petch coefficient was 371 MPa (µm)1/2. Such a high value of Hall–Petch coefficient suggests that grain boundary strengthening can be a very effective strengthening mechanism for the HEA Al0.1CoCrFeNi.

Drastic improvement in mechanical properties and weldability of 316L stainless steel weld joints by using electromagnetic vibration during GTAW process

Abstract: In this study, the influence of applying electromagnetic vibration during welding on the microstructural transformations, mechanical properties, and hot-cracking susceptibility in 316L stainless steel welding joints have been investigated. For this purpose, sheets of 6 mm thick were welded using Gas-Tungsten Arc Welding (GTAW). During welding, electromagnetic vibrations with voltages of 0, 20 and 40 V were applied to the weld pool in contact with welding. Afterwards, in order to investigate the microstructure of different zones in the weld joint, optical and scanning electron microscopes (SEM) were carried out. In order to investigate the mechanical properties of weld joints, tensile, Charpy impact, and Vickers microhardness tests were carried out. Then, to study the fracture mode of joints after that tensile test, the fracture surfaces of the joints are investigated using SEM. In order to investigate the hot-cracking susceptibility of the 316L stainless steel weld joints, the longitudinal Varestraint test was carried out. Microstructural observations showed that increasing the electromagnetic vibration during welding process decreases the number and length of columnar dendrites in the weld metal and shifts the microstructure from columnar to fine equiaxed dendrites. Also, it was revealed that the microstructure of weld metal included austenite grains with grain-boundary delta ferrite. Increasing electromagnetic vibration during welding process results in a reduction of delta ferrite in the weld metal; and, also increases the extent of an unmixed zone. Mechanical tests reveal that increasing magnetic vibration during welding process results in drastic increases in mechanical properties including yield strength, toughness, and the hardness of welding joints. The results of longitudinal Varestraint tests show that increasing electromagnetic vibration during welding process results in decreasing the hot-crack susceptibility in the 316L stainless steel welding joints. Also, the analysis of fracture mode shows that increasing the electromagnetic vibration voltage during GTAW process results in a more ductile fracture with deeper dimples in the 316L stainless steel weld joints.