A novel way to enhance the strength of twinning induced plasticity (TWIP) steels

In this paper, a novel technique to enhance yield strength of twinning induced plasticity (TWIP) steels has been reported by producing a gradient microstructure. Such a microstructure is generated using surface mechanical attrition treatment (SMAT). The SMAT processed steel exhibits a composite microstructure, comprising of hard phase at the surface and soft phase at the core. The deformed microstructure consists of a graded distribution containing of twins, high density of dislocations and nano-crystalline grains. As a combined effect of the three, a significant improvement in the yield strength is observed without much loss of ductility. (C) 2018 Acta Materialia Inc Published by Elsevier Ltd. All rights reserved

Deformation mechanisms during large strain deformation of high Mn TWIP steel

The evolution of texture and microstructure has been studied up to very large strains (epsilon(t) approximate to 3.9) on a twinning induced plasticity (TWIP) steel. Different micromechanisms have been envisaged during different deformation regimes. At early stage of deformation, the mechanism is normal slip dominated, while deformation twining starts at similar to 20% rolling and increases up to 40% deformation level. Further deformation takes place by macroscopic shear banding (SBs). A Brass (Bs) type texture forms and strengthens throughout the deformation, which has been simulated by visco-plastic self consistent (VPSC) modelling. The results of VPSC simulations correlate the relative contributions of normal slip, Shockley partials and twin activities at different strain levels, which were observed by microstructural investigation. The Lankford parameter is estimated from texture, indicate that above 70% deformation level, the material develops very high in-plane anisotropy

Effects of Stacking Fault Energy on Deformation Mechanisms in Al-Added Medium Mn TWIP Steel

In this study, the effect of aluminum (Al) addition to a manganese (Mn) steel Fe-12Mn-0.5C in regard to the change in stacking fault energy (SFE) and the consequent evolution of deformation microstructure and texture were investigated during cold rolling. An analysis of the texture and microstructure was performed to understand the deformation micro-mechanisms. Deformation micro-mechanisms were substantiated by the estimation of dislocation density and the arrangement of dislocations in the deformed microstructure by X-ray line profile analysis, which revealed significant changes in the dislocation structure with the addition of Al. Three stages of deformation mechanism were observed in all Al-added compositions. In the early stages of deformation, slip as well as twinning prevailed. In the intermediate stage, twinning took over completely and at large strains, macroscopic shear bands became the dominant deformation mode. An increase in the propensity of nanometer-sized deformation twins was observed with rolling strain. However, the addition of Al decreased the overall twin fraction in the deformed microstructure. The theoretical twinning stress was calculated to explain the crucial role of SFE on the occurrence of deformation twins in these steels. The deformation texture was predominantly of the brass type for all the Al-added compositions; however, appreciable differences were seen with Al content. The < 111 >//ND -fiber, which develops in Al-free Fe-12Mn-0.5C, completely disappeared in 3wtpct Al-containing material

Grain Boundary Engineering of Medium Mn TWIP Steels: A Novel Method to Enhance the Mechanical Properties

The grain boundary engineering (GBE) approach was employed on a medium manganese (Mn) based twinning induced plasticity (TWIP) steel to improve its mechanical properties. Two specially designed thermo-mechanical processing (TMP) routes, one involving unidirectional rolling (UDR) and the other one employing multi-step cross rolling (MSCR), with intermediate short term annealing treatment have been used. The annealing temperatures are chosen considering recrystallization and grain growth. Of the two routes, the one involving MSCR, has shown a higher fraction of special or coincident lattice site (CSL) grain boundaries. A detailed grain boundary microstructural analysis has been carried out by electron backscatter diffraction (EBSD) for differently processed samples. A significant improvement in ductility is observed in MSCR processed samples due to increase of CSL boundary fraction

Influence of homogenisation time on evolution of eutectic phases, dispersoid behaviour and crystallographic texture for Al-Zn-Mg-Cu-Ag alloy

Microstructural changes for Al-Zn-Mg-Cu-Ag alloy at the time of homogenisation (0-48 h) at 465 degrees C were examined by optical microscope (OM), field emission scanning electron microscope (FESEM), energy dispersive X-ray Spectroscopy (EDS), transmission electron microscope (TEM), differential scanning calorimetry (DSC), and X-ray diffraction (XRD) in detail. alpha (Al), eta Mg (Zn, Cu, Al)(2)], Al2Cu, and coarse Al3Fe emerged as predominant phases in the as-cast condition. The grain boundary areas were enriched with the main alloying elements i.e. Cu, Zn, Mg, and Ag. After 6 h of homogenisation, a phase change from it to S (Al2CuMg) was found to be initiated. By prolonging the homogenisation time, the dendritic network and the secondary eutectic phases were gradually dissolved in the matrix and eventually vanished after 48 h of homogenisation, which corroborated well with the proposed kinetic model. TEM micrographs demonstrated a high density of fine dispersoids after a homogenisation period for 6 h. In addition, higher homogenisation time accelerated the coarsening of dispersoids, following Ostwald ripening mechanism and lowering of Zener pinning pressure (ZPP). Crystallographic texture analysis demonstrated the presence of two completely different sets of texture components during casting and subsequent homogenisation treatments. Dominant Goss{011}< 100 >, Brass{011}< 211 >, P{011}< 111 >, CuT {552}< 115 > and S{123}< 634 > texture components appeared after casting, while Cube{100}< 001 >, rotated cube{110}< 011 >, E{111 }< 110 > and F{111}< 112 > components became dominant after homogenisation

Effects of alloying addition on deformation mechanisms, microstructure, texture and mechanical properties in Fe-12Mn-0.5C austenitic steel

In the present investigation, the dependence of deformation mechanisms on quaternary alloying addition has been investigated for medium Mn austenitic steel. A steel with composition Fe-12Mn-0.5C-X (X: Ni and Al), a medium Mn austenite steel was deformed up to 60% by cold reduction to investigate the deformation mechanisms and texture evolution. Electron Back-scattered Diffraction (EBSD) and X-ray bulk texture measurement have been performed to study the deformation behaviour. Deformed microstructure with increasing strain was systematically analyzed with respect to the alloying addition. SFE of the alloy can be tailored by the addition of alloying elements. In the present investigation, SFE has been tailored by addition of Carbon, Aluminium and Nickel. The highest deformation twin fraction has been observed in Ni added sample and the lowest in the Al added sample. Visco plastic self-consistent (VPSC) simulation has been performed to understand the contribution of slip and twin activity during deformation

Effect of Stacking Fault Energy on Microstructure and Texture Evolution during the Rolling of Non-Equiatomic CrMnFeCoNi High-Entropy Alloys

The evolution of microstructure and texture in three non-equiatomic CrMnFeCoNi high-entropy alloys (HEAs) with varying stacking fault energy (SFE) has been studied in up to 90% rolling reductions at both room and cryogenic temperature. All the HEAs deform by dislocation slip and additional mechanical twinning at intermediate and shear banding at high rolling strains. The microstructure is quite heterogeneous and, with strain, becomes highly fragmented. During rolling, a characteristic brass-type texture develops. Its strength increases with a decreasing SFE and the lowering of the rolling temperature. The texture evolution is discussed with regard to planar slip, mechanical twinning, and shear banding. © 2020 by the authors. Licensee MDPI, Basel, Switzerland

Probing lamellar twins in spark plasma sintered CaTiO3 using Electron Backscattered Diffraction

The twinning characteristics of spark plasma sintered CaTiO3 with orthorhombic perovskite structure is critically analysed using Electron Backscatter Diffraction (EBSD) technique. The twins are characterized by a sub-micron interlamellar spacing with a misorientation of approximate to 90. The crystallographic relationship between the matrix and the twin has been analysed in terms of misorientation matrix using the Kikuchi patterns obtained from the EBSD scan. From the analysis of angle/axis pairs at the boundary, the twin axis was found to be of type 101]. These twins with high angle boundaries are expected to enhance fracture resistance through crack deflection and crack tip shielding mechanisms. (C) 2017 Elsevier Ltd. All rights reserved