Papers by Author: Satyam Suwas

Abstract: Rolling texture evolution of pure nickel, and nickel – cobalt alloys containing 20wt.%, 40wt.%, 60wt.% cobalt content has been studied to very large true strain (ε ~ 4). The texture evolution in pure nickel and Ni-20Co was very similar, and resulted in typical Cu-type rolling texture. Microstructural analyses showed that the deformation was mostly slip dominated up to 95% beyond which it shear bands. Deformation twinning was a major deformation mechanism up to 50% reduction, and at higher strains, microstructure showed extensive shear banding. The evolution of final Goss texture in low SFE Ni-Co alloys could be explained based on the twin fraction and shear band volumes which showed grains preferably oriented towards Goss.

Abstract: Surface mechanical attrition treatment (SMAT) technique has became popular to develop a nanostructured surface layer on metallic materials for upgrading their overall properties and performance. In this paper, we have presented the SMATing behavior of low stacking fault energy material like AISI 304 using optical microscopy, SEM, microhardness measurement and XRD analysis. SMATing was performed for 15, 30, 45, 60, 75, 90 min by using hardened bearing-steel balls (size: 5.7 mm diameter, hardness: 500HV_0.1) at 50 Hz vibrating frequency. XRD analysis indicated the lowest grain-size of about 8.6 nm in the surface region of specimen SMATed for 60 min. In comparison with the non-SMATed specimen, 17 times increase in the dislocation density and 4 times increase in the micro-strain were observed in this SMATed specimen. Improvement in the surface-hardness due to the SMAT was almost two times hardness before SMAT was 190 HV_0.1 and after SMAT it was 400 HV_0.1. There is a gradual decrease in the hardness value across the cross-section of the specimen, and core-hardness value was reached after 300 μm depth below the surface. XRD results indicated the possibility of martensitic phase transformation at the surface during SMATing of AISI 304 steel. SMATed AISI 304 specimens showed good thermal stability at 550°C for 6 h which was confirmed by microhardness measurement

Abstract: Mg alloys show limited room temperature formability compared to its lightweight counterpart aluminium alloys, which is a main obstacle in using this metal for most of the structural applications. However, it is known that grain refinement and texture control are the two possibilities for the improvement of formability of magnesium alloys. Amongst the approaches attempted for the texture weakening, additions through of rare-earth (RE) elements have been found most effective. The relationship between the texture and ductility is well established. In this paper, the effect of rare earth addition on texture weakening has been summarized for various magnesium alloys under the two most common modes of deformation methods.

Abstract: Deformation and recrystallization textures in nanocrystalline nickel with average grain size of 20 nm were investigated using X-ray diffraction, electron microscopy and differential scanning calorimetry. The deformation behaviour of nanocrystalline nickel is quite complicated due to intervention of other deformation mechanisms like grain boundary sliding and restoration mechanisms like grain growth and grain rotation to dislocation mediated slip. Recrystallization studies carried out on the deformed nanocrystalline nickel showed that the deformation texture was retained during low temperature annealing (300°C), while at higher temperature (1000°C), the texture got randomised. The exact mechanism of texture formation during deformation and recrystallization has been discussed.

Abstract: Multi-layered materials have been made from Cu-Fe with approximately equal volume fractions using the Accumulated Roll Bonding (ARB) technique with less than 1 μm thickness of the individual layers. The so-obtained multi-layers have been subjected to deformation by cold rolling to 25, 50, 75, 87 and 93% reduction in thickness. A detailed characterization has been carried out using X-ray diffraction (line profile analysis and texture measurement) and electron (scanning and transmission) microscopy. It has been found that Fe layers are disintegrated whereas Cu retains its continuity within a layer. Microstructural Characterization from X-Ray Line profile Analysis (XRDLPA) through Variance Method reveals that large amount of strain is initially carried by Cu layers during deformation. In the Cu-Fe layer, the texture is comparatively weaker in Cu layer and strong in Fe layers. Brass Component increases up to 75% reduction and then decreases, while the ratio of Cu/S and Bs/S remains almost constant through out the deformation. After 50% reduction, dynamic recovery is predominant as indicated by the increase in the amount of low angle grain boundaries and decrease in dislocation density. The presence of R component indicates continuous dynamic recovery and recrystallization (CDRR) at the advanced stage of deformation.

Abstract: This paper covers the influence of crystallographic texture on the mechanical properties in two of the most important high strength Al-Zn-Mg family of aluminium alloys, viz., AA7075 and AFNOR7020 alloys, used in the Aerospace industry. AFNOR7020 Alloy developed a stronger texture compared to the other two alloys. S component of texture is stronger in AA7075 alloy whereas the Bs component is stronger in AFNOR7020 alloy. This is attributed to the shear banding which was found absent in the other alloy. The starting material, AA7075 in T7352 condition and AFNOR7020 in T652 condition show some degree of anisotropy of mechanical properties with regard to yield strength and ultimate tensile strength. Higher degree of deformation leads to more pronounced anisotropy in mechanical properties with regard to yield strength and ultimate tensile strength, with a maxima along the transverse direction. For the alloys, experimentally measured Plastic Strain Ratio, r value, which is a measure of the texture present in the material in the deformation conditions, agree well with the computed values with a maximum at 45^o orientation to the rolling direction.

Abstract: A ferrite-bainite-martensite (F-B-M) microstructure was produced in a medium carbon microalloyed steel through two routes, namely, low temperature finish forging or rolling, followed by a two step cooling and annealing. The texture formed in control forged and rolled material after two step cooling followed by annealing (TSCA) was examined. Texture investigation was also carried out after low cycle fatigue testing at low and high total strain amplitudes. Transmission electron microscopy was employed to study the microstructural evolution. Fatigue tested F-B-M microstructure obtained through the rolling route was stable up to a total strain amplitude of 0.6%. This paper reports the evolution of texture and microstructure in two-step cooled F-B-M microstructure and their stability during fatigue loading.

Abstract: In this study, severe plastic deformation (SPD) of Ti-bearing interstitial-free steel was carried out by multi-axial forging (MAF) technique. The grain refinement achieved was comparable to that by other SPD techniques. A considerable heterogeneity was observed in the microstructure and texture. Texture of multi-axially forged steels has been evaluated and reported for the first time. The material exhibited a six-fold increase in the yield strength after four cycles of MAF.

Abstract: Present work addresses the evolution of texture and microstructure of equal channel angular extrusion (ECAE) processed AA 2014 Al alloy upto four passes at room temperature by adopting route B_C. TEM is used to assess the microstructural changes during each ECAE pass. Texture measurements on samples of each pass were carried out by XRD technique. The evolution of texture components after each ECAE pass are analyzed and the changes are discussed with respect to the initial texture.

Abstract: Even anisotropic superplastic flow, which is a result of an elongated grain shape and texture, can lead to extreme elongations to fracture (superplasticity). Therefore, to identify the mechanisms of deformation present during superplastic flow alone, the effects of the microstructure should be eliminated first. Using an Al 5083 alloy, in which an equi-axed microstructure is present from the beginning, it is shown that grain boundary sliding, accompanied by grain rotations, is the rate controlling mechanism.