S. Bhargava

On the formation of TiAl3 during reaction between solid Ti and liquid Al

Abstracts are not published in this journal

Evolution of hot rolling textures in a two-phase (α2+β) Ti3Al base alloy

Texture development during thermomechanical processing of two-phase (α2+β) Ti–24Al–11Nb alloy was studied as a function of variables like initial microstructure, rolling temperature, cooling conditions, etc. The evolution of texture in different conditions has been critically analysed. It has been found that unrestricted rolling of primary α2 at lower temperature leads to a good basal {0001}〈uvtw〉 texture, while at higher temperatures, the α2→β→α2 phase transformation leads to weakening of the basal texture. Texture of secondary α2 derived from rolled β is generally non-basal. However, the texture of secondary α2 derived from recrystallized β has a basal character.

Effect of prior β processing on superplasticity of (α+β) thermo-mechanically treated Ti–632Si alloy

Abstract A new thermo-mechanical schedule involving processing in β and (α+β) phase fields for obtaining good superplastic properties in Ti–6.8Al–3.2Mo–1.8Zr–0.3Si alloy has been proposed and tested for optimum superplasticity. Superplastic behavior of the as-rolled and annealed sheets has been studied systematically in different temperature and strain rate ranges. It has been inferred that in addition to the grain size, prior to β processing and annealing in the (α+β) phase field also have a marked effect on superplasticity of the alloy sheets. As-rolled sheets in the (α+β) phase field having undergone annealing in β phase field after β rolling exhibit maximum superplastic elongation. Any further heat treatment of the as-rolled sheet reduces the extent of superplastic elongation.

Analysis of cold densification rolling of a sintered porous metal strip

Abstract Cold densification rolling of a sintered porous metal strip has been analyzed by the upper-bound technique coupled with the plasticity theory of porous metals. The analysis considers plane-strain deformation and incorporates work-hardening effects during cold rolling. A stream function form which produces a kinematically admissible velocity field has been assumed in the upper-bound analysis. The total power for rolling, which is the sum of the internal power for plastic deformation, frictional power and shear discontinuity losses along the surface of velocity discontinuity, has been minimized to find the velocity and density distributions. The calculated results for density and strains have been verified experimentally for the multi-pass rolling of a sintered porous copper strip.

Effect of thermomechanical treatments on the room-temperature mechanical behavior of iron aluminide Fe3AI

The room-temperature hydrogen embrittlement (HE) problem in iron aluminides has restricted their use as high-temperature structural materials. The role of thermomechanical treatments (TMT),i.e., rolling at 500 °C, 800 °C, and 1000 °C, and post-TMT heat treatments,i.e., recrystallization at 750 °C and ordering at 500 °C, in affecting the room-temperature mechanical properties of Fe-25A1 intermetallic alloy has been studied from a processing-structure-properties correlation viewpoint. It was found that when this alloy is rolled at higher temperature, it exhibits a higher fracture strength. This has been attributed to fine subgrain size (28/μ) due to dynamic recrystallization occurring at the higher rolling temperature of 1000 °C. However, when this alloy is rolled at 1000 °C and then recrystallized, it shows the highest ductility but poor fracture strength. This behavior has been ascribed to the partially recrystallized microstructure, which prevents hydrogen ingress through grain boundaries and minimizes hydrogen embrittlement. When the alloy is rolled at 1000 °C and then ordered at 500 °C for 100 hours, it shows the highest fracture strength, due to its finer grain size. The alloy rolled at 500 °C and then ordered undergoes grain growth. Hence, it exhibits a lower fracture strength of 360 MPa. Fracture morphologies of the alloy were found to be typical of brittle fracture,i.e., cleavage-type fracture in all the cases.

Effect of Prior βProcessing on Superplasticity of (α + β) Thermomechanically Treated Ti–6Al–4V Alloy

Abstract A new thermomechanical schedule involving processing in βand (α + β) phase fields for obtaining good superplastic properties in Ti–6Al–4V alloy has been proposed and tested for optimum superplasticity. Superplastic behavior of the as-rolled and annealed sheets has been studied systematically. It has been inferred that in addition to grain size, prior βprocessing and annealing in the (α + β) phase field also have a marked effect on superplasticity of the alloy sheets. As-rolled sheets in (α + β) phase field having undergone annealing in (α + β) phase field with prior βrolling exhibit maximum superplastic elongation.

X-ray powder diffraction line profile analysis of mechanically alloyed Cu–Cr powder

Abstract Four different compositions of Cu–Cr system (Cu0·90Cr0·10, Cu0·75Cr0·25, Cu0·60Cr0·40 and Cu0·50Cr0·50) were mechanically alloyed using different milling parameters. Samples collected from the milled powder of 24 batches after different time intervals were studied by X-ray diffraction. The diffraction data were analysed by three different line profile analysis methods, namely, Williamson–Hall method, integral breadth method and peak fitting method to calculate the crystallite size and microstrain in the materials. Peak fitting and integral breadth methods were found to be more suitable for the systems under study. Logarithmic relationships between the milling time and crystallite size or microstrain are proposed. The model was further validated by time interpolated data from two of the present batches and two composition extrapolated batches (Cu0·25Cr0·75 and Cu0·10Cr0·90).

The Knoop hardness yield locus of Ti-24Al-11Nb alloy

The yield locus has been determined for a Ti3Al base alloy subjected to different thermomechanical treatments in order to have an idea of mechanical anisotropy. The anisotropy of yield loci has been found to be dependent on the type and severity of crystallographic texture developed in the materials. A strong basal texture has been found to be responsible for yield locus anisotropy. D 2003 Published by Elsevier Science B.V.

The Effect of Deformation Processing on Microstructural Evolution in a Boron Containing Fe-25Al Intermetallic Alloy

The effect of deformation processing on the resulting microstructure of an Fe-25Al-1B alloy prepared via an ingot metallurgy route has been studied. The alloy has been subjected to several hot/warm rolling and/or heat treatments. Hot/warm rolling was done to achieve different thickness reductions at temperatures ranging from 773K to 1373K. The microstructure of the as-cast alloy consisted of a continuous layer of iron borides in a matrix of iron aluminides. Hot rolling of the alloy caused breakage of the boride particles resulting in a particulate boride-aluminide composite microstructure. Warm rolled specimens of boron-modified alloy have shown better mechanical properties as compared to boron-free alloy rolled under the same conditions of processing and testing. Improvement in the tensile strength and ductility of these samples has been explained in terms of the changes occurring in the microstructure.

Enhanced properties of functionally graded Cu–Cr powder compacts

Abstract The paper aims to present the processing and development of functionally graded Cu – Cr materials, widely used as a monolithic contact material in vacuum circuit breakers. Simple and novel processing routes, used in this study, in addition to being cost-effective and energy efficient, generate higher density and electrical conductivity of the Cu – Cr compacts. It is shown that the use of mechanically alloyed Cu – Cr powders enhances the properties of the compacts, as compared to those prepared from as-received powders. Furthermore, explosive compaction and application of coated powder were found to result in still better properties. Scanning electron microscopy and atomic force microscopy were used to explain the scientific significance of this development.