Showing papers by "Bhagwati Prasad Kashyap published in 2013"

Dynamic Recrystallization during Hot Deformation of 304 Austenitic Stainless Steel

Abstract: The kinetics of dynamic recrystallization (DRX) during hot compression of 304 austenitic stainless steel was studied over the temperature range of 900-1200 °C and strain rate range of 0.002-0.1 s−1. The initiation and evolution of DRX were investigated using the process variables derived from flow curves. By the regression analysis for conventional hyperbolic sine equation, the activation energy for DRX was determined as Q = 475 kJ mol−1. The temperature and strain rate domain where DRX occurred were identified from the strain rate sensitivity contour map. The critical stress (and strain) for the initiation of DRX was determined from the inflection point on the work hardening rate (θ = dσ/de) versus flow stress (σ) curve. The saturation stress of the dynamic recovery (DRV) curve was calculated from the θ-σ plot at the same condition at which DRX occurred. Progress of fraction recrystallization was determined from the difference between the generated DRV curve and the experimental DRX curve. In addition, the microstructural evolution at different strain levels during DRX was characterized and compared with the calculated fraction recrystallization.

Recrystallization Phenomena During Friction Stir Processing of Hypereutectic Aluminum-Silicon Alloy

Abstract: Microstructural evolution and related dynamic recrystallization phenomena were investigated in overlapping multipass friction stir processing (FSP) of hypereutectic Al-30 pct Si alloy. FSP resulted in the elimination of porosities along with the refinement of primary silicon particles and alpha aluminum grains. These alpha aluminum grains predominantly exhibit high angle boundaries with various degrees of recovered substructure and dislocation densities. The substructure and grain formation during FSP take place primarily by annihilation and reorganization of dislocations in the grain interior and at low angle grain boundary. During multipass overlap FSP, small second phase particles were observed to form, which are accountable for pinning the grain boundaries and thus restricting their growth. During the multipass overlap FSP, the microstructure undergoes continuous dynamic recrystallization by formation of the subgrain boundary and subgrain growth to the grain structure comprising of mostly high angle grain boundaries.

Effect of High Temperature Caliber Rolling on Microstructure and Room Temperature Tensile Properties of Mg-3Al-1Zn (AZ31) Alloy

Abstract: Mg-3Al-1Zn (AZ31) alloy was caliber rolled at 250, 300, 350, 400 and 450 °C. The effects of caliber rolling temperature on the microstructure and tensile properties were investigated. The room temperature tensile tests were carried out to failure at a strain rate of 1 x 10 -4 s-1. The nature of stress-strain curves obtained was found to vary with the temperature employed in caliber rolling. The yield strength and tensile strength followed a sinusoidal behaviour with increasing caliber rolling temperature but no such trend was noted in ductility. These variations in tensile properties were explained by the varying grain sizes obtained as a function of caliber rolling temperature.

Kinetics of γ-Mg17Al12 Phase Dissolution and its Effect on Room Temperature Tensile Properties in As-Cast AZ80 Magnesium Alloy

Abstract: As-cast AZ80 magnesium alloy consists of α-Mg, eutectic product of α-Mg and γ-Mg17Al12, with the latter present in the form of partially and fully divorce eutectic. There occurs dissolution of harder γ-Mg17Al12 phase during homogenization treatment at 400 ᵒ and 439 ᵒC. The proportion of the α-Mg and γ-Mg17Al12 phase was varied by solutionizing the alloy for various lengths of time at these temperatures, in order to investigate the kinetics of phase transformation and to evaluate the effect of phase proportion, size and morphology on room temperature tensile properties. It was found that the yield strength decreases with the increase in solutionizing temperature from 400ᵒ to 439 ᵒC and at the same time, ductility in general increases with the increasing solutionizing temperature. The variation in tensile properties and the nature of fractographs were analyzed in terms of the effects of microstructure

Effect of plating on consolidation of commercially pure titanium powders

Abstract: Blending of elemental powders is a common powder metallurgical processing route to produce titanium alloys designed to meet the required properties. An alternative to blending is coating the base titanium powders with specific metal ions by an electroless route to maximise advantages associated with homogeneous coating. In this work, Ni–P is being used as the coating material, to coat hydrogenated/dehydrogenated titanium powders. The particle size distribution of uncoated and coated powders was used to explain the change in tap density. A diametrical compression test was carried out to evaluate green strength of the particles when consolidated before and after coating.

Cavity growth during superplastic deformation in 7475 aluminum alloy

Abstract: Tensile specimens of the 7475 aluminium alloy were investigated in order to understand the mechanism of cavitation at different levels of strain. For this purpose a temperature and strain-rate pertinent to maximum level of cavitation were selected and the constant strain rate tests were interrupted at appropriate strain levels. This was supplemented with microstructural observations and density measurements. The percentage cavitation increases with strain in this alloy. The experimental result is assessed with respect to Stowell's model and plasticity-controlled hole growth.