Showing papers by "Bhagwati Prasad Kashyap published in 2000"

Instability criteria for hot deformation of materials

Abstract: Forming and forging processes are among the oldest and most important materials related technologies. New materials technologies centre on the development and widespread use of thermomechan...

Insight into the microstructural characterization of ferritic steels using micromagnetic parameters

Abstract: The influence of tempering-induced microstructural changes on the micromagnetic parameters such as magnetic Barkhausen emission (MBE), coercive force (Hc), residual induction (Br), and maximum induction (Bmax) has been studied in 0.2 pct carbon steel, 2.25Cr-1Mo steel, and 9Cr-1Mo steel. It is observed that, after short tempering, the micromagnetic parameters show more or less linear correlation with hardness, which is attributed to the reduction in dislocation density, but long-term tempering produces nonlinear behavior. The variation in each of these parameters with tempering time has been explained based on the changes in the size and distribution of ferrite laths/grains and precipitates. It has been shown that the individual variation in the microstructural features such as size and distribution of laths/grains and precipitates during tempering can be clearly identified by the MBE parameters, which is not possible from the hysteresis loop parameters (Hc and Br). It is also shown that the MBE parameters can not only be used to identify different stages of tempering but also to quantify the average size of laths/grains and second-phase precipitates.

Superplastic behaviour of as received superplastic forming grade IN718 superalloy

Abstract: Tensile specimens of superplastic forming grade IN718 superalloy, containing banded microstructure in the as received state, were deformed at high temperatures T to investigate the stress σ versus strain rate ɛ · behaviour, the nature of the stress versus strain ɛ curves, ductility, and microstructure upon failure. The log σ–log ɛ · plot for the ɛ · range ∼5 × 10-6–3 × 10-2 s-1 at T = 1173–1248 K exhibited a strain rate sensitivity index m = 0·62 at low strain rates and m = 0·26 at high strain rates, representing region II and III behaviour, respectively. The activation energies were estimated to be 308 and 353 kJ mol-1, respectively. All the σ–ɛ curves, obtained at ɛ · = 1 × 10-4 s-1 for the temperature range 1173–1273 K, and at T = 1198 K for the strain rate range 1 × 10-4–1 × 10-2 s-1, exhibited initial flow hardening, followed by flow softening. The microstructures revealed dynamic recrystallisation, grain growth, cavitation, and a variation in the amount of second phase particles. Grain growt...

Stain anisotropy in AA8090 Al–Li alloy during high temperature deformation

Abstract: An aluminum–lithium alloy AA8090 was deformed under superplastic condition to investigate the effect of strain, strain rate and test temperature on deformation anisotropy and microstructural evolution. The plastic anisotropy ratio was found to increase towards 1 with the increase in strain and strain rate. The initially elongated microstructure with rolling texture underwent dynamic recrystallization and tended to become equiaxed with cubic or random texture during superplastic deformation. The grain size increased with increasing strain and test temperature but decreased with the increase in strain rate. Such microstructural changes and the mechanisms involved in superplastic deformation, including the dislocation-based accommodation process, are suggested to develop isotropy.

Variation in tensile ductility and terminal microstructure of the binary two-phase Al-Cu alloys at elevated temperatures

Abstract: Tensile specimens of the Al-Cu alloys containing 5.6 to 33.4 wt.% Cu were deformed to failure for investigating the effects of strain rate, test temperature, initial grain size and the volume fraction of θ phase on ductility, grain growth and cavitation level. The ductility increases with the increase in temperature and decrease in grain size. The other variables, however, influence the ductility more in an interdependent manner. There occur grain growth and cavitation to varying extent depending on test condition; but the latter appears to show a systematic effect in limiting the ductility.