Papers by Author: K. Chattopadhyay

Abstract: The development of preferred grain orientation has been investigated in the directionally solidified samples of Tb_0.3Dy_0.7Fe_1.95 as a function of pulling speed viz. 10, 40, 70 and 100 cm/h. The study indicates that at lower solidification rate (10 cm/h) growth of and texture components are preferred, whereas, texture component becomes dominant at higher pulling rate (100 cm/h). However, as the solidification progresses, growth of texture component is observed subduing the other components. Consequently, the magnetostriction improves from 1100 to 1350 micro-strains with higher pulling speed.

Abstract: The stability of a unique single, rotated Brass-{110}á556ñ component developed in a Al-Zn-Mg-Cu based 7010 alloy, during long term thermal annealing and cold rolling deformation has been systematically investigated. It is observed that this component remains stable during annealing at 465 °C over the period of 96 hrs and up to a uniaxial cold rolling reduction of 60%. The thermal and mechanical stability of the single component texture is discussed in terms of preferential growth advantage of recrystallized grains and confinement of slip activity in two major slip systems, respectively.

Abstract: Mechanical property anisotropy in terms of in-plane anisotropy (A_IP) of yield strength, and work hardening behavior of a heat treated 7010 aluminum alloy sheet has been investigated. The specimens were given two different types of heat treatments that result in a unique single rotated Brass-{110}á556ñ component with different texture intensity and volume fraction of recrystallization. It has been observed that the A_IP increases with increase in texture intensity and volume fraction of recrystallization. The results are discussed on the basis of Schmid factor analyses in conjunction with microstructural features namely, grain morphology and precipitation. On the other hand, work hardening behavior appears to be significantly affected by the microstructural features rather than type of texture present in the samples.

Abstract: A comparative study on the microstructure-mechanical property relationships in the molybdenum and niobium silicide based composites has been carried out with emphasis on the role of the ductile and brittle phase constituents at ambient and elevated temperatures. The MoSi2, MoSi2-20 vol.% SiC and -Mo-Mo3Si-Mo5SiB2 composites have been prepared by powder metallurgy processing. Furthermore, the niobium silicide based composites, having a eutectic of Nb solid solution (Nbss) and (Nb,Mo)5Si3, and either Nbss or (Nb,Mo)5Si3 as the primary phase in the hypoeutectic or hypereutectic compositions, respectively, have been processed by arc melting. The increase in fracture toughness with respect to that of MoSi2 is modest in the MoSi2-SiC composites, and more significant in the multiphase Mo-Mo3Si-Mo5SiB2 and Nbss-(Nb,Mo)5Si3 based in-situ composites with ductile reinforcements. The ductile phase, either Mo or Nbss aids in toughening chiefly through crack arrest and bridging, and undergoes plastic yielding under constraint during deformation, leading to a higher energy of fracture. In the MoSi2 and MoSi2-SiC composites, the matrix grain size has a significant role in high temperature strength retention and strain hardening behaviour. In the ductile phase reinforced composites, the hard silicide-based intermetallic phases contribute to elevated temperature strength, while the constrained plastic deformation of the -Mo or Nbss is responsible for much higher rate of strain hardening than in the MoSi2 and MoSi2-SiC composites.