Papers by Author: Pinaki Prasad Bhattacharjee

Abstract: The effect of ultrahigh straining on the evolution of cube texture in high purity nickel (99.97%) processed by Accumulative Roll Bonding (ARB) is investigated in the present study. Fully recrystallized nickel sheet having average grain size of 28 μm is deformed by ARB to the strain levels of εeq=3.2 and εeq=6.4 corresponding to 4 and 8 cycles of ARB processing, respectively, and subsequently annealed at different temperatures. The 8 cycle ARB processed material consistently shows much higher cube volume fraction as compared to the 4 cycle processed material after different annealing treatments. Almost 100% cube volume could be obtained in the 8 cycle processed material after annealing at 800°C. The development of extremely sharp cube texture in the 8 cycle processed material could be attributed to the oriented nucleation of cube grains at early stages of recrystallization and subsequent growth of these grains. The results indicate that ultrahigh straining could be useful for applications requiring near perfect cube texture such as substrates for coated superconductors applications.

Abstract: A pure Ni sheet was heavily deformed up to an equivalent strain of 6.4 at room temperature and then annealed to obtain highly Cube textured material, which is a polycrystal subdivided by many low-angle grain boundaries. The highly Cube-oriented sheets were cold-rolled to various reductions up to 90%. It was found that large fraction of Cube oriented grains remained stable in cold-rolling although the orientation is theoretically unstable. The stability of Cube orientation was considered to be associated with the constraint by grain boundaries in the materials.

Abstract: An attempt has been made to fabricate highly cube textured ({001}<100>) polycrystalline nickel substrate tapes for coated superconductor applications using severe plastic deformation route. For this purpose high purity Ni (~99.97%) plates with widely different average grain size (28 µm or fine grained starting material and 650 µm or coarse grained starting material, respectively) are severely deformed by Accumulative Roll Bonding (ARB) up to an equivalent strain level of (εeq = 6.4) and annealed at various temperatures between 300° to 800°C for one hour. Upon annealing at different temperatures, the fine grained starting material developed a much stronger cube texture than the coarse grained starting material. By suitable annealing treatment near 100% cube textured tape could be obtained in the SPD processed fine grained nickel tapes having a predominantly low angle boundary network. The observed difference in the strength of cube texture in the two materials could be explained based on the oriented nucleation mechanism of formation of cube texture. The present results indicate that SPD processing route such as ARB is very effective in fabricating high purity Ni or Ni alloys intended for coated superconductor substrate applications.