Rajeev Kapoor

Bio: Rajeev Kapoor is an academic researcher from Bhabha Atomic Research Centre. The author has contributed to research in topics: Strain rate & Flow stress. The author has an hindex of 15, co-authored 57 publications receiving 618 citations. Previous affiliations of Rajeev Kapoor include Homi Bhabha National Institute.

Discontinuous dynamic recrystallization in α-Zr

Abstract: This study attempts to identify the type of dynamic recrystallization (DRX) occurring in hot deformed zirconium. For this, samples of Zr were uniaxially compressed at 800 °C and 0.1 s−1 to varying strains. Microstructural characterization was done using electron back scatter diffraction (EBSD). The flow stress showed an initial hardening followed by softening to a steady state value. DRX grains were identified as those with a grain orientation spread of less than 2°. Fine recrystallized grains were observed along grain boundaries at low to intermediate strains (0.15 and 0.6). The grain size decreased with increasing strain up to a strain of 0.6, beyond which it showed no further decrease. The degree of misorientation of boundaries was used to distinguish between discontinuous and continuous dynamic recrystallization (dDRX and cDRX, respectively). Most recrystallized grains had their boundaries of very high misorientation (> 50°) suggesting that dDRX was prevalent. The evidence of cDRX was weak, although it cannot be ruled out at higher strains. It was concluded that Zr undergoes dDRX when deformed at 800 °C and 0.1 s−1.

Fast parallel algorithms for short-range molecular dynamics

Abstract: Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

Surface diffusion and coalescence of mobile metal nanoparticles.

Abstract: The diffusion and coalescence of metal nanoparticles play important roles in many phenomena. Here, we offer a new integrated overview of the main factors that control the nanoparticle coalescence process. Three factors are considered in our description of the coalescence process: nanoparticle diffusion across the surface, their physical and thermodynamic properties, and the mechanism of coalescence. We demonstrate that the liquid-like properties of the surface layers of the nanoparticles play an essential role in this process. We present experimental evidence for our opinion, based on the high-resolution electron microscopic analysis of several different types of nanoparticles.

Developing stable fine-grain microstructures by large strain deformation - Discussion

Abstract: Methods of deforming metals to large strains are reviewed and the process of equal channel angular extrusion is analysed in detail. The development of microstructure during large strain deformation is discussed, and it is concluded that the main criterion for the formation of a sub–micron grain structure is the generation of a sufficiently large fraction (> 0.7) of high–angle grain boundary during the deformation process. For aluminium alloys, it is found that a low–temperature anneal is required to convert the deformed microstructure into an equi–axed grain structure. The material, microstructural and processing factors that influence the formation of such fine–grain microstructures are discussed, and the stability of these microstructures at elevated temperatures is considered.