Papers by Author: Vikram Jayaram

Abstract: As-deposited amorphous (determined through XRD) electroless Ni-B coating upon heat treatment transforms to crystalline phases, Ni3B, Ni2B and Ni whose volume fractions can vary widely. A micro and nano tribological study through ball-on-disk tribometer and lateral force microscopy has been performed to understand the effect of phase mixture (Ni3B +Ni2B) on the frictional properties of this coating. Though scaling of the contact area from micro to nano level strongly influences the friction coefficient, it has also been found that increase in the Ni2B:Ni3B ratio of the crystalline coating reduces the friction coefficient significantly.

Abstract: Transition metal borides, carbides and nitrides are candidates for very high temperature applications. A review of various processing techniques to fabricate dense monolithic and composite materials is presented. In particular, we focus on reactive hot pressing (RHP) which allows synthesis and densification to be achieved simultaneously. We report the RHP of composites in the Ti-B-N, Zr-B-C and Zr-B-Si-C systems using the reactions of Ti/BN, Zr/B4C (Si, SiC particulate) powder mixtures at moderate pressures and temperatures. Substantial reductions in processing temperature may be realized from those in excess of 1800°C down to as low as 1200°C by exploiting a combination of transient liquid phases, plasticity in a non-stoichiometric ZrC and enhanced transport in a sub-micron microstructure.