Vikash Kumar

Development of cBN reinforced Ti6Al4V MMCs through laser sintering and process optimization

ABSTRACT In this work, a systematic study and optimization on direct metal laser sintering (DMLS) of a cBN reinforced Ti6Al4V metal matrix composite (MMC) has been carried out using the response surface methodology (RSM). Variable process parameters such as volume % of cBN (5–15%), laser power (50–60 W), scanning speed (3500–4500 mm/min), and constant parameters such as laser spot diameter (0.2 mm), hatching gap (0.2 mm), and layer thickness (0.4) were considered for the experiments. The RSM was employed to establish a regression equation to predict different output parameters of the sintered samples such as the wear rate, relative density, and microhardness. Based on the developed model, the influence of process parameters on the wear rate, density, and microhardness were accomplished with optimized results. Hence, the result, thus, obtained showed the maximum hardness and density of 519 HV0.2 and 4.23 g/cm3, respectively, and the minimum wear of 26.49 µm in a testing time duration of 10 minutes. X-Ray Diffraction (XRD) analysis of the fabricated MMC confirms the presence of different phases such as cBN, AlN, TiN, TiB2, and TiO2 as a consequence of a series of chemical reactions among cBN and different elements of Ti6Al4V in an argon atmosphere.

Elastic properties of zincblende III-nitrides: A first-principles study

We have performed first-principle calculations to calculate elastic stiffness constants (C11, C12, C44) and bulk modulus (B) of AlN, GaN and InN semiconductors in the zinc blende structure. These properties are calculated using an ab initio pseudo potential method based on density functional theory (DFT) with the generalized gradient approximation (GGA) for the exchange-correlation functional. The Calculated values are in fair agreement with the values reported by earlier workers.

Minimizing coupling losses between bend and straight waveguides

In photonics integrated circuits two straight waveguide are required to be connected by a bend waveguide incurring coupling losses. In this paper such coupling losses are optimized by the analyzing the bend waveguide by Multiple Scale Method (MSM). The axial shift in electric field is estimated and coupling losses are optimized by introducing offset between straight and bend waveguide.

First-principle calculations of optical and phonon properties of wurtzite gallium nitride

In this paper, we have been studied the optical properties such as refractive index n(ω), absorption coefficient α(ω), and dielectric constant of wurtzite (WZ) GaN semiconductor using the plane-wave pseudopotential method within density functional theory (DFT). We have also been calculated the optical phonon modes using phonon calculation on Cambridge Serial Total Energy Package (CASTEP) software at 0 GPa. The calculated values of all above parameters are compared with the available experimental values and the values reported by different workers. A fairly good agreement has been found between them.

Theoretical investigations of structural, electronic and optical properties of ZnGeAs 2 under different pressures

The plane wave pseudo-potential method within density functional theory (DFT) has been used to investigate the structural, electronic and optical properties of ZnGeAs2 chalcopyrite semiconductor. The lattice constants are calculated from the optimized unit cells and compared with the experimental values. The band structure, total density of states (TDOS) and partial density of states (PDOS) have been discussed. The optical properties such as dielectric function, refractive index, optical reflectivity, extinction coefficient, electron energy loss spectrum and absorption spectra have been studied under three different hydrostatic pressures 0, 20 and 40 GPa in the energy range 0-20 eV. The calculated values of all parameters are compared with the available experimental values and the values reported by different workers. A fairly good agreement has been found between them.