A.K. Shukla

Synthesis and Characterization of A356-Sicp Composite Produced through Vacuum Hot Pressing

The aim of this research is to analyze the effect of SiC particle addition and heat treatment on the microstructure and mechanical and thermal properties of A356 aluminum alloy–based metal matrix composite. Aluminum alloy powder in the size range 25–50 µm and SiC particles of 1 µm average size in 0, 5, 10, 15, and 20 volume percentages were used as raw materials. Powders were blended in a ball mill and then sintered in vacuum hot press. The hot pressed composites were heat treated using T6 heat treatment. Microstructure analysis was carried out to assess the distribution of the SiC particles in the Al matrix. Hardness, tensile strength, compressive strength, and coefficient of thermal expansion (CTE) have been measured both on base alloy and composite materials, before and after the heat treatment. The result showed that addition of SiC particles improved the hardness, compressive strength, and decreased the CTE on both heat treated and as hot pressed samples. However, the tensile strength increased with increase in SiC particles in the range 5 to 15% and then decreased for composite with 20% of SiC particles.

On the Possibility of Occurrence of Anisotropy in Processing of Cu-CNT Composites by Powder Metallurgical Techniques

Copper - multiwall carbon nanotubes (MWCNT) composite was processed by powder metallurgical processing technique. Pure copper powder and MWCNT were mechanically alloyed by high energy milling to produce Cu-MWCNT composite powder. The composite powder was subsequently consolidated by vacuum hot pressing. Characterization studies were conducted along axial (hot pressing direction) and radial (transverse) directions. Microstructural observations of the processed composite revealed random distribution of MWCNT in axial direction and aligned distribution in radial direction. The structure property correlation was established and it revealed certain degree of anisotropy in mechanical and electrical properties of the composite.

Densification of silicon carbide using oxy-nitride additives for space-based telescope mirror applications

Densification behavior of alpha silicon carbide (SiC) during vacuum hot pressing was studied up to 1900oC with sintering additives based on AlN and Y2O3 in different proportions. Near theoretical density was obtained with a total sintering additive content of < 4 vol.%. The microstructure of SiC sintered with AlN+Y2O3 revealed fine equiaxed grains against the additional elongated grains exhibited by SiC sintered with AlN alone. The SiC having high density exhibited very good strength, elastic modulus, high thermal conductivity, low coefficient of thermal expansion and excellent polishability for telescope mirror applications.