P. Ramakrishnan

Structure–property correlation in discontinuously reinforced aluminium matrix composites as a function of relative particle size ratio

Abstract Metal matrix composites made by a powder metallurgy route often exhibit clustering of the reinforcements due to geometrical reasons. The clustering tendency was studied in 2124 Al/30 v/o SiC p composites as a function of relative particle size ratio between the matrix and reinforcement particles. Dry blended composite powders, with different RPS ratios, were vacuum hot-pressed and microstructures were examined to assess the uniformity of the microstructure by measuring the local area fraction of the constituents. It was found that a decrease in RPS ratio resulted in an increase in strength as well as ductility, as a result of improved distribution of the SiC p . The improved response to the homogenisation treatment, observed in the composite with lower RPS ratio, is attributed to the smaller diffusion path length for the alloying element.

Processing and properties of SiC particulate reinforced Al6.2Zn2.5Mg1.7Cu alloy (7010) matrix composites prepared by mechanical alloying

Abstract SiC particulate reinforced aluminium alloy (7010) matrix composites have been processed by mechanical alloying route starting from elemental powders. Proper post-consolidation by hot pressing or hot extrusion results in a fully dense composite compact that retains the fine microstructure developed during mechanical alloying. Addition of SiC was found to result in lower strengths at room temperature but higher strength at temperatures above 200°C. There was nearly a 64% increase in the yield strength at 350°C, brought about by addition of 20 wt.% SiC. The beneficial effects of SiC additions on mechanical strength are best realized at elevated temperatures. Fine precipitates of various intermetallics (CuAl2, Mg2Zn11, etc.) are found to be present in the solutionised and aged samples in addition to fine dispersoids of Al2O3, MgAl2O4, etc. inherited from the as-milled powders and/or formed during subsequent degassing and consolidation.

Synthesis of nanosized titanium powder by high energy milling

Titanium powders of about 2 μ particle size were subjected to high energy attrition milling in an argon atmosphere. Selecting suitable milling parameters, nanosize (<100 nm) titanium powders were prepared after 15 h of milling. An average particle size of 35 nm was obtained at 30 h of milling after which the particle size stabilized with continuation of milling to 75 h. The powders after milling for various durations were characterized by TEM, ICP and XRD, and these results are reported and discussed.

Sintering mechanisms of attrition milled titanium nano powder

Detailed sintering studies have been carried out on attrition milled nanocrystalline titanium powder through isothermal dilatometry over a temperature range of 300–1250 °C along with microstructural and x-ray diffraction studies. The sintering behavior of attrition milled nanocrystalline titanium appears to be characterized by: (i) very low activation energies, (ii) high shrinkage anisotropy, (iii) very rapid grain growth in the beta range, and (iv) two kinds of densification processes, namely, intra-agglomerate and inter-agglomerate. Analysis of the kinetic data through sintering diagram approach indicates the operation of particle sliding and grain boundary rotation, type of mechanism in addition to the grain-boundary diffusion, and lattice diffusion as the dominant mass transport mechanisms.

Dilatometric sintering study of titanium-titanium nitride nano/nanocomposite powders

Abstract The sintering behaviour of titanium–titanium nitride nano/nanocomposite powders has been investigated by dilatometry. The nanosized titanium powders (40 nm) were produced by the attrition milling of micron sized titanium powders (12 μm) in Ar atmosphere while the nanosized titanium nitride powders (50 nm) were as procured. Two compositions of the nano/nanocomposite powders, i.e. Ti–8TiN and Ti–15TiN (wt-%) were produced by physical mixing and ultrasonification. Dilatometry was carried out at a constant rate of 10 K min−1 heating to various temperatures in the range of 450–1250°C followed by holding for 1 h. The effect of nanoTiN reinforcement on the sintering onset temperature, linear shrinkage, shrinkage rate, activation energy for sintering, microstructure and grain growth has been reported and discussed.

Initial sintering kinetics of titanium-titanium nitride nano/nanocomposite powders

Abstract The present investigation deals with the mass transport mechanisms operating during the initial sintering of titanium–titanium nitride nano/nanocomposite powders. Two compositions of the nano/nanocomposite powders, i.e. nano Ti–8 wt-% nano TiN and nano Ti–15 wt-% nano TiN along with nano Ti were used in the present study. Sintering studies have been carried out by dilatometry of the powder compacts using a constant rate of heating (CRH) and employing model equations to the initial sintering portion. The shrinkage values obtained were analysed using Young and Cutlers equations and a model proposed by Johnson and Berrin. Based on the analysis of experimental data the effect of second phase TiN on the mass transport mechanisms of nano Ti was determined.