V.V. Bhanu Prasad

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.

Preparation of Ti-TiB-TiC & Ti-TiB composites by in-situ reaction hot pressing

Discontinuously reinforced Titanium matrix composites, with TiB and TiC reinforcements, have been produced by the reaction hot pressing process. Powder metallurgy approach has been adopted with two different starting powder mixtures, namely Ti+TiB2 and Ti+B4C, the former leading to a composite with only TiB reinforcement, while the latter resulted in a combination of TiB+TiC reinforcement. The initial composition was adjusted in such a way as to have a reinforcement content of 70% by volume, the rest being matrix titanium. The X-ray diffraction analysis confirmed the completion of reaction and the scanning electron microscope studies revealed the morphology of the reinforcement. The effect of morphology and reinforcement type on mechanical properties was evaluated with hardness measurement and 3-point bend tests. It is concluded that the composite with the TiB+TiC reinforcement has a better strength and toughness, due to the presence of needle shaped TiB, while the composite with only TiB reinforcement in the form of TiB particulate has inferior strength and fracture resistance.

Composite strengthening in 6061 and Al-4 Mg alloys

Metal matrix composites using prealloyed 6061 Al (containing 1% Mg) and elemental blend Al-4 Mg alloys with 10 vol% SiC particulate reinforcements were fabricated using powder metallurgy techniques. The consolidation of the powders was effected by the section rolling process recently developed at the Defence Metallurgical Research Laboratory. This process involves the successive steps of cold isostatic pressing, vacuum sintering and special canning followed by section rolling. This resulted in a high-integrity composite product. An interfacial layer containing magnesium-rich precipitates observed in both the composites is suggested to be the major reason for the low (compared to the value predicted by the rule of mixtures) modulus and strength values in these composites. This layer also appeared to promote interfacial failure at the alloy/SiC interface. The Al-4 Mg alloy, which is known to be non-heat treatable, was found to respond to precipitation hardening heat treatment in the composite. The enhanced generation of dislocations due to the presence of SiC, promoting a more homogeneous precipitation of the second phase and the possibility of an inhomogeneous distribution of magnesium (as a result of elemental blending) are suggested to be the major factors responsible for rendering the Al-4 Mg alloy amenable to the precipitation hardening heat treatment.

High temperature C/C–SiC composite by liquid silicon infiltration: a literature review

The ceramic matrix carbon fibre (CMC) reinforced composite has received great attention for use in aerospace engineering. In aerospace, the atmosphere is highly oxidative and experiences very high temperature. In addition to this, the materials require high thermal stability and high abrasion resistance in that atmosphere. The C/C–SiC composite meets with these requirements. In this paper, the C/C–SiC composite by liquid silicon infiltration is reviewed thoroughly.

EFFECT OF EXTRUSION PARAMETERS ON STRUCTURE AND PROPERTIES OF 2124 ALUMINUM ALLOY MATRIX COMPOSITES

Discontinuously reinforced aluminum matrix composites (DRA) have been attracting attention because of their amenability to undergo deformation processing by conventional metalworking techniques. Extrusion is used in processing of DRA composites for consolidation, redistribution of reinforcements, and shape forming. The important parameters that control the extrusion process are temperature and strain rate, which is a function of several equipment/extrusion parameters. Vacuum hot-pressed (VHP) 2124 Al/30 SiCp composite billets were extruded at different ram speeds (1, 10, 100 mm sec−1) and using different extrusion ratios (4:1, 10:1, and 20:1). The extruded samples were studied for their integrity, microstructure, and mechanical properties. The integrity of the extruded composite rod was very good at minimum extrusion speed of 1 mm sec−1, whereas 100 mm sec−1 extrusion speed resulted in extensive fir tree cracking. Extrusion of VHP billets, with necklace structure, resulted in elongated alternate stringers of matrix and SiCp in the extrusion direction. Matrix stringer width and aspect ratio were found to vary with extrusion ratio. Because of the microstructural refinement, both the strength and ductility of the metal matrix composites (MMCs) were improved. Microhardness of the matrix stringers was found to be a function (power relation) of their width, irrespective of the location and extrusion ratio.

Effect of homogenization treatment on fatigue behaviour of 2124Al/20 vol % SiCp composite

The fatigue behaviour of 2124Al/20 vol % SiCp composite was studied in the as vacuum hotpressed condition, as well as after a homogenization treatment subsequent to vacuum hot pressing. It was found that there was a significant improvement in the tensile strengths, fatigue threshold stress intensity range, ΔKth, and cyclic fracture toughness, Kfc, as a result of the homogenization treatment. The improvement in the properties of the composite after homogenization is attributed to the dissolution of the coarse intermetallic precipitates present in the composite in the as-vacuum hot-pressed condition.

Structural, ferroelectric and piezoelectric properties of chemically processed, low temperature sintered piezoelectric BZT–BCT ceramics

0.5Ba(Zr0.2Ti0.8)O3–0.5(Ba0.7Ca0.3TiO3) nanopowders were synthesized at very low temperature using a soft chemical approach. The synthesized powders and the consolidated disks were structurally characterized thoroughly by XRD, SEM, TEM and EPMA and also by ultraviolet and Raman spectroscopy. The 1350 °C sintered BZT–BCT disk displayed the highest density, underwent diffused phase transition centered at ~100 °C and showed the highest dielectric constant (8917) and lowest dielectric loss (0.015). The sintered BZT–BCT sample with the highest density showed a maximum polarization (P max) of 13 μC cm–2 and remnant polarization of 6 μC cm–2. The same sample exhibited very high electrostrain of ~0.12% under a relatively low electrical field of 3.5 kV mm−1.

Synthesis and study of magnetic properties of high temperature stable Ni nanoparticles in a nearly amorphous AlPO4 matrix in an oxidative atmosphere

Graphitized carbon coated Ni nanoparticles were synthesized in an AlPO4 matrix in situ in an oxidative atmosphere without using any foreign reducing agent. The Ni nanoparticles were evenly distributed in an inactive AlPO4 matrix and protected from the oxidation in air up to 900 °C. Carbon coating over the nanoparticles remained intact even when the samples were calcined at 900 °C in air. Magnetization of the Ni nanoparticles in the composite approached ∼89% of their bulk magnetization value when calcined at 900 °C in air. Magnetization increased with increasing the calcination temperature up to 900 °C.

Effect of boron carbide particle size and volume fraction of TiB–TiC reinforcement on steady state creep behaviour of PM processed titanium matrix composites

AbstractTiB–TiC reinforced titanium matrix composites (TMCs) were synthesised through pressureless sintering of titanium and boron carbide (B4C) powder compacts. Effect of boron carbide (B4C) particle size and volume fraction of TiB–TiC reinforcement on steady state compression creep behaviour of composites was investigated in the temperature range of 773–873 K. The creep rates of composites are found to be about two orders of magnitude lower than those of unreinforced titanium. The creep rates further lowered with decrease in size of B4C particles (from 16 to 3 μm) used in preparation of composites as well as with increase in volume fraction of the TiB–TiC reinforcement from 10 to 30 vol.%. By using the concept of effective stress as well as incorporation of load transfer and substructural strengthening effect produced by the reinforcement into analysis, the entire creep data of Ti and the composites can be made to merge on to a single line within a scatter band of factor of 2–3 and can be represented by...

Influence of B 4 C Particle Size on the Synthesis of ZrB 2 by Boro/Carbothermal Reduction Method

ZrB2 powders were synthesized using B4C of different particle sizes through boro/carbo thermal reduction (BCTR) of ZrO2 with B4C and carbon as reducing agents. The XRD patterns of all the five different powders produced were similar and showed ZrB2 as a major phase. An increase in B4C particle size showed a significant increase in oxygen and carbon content and the size of agglomerates of the synthesized powders. Even though, the average size of the ZrB2 particles associated with all the agglomerates were same. It was concluded that B4C of fine particle size is necessary for the synthesis of ZrB2 powder with low oxygen and carbon content and lower agglomerates sizes. The synthesis route also provided a novel route to synthesize ZrB2 powder with the required size of agglomerates.Graphical Abstract