Advanced Materials and Processes Research Institute
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Solidification, structures, and properties of cast metal-ceramic particle composites.
No full textSolidification synthesis of cast metal-ceramic particle composite materials by dispersing hard or soft ceramic particles (including microballoons) and short fibres in molten alloys before solidification is described. Microstructures synthesized using a variety of casting techniques such as gravity or pressure die casting, centrifugal casting, and squeeze casting are discussed. Techniques to obtain a selected distribution of dispersed particles in cast alloy matrices by controlling solidification parameters and inducing melt particle wettability are reviewed. These cast metal-ceramic particle composites represent low cost, high performance, tailor made substitute materials for a variety of automotive and electromechanical applications such as pistons, cylinder liners, bearings, and current collectors, resulting in savings of material and energ
The Effect of Thermal Cycling on the Kinetics of Cellular Phase Transformation in a Cu-In Alloy\ud
No full textThe effect of thermal cycling on the\ud
kinetics of cellular phase transformation in\ud
a Cu-15wt.%In alloy was studied. The\ud
growth velocity was obtained using growth\ud
distance measurements obtained by optical\ud
microscopy; the interlamellar spacing and\ud
the composition of the depleted ~ phase were\ud
measured from bright field images using\ud
transmission electron microscopy.\ud
The thermally cycled alloys showed a\ud
higher rate of growth of cells. The interlamellar\ud
spacing and the composition of\ud
the ~ phase remained more or less the same\ud
as those for well-annealed alloys. In comparison\ud
with the well-annealed alloys, the\ud
thermally cycled alloys showed increased\ud
values of the diffusivity and chemical driving\ud
force and a decrease in the apparent activation\ud
energy during cell growth. This is\ud
explained in terms of the non-equilibrium\ud
structure of the grain boundaries associated\ud
with the thermally cycled alloys
Al alloy-solid lubricant talc particle composites.
No full textThis paper describes the method of synthesizing cast aluminium alloy talc particulate composites and their mechanical and wear properties. Talc particles were characterized using X-ray diffraction, infrared spectroscopy and differential thermal analysis techniques. Composites with two Al-Si alloys (LM 13 and LM 6) as matrices were prepared by heating the molten alloys to 750° C and adding the preheated talc powder (−150 + 50 μm size) after creating a vortex by mechanically stirring the melt. Simultaneous addition of 2 wt% Mg was found to facilitate the introduction and dispersion of talc particles in molten Al-Si alloys. Composites containing 2.8 wt % talc in LM 13 and 2 wt % talc in LM 6 have been prepared. Optical micrographs of composites revealed uniform distribution of talc particles. Hardness and tensile strength of LM 13+2.8% talc were 85 BHN and 126 MPa, respectively. After suitable heat treatment hardness and strength were increased to 125 BHN and 211 MPa respectively. Wear rates of LM 13+2.8 wt% talc and LM 6+2 wt % talc composites were found to be 22 to 30% less than the wear rates of corresponding base alloys without any dispersions
Aluminium alloy-silica sand composites: preparation and properties
No full textCeramic particulate composites containing up to 25 wt% silica sand in commercially pure aluminium (LM-O) and its eutectic silicon alloy (LM-6) were prepared by liquid metallurgy techniques. Pre-treated sand particles of sizes ranging from −180 to +90μm were added to the alloy melts, followed by pouring the resulting mix into permanent moulds. Quantitative metallographic examination revealed that sand particles were uniformly distributed in both types of cast composite. Scanning electron microscopic examination of the composites showed voids around the sand particles. Tensile specimens, when fractured in an Instron machine, showed an interfacial mode of failure of the composite without affecting the sand particles, indicating poor bonding with the matrices. The hardness of LM-O alloyed with magnesium increased from 52 to 78 BHN, whereas the ultimate tensile stress (UTS) decreased from 92 to 62 MPa as a result of the addition of 20 wt% sand particles. In the case of LM-6-sand composites, the hardness remained almost constant but the UTS decreased from 184 to 112 MPa with the addition of 20 wt% sand particles. The compressive strength of both types of composite also decreased as a result of sand additions. However, a favourable effect of magnesium alloying on the strength of the cast composite was also observed
Properties of composites of 2014 aluminium alloy with Ni-Mo-based metallic glass particles
No full textComposites of 2014 aluminium alloy containing dispersions of metallic glass particles (51.5wt% Ni, 38.0wt% Mo, 8.0wt% Cr and 1.5wt% B) have been prepared by a conventional powder metallurgy route involving powder mixing, compaction, sintering and heat treatment. Physical and mechanical properties of the composites, such as dimensional changes, hardness, electrical resistivity and corrosion behaviour, were studied. Dimensional growth up to a maximum of 6% in a linear direction was observed in all sintered composites. HardnessHv increased from 40 to 55kgmm−2 with the addition of 4vol% of dispersoid, followed by a gradual decrease with increasing additions of dispersoid. The decrease in hardness above 4vol% of dispersoid was attributed to the presence of increasing amounts of porosity. Electrical resistivity increased from 50nΩm (for 2014 aluminium alloy) to 180nΩm at 20vol% dispersoid. The corrosion rate in an artificial sea water environment decreased linearly with the volume fraction of dispersoid. Re-pressing and re-sintering (in an argon atmosphere) of composites containing 4vol% of metallic glass particles resulted in an increase inHv from 55 (argon sintering) to 83kgmm−2, and a decrease in electrical resistivity from 57 to 52nΩm due to the increase in density. The corrosion rate in an artificial sea water environment of composites containing 4vol% of metallic glass decreased from 70×10−3 to 50×10−3 mgdm−2 per day due to re-pressing and re-sinterin
