Papers by Author: K. Balasubramanian

Abstract: Friction stir processing is applied for property improvement of cast alloys for last two decades and many developmental studies were carried out in this topic on various alloys. In the current work, friction stir processing was carried out on rare earth containing magnesium alloy AE42. This alloy was specially developed for automobile application as it has better creep resistance than commercial magnesium alloys. Multi-pass Friction Stir Processing was carried out with varying the distance between passes from 0.5 mm to 2.5 mm using 12 mm shoulder diameter tool. Pin was with conical (tapered) and flat configurations with 3 mm height. After processing, the resultant mechanical and metallurgical properties were evaluated. Microstructure was refined to 5 micron and the secondary phases were made in to tiny pieces of 0.5-1 micron and evenly distributed in the matrix. Continuous network of grain boundary which is reason for poor mechanical properties was eliminated. Mechanical properties were improved by 30%. The variation of mechanical properties of processed material with respect to variation of distance between passes was negligible from 1 mm to 1.5 mm for flat pin tool.

Abstract: Friction stir processing was performed on rare earth containing magnesium alloy AE42 with the aim of improving the mechanical properties. The resultant stir zone mechanical and metallurgical properties were analyzed to determine the application temperature of the zone. Stir zone microstructure was refined to 5 micron and the grain morphology was completely changed. Second phase intermetallics Al11RE3 Al2RE were refined to submicron level tiny pieces and homogenously distributed throughout magnesium matrix. As a major achievement, both toughness and strength of the stir zone was improved by 15 to 25%. High temperature properties up to 250°C were better than base metal. The stir zone was capable of withstanding more temperature and stress than the base metal.

Abstract: The focus of this research article is on the requirement, preparation and application of an improved material system composed of boron and carbon. These are known as boron rich boron carbides. The ability to form BRBC other than widely studied B4C composition through solid state reactive processes; hold an appeal owing to their potential for a variety of application in tribological, refractory, ballistic, nuclear energy, aerospace and other manufacturing industries. Study of the boron-carbon phase diagram, combined with the available literatures on ‘low yield’ vapor deposition processes and boron doping of B4C to prepare BRBC provided the impetus for this investigation on BRBC through solid state reactive processes, mainly micropyretic and plasma. This article summaries the ‘high yield’ experimental studies carried out for obtaining BRBC and their encouraging performance with respect to existing B4C composition based products.