Showing papers by "Satish V. Kailas published in 2005"

The compressive deformation and impact response of a magnesium alloy: influence of reinforcement

Abstract: Reinforcement of magnesium alloys with ceramic particulates has engineered a new family of materials that are marketed under the trade name metal matrix composites. In this paper is reported the results of a study aimed at understanding the role of particulate reinforcements on compressive deformation and impact response of a magnesium alloy discontinuously-reinforced with silicon carbide (SiC) particulates. An increase in carbide particulate reinforcement content in the magnesium alloy metal matrix was observed to have only a marginal influence on compressive strength and impact energy absorption when compared to the unreinforced counterpart. Microcracking in the metal matrix coupled with failure of the reinforcing SiC particulates both independently dispersed and in clusters dominated the fracture sequence at the microscopic level. The mechanical response of this composite material is discussed in light of the interactive influences of intrinsic microstructural effects, deformation characteristics of the composite constituents, nature of loading and local stress state.

Influence of reinforcement and processing on the wear response of two magnesium alloys

Abstract: Reinforcement of magnesium alloys with ceramic particulates has engineered a new family of materials that are marketed under the trade name metal-matrix composites. Rapid strides in the processing of these materials during the last two decades have provided the necessary impetus for their emergence and use in structure and automotive-related components. In this paper are reported the results of a study aimed at understanding the role of the reinforcing phase on the wear behavior of two magnesium alloys discontinuously reinforced with silicon carbide (SiC) particulates and saffil alumina short fibers. The wear rate of the reinforced magnesium alloy metal matrices is lower than that of the unreinforced counterpart (AM60-T5 and AZ92-T6). The improved wear resistance of the composite microstructures is attributed to the presence and distribution of the ceramic reinforcement phase, which minimizes the tendency for material flow or plasticity at the surface during sliding. Wear rate is influenced by sliding speed, nature, and volume fraction of the reinforcing phase. For the unreinforced magnesium alloys, an increase in sliding speed results in a marginal increase in wear rate. For a given reinforcement (particulate and saffil fiber) in the magnesium alloy metal matrix, an increase in sliding speed had a negligible influence on wear rate. An increase in volume fraction of the reinforcing phase in the magnesium alloy metal matrix resulted in a noticeable drop in wear rate. Coefficient of friction of the unreinforced magnesium alloys AM60 and AZ92 decreased with an increase in sliding speed regardless of the amount of applied load. Addition of reinforcement, i.e., particulates and short fibers, to the magnesium alloy metal matrix resulted in a significant drop in coefficient of friction. However, increase in volume fraction of the reinforcing base in the magnesium alloy metal matrix had negligible influence on coefficient of friction. The wear characteristics of the reinforced metal matrix are discussed in light of the mutually interactive influences of intrinsic microstructural effects, strength of the microstructure, sliding speed, and local stress state.

Role of Surface Topography on Friction and Transfer Layer Formation: A Study Using Inclined Scratch Test

Abstract: Tribological interaction between two contacting surfaces is influenced by many factors such as relative motion, normal load, environment, and lubrication apart from surface characteristics of the mating surfaces. Though surface characteristics such as roughness was dealt by many researchers for decades, the other important characteristic of surfaces, surface topography, has not got its share of attention. In the present investigation, basic studies were conducted using Inclined Scratch Tester to understand the role of surface topography on friction and transfer layer formation. A tribological couple made of copper pin against EN8 flat was used in the tests. Two surface parameters of steel flats — roughness and texture — were varied in tests. Care was taken to ensure that the surface roughness, measured along the scratch direction, had similar values for different textures, namely Unidirectional, 8-ground, and Random. It was observed that the transfer layer formation and the coefficient of friction along with its two components, namely adhesion and plowing, are controlled by the nature of surfaces and are independent of surface roughness. The plowing component of friction was highest for the surface that promotes plane strain conditions near the surface and was lowest for the surface that promotes plane stress conditions near the surface.Copyright © 2005 by ASME

Damage Tolerant Magnesium Metal Matrix Composites: Influence of Reinforcement and Processing

Abstract: A growing impetus to enhance our understanding of the behavior of magnesium-based alloys for use in weight critical applications resulted as a consequence of the low density of magnesium. In an attempt to enhance the applicability of magnesium for a wide spectrum of performance-critical applications, the addition of reinforcement to the alloy was considered as an economically affordable and potentially viable scientific alternative. In this paper are reported the results of a study aimed at understanding the influence of saffil alumina short fiber reinforcement on microstructural development of a squeeze-cast magnesium alloy. Preliminary results confirm promise of the reinforced alloy, which retains hardness, strength, and stiffness better at elevated temperatures compared to the unreinforced counterpart.However, impact strength and toughness of the reinforced alloy are inferior. The importance of the matrix alloy in governing the overall mechanical response of the composite microstructure is discussed based on fractographic observations. The importance of volume fraction of there inforcing phase on properties of the composite microstructure is highlighted.

Effect of Directionality of Grinding Marks on Friction at Different Surface Roughness Using Inclined Scratch Test

Abstract: Surface topography of a tool plays an important role as it predominantly controls the frictional behavior at the interface. In the present study, Inclined Scratch Tester was used to understand the effect of directionality of surface grinding marks on coefficient of friction and transfer layer formation. EN8 steel flats were ground to attain different surface roughness with unidirectional grinding marks. Then Al-Mg alloy pins were scratched against the prepared EN8 steel flats. Grinding angle (angle between direction of scratch and grinding marks) was varied between 0° and 90° during the scratch tests. It was observed that the coefficient of friction and transfer layer formation depend primarily on the directionality of grinding marks of the harder mating surface, and independent of surface roughness of harder mating surface. The grinding angle effect on coefficient of friction was attributed to the variation of plowing component of friction with grinding angle.Copyright © 2005 by ASME