Macro and micro scale modeling of thermal residual stresses in metal matrix composite surface layers by the homogenization method

Abstract

The modeling of thermal residual stresses generated in TaC/stellite and TiC/stellite composite surface layers produced by the oscillating electron beam remelting on low alloys steel is presented. The homogenization method is applied to analyze the real composite microstructures by utilizing the digital image-based (DIB) geometric modeling technique. Two scales of elastic stress analysis are studied: macroscopic one referring to the global structure of composite layer produced over the substrate of low alloy steel and microscopic, comprising the selected unit cell of composite microstructure.The results of the analysis show the microscopic stress to be few times higher than the macroscopic one with stress level much above the elastic limit of matrix material, which implies the development of plastic field around the inclusions. The ceramic inclusions within the unit cell are found to be under high compressive stresses. Also, the composite surface layer stays in compression, mainly by the influence of the stress component parallel to the layer/ substrate interface. The effect of hardphase volume fraction is examined and it is found that for a small volume fractions the macro and micro stress does not differ substantially between composites with TaC and TiC hardphases despite their mismatch in thermophysical properties. Also, the stress modeling is presented for the composite containing other inclusions and the problem of the selection between 2D and 3D model for the stress analysis is discussed. IntroductionThere are several industry fields like aircraft, electrical, nuclear or building where metal matrix composites (MMC) are preferably used for engineering applications reducing the use of traditional materials. High strength of MMC together with high stiffness and high thermal stability at elevated temperatures makes them very attractive for engineering structures.One of the fields where application of MMC can be beneficial are composite surface layers produced over a substrate of conventional material. The role of a surface layer is to secure the surface of material against the action of external factors like corrosion as well as mechanical factors (intensive wear, cycling loading) resulting in the excessive wear of material during service life (Rohatgi et al. (1994)). An example of application of composite surface layers is for many machine parts and tools (e.g. drilling and boring tools) which are often subject to extreme working conditions. Although the commonly used materials for such applications are characterized by high strength, wear and corrosion resistance, yet there is still need to improve the service condition for this kind of layers because of the increase of working temperatures and loads. The metal matrix composite may be suitable for this purpose as their unique properties can sustain these demanding service conditions. By embedding hard ceramics in the form of fibers, whiskers or particulates into the metal matrix, we can expect the hard inclusions to carry on the main load resulting from the in...

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