Tribological behaviour of semisolid-semisolid compocast Al-Si matrix composites reinforced with TiB_2 coated B_4C particulates

摘要

The purpose of this paper is to provide a deeper understanding of the wear behavior of the sol-gel coated B_4C particulate reinforced A356 matrix composites. A typical microstructure of the composite consists of relatively large primary phase globules which are surrounded by B_4C particles. In fact the globules themselves are B_4C particles free and consequently the sample is not homogeneous on a scale smaller than the globule size. The wear sliding test disclosed that the wear rate of the coated B_4C reinforced composites is less than that of the unreinforced alloy and decreases with increasing volume fraction of B_4C particulates. As the hardness of the composites is higher, this reduces the cutting efficiency of the abrasives and consequently the abrasion wear loss. Once the particles fracture or loosen from the matrix alloy, they can be removed easily from the matrix, contributing to the material loss. Two kinds of debris present irregular-shaped flake, which has withstood a large of plastic deformation and then pull off from the surface. During the sliding wear, Iron is transferred to the surface of the composites from the steel counterface forming the iron-rich layer on the contact surfaces which increases with increasing the B_4C content and is substantially harder than the bulk material largely because it contains a fine mixture of Fe phase, Al and B_4C.