Functionally graded materials with laser cladding

Abstract

Al-40 w/o Si functionally graded materials (FGMs) were produced by a onestep laser cladding process on cast Al-alloy substrate as a possible solution for interfacial problems often present in laser coatings. The microstructure of the FGMs consists of a large amount of silicon primary particles surrounded by alpha -Al dendritic halos and by Al/Si eutectic. The Si particles exhibit a continuous increase in both size and volume fraction, from 8.5 mum and 22.7% at the bottom to 52 mum and 31.4% at the top of the FGM layer, respectively. Many five-fold branched Si particles (Si-p) were observed in Al-40wt%Si functionally graded materials produced by a single step laser cladding process on cast Al-alloy substrate. In this paper in particular the five-fold twinning and growth features of Si-p are scrutinized with orientation imaging microscopy and electron microscopic examination. The most remarkable facts of the study are that the five-fold branched silicon particles are much bigger in size (25 similar to 40 mum) than the previously reported sizes in literature of nanometer sizes and that the 7.5 degrees mismatch is accommodated mainly by multiple small angle grain boundaries (SAGBs). The examples of a single SAGB reported before are just a special case of the SAGB mechanism.