Functionally Graded Materials Produced by Laser Cladding: A Novel Approach

摘要

Many five-fold branched Si particles (Si_p) were observed in Al-40 wt.% Si functionally graded materials (FGM) produced by a single step laser cladding process on a cast Al-alloy substrate. The microstructure of the FGMs consists of a large amount of silicon primary particles surrounded by α-Al dendritic halos and by Al/Si eutectic. The Si particles exhibit a continuous increase in both size and volume fraction, from 8.5μm and 22.7% at the bottom to 52 μm and 31.4% at the top of the FGM layer, respectively. In this paper the five-fold twinning and growth features of Si_p are scrutinized with orientation imaging microscopy and electron microscopic examination. These Si particles have grown from twinned decahedron nuclei consisting of five tetrahedrons that share a common 110 axis. The twin plane reentrant edge (TPRE) mechanism explains both the branch growth in the radial direction and the elongation of Si_p along their common 110 axis.