Functionally graded materials produced by laser cladding

AlSi40 functionally graded materials (FGMs) were produced by a one-step laser cladding process on cast AI-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 mu m and 22.7% at the bottom to 52 mu m and 31.4% at the top of the FGM layer, respectively. The morphology of the Si particles changes accordingly from a small polygonal shape to a coarsely branched equi-axial shape. The a-Al halos and eutectic areas show less change over the same distance. From an analysis of the temperature field of the laser pool, Si particles heterogeneously nucleate on incompletely melted Si particles. The number density of Si particles is most likely being controlled by the non-homogeneous temperature field of the pool that determines the decomposition of the original Si phase in the AlSi40 powder. The growth rate and time available at different depths of the laser pool mainly affect the final size of Si particles. (C) 2000 Acta Metallurgica Inc. Published by Elsevier Science Ltd. All rights reserved.