Functionally graded materials produced with high power lasers

In this keynote paper two examples will be present of functionally graded materials produced with high power Nd:YAG lasers. In particular the conditions for a successful Laser Melt Injection (LMI) of SiC and WC particles into the melt pool of A18Si and Ti6Al4V alloys are presented. The formation of a relatively thick aluminium oxide layer on Al melt surface was confirmed during in-situ melting in an Environmental Scanning Electron Microscope (ESEM) at temperatures above 900 degreesC. This oxide layer acts as a barrier for particle penetration but it can be dissolved in the melt at temperatures above 1250 degreesC and consequently it opens a "window" for particles injection. The finite element analysis of the laser melting process of AI-Si alloy leads to the conclusions that the laser scan velocity has only a small influence on the substrate temperature distribution in the vicinity of the laser beam and that the size of an elongated laser melt pool (which is the best place for injection) is extremely small. This is in contrast to the second example of particle injection in Ti-alloys in which an extension of a melt pool size behind the laser beam serves as an effective instrument for successful LMI of ceramic particles. Further, the relationships between microstructure, tensile and wear properties have been investigated for SiC/Al-Si and WC/Ti-Al-V metal matrix composite layers.