MICROSTRUCTURES OF TITANIUM ALUMINIDES PRODUCED BY LASER SURFACE ALLOYING

The microstructures of Ti-Al layers (from 43-80 at %Al) produced by laser surface alloying of titanium substrate with a powder feed technique have been investigated. The laser processing parameters were; 1.8 kW laser power, 3 mm beam diameter, 7 mm s-1 traverse speed, and values of powder flow rates of aluminium ranging from 0.07-0.11 g s-1. The microstructures were dendrites of alpha-2 and interdendritic regions of alpha-2 + gamma in the Ti-43 at %Al alloy; dendrites of either alpha-2 or alpha-2 + gamma with interdendritic-gamma in the Ti-50 at %Al alloy; dendrites of alpha-2 + gamma with interdendritic-gamma in the Ti-55 at %Al alloy; single phase-gamma in the Ti-60 at %Al alloy and TiAl3 dendrites and Al solid solution in the interdendritic regions in the Ti-80 at %Al alloy. The microstructures were fine and comparable to those produced by other methods of rapid solidification processing. The microstructures of the Ti-50 and Ti-55 at %Al alloys were in agreement with the existence of the peritectic reactions: L + beta --> alpha and L + alpha --> gamma, in the Ti-Al system.