MARTENSITE FORMATION IN TI-AL LAYERS PRODUCED BY LASER SURFACE ALLOYING

The microstructures of Ti-Al layers produced by laser surface alloying of a Ti substrate have been investigated for Al contents in the range 17-36 at.-%. The alloyed layers were obtained using a continuous wave CO2 laser and a powder feed technique employing the following laser processing parameters: 1.8 kW power, 3 mm beam diameter, 7 mm s-1 traverse speed, and feedrates of Al powder ranging from 0.03 to 0.07 g s-1. The microstructures were disordered lath martensite alpha' in 17 at.-% Al alloy, ordered massive and acicular martensite in 23 at.-% Al alloy, and ordered massive, acicular, and lath martensite in 30 and 36 at.-% Al alloys. The change in martensite type and morphology is discussed in relation to the available data for the beta to alpha' transformation in Ti alloys.