Hard coatings by laser gas alloying of Ti6Al4V. (4th August 2014) - Damborenea, J. De
Laser surface alloying with nitrogen involves melting of the Ti6A14V base material in a saturated nitrogen atmosphere. The nitrogen becomes alloyed with the molted titanium both by convection and by diffusion, and the cast metal is rapidly solidified by the self–quenching effect of the solid substrate. Surface gas alloying was carried out using a 5 kW Spectra–Physics transversal flow carbon–dioxide laser operating in TEM 20 at different speeds (0.3, 0.5 and 0.8 m/min) and input flow of 15, 30 and 50 l/min. Afterwards laser gas alloying, tracks of a light gold colour could be seen by the naked eye. The initial microstructure of Ti alloy (equiaxed grains of primary α in a matrix of transformed β containing fine acicular α), changed to a surface layer of dendrites of TiN in a nitrogen–enriched alpha matrix covering the melted surface. Microhardness on the dendrite reached a value till 1800 HV (hardness of the base material was of 354 HV). This hardness decreased till 600 HV in the interdendritic space. No surface cracking was observed within the melted zones for any of the conditions tested.