Laser surface alloying and laser cladding were applied to enhance the tribological properties of titanium alloys. Wear resistant Cr7C3/NiCr, T5Si3/T and Ti5Si3/NiT2 in-situ metal matrix and intermetallic matrix composite coatings were fabricated on substrate of titanium alloys by the laser surface processing processes. The room and elevated temperature tribological properties of the laser surface processed wear resistant composite coatings were evaluated as functions of coatings microstructural parameters and laser processing conditions. The responding wear mechanisms were discussed based on worn surface and debris morphologies observations. The potential applications of laser surface modifications of titanium alloys for the aerospace industries are prospected.

The carbide of group IVB and group VB elements, i.e. MC carbide, is an important constitution and strengthening phase for many alloy tool steels and cast nickel-base superalloys. Since the as-solidified growth morphology, size and distribution have an important influence on both the mechanical properties and hot workability, research on the solidification behavior of MC carbide is an important subject for cast superalloys and many high alloy tool steels. The growth morphology and mechanisms of MC carbide, under slow-cooling and rapid solidification conditions, has been studied intensively as functions of the solidification cooling rate. The solidification behavior of MC carbide under quasi-rapid solidification conditions has not been reported in open literature. In this paper, the growth morphology and mechanism of an MC carbide (TiC type) under quasi-rapid solidification conditions is studied in a laser surface alloyed coating on a titanium aluminide alloy Ti–48Al–2Cr–2Nb (at.%). The growth morphology of the quasi-rapidly solidified MC carbide with a cooling rate of 4×102°C is found to be dendritic with strong faceted, double zigzag brick-stacking growth characteristics on the dendrite arms. The growth mechanism of the MC carbide is found to be a brick-stacking/double zigzag micro-branching lateral growth from steps on the intersecting {111} planes.

Laser surface alloying with both Si and SiC powder pre- coatings is utilized to improve the wear resistance of the Ti- 6Al-4V alloy. Rapidly solidified 'in-situ' composite coatings reinforced by TiC and Ti5Si3 phases are produced on substrate of the titanium alloy. Microstructure of the laser surface alloyed composite coatings is characterized and the wear resistance is evaluated under two-body abrasive wear condition. Results show that both the hardness and the wear resistance of the titanium alloy are considerably enhanced after laser surface alloying with Si and SiC powder pre- coatings.

Laser surface alloying with gaseous nitrogen was utilized to improve the wear resistance of a Ti–6Al–4V alloy. Wear-resistant composite coatings reinforced by hard TiN dendrites were produced ‘in-situ’ on a substrate of a Ti–6Al–4V alloy. The hardness and wear resistance of the laser alloyed coating under two-body abrasive and block-on-ring full-sliding wear conditions were significantly enhanced.

Laser surface alloying with TiC powder pre-coatings or laser surface carbonization is utilized to modify the wear resistance of a (gamma) -TiAl intermetallic alloy Ti-48Al- 2Cr-2Nb. An `in-situ' wear resistant composite coating reinforced by rapidly solidified TiC dendrites is made on substrate of the (gamma) -TiAl intermediate alloy. Crack-free TiC/TiAl composite coatings in thickness up to 1.6 mm, can be produced by laser surface alloying with preheating and slow post-treatment cooling. The hardness and wear resistance under dry sliding wear conditions are remarkably increased after the laser surface carbonization treatment of the (gamma) -TiAl intermetallic alloy.