LAUSR

ABSTRACT In situ synthesized TiN and TiB reinforced metal matrix composite coating was fabricated on Ti-55511 by laser cladding with Ti-55511/BN powder mixture (2 wt-% BN). Results indicated that coating was mainly composed of TiB, dendrite TiN and α phase. The diameter of small-sized hollow tubular TiB was less than 400 nm, and the width of the other rod-shaped TiB was less than 1 μm. The flower-like structure formed during solidification consisted of TiN dendrite in centre and rod-shaped or hollow tubular TiB at edge. Coating had high hardness (540 HV) due to formation of TiB and TiN. After direct aging (600°C/5 h/AC), the hardness of coating and HAZ increased to 660 and 450 HV respectively because of nano-scaled α phase precipitation. In the friction and wear test, the weight loss of the coating was only 62% of that of substrate, which further reduced to 47% after aging.