Surface Depression Control and Subsequent Improvements to the Formation Process of Laser Clad TiB2 Coatings
Y-H. Lin, J-H. Yao, Y-P. Lei, H-G. Fu, G-L Wu and L. Wang
Over the past decade researchers had demonstrated much interest in laser clad TiB2 composite coating for its good wear resistance, corrosion resistance and high temperature properties; however, the surface depression of TiB2 composite coating was obvious. In this paper the flow behaviour of the molten pool was observed by the high-speed camera. The formation process of the coating depression was analysed and the suppression methods of the coating depression were also studied. The results showed that the depression formation of the coating undergoes three stages: downward deposition of particles; the molten liquid flows into the low temperature region; and rapid solidification process. The depression of the coating can be improved by pre-heating and laser track overlapping. These two measures were helpful to improve the fluidity and the amount of the molten liquid. Meanwhile, the depression degree of the coating can be gradually reduced with the increasing scanning speed.
Keywords: Fibre laser, Ti-6Al-4V alloy, TiB2 composite, laser cladding, powder, coating, surface morphology, depression