Effect of heat input on the microstructure of in-situ synthesized TiN-TiB/Ti based composite coating by laser cladding

摘要

In situ synthesized TiN and TiB particulate-reinforced metal matrix composite coating was formed on Ti-3Al-2V alloy by laser cladding with a Ti/h-BN powder mixture. The phase structure, microstructure, microhardness and wear performance of the composite clad layer were analyzed by optical microscope (OM), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM), micro-hardness tester and wear testing machine. It has been found that the clad layer mainly consisted of α-Ti, TiN and Ti _4N _(3-x) at the laser power density of 120W/mm ~2; While, TiB and TiN were synthesized at the laser power densities of 150 and 180W/mm 2. TiN and TiB were compared with dendrite and needle platelet type microstructures. The microhardness of laser clad layer was 800-1200HV _(0.3) which was about 5 times of the substrate. The lost height of the substrate is almost 2 times of the clad layers.