LASER IN SITU SYNTHESIZED TITANIUM DIBORIDE AND NITINOL REINFORCE TITANIUM MATRIX COMPOSITE COATINGS

Laser cladding is a technique in which a laser beam is used as the heating source to melt the alloy powder to be clad on the surface of titanium alloy substrate. Currently, the surface of many titanium alloy components needs repairing after a period of service in order to extend their service life. TiB and TiB2 are considered as the excellent ceramic reinforced particle for their compatible physical and thermodynamic properties, high hardness and Young's modulus of elasticity. The intermetallic compound NiTi, well-known for its shape memory effect and pseudo- elasticity, is one of the rarely few intermetallic compounds having excellent combination of high strength, ductility and toughness as well as excellent wear resistance and fabrication processing properties. An insitu TiB/TiB2 structured ceramic materials as the reinforcing phase and NiTi intermetallic phase as the matrix would be expected to have an outstanding combination of high hardness and toughness. NiTi alloy, TiB short fiber and TiB2 particulate reinforced titanium matrix composite coatings were prepared by laser in situ synthesis on titanium surface with different ratios of Ni powder and TiB2 powder mixture as a preset level. Synthesis of titanium matrix composite coating was analyzed by XRD, SEM and EPMA. The results show that the surface quality of the coating increases with increasing laser power density and the amount of Ni powder. Whereas, the new phase of NiTi2 and coarse diameter of TiB short fiber are found in the coating when the amount of Ni added is improved. The reaction mechanism is discussed based on thermodynamic calculations. The reaction driving force size to Ni3Ti>NiTi2>NiTi>TiB order arrangement are found by thermodynamic calculation, and reaction mechanism of competition between the different elements is discussed based on phase variation of the type and content in the coating.