Microstructure and tribological properties of REs borided TC21 alloy

The hard titanium boride layers are produced on titanium alloy TC21 using rare earth (RE) additions boriding technique. The microstructural evolution and phase transformations of the boride layers are examined using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy and X-ray diffraction. Moreover, the friction and wear behaviour of boride layers under dry sliding conditions are evaluated using an HT-1000 friction and wear tester, and the microstructures of worn surfaces are also characterised by SEM. The results show that the boron concentrations in the surface layer during surface boriding have been improved with a small amount of RE additions, coupled with enhanced surface hardness and coating layer thickness. Moreover, all of the borided alloys appear to have better wear resistance and lower friction coefficient than as received alloy; furthermore, the RE borided samples show higher hardness and better wear resistance than conventional one, without RE additions.