Microstructure and High Temperature Tribological Properties of NiCr-ZrB₂ Composite Coating

NiCr coating and NiCr-ZrB₂ composite coating are prepared on pure Ti substrate by the laser cladding. The composition and microstructure of the coatings are analyzed by X-ray diffraction, scanning electron microscopy and high resolution transmission electron microscopy. The tribological properties of NiCr coating and NiCr-ZrB₂ composite coating are evaluated on a SRV-IV tribo-tester at elevated temperatures (20~500 ℃). The results show that NiCr-ZrB₂ composite coating is mailnly composed of Ni, Ti, Cr₂Ti, ZrB₂, ZrB, Ni₃Cr₂, Ti₂Cr, TiB₂ and TiB phases. The NiCr-ZrB₂ composite coating is metallurgically bonded to the titanium substrate, and the coating contains dentritic and block-like microstructure. In addition, the NiCr-ZrB₂ composite coating has a microhardness of ca HV_0.21000 and with thickness of 0.7~1.0 mm. The friction efficient and wear volume of the NiCr-ZrB₂ composite coating decrease with increasing temperature. The NiCr-ZrB₂ composite coating has higher wear resistance than that of titanium substrate. The wear mechanisms of NiCr-ZrB₂ composite coating at elevated temperatures are abrasive wear and adhesive wear.