Study Of High Temperature Anti-wear Composite Coatings On Titanium Alloy With The Addition Of HBN

Laser cladding composite coating is an effective approach to improve the tribological properties of titanium alloys. Although many kinds of researched coatings are beneficial to improve the tribological properties of substrates with the increasing of surface hardness and stength, they usually present high friction coefficient under severe working conditions(high temperature, heavy load and uneasy lubricated conditions), which is harmful to the durability of titanium alloy, especially for their mating counterparts. A valid method to overcome this difficulty is to design a composite coating with high-temperature self-lubricating properties.Ni60 anti-wear coating, Ni60-5%h BN and Ni60-10%h BN high-temperature self-lubricating anti-wear composite coatings were fabricated on Ti-6Al-4V alloy by laser cladding. The phase compositions and microstructure of the coatings were investigated using X-ray diffraction(XRD) and scanning electron microscope(SEM) equipped with energy dispersive spectroscopy(EDS). The tribological behaviors were evaluated using a ball-on-disc tribometer under dry sliding wear conditions and the corresponding wear mechanisms were discussed.Results indicate that there is no crack and pore that exists in coatings and a fine metallurgical bonding is obtained between the coating and the substrate. There are three different regions of the cross section: cladding zone(CZ), bonding zone(BZ) and heat affected zone(HAZ). Ni60 coating consists of γ-Ni solid solution, Ti C as well as Ti B2. All of the above three phases also exist in Ni60-5%h BN and Ni60-10%h BN coatings. Moreover, the diffraction peaks of Cr B, Ni3 B and h BN appear in the XRD spectrum. With increasing of the content of h BN, the volume fraction of borides is higher and forming special and complicated phase structure during rapid solidification. Compared with the substrate, the micro-hardness values of the whole coatings are higher, and the corresponding averages(946, 1052 and 1109 HV0.2) are about 3 times higher than that of the substrate. The micro-hardness of Ni60 coating is slightly lower than that of Ni60-h BN coatings.Although the friction coefficient and wear rate of Ni60 coating ascends with the increasing temperature to the highest value at 600 ℃, its wear rate still reduced by 85% than that of substrate, which indicates Ni60 coating has good wear resistance. Compared to Ni60 coating, Ni60-h BN high-temperature self-lubricating composite coating exhibits superior tribological properties in a wide range of temperature. The friction coefficient and wear rate of Ni60-h BN composite coating decreases gradually. Especially for Ni60-10%h BN coating, at 600 ℃, its friction coefficient is 0.23 and its wear rate is 4.2×10-6 mm3/Nm, which is reduced by 75% than that of Ni60 coating. These results well prove that Ni60-h BN composite coatings possess outstanding high-temperature friction-reducing and anti-wear properties the combined effects of the reinforced carbides, borides and lubricating films.At room temperature, the friction coefficient and wear rate of Ni60 coating improves with the increasing of normal load, the wear resistance of Ni60 coating is excellent under low/medium load. On the contrary, both friction coefficient and wear rate of Ni60-10%h BN composite coating decreases firstly and then increases. It is demonstrated that the composite coating has excellent tribological properties at 600 ℃ under 5 N normal load.