Preparation of NiCoCrAlYTa/Ag/Mo composite self-lubricant coating and its high-low temperature cycling tribological properties

Abstract

In order to develop a self-lubricating coating with long life and high reliability suitable for harsh working conditions, the composite coating with NiCoCrAlYTa as matrix phase, Ag as lubricant phase and Mo as the reinforcing phase were prepared by high-velocity oxy-fuel spraying（HVOF）technology. The high-low temperature cycling tribological properties of the composite coating were investigated at 25 ℃ and 800 ℃. The morphology features, chemical composition and phase structure of the worn surface were studied to reveal the interaction between different elements in the friction process and physicochemical nature of friction interface. In addition, the multi-cycles adaptive lubrication mechanism under the alternating environment of high and low temperature was explored as well. The results show that the composite coating is dense and uniform, and has better mechanical properties. The phases of the composite coating mainly contain γ-Ni, β-NiAl, γ'-Ni3Al, Ag and Mo. The β-Ag2MoO4 layer-like lubricant generated on the surface can greatly improve the friction and wear performance of the composite coating at high temperature. Under the condition of multi-cycles, the friction coefficient of subsequent cycle of the composite coating is increased compared with the first cycle, but the wear rate of the composite coating at room temperature is decreased. This is caused by the interaction between the lubricating phase of β-Ag2MoO4 and the hard phases of Al2O3 and MoO3 with the action of frictional shear force.

Keywords

• composite coating
• layer-like structure
• self-adaptive lubricant
• thermal cycling
• friction and wear properties