Research On Contact Fatigue And Tribology Performance Of Ni/Ti Alloy Cladding Layers Reinforced By In-situ Synthesized TiN

Wear failure and contact fatigue failure are the main failure modes of cam under alternating loads.The remanufacturing plasma cladding technology can improve the performance of the cam significantly by strengthening the surface of cam material.Compared with the traditional alloy cladding coating,the In-situ cladding coating possesses the higher strength due to the in-situ enhanced phase within the alloy serve as strengthening phase.The strength and lifetime of parts generated by in situ synthesis can be improved.In this paper,the in-situ TiN phase enhanced Ni/Ti alloy cladding layer was prepared by mixturing the Ni₁₅A and titanium alloy powder under the nitrogen by plasma cladding technology.The Cladding parameters have been optimized by using different cladding current and feeding rate.The hardness and quality of cladding layer are used to measure the quality of plasma cladding coating prepared by three different mass ratio of Ni₁₅A and Ti mixed powder and get the optimum proportioning ratio of powder further.The macrostructure,microstructure and mechanical properties of the optimized plasma cladding layer were characterized and tested,besides the macrostructure and microstructure of the cladding layer formation process were analyzed.The wear mechanism and wear resistance of the cladding layers under different load were also studied.At the same time the contact fatigue failure mode of the cladding layers under different load were counted,and the life curve of the cladding layers under different load was established.Plasma cladding parameters and powder proportioning optimization show that the cladding layer has a good quality when the cladding current is 80A,the powder feeding speed is 3 mm/s and the Ti ratio is 7:3.The TiN phase within cladding layer is formed by many single TiN cellular particles clustered together,and the in situ synthesis Ti N phase presents petals or dendritic grain aggregate.The single TiN cellular particle diameter has a range of300nm to 500nm.The main phase of cladding layer is Ni₃Ti phase,and the Ti phase,TiN phase and（Fe,Ni）phase also existed.The macrostructure of cladding layer from the bottom to up include fine grain area,columnar dendrites and columnar crystal area successively.TiN volume fraction in the cladding layer is 3.2%,and the cladding layer possesses a high microhardness reaches 760 HV_0.2,and the fracture toughness of cladding layer at 4.9N reached 5.15 MPa·√m.The friction coefficient of cladding layer is less than substrate under three loads,and there are a little furrow and wear debris in wear scar.So the furrow deformation and abrasive wear resistance of cladding layer are better than substrate.The wear resistance of cladding layer presents growing tendency within creasing load.The contact stress determines the contact fatigue lifetime and failure mode directly.The contact fatigue lifetime obeys the Weibull distribution,and the P-N curve and P-S-N curve are established to provide the lifetime forecast of cladding layer.