Study Of Laser Cladding Nickel Wrapped Graphite Coating Onto Titanium Alloy Substrate

In-situ producing composite coating is characterized by thermodynamic stability, distributed uniformly, clear interface and good wettability between reinforcement phases and matrix. In order to obtain wear-resistant coatings with good properties, a process of laser cladding coating on TC11 substrate with pre-placed nickel wrapped graphite powder was studied. Through the comparison analyses of the macroscopic and microscopic qualities for the laser clad coating, the laser cladding parameters were optimized. Microstructure of the nickel wrapped graphite clad coating was characterized using XRD, SEM, EDS and TEM. The microhardness of the laser cladding coating was measured using HV-1000 type micro-sclerometer. Coatings were examined using an M-200 type pin-on-disk friction wear tester.Experimental results show that the macroscopic and microscopic quality is related to process parameters of laser cladding. Under the optimized laser cladding parameters of P=700W, D=Φ3mm,δ=0.6mm, V=5mm/s, nickel wrapped graphite cladding coating, in which no pores and cracks appear and surface is distributed uniformly are obtained, and the laser cladding coatings are metallurgically bonded with TC11 alloy substrate. The microstructure analyses showed that three regions with different microstructure existed in the surface of coating of laser cladding samples: the clad coating, the binding zone of the clad coating with the substrate, and the heat-affected zone in the substrate.The microstructure analysis shows that there was a reaction between C and Ti, in-situ producing TiC reinforcement phases. The coating is composed of Ti,TiC,Ni₄Ti₃ and Ni₃(AlTi) phases. The in-situ produced TiC shows the morphologies of fine dendrite and flowerlike. The average microhardness of laser clad coating is remarkably improved. The microhardness is HV1000¹100 in the coating zone of laser cladding coating, which is 2³ times that of the TC11 substrate (HV330-340).Wearing by YG8 hard alloy, the friction coefficient of TC11 alloy is in the range of 0.492⁰.537; the friction coefficient of the laser cladding coating is in the range of 0.519⁰.688. The wear mechanism of TC11 alloy is a mixture of...