Investigation Into Ni/WC_p Wear-Resistant Composite Coating Produced By Diode Laser Cladding

The excellent corrosion resistance,wettability,moderate price and high temperature self-lubricating effect of Ni-based alloy make it widely used in military,aerospace,chemical,and petroleum industry,etc.However,traditional single alloys are hard to meet the requirements of the work piece under severe conditions with high wear resistance and hardness requirements.Therefore,the alloy by Laser cladding can further improve the wear resistance and hardness by adding the WC ceramic phase material of the high hardness and high wear resistance.But large physical properties exist between the Ni-based alloy and WC particle and the Ni-based alloys with high hardness have a poor toughness,which resulted of cracks and pores in the composite coating.And the fabrication properties of Ni-based alloys with low hardness bonding phase is good,but in the course of service,low hardness of the bond phase prone to selective wear,reducing its ability to control the WC particles,thereby reducing the wear resistance of the coating.Therefore,it is difficult to obtain high hardness nickel-based alloy composite coating without any pores,crack defects and with excellent wear resistance.In the present study,with a self-made high hardness of nickel-based alloy 440 as the bonding phase,Ni/WCp composite coating were fabricated onto an austenitic stainless steel AISI 304 by high-power diode laser cladding technology.The effects of laser power and other parameters on the degree of WC particles heat damage,the formability of cladding layer and the defects of cladding layer were investigated.The effects of WC content on the surface morphology,the microstructure,the sensitivity of the defects,hardness and wear resistance were also investigated.The Ni/WC_p composite laser cladding layers with high hardness and good wear resistance and without any defects were obtained by using the optimized laser process parameters.It is found that with the increase of laser power to a high value,the formability of composite coatings increase clearly,but the defects of the composite coatings,such as pores and cracks,also increase;With the increase of WC content to a high value,the degree of the heat damage and the defects of composite coatings increase.Each Ni/WC_p composite coating with different WC content has a critical power.When the laser power is higher than the critical power,WC particle suffered a serious heat damage,pores and cracks also increased clearly,and at the critical power,composite coating had the best formability.With the increasing of WC content,the critical power of composite coating increases.Therefore,Ni-0%WC and Ni-10%WC composite coatings selected laser power of 2.8kW and 3.0kW;Ni-30%WC composite coatings selected laser power of 2.0kW and 2.2kW;Ni-50%WC composite coatings Selected laser power of 1.8kW and 2.0kW,whose multi-channel coatings have smooth surface,good shape,fine cladding/substrate interface and less defects.The WC particles had a fine bonding interface with the bonding phase,with the increase of laser power,a higher degree of WC heat damage and the thicker of the alloy reaction layer on the WC particle surface were happened.With the lower laser power,WC particles mainly occur in the diffusion-disolussion heat damage;the carbides mainly precipitated with block.With the higher laser power,WC particles mainly occur in the collapsing-diffusion-disolussion hybrid heat damage;the acicular carbides mainly precipitated.The laser-clad Ni/WC_p coating consists mainly of?-Ni,WC,W₂C,Fe₃C and M₇C₃.The hardness of compositer coatings,which have a high hardness bonding phase?46HRC?,were significantly improved compared with the pure Ni-based alloy.The results of wear test showed that the composite coatings with high hardness bonding phase possess high wear resistance at room temperature and 600?.With the increase of WC content,the wear resistance of the composite coating increase clearly.In the case of test load of 200N,rotate speed of 50rpm and wear time of 4h,the weight loss of pure Ni base alloy at room temperature and high temperature at 600?was 86.6mg and 226.5mg respectively,and the weight loss of the Ni-50%WC cladding layer at room temperature and 600?was 0.6 mg and 20.8 mg respectively.At room temperature,for pure Ni/Co-based alloy,adhesive wear dominate the wear process of the coating,as well as little abrasive wear,with increasing the content of WC,abrasive wear and adhesive wear decreased.At high temperature,adhesive wear and oxidation wear are the main way for all the coatings.