Study On Microstructure,wear Resistance,and Corrosion Resistance Of Ni/WC Gradient Coating Prepared By Laser Cladding

With the development of the social economy,the exploitation of oil and natural gas is becoming more and more difficult,and the drilling and production environment is becoming worse and worse.As one of the most important components of drilling tools,non-magnetic drill collars are not only subjected to stress,but also to the friction of well walls and corrosion of drilling mud and oil.In addition,there are corrosive substances such as H₂S,CO₂,and Cl^-in some oil and gas fields,so wear failure and corrosion failure have become common failure forms of non-magnetic drill collars.Therefore,it is necessary to improve the wear and corrosion resistance of the surface of the non-magnetic drill collar.Laser cladding technology is widely used in the field of material surface modification because it has the advantages of a small heat-affected zone,easy automation,and no pollution compared with traditional surface modification technology.In this paper,Ni/WC cermet composite coating was prepared on the surface of non-magnetic drill collar steel by laser cladding technology to improve the wear and corrosion resistance of non-magnetic drill collar steel.The effects of material composition on the microstructure,wear resistance,and corrosion resistance of the single-layer coating were studied and analyzed.The microstructure,wear resistance,and corrosion resistance of gradient coating were studied and analyzed.The main research contents are as follows:（1）The process parameters of single-layer coatings with WC addition ratio of 0wt%,15wt%,and 30wt%were optimized by orthogonal test,and 0wt%,15wt%,and 30wt%single-layer coatings were prepared.Then prepare gradient coating according to the process parameters of the single-layer cladding layer:Inconel 625 cladding layer is used as the first gradient sublayer,Inconel 625/WC composite coating of 15wt%WC is used as the second gradient sublayer,and Inconel 625/WC composite coating of 30wt%WC is used as the third gradient sublayer.（2）To study the effect of WC on the microstructure,wear resistance,and corrosion resistance of the coating,the microstructure,phase structure,and microhardness of different single-layer coatings were characterized and analyzed;The wear resistance and corrosion resistance of single-layer coating were studied and analyzed by reciprocating friction and wear test and salt spray corrosion test.The results show that the coating mainly includes columnar crystal,dendritic crystal,and equiaxed crystal;WC in the cladding powder will decompose and react with Ni-base to form a carbide phase,to improve the microhardness of the coating;The microhardness and wear resistance of the coating are positively correlated with the WC content in the cladding material,and the corrosion resistance of the coating is negatively correlated with the WC content in the cladding material.（3）To improve the wear resistance and corrosion resistance of the coating,gradient coating was prepared.The bonding between the sub-layers of gradient coating was studied and analyzed.The microstructure,coating phase,and microhardness of different areas of gradient coating were studied and analyzed.The wear resistance and corrosion resistance of gradient coating were studied by reciprocating friction and wear test and salt spray corrosion test.The results show that the bonding between sub-layers of gradient coating is good;The microstructure and phase composition of gradient coating are similar to that of composite coating added with 30wt%WC;The wear resistance and corrosion resistance of gradient coating are better than that of 30wt%WC composite coating,which can improve the wear resistance and corrosion resistance at the same time.