The Fabrication And Properties Analysis Of Laser Cladding Ni-Cr-Mo Alloy Coating

Laser cladding technique plays an significant role in fabricating the abrasion-resistant and corrosion-resistant cladding coating.And it has broad application prospects in the field of civil and national defense.In order to improve the corrosion resistance and extend the service life of metal components usin in the marine environment,four different speed parameters(20mm·s-1,30mm·s-1,40 mm·s-1&50mm·s-1)were using to fabricate the Ni-Cr-Mo alloy cladding layer on Q235 steel by high power semiconductor laser cladding technique.And Ni-Cr-Mo-Cu alloy cladding layer with different Cu contents(5%and 10%,wt.%)were also perpared using the speed of 40 mm·s-1.The phase composition and microstructure of the clad layer were analyzed by X-ray Diffraction(XRD),Scanning Electron Microscopy(SEM)and Energy Dispersive Spectrometer(EDS).The micro-hardness of the cladding coatings were investigated by micro-Vickers hardness tester.The corrosion behavior of the cladding layer in simulated seawater was measured by electrochemical testing.The copper ion exudation rate of Ni-Cr-Mo-Cu cladding layer in simulated seawater solution was measured and calculated to evaluate the biological fouling performance initially.Ni-Cr-Mo alloy cladding layer,metallurgically bonded to the substrate,is composed of Ni-based solid solution of Cr,Mo,Fe,W.And the sample prepared at high cladding speed(40 mm s-1&50mm·s-1)contains a small amount of Mo6Ni6C.The microstructure of the Ni-Cr-Mo cladding layer exists rich Mo phenomenon in the grain boundary.With the increase of the cladding speed,the ratio and size of the grain boundary is increased,and the grain size of the cladding layer is decreased.During the sample erosion,the grain is gradually etched from the grain edge to the center and the grain boundary is preserved.The micro-Vickers hardness of the four Ni-Cr-Mo alloy cladding samples is 300HV-325HV,which is about 2 times of the Q235 steel.As the cladding speed increases,the microhardness increases slowly.In the 3.5wt.%NaCl aqueous,the corrosion resistance of the four Ni-Cr-Mo alloy cladding layers is similar,and much better than that of the Q235 steel.The corrosion resistance of Ni-Cr-Mo alloy cladding layer prepared by 40 mm s'-1 is the best.Ni,Cr,Cu,Fe and Ni form Ni-based solid solution in the Ni-Cr-Mo-Cu alloy cladding layer,and the grain boundary is also rich in Mo.With the increase of the content of copper,the size and proportion of the grain boundary gradually decreased,which indicates that the addition of copper can promote the microstructure homogeneity in the Ni-Cr-Mo-Cu alloy cladding layer.As the copper element is easily oxidized at high temperatures,and there are more defeets(oxides particles or proes)in the C10 sample.Under the same preparation conditions,the microhardness of the Ni-Cr-Mo-Cu alloy cladding layer is slightly higher than that of the Ni-Cr-Mo alloy cladding layer,and the corrosion resistance is slightly lower than that of the Ni-Cr-Mo alloy cladding.And the corrosion resistance of C10 is slightly better than that of C,,which may be related to the composition of the passivation film on the surface of the cladding layer,the degree of uniformity of the surface structure and the influence of the defects.The addition of copper element is beneficial to the formation of pure Cu(or Cu oxide)and Mo oxide composite passivation film,and it can also improve the uniformity of the Ni-Cr-Mo-Cu cladding layer,which is conducive to improving the corrosion resistance of materials.But the defects such as oxide particles and pores in the surface of the cladding coating may reduce the corrosion resistance.The addition of Cu may promote the formation of Mo-rich ? phase,and the formation of poor-Mo zone in vicinity would lead to the decrease of corrosion resistance.Owing to the low content of copper in the Ni-Cr-Mo-Cu cladding layer,the copper ions exudation rate of two Ni-Cr-Mo-Cu cladding layer is lower than 10?g·cm-2·d-1,which can not inhibit the growth of common marine organisms.