Research On Microstructure Evolution And Mechanics Features Of Ternary Ni-Mo-Si Alloy Coatings By Laser Cladding

With the rapid development of science and industry,parts often need to service in harsh environments such as corrosion,wear,high-temperature and so on.Then,traditional alloy components unsatisfy the performance requirements of the harsh environments.The silicide alloys is used as a candidate for harsh service environment due to its excellent corrosion and oxidation resistance,as well as its high hardness,good wear resistance.In this paper,three metal silicide alloy coatings were fabricated on a pure Ni plate by laser cladding.Systematic studies on microstructure evolution with different contents were conducted by XRD,SEM,EBSD and TEM.Results indicated that the phases of three coatings were Ni₃Si₂/Ni₂Si/Mo₂（Ni,Fe）₃Si as matrix phases and Mo₂（Ni,Fe）₃Si/Mo₆Ni₅Si₂as primary phases,Ni₃Si₂/γ-（Ni,Fe）+Ni₃₁Si₁₂/γ-（Ni,Fe）as matrix phases and Mo₂（Ni,Fe）₃Si/Mo₆Ni₅Si₂ as primary phases,andγ-（Ni,Fe）as the matrix phase and Mo₂（Ni,Fe）₃Si as the primary phase for Coatings 1,2,and 3,respectively.When the Si content of the coatings was changed,the primary phase Mo₂（Ni,Fe）₃Si was not changed.But,the matrix phases were changed.With the increase of Si content in the coating,the Ni-Si bonds was increased.For metal silicide alloys,ideal configurational entropy of alloys was increased as the composition tends to equimolar ratio.High entropy makes to simplify phase constitution of the coatings.Results of TEM indicated that Ni₃₁Si₁₂/Mo₂（Ni,Fe）₃Si interface is semi-coherent interface.Eutectic interface of Ni₃₁Si₁₂/γ-（Ni,Fe）were coherent interface with elastic distortion.The OR between Ni₃₁Si₁₂ and Mo₂（Ni,Fe）₃Si obeys[0001]_{Mo2（Ni,Fe）3Si}//[01-10]Ni31Si12,（-1100）Mo2（Ni,Fe）3Si//（0003）Ni31Si12.The OR between Ni31Si12 andγ-（Ni,Fe）obeys（002）γ（Ni,Fe）//（-2116）Ni31Si12,[100]Mo2（Ni,Fe）3Si//[01-10]Ni31Si12.The average micro-hardness for Coatings 1–3 is 987,977,and 734 HV,respectively.The micro-hardness of Coatings 1–3 was enhanced by approximately 8.2,8.1,and 6.1times compared with the pure Ni.With increasing Si content（Coating 3 to Coating 1）,the hardness of the three coatings showed an increasing tendency,owing to the formation of more M-Si bonds.The wear properties of three coatings were evaluated under large contact load at room-temperature,dry-sliding wear-test conditions.Results indicated that the three coatings exhibited outstanding wear resistance.The average friction coefficients were calculated to be 0.41（Coating 1）,0.38（Coating 2）,and 0.47（Coating 3）.The average wear volume loss rate was 1.8×10^-3,1.12×10^-3,3.81×10^-3,and 7×10^-3 mm³/min for Coating 1,2,3,and 304 stainless steel,respectively.Then,the wear resistance of Coating 2was the best due to its combination of excellent hardness and toughness.For the high-temperature wear test,the results showed that the average friction coefficients were 0.32,0.32,and 0.32 for Coating 1,2,and 3,respectively.Then,three coatings have self-lubrication at high temperature,because a number of metal oxides with low shear stress were formed on surface of wear scar（such as Mo O₃,WO₃ and Ni WO₄）.The average wear volume loss rate was 0.59×10^-3,0.84×10^-3,1.23×10^-3,and 2.34×10^-3 mm³/min for Coating 1,2,3,and pure nickel board,respectively.Then,the wear-resistance of high-temperature for Coatings 1–3 was enhanced by approximately 4,3,and 2 times compared with the pure Ni.