The Research On Stellite 3 Composite Coatings On Nickel-Based Superalloy By Laser Cladding Technology

As the core component of aero-engine,the brush-sealed turbine rotor shaft has been exposed to harsh environments such as high speed,high temperature gas,strong molten salt corrosion and strong thermal cycle for a long time,so it is very important to improve its service life.Inconel 718 superalloy is mainly used to make turbine rotor shaft due to its stable chemical composition,resistance to fatigue fracture and various corrosion and stable mechanical properties.However,its hardness is low and its wear resistance is poor.Therefore,a layer of multifunctional wear-resistant composite coating needs to be coated on the surface of brush sealed turbine rotor shaft.In this study,the Stellite 3 alloy powder with good wear resistance and the lubricating phases Cu and Ti3SiC2 were mainly used in the composite coating powder system,and six kinds of coatings with different contents were cladded on the Inconel 718 superalloy by laser,100wt.%Stellite 3,5wt.%Ti3SiC2,10wt.%Ti3SiC2,15wt.%Ti3SiC2,10wt.%Cu and 5wt.%Ti3SiC2+10 wt.%Cu,respectively.The different kinds ways of characterization(SEM,EDS,XRD,etc.)were used to study their mechanical behavior,the ability to resist wear,and oxidation characteristics.The main phases in the added Ti3SiC2 coatings were solid solution γ-Co and(Fe,Ni),carbides WCx and Cr7C3,and intermetallic compound Cr2Ni3.However,the Cu-added coatings had diffraction peaks of Cu.Due to the different amounts of additives,the evolutions of the structures of the coatings were also different,resulting in different coatings properties.Specifically,the main microstructures of the four composite coatings without Cu were dendrites,equiaxed crystals,cellular dendrites and cellular crystals,respectively.The microstructures in the two Cucontaining coatings were mainly composed of light gray dendrite,dark gray interdendritic and black cell dendrites.The microhardnesses of six composite coatings were 740.10 HV0.5,662.74 HV0.5,521.47 HV0.5,419.44 HV0.5,701.67 HV0.5 and 490.02 HV0.5,respectively.Due to the dispersion strengthening,solid solution strengthening and grain refinement strengthening produced in laser cladding,the microhardness of the coatings is improved to different degrees compared to the substrate.The oxidation resistance of the added Ti3SiC2 coatings were investigated.It could be seen from the data results that the degree of oxidation of the coating was not serious,and the oxidation kinetics curve showed that the weight gain of the substrate and the four composite coatings were 26、..56 and 24.39,22.03,14.14,17.03 mg/cm2,respectively.The oxidation rate constants were 2.674,2.374,2.345,1.109,2.019 mg2/(cm4·h),respectively.The substrate surface was mainly oxides of Cr and Fe,while the oxides of Ti,Si,W and Co appeared on the surfaces of coatings.The presence of Co,Ti and Si oxides was the main reason for the improved oxidation resistance of coatings.In addition,the oxidation surface with 5wt.%Ti3SiC2 coating was smooth without obvious peeling marks,and the overall oxidation resistance was better.From the wear data results,it can be seen that at room temperature,the average friction coefficient and wear rate of the substrate and the six coatings were 0.687,0.605,0.546,0.572,0.571,0.664,0.718 and 3.84×10-4,2.19×10-5,5.51×10-5,6.24×10-5,1.96×10-4,4.76×10-5,4.45×10-6 mm3/(N·m).At high temperature,the average friction coefficient and wear rate of the substrate and six coatings were 0.671,0.543,0.656,0.678,0.676,0.544,0.579 and 2.98×10-4,1.32×10-4,6.75×105,6.09×10-5,6.36×10-5,1.19×10-4,9.93×10-5 mm3/(N·m).The friction coefficient of the composite coating without Ti3SiC2 at high temperature was the lowest in the whole study coating system,and its wear was mainly caused by adhesion and slight oxidation;The lowest wear rate appeared in the 5%Ti3SiC2+10%Cu composite coating at room temperature,and the wear was mainly caused by adhesion and oxide film peeling.Overall,Cu and Ti3SiC2 synergistically lubricate and together improve the coating wear characteristics.This paper deeply discusses the role of Ti3SiC2 and Cu in the coatings,which will provide a theoretical basis for enriching the laser cladding material system,and also provide a technical reference for improving the service life of the turbine rotor shaft.