Process Optimization Of Powder Thermal Diffusion Niobium Infiltration And Study Of Coating Wear Resistanc

Since the transition metal carbide coating has the characteristics of high melting point,high hardness,wear resistance,oxidation resistance and corrosion resistance,it is widely used in the field of surface modification and strengthening of materials.For steel failure cases,most of them occur on the surface of the material,or a large area of failure behavior is caused from the surface of the material.To some extent,surface modification treatment is a direct and convenient way to solve this problem.As one of the surface modification methods,the thermal reaction diffusion method has the advantages of convenient and simple operation,excellent performance of coating,and low cost.By the method,a niobium carbide coating with excellent wear resistance can be prepared,improving the wear resistance of the workpiece and delaying the failure of a components.In this study,the Pack Cementation treatment of 45 steel,and 40Cr steel were carried out,and the process parameters,properties and growth kinetics of coating preparation were studied.The main conclusions are listed as follows:1.A suitable process route for preparation of coatings on 45 steel:processing temperature was 950℃,holding time was 5 h,powder mixture was composed of 40 wt.%Ferroniobium powder and 3 wt.%Ammonium chloride;A suitable process route for preparation of coatings on 40Cr steel:the content of ammonium chloride was 2 wt.%,Ferroniobium powder 10 wt.%,The temperature 1000℃ and the time 5 h;Rare earth doping diffusion was carried out on 45 steel,and a suitable rare earth doping amount was found to be 1.5 wt.%.2.Through the variable analysis of orthogonal experimental,the order of influence of each variables of the diffusion process on the 45 steel was studied:processing temperature>holding time>content of ferroniobium powder>content of ammonium chloride;and the order of influence of each variables of the infiltration process on the 40Cr steel wasstudied:treatment temperature>content of ferroniobium powder>content of ammonium chloride>holding time.3.Through the analysis of variance,the influence of each variable on the thickness and hardness of the coating was quantified.It was found that whether for 45 steel or 40Cr steel,the influence of various types of variables on the thickness and hardness of the coating tended to be consistent,especially the temperature effect accounted for half of the thermal reaction diffusion treatment.4.The corresponding niobium carbide coating according to the optimized process was prepared.Afte analysis and calculation,the coating phases were all NbC,and the thickness of the coating could reach about 10 μm.It was also found that the grain size of the coating increased with the increase of the treatment temperature,and the addition of an appropriate amount of rare earth could improve the surface properties of the coating.In the subsequent friction and wear experiments,it was found that the niobium carbide coating has wear reduction and wear resistance.Comparing the coatings prepared under several different processes,it was found that the wear resistance of the coatings improved by rare earth was the better.It was also found that the properties of the substrate and the surface morphology of the coatings affected the frictional behavior to a certain extent.5.The coating thickness growth formulas for the three systems were obtained through the study of coating dynamics.Through kinetic calculations,the diffusion activation energy and diffusion coefficient of the niobium carbide coatings in the three systems were obtained.The effects of substrate composition and rare earth on the growth of the coating were analyzed from the mechanism.