Microstructure And Properties Of Niobiumizing Layer Prepared On GCr15 Steel

With the development of high-end equipment,bearings are required to have higher wear resistance and contact fatigue performance.Surface strengthening treatment of bearing steel to improve its surface hardness is significant to prolong the service life of bearings greatly.In this paper,GCr15 bearing steel is used as the substrate to prepare a niobiumizing layer with rare earth oxides addition by thermal reaction diffusion method.By using microscope,scanning electron microscope,micro hardness tester,X-ray diffractometer,friction and wear tester,electrochemical workstation,the effects of different types of rare earth oxides（lanthanum oxide,yttrium oxide,cerium oxide,neodymium oxide）and different contents of lanthanum oxide（0.5%,1%,2%,and 4%）on the structure,composition,friction and corrosion properties of the niobiumizing layer are researched.And the growth kinetics of the rare-earth niobiumizing layer is explored preliminarily.The results show that:Adding different types and different contents of rare earth can obtain a bright white niobiumizing layer.The main phase composition of the niobiumizing layer is Nb C.When cerium oxide is added,the thickness of the infiltration layer is 10.5μm.The microhardness of the infiltration layer is 2681.82HV_0.2.In the case of lanthanum,the friction coefficient of the niobiumizing layer is 0.3952,the self-corrosion potential is-0.7258V,and the self-corrosion current is 2.1124×10-6A/cm².When adding different content of lanthanum oxide,the thickness of niobiumizing layer increases with the increase of lanthanum oxide content,and the maximum is 15.2μm when the added content is 4%;when the content of lanthanum oxide is 2%to 4%,the increase in infiltrated layer thickness is not obvious;As the content of lanthanum oxide increases,the microhardness of the niobiumizing layer gradually increases.When the content of lanthanum oxide reaches 4%,the microhardness is 2007.6HV_0.2.As the content of lanthanum oxide increases,the dry friction coefficient of the niobiumizing layer gradually reduced.When the content of lanthanum oxide reaches 4%,the average dry friction coefficient is 0.3951;when the content of lanthanum oxide is 2%,the corrosion resistance of the niobiumizing layer is the best,its self-corrosion potential is-0.5759V,and its self-corrosion current is 5.2365×10^-7A/cm².The diffusion activation energy of the niobiumizing layer added with 2%lanthanum oxide is 171.22 k J/mol,and the diffusion activation energy of the niobiumizing layer without added rare earth oxide is 90～150 k J/mol,the former is significantly greater than the latter.The addition of rare earth promotes the rapid growth of the niobium-impregnated layer.