Preparation And Mechanical Properties Of TaC Cerramic Enhance Layer On Bearing Steel(GCR15)

Micro-nanostructured dense TaC ceramic enhancement layer were produced on bearing steel(GCr15)surface by in-situ reaction method.The thermodynamic conditions of GCr15/Ta system were calculated by Gibbs free energy function method.Calculate the growth coefficient and activation energy of TaC ceramic enhance layer by the ceramic layer growth kinetic model combined with Arrhenius formula.The microstructure,phase composition,phase distribution of the tantalum carbide ceramic enhancement layer and morphology of TaC particles were characterized by Scanning electron microscopy(SEM),X-ray diffractometer(XRD),transmission electron microscope and Electron backscatter diffraction technology(EBSD).The mechanical properties such as hardness,elastic modulus,fracture toughness and bonding properties of the prepared TaC ceramic reinforced steel matrix composites were evaluated by nanoindentation testing,miscrohardness testing and automatic scratch tester.The results show that:(1)In the GCr15/Ta system by the DSC analysis and thermodynamic calculation,the reaction temperature of the in-situ reaction is determined to be 1150,1200,and 1250?.(2)The micro-nano structured TaC ceramic enhancement layer generated by the in situ is well bonded to the steel substrate,and there are no interfacial defects such as pores and inclusions;There are Ta,TaC,FeC and ?-Fe in the longitudinal section of the sample,and the structure is unreacted Ta plate,TaC ceramic enhancement layer and substrate;TaC ceramic layer has only TaC phase on the surface and no other miscellaneous phase exists,indicating TaC ceramic surface is very dense.(3)In the system experiment of different holding temperature and reaction time,at the same temperature,with the extension of time,the thickness of the TaC ceramic enhancement layer also gradually increased prepared by the in-situ reaction method,and the growth coefficient increased with the increase of temperature.The growth coefficient K0=1.35×10-9 cm2/s,the growth activation energy of the TaC ceramic enhancement layer Q=402.41 kJ/mol.According to the growth kinetics model of the diffused ceramic layer and the Arrhenius formula,it can be known that the thickness of the TaC ceramic enhancement t layer on the surface of GCr15 has a certain functional relationship with the holding temperature and time.(4)The elastic modulus of the TaC ceramic enhance layer on the GCr15 surface is up to 537.9 GPa,which is about 2.26 times that of the steel base;the maximum hardness is 27.5 GPa,which is about 2.4 times that of the steel base.The hardness of the interface of the TaC ceramic enhance layer is along Ta The normal direction of the plate shows a gradient change;the fracture toughness of the TaC ceramic enhancement layer on the surface of GCr15 is KIC=10.06 MPa·m1/2 calculated by the Vickers hardness method;the scratch experiment shows that the surface of the reinforcement layer is scratched with increasing pressure The depth of the marks also increases,and the reaction enhancement layer prepared by in-situ reaction is excellent in scratch resistance,and the bonding performance between the reaction enhancement layer and the substrate is good.