| GCr15 steel is the most widely used in the bearing field because of its good machinability,simple heat treatment process and low cost,and its annual production accounts for about 85%of the global bearing steel production.g Cr15 steel will undergo the transformation of residual austenite to untempered martensite in the process of long-term service after traditional heat treatment,thus decreasing its hardness,losing accuracy and fatigue life.Scanning electron beam is a new type of energy-carrying beam technology,which has the advantages of high energy utilization,low processing deformation and easy control.In this paper,scanning electron beam technology is used to prepare ceramic enhanced coatings on the surface of GCr15 steel to enhance the surface properties and extend the service life of GCr15 steel.In this paper,pre-experiments and temperature field modeling simulations for the preparation of ceramic reinforced coatings on GCr15 steel by scanning electron beam are carried out.The heat source model is compared and validated by the pre-experimental results,and the temperature field simulation is solved for different process parameters based on the calibrated heat source.With the results of temperature field simulation,the heat flow density of different process parameters was analyzed and the optimal process parameters were obtained to guide the subsequent process tests;the Ti C-reinforced coating was prepared by direct addition method and the effects of different ratios on the coating structure and mechanical properties were investigated;the Ti（C,N）ceramic-reinforced coating was prepared by in situ synthesis method and the effects of different ratios of Ti-MWCNT/Ti N on the coating structure and properties were investigated.The effects of different Ti-MWCNT/Ti N ratios on the organization and properties of the coatings were investigated,and the thermodynamic effects of in situ synthesis and the mechanism of in situ synthesis were investigated,and the effects of the two preparation methods on the coatings were analyzed and compared.The results show that the process of preparing the coating by scanning electron beam will cause the bonding phase in the preset powder to instantaneously warm up to the melting point with the substrate,forming a molten pool on the substrate and encapsulating the preset powder,followed by immediate cooling and solidification to form the enhanced coating.After the scanning electron beam treatment,the cross-sectional morphology along the scanning trajectory consists of three regions:the coating region,the heat affected region and the substrate.The enhanced coating prepared by direct addition of Ti C particles has limited effect on enhancing the tissue morphology and mechanical properties,in which the coating is mainly composed of Ni3Fe phase and Ti C particulate matter.With the increase of Ti C added particulate matter,the agglomeration of Ti C particles in the coating becomes more and more obvious and transforms from fine particulate matter to fishbone phase,and Mo elements are enriched around Ti C particles,which improves the wettability of Ti C phase.The microhardness of the prepared coatings increased with the increase of Ti C content,and the average hardness of 70wt.%Ti C coating reached 920.5HV0.2.In the wear experiments,the coating with 50wt.%Ti C had the lowest friction coefficient（0.51）reduced by 37%compared to the substrate,while the coating with 70 wt.%Ti C had the lowest wear amount.The Ti C and Ti（C,N）coatings prepared by in-situ synthesis technique have dense structure and more uniform composition,and have better night effect with the matrix.This has a significant effect on improving the mechanical properties of the coating.With the decrease of Ti-MWCNT addition,the hardness of the coating increases and then decreases,and the wear amount decreases and then increases,among which the C3 coating has the highest hardness and the lowest wear amount and friction coefficient,and the highest hardness in the coating reaches 1304.7 HV0.2 which is 4.7 times higher than that of the matrix.The wear amount of the coating is 0.3 mg,which is 0.67 times lower compared to the substrate,while the friction substrate also obtains the lowest wear amount.Comparing the two preparation methods,the coating prepared by direct addition inhibits the beam energy propagation in the melt pool due to the weak conductivity of the enhanced phase,and reduces the mobility of the melt pool,the agglomeration phenomenon in the coating is more obvious,and the coating performance improvement is more limited.While the in situ synthesis method prepared by the coating enhancement of particulate matter is more fine,more uniform distribution within the coating,mechanical properties than the matrix has a greater improvement. |
