| Dievar die steel,a kind of Cr-Mo-V alloy,has excellent thermal strength and good toughness,which was developed by the Sweden Uddeholm Tooling and is widely used in automotive,electronics,aviation manufacturing,nuclear power equipment,petrochemicals,offshore platforms and other fields that require high performance of materials.During the service process of hot work die steel work pieces,the general failure location starts from the surface.When there is a sliding motion between the two work pieces,there will be friction or scratches.In severe cases,the work piece will wear and fail.In addition,hot work die steel works in an environment of alternating cooling and heating,which is also prone to thermal fatigue failure problems.Therefore,while improving the friction and wear performance of hot work die steel,it is also necessary to improve its thermal fatigue performance.In this subject,Ultrasonic Surface Rolling Processing(USRP)was performed on Dievar die steel,and a gradient nanometer modified functional layer with a certain thickness was prepared on the surface of the material.Subsequently,high energy ion implantation(High Energy Ion Implantation,HEII)tungsten carbide process optimization test was carried out on the surface of the sample after the ultrasonic surface rolling treatment and the sample surface without any treatment to prepare a high energy ion implanted tungsten carbide layer.The chemical compositions,hardness,friction and wear properties and thermal fatigue properties were studied to analyze the effects of surface nanocrystallization on the performance of high-energy ion-implanted tungsten carbide layer.The research shows that after the ultrasonic surface rolling treatment,a gradient nanostructure surface layer with a thickness of about 60 ?m is formed on the surface of the material.After surface nano-treatment,the hardness of the sample wasincreased from 200 HV to 301 HV,and the hardness was increased by about 50%.When the material is subjected to ultrasonic surface rolling,the surface is subjected to cyclic alternating loads.The degree of grain refinement is different in the direction perpendicular to the surface,and a large number of non-equilibrium defects are generated,which increased and enhanced the adsorption of active ions or active atoms on the surface.The large number of grain boundaries produced by grain refinement increased the channels for rapid diffusion of atoms.These characteristics all indicate that ultrasonic surface rolling can promote high-energy ion implantation.Compared with the sample treatment with the HEII process,the gradient nanostructured surface layer of the sample treated with the USRP + HEII process significantly enhances the effect of high energy ion implantation of tungsten carbide.Compared with the HEII sample,the surface microstructures of the USRP + HEII sample is denser and uniform.The hardness of the outermost layer of the USRP + HEII sample reaches 944.9 HV,which is about 69% and 27% higher than the surface hardness of the base material and the HEII sample.Both samples formed a certain thickness of the enrichment layer and diffusion layer,and the thickness of the tungsten carbide enrichment region was about 200 ?m.The thickness of the diffusion layer of the USRP + HEII treated sample is increased by about 27% compared to the HEII treated sample.The friction and wear test results show that the average friction coefficient and volumetric wear of the samples processed by the USRP + HEII process are lower than the samples processed by the HEII process under different loads and different temperature conditions,indicating that the USRP + HEII process The sample has more excellent friction and wear performance.In the variable loads friction and wear test,the samples treated with HEII are prone to fatigue wear and abrasive wear.The wear mechanism of the samples treated with USRP + HEII is always dominated by oxidative wear and slight abrasive wear.In the variable temperature friction and wear experiment,the HEII-treated samples showed fatigue wear at low temperatures and the adhesive wear was significantly increased with the increase of temperature.The USRP + HEII-treated samples were mainly oxidized at low temperatures with the temperature Elevated adhesive wear also began to increase,but the degree of adhesivewear was lighter than the samples treated with HEII.The thermal fatigue test found that compared with the samples processed by the HEII process,the surface cracks of the samples processed by the USRP + HEII process are relatively few.The maximum depth of cracks along the cross section of the samples processed by the USRP + HEII is reduced by about 37%.The width is also relatively small.The area near the surface of about 30 ?m,the hardness of the sample treated with USRP + HEII is higher than that of the sample treated with HEII.According to the research above,the samples prepared by USRP + HEII have better thermal stability and comprehensive mechanical properties. |
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