Research On Process And Properties By Shot Peening Strengthening Of Plasma Multi-Element Penetrating With Rare-Earth Catalytic

With the increasing demand for the quality and service life of metal parts in the market,single plasma nitriding process is difficult to satisfy the actual production needs,so composite strengthening process has become an important development direction.The shot peening process can make the surface of metal parts undergo elastic and plastic deformation at ordinary temperature.The grain size decreases,the interfacial area increases,the dislocation density increases,the lattice distortion intensifies,and being the residual compressive stress on the surface,so then strengthening the surface performance of metal parts.Rare earth elements can activate the gas phase,accelerate the ionization of the permeation element,and produce more active atoms.Moreover,the concentration difference caused by the "air mass" formed by the adsorption of a large number of active atoms by rare earth elements can promote the diffusion of active atoms to the matrix and increase the thickness of the penetrating layer.In this dissertation,the composite process of shot peening strengthening and rare earth catalytic based on plasma multicomponent penetrating is used to treat the samples,which provides a reference direction for the development of new plasma nitriding process.In this experiment,38 CrMoAl steel and 40 Cr steel were selected as test materials.The main research factors of plasma multi-element co-permeation were holding temperature,holding time,ammonia flow rate and rare earth.The experimental scheme was designed by orthogonal test method.The surface hardness and the depth of the layer were selected as the reference standard for the effect of co-permeation.The optimum process was selected according to the range analysis method.Then,shot peening strengthening and rare earth catalytic plasma multi-element penetration test,rare earth catalytic plasma multi-element penetration test and plasma multi-element penetration test were carried out under the optimum technological parameters.By means of surface hardness testing,penetration layer depth testing,metallographic microstructure observation,SEM morphology observation,EDS energy spectrum analysis and X-ray diffraction analysis,the effect of three different processes to plasma multi-element penetration was compared.The composite strengthening mechanism of shot peening and rare earth catalytic to plasma multicomponent penetration was analyzed.The results show that under the same technological parameters,the effect of shot peening strengthening and rare earth catalytic plasma multi-element co-permeation process,rare earth catalytic and plasma multi-element co-permeation process and plasma multi-element co-permeation process decreases in turn.Rare earth can enhance the effect of plasma multi-element co-permeation,increase the surface hardness of the sample,and increase the thickness of penetrating layer.The optimum technological parameters of shot peening strengthening and rare earth catalytic plasma multi-element co-permeation process are holding temperature 540?,ammonia flow rate 2.0L/min,holding time 9h,mixed gases of ethanol and carbon disulfide(ratio 4:1)0.2L/min;the optimum technological parameters of shot peening strengthening and rare earth catalytic plasma multi-element co-permeation process are holding temperature 530?,ammonia flow rate 2.0L/min,holding time 9h,mixed gases of ethanol and carbon disulfide(ratio 4:1)0.2L/min.In this test,38 CrMoAl steel sample the maximum surface hardnes is 1221 HV,and the maximum thickness of infiltration layer is 355um;40Cr steel sample the maximum surface hardnes is 889 HV,and the maximum thickness of infiltration layer is 375 um.Carbon elements provided by the co-permeating elements can form carbonitriding,which can improve the surface hardness and the thickness of penetrating layer of the sample;oxygen elements can form oxide to slow down corrosion on the surface of the sample;sulfur elements can form porous sulfide layer on the surface of the sample,which is conducive to the storage of grease,reduce friction coefficient and improve the wear resistance of metal parts.