Research Mechanical Property Of Mo-Based Plasma Alloying On 304 Stainless By Finite Element Simulation

With development of material science and surface treatment technology,utilization of functionally graded materials as the modified layer to improve surface mechanical performances,such as surface hardness and abrasion resistance,has been one of the hot research direction in the field of material science.Compared with the homogeneous film,the gradient modified layer has the advantages of higher layer/substrate bonding strength and better contact damage resistance,thereby being widely used in the fields of nuclear energy,automobiles,communication,aerospace and medical science.However,due to the fact that the component and structure of the gradient modified layer change with the depth,its material property also changes correspondingly,which brings great difficulties to quantitative research of contact behavior of the modified layer under the normal load and is unfavorable for following optimization and judgment of the actual service life.Therefore,quantitative research of the mechanical performance of the modified layer and its contact behavior under the normal load has practical significance on material development and actual application.In this article,304 stainless steel was treated with Mo alloying and quantitative research mechanical property and effect on contact stress of Mo modified layer prepared.We can draw the following conclusions:(1)An algorithm for computing material plasticity parameters based on nano-indentation test data was proposed.The algorithm consists of two parts of parametric searching and finite element modeling,which determines the material plasticity parameters by continual comparison tests and modeling of load-displacement curve.(2)The Mo modified layer was prepared on the surface of the 304 stainless steel by adopting double glow plasma surface metallurgy technology.According to SEM,Knoop hardness test and nano-indentation test,the modified layer was 9.1μm thick;the surface hardness of the modified layer/substrate structure affected by the gradient structure and the base effect was reduced constantly with increase of load;the Mo modified layer prepared on the surface of the 304 stainless steel by using the double glow plasma surface metallurgy technology was not the plasticity gradient material.(3)The modified layer was subjected to homogeneous layering treatment,and elasto-plastic parameters of all sublayers of the modified layer were obtained by means of this article proposed algorithm and Vegrad mixing law.Ansys software was used to study the effect of the modified layer on the contact stress in the spherical indenter and Vickers indenter indentation process and compare it with the substrate and homogeneous film.The results showed that the film or the modified layer bore the vast majority of contact stress no matter at the same indentation depth or under the same indentation load conditions,but the modified layer could relieve first main stress and interface shear stress remarkably compared with the film,favorable for improving the reliability of the layer/substrate structure.According to comparison of maximum contact stress of three kinds of materials under the spherical indenter and progressively-increased load conditions,the modified layer had lower growth rate of maximum equivalent stress and interface shear stress compared with the film,indicating that the modified layer/substrate structure can bear larger indentation load without damage.