Research On Fatigue And Wear Properties Of GH4169 Alloy With Gradient Nanostructure

Nickel-based alloys used in the aerospace industry not only need to have good high temperature resistance,but more importantly,they need to have certain fatigue resistance and wear resistance.Shot peening induces surface nanocrystallization is an effective means to improve the fatigue properties of materials and improve the wear resistance of materials.As a surface strengthening technology,it is widely used in industrial production due to its simple operation and stable effect.In this paper,shot peening was adopted to treat the surface of GH4169 alloy specimens,the work-hardening effect and microstructure especially the nanocrystals and deformation twins after shot peening were experimentally investigated.Finally,the effect of shot peening on the fatigue properties and wear properties of GH4169 alloy was analyzed in detail.The main conclusions are as follows:(1)The surface strengthening mechanism of GH4169 alloy was experimentally studied.It was found that the shot peening introduced a hardened surface layer of about96 ?m in thickness,and the surface hardness value of the sample was increased by about34.6% compared with the matrix.In addition,a large amount of deformed twin structure was generated in the hardened layer,and at the same time,the surface grains were refined into nanocrystals.The formation of deformation twins and nanocrystals together contribute to tissue strengthening.On the other hand,the beneficial residual compressive stress introduced by shot peening acts as a stress strengthening effect.(2)According to the fatigue S-N curve analysis,the shot peening specimens showed better fatigue resistance than the unpeened specimens at room temperature and 350°C.However,shot peening did not significantly affect the fatigue properties of specimens at650°C,which is closely related to the relaxation of residual stress at high temperature and the coarsening of twin structure.From the observation of fatigue fracture morphology,itcan be found that the fatigue crack source originates on the surface of the sample.At the same time,the number of crack sources increases with the increase of temperature,and shot peening can significantly reduce the number of crack sources;fatigue fractures can be divided into three area: fatigue crack source area,fatigue crack growth area and instantaneous fracture area;More fatigue striations appear in the crack propagation area of the fatigue fracture under the medium and low temperature area,and the local part of the crack propagation area produces a certain amount of secondary crack at high temperature;The EDS analysis of crack initiation site of untreated specimen at high temperature reveals that the high temperature oxidation of the specimen surface is an important cause of fatigue fracture.(3)The wear behavior of GH4169 alloy before and after shot peening was studied.It was found that shot peening can effectively reduce the friction coefficient of GH4169 alloy.Compared with untreated specimens,the shot peening specimen under the same conditions has less wear mass loss and lighter surface wear.