Research On The Influence Of Surface High-energy Modification On The Notch Fatigue Limit Of Inconel718 Superallo

The most important form of failure in structural components and parts subjected to cyclic alternating loads is fatigue fracture,especially in critical components with stress concentrations used in the aerospace sector,where safety,reliability and longevity are of paramount importance.Fatigue performance is improved primarily through high energy surface modification manufacturing techniques,including high pressure water jet blasting(WJP),ultrasonic tumbling(USRP)and laser blasting(LP).The size effect,which hinders the application of high-energy surface modification processes on practical components.This is the scientific problem of this paper,which uses notched specimens to simulate actual components to investigate the microscopic mechanism of the anomalous phenomenon,in the hope of further improving the fatigue performance of critical components.The main findings are as follows:(1)The surface quality of the WJP-treated specimens is reduced and the W+U treatment can substantially improve the surface quality of the specimens.The W+U treatment of different Kt specimens resulted in a strong work-hardening layer and a residual stress layer on the surface,with the distribution of residual stresses in the radial direction showing a tick-shaped distribution and the secondary surface being the location of the largest residual compressive stress.(2)Fatigue experiments at room temperature showed that the notched fatigue limits of most Inconel 718 high temperature alloys after W+U treatment decreased with increasing specimen Kt(W+U-2.5:350 MPa,W+U-2:400 MPa,W+U-1.73:380 MPa,W+U-1.65:285MPa,W+U-1.45.500 MPa),where the W+U-1.73 specimen is slightly reduced and the W+U-1.65 specimen shows a strong anomalous fatigue limit notch effect.(3)Fatigue cracks sprout inside the specimen under the action of the modified layer,the smaller the Kt of the specimen the greater the probability of its fatigue source sprouting at the location where the sprout diameter is larger than A.The fatigue cracks are mostly caused by microstructural inhomogeneities,and the fatigue source is more likely to sprout at the location where the fatigue source is larger than A.Most of the fatigue cracks are caused by microstructure inhomogeneity,forming the feature of the solution surface.With the increase of the budding diameter ratio A,the area covered by the quasi-dissociation feature of the crack extension stage changes,and the fatigue life rises and then falls as the fatigue source advances to the interior.(4)By counting the location of fatigue crack initiation,it was found that the fatigue crack initiation location shifted to the interior after modification.In comparison with unmodified specimens,fatigue cracks are difficult to develop on the surface due to the effects of work hardening and residual compressive stress.(5)The microscopic analysis shows that there is a certain pattern between the degree of plastic deformation at the crack tip and the sprouting diameter ratio,and the small crack tip has a smaller plastic zone and lower dislocation density when the stress triaxiality is large,which seriously inhibits plastic deformation.By reducing the critical fracture stress σf at the crack tip,small fatigue cracks can be induced to expand rapidly even at low cyclic load loading.