Microstructure And Properties Of Hybrid Modified Layer Of 316L Stainless Steel By Surface Nanocrystallization And Ion Implantation

316L austenitic stainless steel has excellent corrosion resistance,workability,weldability and good comprehensive mechanical properties.During using of the parts made of 316L austenitic stainless steel,load is mainly applied to surface,and relative sliding between parts makes surface material migrate,causing the parts to fail or be destroyed.At the same time,there must be certain requirements for its fatigue performance when subjected to dynamic loads.Therefore,it is necessary to take into account its fatigue performance while its wear resistance is improved.In this paper,effects of ultrasonic surface rolling processing on high energy ion implantation of 316L austenitic stainless steel and its strengthening mechanism were investigated by comprehensive comparison and analysis of metallographic structure,micro-hardness,chemical elements distribution and microstructure.Based on its service conditions,dry-sliding friction and wear tests and fatigue tests of HEII specimens and USRP+HEII specimens at room temperature were carried out to investigate the wear resistance and fatigue properties of USRP+HEII specimens.The results showed that the depth of implanted layer of USRP+HEII specimen reached 100μm,and surface hardness reached 494 HV,which was increased by 100%and 57.8%respectively compared with HEII specimen.Under the action of alternating loads,specimen was plastically deformed due to the coordination of twinning and dislocation motion,finally surface grains evolved into nanocrystals under the interaction ofdislocationentanglements,dislocationwallsandtwins.Surfacegrains nanocrystallization caused a significant increase in grain boundary area to promote ion implantation.The friction and wear data analysis showed that friction and wear coefficient and wear weightlessness of USRP+HEII specimens were always lower at different speeds and loads compared with HEII specimens,showing better wear resistance.With the increase of rotational speed,the main wear mechanisms of HEII specimens changed from oxidative wear to fatigue wear,while oxidative wear and adhesive wear were always the main wear mechanisms of USRP+HEII specimens.In addition,with the increase of load,the main wear mechanisms of HEII specimens changed from oxidative wear to abrasive wear,while for USRP+HEII specimens,oxidative wear was always the main wear mechanisms and fatigue wear was appeared under higher load.Fatigue test analysis showed that maximum stress value that USRP+HEII specimen could withstand increased significantly compared with HEII specimen under the same cycle number.When cycle number was 1×10~6,maximum stress value that USRP+HEII specimen could withstand was improved by 26.3%and when cycle number was 1×10~4,it was increased by 12.2%.In fatigue test,the presence of gradient nanostructures could suppress the initiation of fatigue cracks,reducing the number of fatigue crack sources.