Effect Of Heat Treatment On The Microstructure And Property Of Surface Strengthened Metal Materials

Surface mechanical attrition treatment technology(SMAT) was used to achieve the surface strengthening of hcp metal and the microstructure and mechanical properties were analyzed after heat treatment. The influence of surface residual compressive stress on the fatigue property of metallic materials was discussed.The surface microstructure and grain size were characterized and analyzed by the X-ray diffraction(XRD), optical microscope(OM), scanning electron microscopy(SEM), transmission electron microscopy(TEM). The surface microhardness of the specimen was detected by the hardness tester, the macroscopic residual stress was evaluated by X stress tester, the fatigue limit of sample with different durations was determined by Four-point bending fatigue experiment. The fatigue fracture characteristic was observed by SEM.The results showed that the surface grain of pure zirconium specimens and TC4 titanium alloy was nano. With the increasing of heat treatment temperature, the surface residual compressive stress released gradually as well as the residual compressive stress field depth got smaller.The fatigue limit of pure zirconium samples treated at 450℃ for 120 min was decreased by 13.2 % compared with the SMATed samples. The fatigue limit of TC4 sample treated at 450℃ for 120 min was decreased by 25.5%. The surface dislocation density was reduced with the heat treatment. Decrease in microstrain and surface residual stress was induced. The decrease of the fatigue performance of the specimen was caused can be attributed to the decrease of surface residual compressive stress and dislocation density.