Chengsong Liu

In this study, we have systematically investigated how both shot peening (SP) and re-shot peening (RSP) affect the surface integrity and fatigue performance of TC17 titanium alloy. Surface integrity involves a competitive mechanism with the coexistence of beneficial and detrimental factors, both of which collectively determine the fatigue performance. While compressive residual stress (CRS), dislocation multiplication, and work hardening serve as beneficial factors, surface roughness and surface damage act as the detrimental factors. The results reveal high-intensity SP produced a deeper work-hardened layer. However, it also caused larger surface roughness and more severe surface damage, yielding the relaxation of the surface CRS and poorer improvement of the fatigue performance than that achieved with medium-intensity peening. The RSP treatment demonstrated a superior balance of surface integrity factors by effectively reducing the degree of surface damage and elevating the magnitude of surface CRS. Thus, a 45.9-fold improvement in fatigue life was achieved relative to the base material (BM) specimen. Surface CRS was identified as the primary factor contributing to the enhanced fatigue performance.

The effects of an ultrasonic surface rolling process (USRP) on the localized corrosion behavior of 7B50-T7751 aluminum alloy in a sodium chloride + hydrogen peroxide solution were investigated through microstructural observation, immersion testing, and electrochemical measurements. The results revealed that this alloy is prone to pitting. However, the localized corrosion resistance can be significantly improved via both one-pass USRP and 12-pass USRP treatment. Furthermore, in the test solution, the thickness and the acceptor density of the passivation film were affected by the USRP treatment. The improved corrosion resistance of one-pass USRP-treated samples resulted mainly from the introduced compressive residual stress. However, this stress played a secondary role in the considerable enhancement observed for the corrosion resistance of the 12-pass USRP-treated samples. This enhancement is attributed primarily to the nanocrystalline surface and homogeneous surface microstructure induced by the multiple-pass USRP treatment.

The effect of the ultrasonic surface rolling process (USRP) on the rotary bending fretting fatigue (FF) of Ti-6Al-4V alloy was investigated. The reason for the USRP’s ability to improve the FF resistance of Ti-6Al-4V alloy was studied. The results revealed that the USRP induced a compressive residual stress field with a depth of 530 μm and a maximum residual stress of −930 MPa. Moreover, the surface micro-hardness of the USRP sample was significantly higher than that of the untreated base material (BM) sample, and the USRP yielded a 72.7% increase in the FF limit of the alloy. These further enhanced fatigue properties contributed mainly to the compressive residual stress field with large numerical value and deep distribution, which could effectively suppress FF crack initiation and early propagation. The USRP-induced surface work-hardening had only a minor impact on the FF resistance.