Coupling mechanisms of static and dynamic loads during the ultrasonic impact strengthening of Ti-6Al-4V

The ultrasonic impact-strengthening technology was used to effectively improve the fatigue resistance of the key components, which could be attributed to the association of static and dynamic impact loads. It is widely used in the high-performance manufacturing of critical aerospace components, such as titanium alloys. During the ultrasonic impact-strengthening process, the static and dynamic loading can provide two different deformation mechanisms, which may cause differences in the strengthening effect of the titanium alloys. This study developed an ultrasonic impact-strengthening test platform to investigate the influence mechanisms of static loads and cyclic dynamic impact loads in the ultrasonic impact-strengthening process. Meanwhile, the experiment platform was based on displacement control and could apply either static loads or cyclic dynamic impact loads individually on the surface of the Ti-6Al-4V. The force values in the static load experiments, cyclic dynamic impact experiments, and ultrasonic impact strengthening experiments were analyzed. The results show that the force value in the ultrasonic impact strengthening process is not only the superposition of the static load and the cyclic dynamic impact load, but indicating a coupling effect. The force of ultrasonic impact strengthening process increased by more than 55% compared to the sum of the static load and the maximum dynamic impact load. Moreover, the deformation strain rate of Ti-6Al-4V under separate cyclic dynamic impact loading was simulated. During the ultrasonic impact strengthening process, the deformation strain rate of Ti-6Al-4V could reach 960 s −1 , 1587 s −1 , and 2043 s −1 when the cyclic impact depths of 5 μm, 10 μm, and 15 μm, respectively. At the same time, the material surface hardening mechanism under the high strain rate cyclic impact loading was analyzed. The hardness of Ti-6Al-4V after the ultrasonic impact-strengthening process increased by more than 11% compared to the original hardness. At last, the strengthening performance of Ti-6Al-4V after the ultrasonic impact strengthening was evaluated. The strengthening mechanisms of static and dynamic loads during the ultrasonic impact strengthening of Ti-6Al-4V was investigated.