Effect of heat treatment on microstructure evolution mechanism of hydrogenated TC4 alloy via friction stir processing

In recent years, friction stir processing (FSP) of the TC4 alloy has drawn growing attention. This is attributed to its advantages, including low cost, high efficiency, and the ability to control the microstructure and enhance mechanical properties. Nevertheless, research on Friction stir processed (FSPed) TC4 alloy still encounters several challenges. Firstly, the substantial deformation resistance during processing hinders material deformation. Secondly, the short service life of the costly W25Re alloy stirrer raise processing costs. Therefore, reducing the deformation resistance of the TC4 alloy during FSP is crucial for overcoming the application bottleneck of titanium alloys. In this study, TC4–0.37wt.%H alloy was fabricated and subjected to FSP. The addition of hydrogen significantly reduced the material's deformation resistance, thereby prolonging the service life of the stirring tool. However, to improve the mechanical property degradation caused by hydrogen embrittlement, post-treatments were carried out on the FSPed TC4–0.37wt.%H alloy. These treatments include dehydrogenation treatment (No.1), solution-dehydrogenation treatment (No.2), and solution-aging-dehydrogenation treatment (No.3). The research findings revealed that specimens containing hydrogen exhibited markedly inferior mechanical properties. After dehydrogenation treatment, the tensile strength of the No.1 specimen increased considerably, from 546.5 MPa to 1023.9 MPa. However, there was no notable improvement in elongation. Notably, the elongation of No.2 specimen reached a maximum of 10 %. Meanwhile, the tensile strength of No.3 specimen achieved the highest value of 1268.2 MPa. Additionally, the microstructural evolution mechanism of hydrogened titanium alloys was explored, providing a theoretical foundation for expanding the application of FSPed titanium alloys.