The microstructure evolution of V-4Cr,V-4Ti and V-4Cr-4Ti alloys was studied before and after hydrogen implantation at 500℃. Before hydrogen implantation the matrix of V-4Cr alloy is clean,while parallel and vertical needle-like precipitates exist in the matrix of the other two alloys,and there are a lot of dislocations around the precipitates. After hydrogen implantation at 500℃ a large amount of uneven-distributed black dot defects and defect clusters appear in V-4Cr alloy. Besides the black dot defects,a lot of bubbles are found in V-4Ti and V-4Cr-4Ti alloys,and the average size of bubbles in V-4Cr-4Ti alloy is smaller than that in V-4Ti alloy. In addition,the dissolution phenomena of the precipitates happen in the both alloys. There are very few bubbles found near the grain boundary in the range of 25 nm in V-4Cr-4Ti alloy,which probably indicate that the defects,such as bubbles,caused by irradiation can be restrained by the existing of grain boundaries in this material.
