Effect of rare earth Y on mechanical properties of near α titanium alloy with different microstructure states

Abstract:

Ti6321 ingots containing 0~0.20 wt.% rare-earth yttrium (Y) were subjected to multi-pass hot rolling, and equiaxed structure (EQ), bimodal structure (BM) and Widmanst?tten structure (WM) were obtained by different annealing processes. The microstructures were characterized using optical microscopy (OM) and scanning electron microscopy (SEM). Tensile and instrumented impact tests were conducted to systematically investigate the effect of Y content on the microstructural evolution and mechanical properties of Ti6321 alloys with different microstructural states.The results show that Y has a significant refinement effect on the three microstructures. With the increase of Y content, the Y₂O₃ second phase with sub-micron to micron size and gradually increasing size is formed in the alloy matrix of the three microstructures, and the distribution characteristics in different microstructures are obviously different. In the EQ and BM conditions, Y?O? particles were mainly distributed within α_p, at α_p/β_t interfaces, and inside β_t regions, whereas in the WM condition, they were predominantly located at lamellar α/β interfaces. At the same time, it is found that there is a deformation incompatibility between Y₂O₃ and Ti6321 matrix during the deformation process. There is a competitive relationship between the damage intensification effect introduced by Y₂O₃ as a potential microcrack source and the multiple strengthening effects introduced by Y element. As a result, the tensile strength of the EQ alloy decreases significantly with increasing Y content, whereas the reduction is less pronounced in the BM condition. In the WM microstructure, the lamellar α phase effectively suppresses crack initiation and propagation associated with Y₂O₃ particles, leading to a tensile strength that first increases and then decreases with increasing Y content.In addition, the addition of Y significantly reduces the impact properties of Ti6321 alloy with BM and WM. The main reason is that Y₂O₃ weakens the energy absorption capacity in the crack propagation stage.