稀土Y对不同组织状态近α钛合金力学性能的影响

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

摘要:

对稀土钇(Y)元素含量为0~0.20 wt.%的Ti6321铸锭进行了多道次热轧,并通过不同退火工艺获得了等轴组织(EQ)、双态组织(BM)及魏氏组织(WM)。利用光学显微镜(OM)和扫描电子显微镜(SEM)对不同组织状态下合金的显微组织进行了观察,并结合拉伸试验和示波冲击试验,系统研究了Y含量对不同组织状态Ti6321合金显微组织演变及力学性能的影响机制。结果表明：Y对三种组织都起到了显著的细化作用。随着Y含量增加,三种组织的合金基体中均形成了亚微米至微米级且尺寸逐渐增大的Y₂O₃第二相,且在不同组织中的分布特征存在明显差异。等轴组织和双态组织中的Y₂O₃主要分布在α_p、α_p/β_t相界及β_t中,而魏氏组织中的Y₂O₃主要分布在片层α/β相界。同时,发现变形过程中Y₂O₃与Ti6321基体间存在变形不协调性,Y₂O₃作为潜在微裂纹源引入的损伤加剧效应与Y元素引入多种强化效应间存在竞争关系,最终导致等轴组织Ti6321合金的抗拉强度大幅下降,而双态组织的降幅较小。在魏氏组织中,片层α相有效抑制了Y₂O₃引起的裂纹萌生及扩展,使抗拉强度随Y含量变化呈现先升高后降低的趋势。此外,Y的添加显著降低了双态和魏氏组织Ti6321合金的冲击性能,其主要原因在于Y₂O₃削弱了裂纹扩展阶段的能量吸收能力。

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.