热等静压对铸造Ti-47.5Al-2.5V-1.0Cr合金持久性能的影响

Influence of hot isostatic pressing treatment on stress rupture behaviour of a cast Ti-47. 5Al-2. 5V-1. 0Cr alloy

将定向层片组织铸造Ti-47.5Al-2.5V-1.0Cr(at%)合金在α+γ两相区分别进行了1270℃,180 MPa下1 h,1.5 h和2.5h的热等静压处理,然后在800℃和300 MPa条件下进行了持久断裂试验,以研究热等静压处理对该合金持久性能的影响。试验结果表明,在1270℃/180 MPa条件下,热等静压分别持续1 h,1.5 h和2.5 h后,相比未经热等静压处理的铸态试样,其800℃/300 MPa持久寿命均明显降低,降低幅度分别为64.4%,70.2%和82.0%,但其持久塑性均明显提高。结合持久断口的断裂特征分析及微观组织观察认为,热等静压过程中析出的等轴γ晶粒可促进持久加载过程中动态再结晶的发生以及显微空洞的生成,由此导致了持久寿命的降低;此外,相比等轴γ晶粒析出的体积分数,其本身的存在对该合金800℃和300 MPa持久寿命有更直接的影响。

A cast Ti-47.5A1-2.5V-1.0Cr（ at% ） alloy with directional lamellar microstructure was hot isostatic pressing （HIP） treated at a temperature in α ＋ γ phase field for 1, 1.5 and 2. 5 h, respectively, then stress rupture test at 800 ℃ and 300 MPa was carried out to investigate the influence of HIP treatment on the stress rupture properties of this alloy. The results show that, after HIP treatment at 1270 ℃ and 180 MPa for 1, 1.5 and 2. 5 h, the stress rupture life of the alloy significantly decreased by 64.4% , 70.2% and 82.0% , respectively, but the rupture elongation improved evidently regardless of HIP treatment time. The characteristics of the rupture fracture surface were identified and the microstructure near the rupture fracture surface was examined by scanning electron microscopy （SEM）. It suggests that the equiaxed γ grains precipitated at the colony boundaries or in the colonies during HIP treatment can accelerate the dynamic recrystallization and the formation of micro-cavities during stress rupture, which lead to the decrease of rupture life directly; moreover, the existence of the equiaxed γ grains rather than their volume fraction exerts a more direct influence on the rupture life of this alloy at 800 ℃ and 300 MPa.