一种高强钛合金疲劳裂纹扩展行为

Fatigue crack propagation behavior of high strength titanium alloy

高强Ti-5Al-3Mo-3V-2Zr-2Cr-1Nb-1Fe(Ti-5321)合金是顺应我国新一代飞机对高性能钛合金的需求设计而开发的一种新型高强损伤容限型钛合金。以Ti-5321合金为研究对象,构造等轴组织(EM)、网篮组织(BW)和细网篮组织(F-BW)三种典型组织,研究拉伸及疲劳裂纹扩展行为,利用光学显微镜(OM)和扫描电镜(SEM)观察组织和断口,揭示高强钛合金Paris及失稳扩展区的疲劳裂纹扩展机制。结果表明:三种组织试样的抗拉强度均在1200 MPa以上,且整个裂纹扩展阶段均表现出优异的疲劳裂纹扩展抗力;细网篮组织疲劳裂纹扩展抗力最高,等轴组织疲劳裂纹扩展抗力最低;Paris区及失稳扩展区疲劳裂纹主要以穿过初生α相和沿着初生α相两种方式进行扩展,裂纹扩展方式与α相的晶体学取向密切相关,裂纹倾向于穿过有利于(1010)<1210>锥滑移的α丛域,绕过有利于(1011)<1210>柱滑移的α丛域。

High strength Ti-5Al-3Mo-3V-2Zr-2Cr-1Nb-1Fe(Ti-5321)alloy is a new type of high strength tolerance titanium alloy designed and developed to meet the demand of high performance titanium alloy for new generation aircraft in China.Ti-5321 alloy with equiaxed microstructure(EM),basket-weave microstructure(BW)and fine basket-weave microstructure(F-BW)was obtained by forging and heat treatment,and the tensile properties and fatigue crack growth behavior were studied.Fatigue crack propagation mechanisms in Paris and unstable propagation regimes were revealed by analyzing the microstructures and fracture morphology using optical microscopy(OM)and scanning electron microscopy(SEM).The results show that the samples with EM,BW and F-BW exhibit the excellent fatigue crack propagation resistance with the tensile strength of 1200 MPa.The sample with F-BW presents the highest fatigue crack propagation resistance in Paris and rapid growth regimes,while the sample with EM presents the lowest fatigue crack propagation resistance.In F-BW,the crack mainly propagates through and alongαphase.Crack tends to propagate across colony oriented for(1011)<1210>pyramidal slip and propagates along colony oriented for(1011)<1210>prismatic planes.