热暴露对Ti60合金性能及断裂行为的影响

Effect of thermal exposure on properties and fracture behaviors of Ti60 alloy

采用光学显微镜和扫描电镜观察分析了Ti60合金热暴露前后拉伸试样的显微组织、断裂方式及其断口形貌。结果表明:Ti60合金塑性对试样表面富氧层较为敏感,带有富氧层的试样塑性较低;热暴露前后试样断裂方式发生变化,未经热暴露的试样,断裂起源于试样中心部位,断面凹凸不平,为典型的韧窝型断裂;毛坯热暴露断口上呈现出大量的解理小平面,也可以观察到韧窝形貌,为混合型断口;试样热暴露后,裂纹起源于试样表面,在微观断口上除了断裂小平面外,还有大量的撕裂棱,表现为断裂沿着α片层界面扩展的特征;在高温长时间暴露过程中,氧除了污染试样表面,还会溶解在基体中形成脆性富氧层,这是影响Ti60合金热稳定性能的重要原因。

The tensile properties of Ti60 titanium alloy after high temperature exposure were investigated. The variation and morphologies of fracture for Ti60 titanium alloy after exposure were analyzed. The results show that the tensile properties of the unexposured specimens at room and high temperature can meet the specification. After thermal exposure, the strength of the specimens increases but the ductility decreases, The dominant damage mechanism changes after thermal exposure. Before exposure, the crack initiates near the center of the specimens, and the fractographs exhibits honeycomb morphology. After thermal exposure, a brittle oxygen-riched subsurface layer forms, the crack initiates on the surface of the tensile specimens, the fracture is hybrid fracture of dimple and quasi-cleavage, and the fracture facet shows the characteristic of lamellar along a platelet colony. During long-term high temperature exposure, the oxygen absorbed in alloy, except for forming oxidation layer, dissolves into the matrix and forms the surface oxygen-enriched layer which becomes an important factor of decreasing the thermal stability of Ti60 alloy.