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

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 α 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.