Influence of Microstructures on the Notched Tensile Strength of Ti-4.5Al-3V-2Fe-2Mo Alloy

Abstract

The notched tensile strength (NTS) of Ti-4.5Al-3V-2Fe-2Mo specimens with distinct heat treatment conditions was investigated and correlated to microstructures. The specimens were solution-treated at either 980 or 870°C (above or below the β-transus) and then water-quenched prior to aging treatments. After aging at 482, 593, and 704°C, titanium martensite (α′ or α″) decomposed into α and β with distinct sizes. Additionally, the specimens aged at 482°C were particularly susceptible to notch brittleness, regardless of the solution temperature. As the aging temperature increased, the lower hardness associated with coarsened α+β structures resulted in decreased notch brittleness of the alloy. In general, the specimens containing primary α in microstructure were prone to brittle fracture and reduced NTS. The alignment of martensite packets (or needles) with respect to the crack growth direction could affect the fracture appearance of the specimens, particularly for the coarse-grained specimens which were solution-treated at 980°C. Furthermore, the existence of grain boundary α for the specimens aged at 593°C or higher promoted grain boundary sliding during notched tensile tests.