Titanium alloys have applications in air frames for commercial aircraft, and jet engine components such as fans and compressor disks, which function at low temperatures (up to 673 K). Near β-type Ti–5Al–2Sn–2Zr–4C–4Mo (Ti-17) exhibits greater strength, crack propagation resistance, and creep resistance at intermediate temperatures compared to the (α + β)-type Ti–6Al–4V. It is important to estimate the fatigue life of engine components made of Ti-17. This requires problem quantitative relationship between the fatigue properties and microstructural factors of Ti-17. Therefore, the fatigue properties including tensile properties and microstructures of Ti-17 samples fabricated by hot-forging at various temperatures, followed by high- and low-temperature solution treatment (ST), and same aging treatment were investigated to define a quantitative relationship between the fatigue properties and the microstructures.
The microstructures of all forged Ti-17 samples exhibit elongated prior β-grains composed of two microstructural feature regions: acicular α and fine equiaxed α-phase regions. The volume fraction of the acicular α region decreases with increasing ST temperature. The Vickers hardness, 0.2% proof stress and tensile strength increases with increasing ST temperature. However, the elongation and reduction of area exhibit a reverse trend. The Ti-17 samples forged at 1173 K followed by solution treatment at 1073 K and aging treatment exhibits the highest fatigue limit of around 975 MPa. The fatigue strength of the forged Ti-17 samples is strongly related to the microstructural factor such as the volume fraction of the equiaxed α-phase region, which is one of the crack initiation sites in the forged Ti-17 samples subjected to low temperature ST and aging, and the strength difference between the acicular α-phase and the fine (α + β)-phase, which leads to the crack initiation in the forged Ti-17 sample subjected to high temperature ST and aging.
(Received 2020/06/10; Accepted 2020/07/14; Published 2020/09/25)
Keywords: aircraft materials, near β type titanium alloy, microstructure, tensile properties, fatigue propertiesPDF (open access) Table of Contents
© 2020 The Japan Institute of Metals and Materials
Comments to us : email@example.com