Effect of Microstructures on Mechanical Properties of a Heat Resistant Titanium Alloy Ti-6242S at Elevated Temperatures

摘要

The weight reduction has been vital to improve the performance of automobile engines for moving components such as intake and exhaust valves, valve springs and connecting rods. Titanium alloys are one of the candidate light weight materials for them. Among them a near alpha Ti-6242S (Ti-6Al-2Sn-4Zr-2Mo-0.1Si) is a promising heat resistant alloy, which is applied to compressor discs of jet engines. Their maximum operating temperature has been limited to 873K and so there are quite few data on its mechanical properties over it. In order to apply Ti-6242S to exhaust valves, its microstructure was optimized to obtain the fatigue and creep strength required up to 1073K. The 19mm round bars in three typical microstructures, equiaxed, bi-modal and acicular, were prepared through thermomechanical processing. Their tensile, fatigue and creep properties were evaluated from room temperature to 1123K. The acicular material exhibited the best combination of all properties, which is most applicable to exhaust valves exposed to 1073K. The equiaxed one with the highest fatigue strength at room temperature showed the lowest mechanical strength at 1073K. The bi-modal material possessed just the intermediate strength between the acicular and the equiaxed ones.