Feasibility Study of Low-Al TiAl Alloys with α2 Phase-Dominated Fully Lamellar Structures for Use as Jet Engine Blades

Despite their potential to improve properties such as the high-temperature strength required for jet engine blades, low-Al TiAl alloys have largely been overlooked. The most significant challenge is ensuring impact resistance, which is crucial for jet engine blade applications. First, this study evaluated the impact resistance of fully lamellar Ti-38.75–50.25 Al binary alloys in relation to the effects of α2 phase ratio and spacing using a Charpy impact test. Subsequently, the impact of reducing Al content in Cr-added forged alloys and cast TiAl4822 was investigated. The results revealed that α2 phase spacing had the most significant impact on impact resistance at 800 °C. Coarse α2 phase spacing of approximately 6 μm, created in the high-Al material, provided the highest impact resistance. In contrast, the impact resistance of the low-Al material was low due to its extremely narrow α2 phase spacing. In forged alloys, reducing both Al content and β-stabilizing elements enabled the removal of the deleterious β phase through heat treatment, while maintaining good forgeability, thereby improving impact resistance and creep strength. In low-Al TiAl4822, the expected improvement in creep strength could not be achieved because the low-strength γ phase located at lamellar colony boundaries underwent preferential deformation.