Comparison of the impact resistance of TiAl4822 and TNM alloy under expected service conditions of jet engine blades

Abstract

Impact resistance is the most important factor affecting the reliability of TiAl alloy blades used in jet engines. We evaluated the impact resistance of TiAl4822 and TNM alloy based on the expected service environment to understand the performance of the actual product blade. Using the surface cut by a diamond grinding wheel as a reference, the impact resistance, including that of the machined surface (under light load) and the oxidized surface (700 °C for 1000 h) was evaluated at room temperature (25 °C), 500 °C, and 700 °C using the Charpy impact test. Both alloys' impact resistance decreased to 70–90 % of the reference values at all temperatures, owing to the microscopic defects on the machined surface. Heating alone (i.e., evaluating the interior of the material after the oxidation test) did not affect the impact resistance of both the alloys. Oxidation hardly affected the impact resistance of TiAl4822 but resulted in a significant decrease in the impact resistance of TNM alloy at all temperatures. This is attributed to the presence of the altered layer under the oxide and nitride layers of TNM alloy, which contains fine β_o-phase precipitates. The high-temperature impact resistance of the TNM alloy after oxidation (which is the most important factor in the reliability of TiAl alloy blades) was less than half that of TiAl4822. Considering factors such as cost, material properties, and reliability, TiAl4822 is considerably superior to TNM alloy for application in jet engine blades.