Impressive improvement of high-temperature creep resistance of a β-solidifying γ-TiAl alloy

Abstract

β-solidifying γ-TiAl alloys are critical materials in turbine blade production due to their superior high-temperature properties and low densities. Ti-43.5Al-4Nb-1Mo-0.1B (known as TNM) is a representative alloy whose service temperature can reach 750 °C. However, due to many impact failures, its application in low-pressure turbine (LPT) blades was discontinued after a few years of commercial flight. Unfortunately, the specific reasons for the alloy's low damage tolerance have not yet been identified. We hypothesize that insufficient creep resistance may have contributed to the reported failures of TNM LPT blades during flights. In an effort to enhance creep resistance, we modified the TNM by adding small amounts of C and Si into a new alloy called TNM+ (TNM-0.3C-0.3Si) and replaced the original HIP and two-step heat treatment to a single post-processing treatment. We show that the new approach boasts the creep life by 3–4 folds. This significant improvement is attributed to three main factors: (1) C addition suppresses the β-segregations, enlarges the colony size, and increases the stabilization of α₂ laths; (2) The precipitated silicides and α-segregations slow down the coarsening of β-segregation, hinder the dislocation migration, and increase the microstructural stability during the creep process; (3) By replacing HIP and subsequent two-step heat treatment with homogenization annealing, the formation of DP areas is retarded or avoided completely.