Analysis of machinability in milling of high-strength brittle thin plates of γ-TiAlNb intermetallic compound

Abstract

γ-TiAlNb intermetallic compound is a highly promising material for aircraft structural components. A 46Ti-46Al-8Nb intermetallic compound was prepared and subjected to three different heat treatments. The changes in phase composition, microstructure, and hardness of the as-cast samples and heat-treated samples were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), and Rockwell hardness. Subsequently, the material was designed for milling of thin-wall structures, with a focus on side milling. The milling process was investigated under different axial and radial cutting depths, and the variations in multi-directional cutting forces were analyzed, taking into consideration the surface quality of the machined parts. The results indicate that the γ-TiAlNb intermetallic compound possesses high hardness and brittleness. With increasing heat treatment temperature, the content of TiAl phase significantly decreases, while the content of AlTi₃ phase increases notably. The β-Ti phase containing Nb remains nearly unchanged and is mainly located at grain boundaries. Heat treatment can enhance the machinability of the TiAlNb intermetallic compound. A heat treatment process involving a 1-hour hold at 1200 °C followed by furnace cooling results in reduced Rockwell hardness, lower milling forces in three directions and improved surface quality.