Abstract:The formation, morphology, size, distribution, growth and structure of Nd-rich rare earth (RE) phases in powder metallurgy (PM) high temperature titanium alloy were investigated. The results show that the RE-rich phases in as-rapidly-solidified high temperature titanium alloy powder precipitate in the process of powder droplet solidification, and the particle size is 50~250 nm in diameter. The majority of the particles are uniformly distributed in the alloy matrix. The particles are nearly spherical within the grains and ellipsoidal along the grain boundary. The major axes of the ellipsoidal particles are lying nearly parallel to the grain boundary. The calculated size and distribution of the second phase particles are in agreement with the TEM experimental results. The diameters of RE-rich phases are largely smaller than 50 nm precipitated from the supersaturated matrix after hot isostatic pressing (HIP) between 700 and 1000 oC in a short time. The size variation of the original RE-rich phases is minimal. However, the particle size including the original and the precipitated is 150~500 nm in diameter after HIP at 1200 oC for 3 h. The HRTEM image and SAED pattern of the RE-rich phases indicate that they are composed of many nanocrystallines while they are still composed of nanocrystallines whose size grows up minutely after HIP at high temperature. Maybe the later nanocrystalline is different from the former one because the tin-rich phases appear on the RE-rich phases “matrix”, resulting in the complex microstructure of the RE-rich phases.