Effect of Preparation Process on the Microstructure and Characteristics of TiAl Pre-Alloyed Powder Fabricated by Plasma Rotating Electrode Process

Abstract

TiAl pre-alloyed powder is the foundation for additive manufacturing of TiAl alloys. In this work, TiAl pre-alloyed powder was prepared using a plasma rotating electrode process (PREP). The effects of electrode rotating speeds and current intensity on the microstructure and characteristics of TiAl pre-alloyed powder have been investigated in detail. The results show that the electrode rotating speeds mainly affected the average particle size of the powder (D50). As the electrode rotating speed increased, the D50 of the powder decreased. The current intensity mainly affected the particle size distribution of the powder. As the current intensity increased, the particle size distribution of the powder became narrower, which was concentrated at 45~105 μm. In addition, the current intensity had a significant effect on the sphericity degree of the powder with the particle size > 105 μm, but it had little effect on that <105 μm powder. TiAl pre-alloyed powder with a particle size > 45 μm demonstrated a dendritic + cellular structure, and the <45 μm powder had a microcrystalline structure. The powder was mainly composed of the α2 phase and γ phase. There were two kinds of phase structure inside the powder, namely the α2 + γ lamellar microstructure (particle size < 45 µm) and the α2 + γ network microstructure (particle size > 45 µm). The phase structure of the powder was related to the solidification path and cooling rate of molten droplets in the PREP. The average thickness of the α2 + γ lamellar was about 200 nm, in which the lamellar γ phases were arranged in an orderly manner in the α2 phase matrix with a thickness of about 20 nm. The network phase structure was corrugated, and the morphology of the γ phase was not obvious.