Abstract
TiAl-based alloys are promising light weight structural materials for high temperature applications in the field of aerospace. Recently, fabrication technologies starting from powders including powder metallurgy and additive manufacturing have been developed to overcome the difficulties in the processing, machining and shaping of TiAl-based alloys. Spherical alloy powders with different particle size distributions are usually used in these fabrication techniques. The purpose of this study is to reveal the size-dependent structural properties of a high-Nb TiAl powder for these fabrication technologies starting from powders. A high-Nb TiAl pre-alloyed powder with nominal composition of Ti-48Al-2Cr-8Nb (at. %) was prepared by the electrode induction melting gas atomization (EIGA) method. The phase structure and morphology of the as-atomized powders were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The size-dependent structural changes of the as-atomized powders with different sizes were studied by differential scanning calorimetry (DSC) and in situ high temperature XRD. It was found that with decreasing the powder size, the content of the γ-TiAl phase decreases and the α2-Ti3Al phase increases. The α2-Ti3Al to γ-TiAl phase transformation was found in the temperature range of 600–770 °C. Based on the present work, the structural characteristics of TiAl powders are strongly dependent on their particle size, which should be considered in optimizing the process parameters of TiAl alloys fabricated from powders.
Highlights
TiAl-based alloys have been considered as promising structural materials for aerospace applications due to their light-weight and excellent high temperature mechanical properties
The high-Nb TiAl powder was produced by the electrode induction melting gas atomization (EIGA) method as follows: Firstly, the alloy ingots were made by cold crucible induction levitation melting of pure Ti, Al, Cr and Nb with purity above 99.9% under argon atmosphere
The structural evolution of a high-Nb TiAl powder (Ti-48Al-2Cr-8Nb) with particle sizes was revealed in the present work
Summary
TiAl-based alloys have been considered as promising structural materials for aerospace applications due to their light-weight and excellent high temperature mechanical properties. Nb content (usually > 5%), the service temperature of TiAl-based alloys can be further increased, which makes them more attractive for applications in gas turbine engines for replacing some Ni-based superalloys [1,2,3,4,5]. In order to overcome the difficulties in the manufacturing of TiAl-based alloy parts, some fabrication technologies starting from powders have been developed. Powder metallurgy technology [6], in particular spark plasma sintering (SPS), was adopted to prepare TiAl-based alloy parts. It was found that the full densification can be achieved at a relatively lower temperature by using pre-alloyed TiAl powders with small size and disorder structures [7]. It is seen that the state of the original powders have great influence on the sintering behavior, microstructure and mechanical properties of Materials 2020, 13, 161; doi:10.3390/ma13010161 www.mdpi.com/journal/materials
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
