Microstructure evolution and its effect on mechanical properties of cast Ti48Al6NbxSi alloys

Abstract

In order to improve mechanical properties of TiAlNb alloys, different contents of silicon were added into Ti48Al6Nb alloy. The Ti48Al6NbxSi (x=0, 0.1, 0.2, 0.3, 0.4 and 0.5, at.%) alloys were prepared by vacuum arc melting. The phase constitution, microstructure evolution and mechanical properties of the alloys were studied. Results show that the Ti48Al6NbxSi alloys consist of γ-TiAl phase, α 2 -Ti 3 Al phase and B2 phase, and Ti 5 Si 3 silicide phase is formed when the addition of silicon is higher than 0.3at.%. The addition of silicon leads to the decrease in γ phase and increase in α 2 phase. The formation of silicide decreases the amount of Nb dissolved in the TiAl matrix, and therefore decreases B2 phase. Compressive tests show that the ultimate strength of the alloys increases from 2,063 MPa to 2,281 MPa with an increase in silicon from 0 to 0.5at.%, while the fracture strain decreases from 34.7% to 30.8%. The increase of compressive strength and decrease of fracture strain can be attributed to the decrease of B2 phase and the formation of Ti 5 Si 3 phase by the addition of silicon. The strengthening mechanism is changed from solid solution strengthening when the addition of silicon is less than 0.3at.% to combination of solid solution strengthening and secondary phase strengthening when the addition of silicon is higher than 0.3at.%.

Influence of Mo on microstructure and nanoindentation hardness of Ti-Al-Si-xMo alloy processed by Laser Engineered Net Shaping (LENS)

“…al. 2020; Xu et al 2020). To date, only cast TiAl alloys processed through hot isostatic pressing (HIP) with subsequent heat treatment is proving to yield considerable positive results.…”

“…In our previous study (Raji et al 2021), the microstructure and mechanical properties of ternary Ti-Al-Si alloy produced through in-situ laser processing using the LENS machine was investigated. Moreover, various researchers have investigated different type of γ-TiAl based alloys such as Ti-45Al (Oehring et al 2021), Ti48Al6NbxSi alloys (Xu et al 2020), Ti-48Al-2Cr-2Nb (Siahboumi et al 2021), Ti-44Al-0.2B (Imayev et al 2021), Ti-44Al-5Nb-0.2B (Imayev et al 2021), Ti-44Al-5Zr-0.2B (Imayev et al 2021), Ti-44Al-2.5Zr-2.5Hf-0.2B (Imayev at al. 2021), Ti-Al-Nb-Mo (Staron et al 2021), Ti-42Al-8.5Nb (Gabrisch et al 2020) and Ti-42.9Al-4.6Nb-2Cr (Xu and Li, 2021) (all compositions are in atomic percent unless stated otherwise) consisting mainly of either two phases α/α 2 and γ or three phases α/α 2 , β/β 0 and γ.…”

“…The principal rationale for the acceptance and the extensive investigation of TiAl alloys containing Si is the refinement of microstructure, increased melt pool wettability and reduction of shrinkages (Raji et al 2020;Xu et al 2020). These occurrences were ascribed to the particle size of Si, distribution and variation at the grain boundaries of lamellae colonies (Raji et al 2020), thus, variations in the microstructural morphology.…”

“…Moreover, the lightweight nature of TiAl alloys with density of about 3.8 g/cm 3 still makes them desirable for airplane engine components (Gao and Wang, 2021;Oehring et al 2021;Raji et al 2021). Also, TiAl-based alloys possess excellent properties such as high strength-to-weight ratio, high strength retention at elevated temperatures, excellent high-temperature stiffness, low density and good creep properties (Raji et al 2020(Raji et al , 2021Xu et al 2020). These attractive mechanical properties give a high prospect to TiAlbased in substituting the heavier nickel-based superalloys typically applied in producing turbine parts of aircraft engines (Kim et al 2019;Raji et al 2020;Xu et al 2020).…”

“…Also, TiAl-based alloys possess excellent properties such as high strength-to-weight ratio, high strength retention at elevated temperatures, excellent high-temperature stiffness, low density and good creep properties (Raji et al 2020(Raji et al , 2021Xu et al 2020). These attractive mechanical properties give a high prospect to TiAlbased in substituting the heavier nickel-based superalloys typically applied in producing turbine parts of aircraft engines (Kim et al 2019;Raji et al 2020;Xu et al 2020). Nevertheless, inadequate hot workability is still a foremost issue regarding TiAl alloys which has led to a lot of interests from researchers in trying to mitigate the associated drawbacks confronting the wider application of these type of material.These difficulties encountered play a considerable role in limiting the advancement of suitable TiAl intermetallic alloys produced by most AM technologies.…”