Vacuum induction melting and casting of TiAl-based matrix in-situ composites reinforced by carbide particles using graphite crucibles and moulds

Comparative Study of Microstructure and Mechanical Properties of Two TiAl-Based Alloys Reinforced with Carbide Particles

“…The studied TiAl-based alloys with designed nominal composition Ti-42.6Al-8.7Nb-0.3Ta-2.0C and Ti-41.0Al-8.7Nb-0.3Ta-3.6C (at.%) were prepared by vacuum induction melting of pure metals (purity 99.99%) and addition of graphite powder in graphite crucibles and centrifugally cast into graphite mold using the procedure described elsewhere [18,52]. The conical as-cast samples with a minimum diameter of 12 mm, maximum diameter of 15 mm and length of 150 mm were subjected to HIP at a temperature of 1260 • C and applied pressure of 200 MPa for 4 h in a protective argon atmosphere.…”

The effect of heat treatment on microstructure and hardness of in-situ Ti-38Al-7.5Nb-5C-0.9Mo composite

“…The volume fraction of the α 2 phase reaches nearly 60 vol.%, which is a significantly higher value than that of the β/B2 phase (Table 4). As has been already discussed in detail in the recent work on the microstructure formation in the composites with a similar chemical composition [18], the fast cooling rates significantly suppress the nucleation and growth of γ(TiAl) lamellae in the α/α 2 phase during the centrifugal casting. Table 2 indicates that the solubility of Nb in (Ti,Nb)C and (Ti,Nb) 2 AlC is high and reaches up to 60-70 % of the average content of Nb in the composite.…”

“…As shown by Lapin et al [13], while the content of carbon below 2 at.% leads to the formation of plate-like (Ti,Nb) 2 AlC particles, both plate-like and coarse irregularly shaped carbides are formed in the microstructure of the composites with the carbon content above 2 at.%. Residual (Ti,Nb)C phase with a significantly higher hardness and elastic modulus than those of (Ti,Nb) 2 AlC phase remains in some coarse irregularly shaped primary carbide particles of as-cast in-situ composites with Al content ranging from 37 to 47 at.% [18,21,[23][24][25]. As shown by Lapin et al [13,26], hot isostatic pressing (HIP) at a temperature of 1250 • C for 4 h applied for removing casting porosity does not lead to a full transformation of the residual (Ti,Nb)C phase to (Ti,Nb) 2 AlC.…”

“…water cooling to room temperature HT2-X cooling at a rate of 5 • C min −1 to a temperature of 700 • C followed by furnace cooling to room temperature HT to a temperature of 1420 • C at a heating rate of 10 • C min −1 holding for 10 min furnace cooling to room temperature the in-situ Ti-Al-Nb-Mo based composites prepared by the vacuum induction melting and solidification in graphite crucibles [21,22] or by the casting to the graphite moulds [13,15,18,23,24]. In the studied insitu composites, the content of Al, Nb, and C varied in the range from 37 to 47 at.%, from 3.5 to 8 at.%, and from 1 to 7 at.%, respectively.…”

“…The thermo-chemically stable reinforcing Ti 2 AlC particles are characterised by a high fracture resistance, good damage tolerance, high thermal conductivity, and density and thermal expansion coefficients similar to TiAl alloys [17]. Several methods based on ingot or powder metallurgy have been already applied successfully to fabricate in-situ metal matrix composites reinforced with carbide particles [18][19][20].…”