Processing map and hot working mechanisms in a P/M TiAl alloy composite with in situ carbide and silicide dispersions

A titanium aluminide alloy composite with in situ carbide and silicide dispersions has been synthesized by mixing 90% of matrix with elemental composition of 46Ti–46Al–4Nb–2Cr–2Mn and 10% precursor with composition 55Ti–27Al–12Si–6C prepared by mechanical alloying. The powder mixture was blended for 2 h followed by hot isostatic pressing (HIP) at 1150 °C for 4 h under a pressure of 150 MPa. In addition to TiAl alloy matrix, the microstructure of the HIP’ed billet showed a small volume fraction of Nb-rich intermetallic phase along with carbide and silicide dispersions formed in situ during HIP’ing. Cylindrical specimens from the HIP’ed billets were compressed at temperatures and strain rates in the ranges of 800–1050 °C and 0.0001–1 s−1. The flow curves exhibited flow softening leading to a steady-state flow at strain rates lower than 0.01 s−1 while fracture occurred at higher strain rates. The processing map developed on the basis of flow stress at different temperatures and strain rates revealed a safe window for hot working as 850–1025 °C and 0.0001–0.001 s−1. Kinetic analysis of the flow stress data yielded a stress exponent of 3.85 and an apparent activation energy of 440 kJ/mol which is higher than that for self-diffusion of Al in γ TiAl.