Solidification microstructure characteristics of Ti–44Al–4Nb–2Cr–0.1B alloy under various cooling rates during mushy zone

Beta-solidifying TiAl alloy has great potential in the field of aero-industry as a cast alloy. In the present work, the influence of cooling rate during mushy zone on solidification behavior of Ti–44Al–4Nb–2Cr–0.1B alloy was investigated. A vacuum induction heating device combining with temperature control system was used. The Ti–44Al–4Nb–2Cr–0.1B alloy solidified from superheated was melted to β phase with the cooling rates of 10, 50, 100, 200, 400 and 700 K·min⁻¹, respectively. Results show that with the increase in cooling rate from 10 to 700 K·min⁻¹, the colony size of α₂/γ lamella decreases from 1513 to 48 μm and the solidification segregation significantly decreases. Also the content of residual B2 phase within α₂/γ lamellar colony decreases with the increase in cooling rate. In addition, the alloy in local interdendritic regions would solidify in a hypo-peritectic way, which can be attributed to the solute redistribution and enrichment of Al element in solidification.