Microstructure and mechanical property optimization of NiTiAl-based alloys: Directional solidification in novel ceramic crucibles

Directional solidification technique was successfully used to prepare highly reactive NiTiAl-based alloys using novel Y2O3-coated crucibles. Compared with the as-cast alloys fabricated by vacuum arc melting, the microstructure of the directionally solidified alloys was optimized and mechanical properties remarkably improved. After directional solidification, the microstructure of the alloys became much finer and preferentially grew along [001] orientation. The tensile strength and strain of the directionally solidified alloys at 1550°C were promoted to 1240 MPa and 2.1% respectively, which were 91.4% and 75% higher than that of the as-cast alloys. The strength increased up to 1328 MPa and 1419 MPa after homogenizing treating. The Y2O3-coated crucibles assured significant purification effect of the alloys. The maximum oxygen increase in the steady-state region of the ingot obtained at 1750°C was no more than 0.014 wt.%.