Phase formation and nanohardness of Ti–48Al–2Cr–2Nb-1.5C alloy by melt spinning: The effect of cooling rates

Abstract

The effect of wheel speed on the phase formation and nanohardness of Ti–48Al–2Cr–2Nb-1.5C alloy by melt spinning was investigated. The results illustrate that with increasing wheel speed, the solubility of C atoms in the matrix increases, which reduces the volume fraction of Ti2AlC precipitates from 7.8 vol% to 2.5 vol%. The length-diameter ratio of precipitated Ti2AlC decreases from 32.2 to 2.2 with increasing cooling rate. Different wheel speeds didn't change the matrix (γ phase), while the primary phase formation was affected by it during solidification. When the wheel speed is 16 m/s, the α phase can directly nucleate in the liquid phase, leading to an increase in the volume fraction of α2 after RS. Meanwhile, owing to the decrease in lamellar spacing, the increase in the solid solution, and the nanoscale Ti2AlC dispersed in the lamellae, the nanohardness of the lamellae increases with increasing cooling rate. It increases from 4.92 ± 0.12 GPa at conventional solidification to 7.69 ± 0.21 GPa at a wheel speed of 24 m/s, which is an increase of approximately 56.1%.