Effect of wheel speed on the microstructure and nanohardness of rapidly solidified Ti–48Al–2Cr alloy

In this work the microstructure and nanohardness of rapidly solidified Ti–48Al–2Cr (at.%) alloy at different wheel speeds were experimentally investigated by using the single roller melt-spinning technique. Conventional cast Ti–48Al–2Cr alloy was prepared by arc melt for comparison. In the arc melted alloy, B2 phases are localized in the lamellar grains or at their grain boundaries. B2 phase is observed to be irregular in shape. The long strip B2 phase that existed in the lamellar structure is parallel to the lamellar structure. After rapid solidification the primary phase is also the β phase. The grain size of B2 phase decreases with the increasing of the wheel speed. The volume fraction of lamellar structure also decreases with wheel speed. When the wheel speed increases to 30 m/s, the matrix changes from γ phase to α2 phase and only a small amount of lamellar structure is occasionally found at the triple grain. The change in nanohardness was discussed based on the microstructural observations. It shows a certain increase of the nanohardness as wheel speed increases. This can be attributed to the changes in the microstructures.