Microstructure and microhardness of Ti-48Al alloy prepared by rapid solidification.

To improve the microstructure and microhardness, Ti-48Al (at.%) alloy was rapidly solidified by melt spinning under different cooling rates. The microstructure and microhardness of rapidly solidified Ti-48Al alloy were systematically investigated. Results show that the average lamellar colony size of the alloy reduces from 60.6 µm to 11 µm as the cooling rate increases from 2.3×105 to 5.1×105 K·s^-1, caused by the increase of nucleation rate at a higher cooling rate. At the high cooling rate of (4.3- 5.1)×105 K·s^-1, the a phase is the primary phase, and a few metastable a phases are reserved, which then transform into a2 phase and subsequently lead to the formation of a2 equiaxed grain. The lamellar spacing also decreases with the increase of cooling rate. The relationship between lamellar spacing (d) and cooling rate (v) is d=33.6v ^-1.34. The microhardness increases with the increase of cooling rate because the refined lamellar spacing and grain size can improve the microhardness. [ABSTRACT FROM AUTHOR]