Rapid Cellular Crystal Growth of TiAl-Based Intermetallic without Peritectic Reaction by Melt-Quenching in Ga-In Liquid.

A rapid cellular microstructure of Ti-48Al-2Cr-2Nb (in atom %) intermetallic was grown without peritectic reaction by the method of melt-quenching in Ga-In liquid. After characterization of the microstructures and phase constituents, it is observed that the cellular crystals mainly consist of the α2 phase and directionally grew in the outer layer of the melt droplet, with the growth length and cellular spacing about 358-460 μm and 0.68-3.6 μm, respectively. Upon detailed analysis of the cellular growth process, it is found that the formation of this characteristic microstructure is derived from the extremely rapid cooling effect of Ga-In liquid, mainly determined by the heat transfer process; the dominant heat transfer mechanism changes from heat convection to heat conduction at a growth distance of about 70 μm. By using the semireverse method, the dependence of the cooling rate on the cellular growth distance can be estimated accurately and conveniently, which ranges from 2.61 × 106 to 1.26 × 105 K/s. The nanoindentation examination proved that the rapid cellular microstructure possesses excellent micromechanical properties (8.457 ± 0.336 GPa in nanohardness), with a significant improvement of about 15-60% than the general microstructures. [ABSTRACT FROM AUTHOR]