Effect of melt treatment on the grain sizes of Ti-48Al-2Cr-2Nb alloy

Microstructures of a cast Ti-48Al-2Cr-2Nb alloy without melt treatment and with melt cycle treatment for 10, 15 and 20 cycles in solid-liquid region (1480~1510°C) were investigated by OM coptical microscope and SEM (scanning electron microscope). The results show that the melt treatment has a significant role in the refinement of grain sizes in the alloys. The microstructure of the alloy is characterized by coarse columnar morphology without melt treatment, while it is characterized by small fine equiaxed grain from coarse lamellar cluster with the melt cycle treatment for 10, 15 and 20 cycles, and it is more uniformly distributed in the microstructure. At the faster heating stages in the melt cycle treatment process, the remelting of grain occurs, resulting in the separation of broken dendrite with the matrix to act as nuclei in subsequently solidification. Meanwhile, under the action of electromagnetic force, the solute field and temperature field are uniformly distributed to inhibit the occurrence of composition undercooling, which is responsible for the refinement of grain size.