| The effect of heat treatment on the microstructures of Ti-48at%Al alloys was investigated. TiAl intermetallic compounds were melted by the plasma arc melting system. The effect of the solidification rate on the cast microstructures was also studied by using three types of mold, i. e., steel, graphite and ceramic. It was found that dendrite arm spacing and thickness of the lamellar structure decreased, and Al segregation at interdendritic r increased as the solidification rate in the molds was increased. The specimen cast in a ceramic mold showed the most rapid rate of recrystallization. In lamellar structures, the recrystallization does not occur from the interface of γ and α₂ phase, but rather from the growth of the new laths, maintaining their crystallographic relationship. In the compressive test at room temperature, the difference of the yield strength that occurred from the various mold decreased with the increase of heat treatment time. |
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