Effect Of Centrifugal Field On Microstructure And Property Of Rapidly Solidified TiAl Based Alloy

Ti-48Al-2Cr-2Nb (at.%) specimens were prepared by permanent mold centrifugal casting and then Hot Isostatic Pressed (HIP) at 1270℃/173MPa/4hrs. Based on the uniform elements distribution in TiAl-based alloy, the variations of grain size and lamellar space, the effect of HIP on precipitation ofγ-phase, as well as the microhardness and the wear resistance of TiAl-based alloy were investigated.Results regarding the distribution of elements in TiAl-based alloy showed that the content of Al was a little lower than the target component due to the volatilization during the melting process, whereas the centrifugal field had slight effect on the uniformity of composition.Also, it indicated that the variations of grain size and lamellar space, as well as the effect of HIP on precipitation ofγ-phase followed certain regulation, which was characterized by the minimum grains existing near the boundary and the maximum ones in the medial region for the selected specimen cross-section. In addition, the variations of lamellar space andγ-phase size were parabolic.Investigation on the distribution of hardness in as-cast sample did not show an obvious regulation which contributed to the existence of micro porosities formed during permanent mold casting and was very difficult to eliminate completely. An abovious descreasement in the hardness could be observed in HIPed sample and the distribution also showed certain regulation, which was characterized by higher hardness value appeared in the center region and lower one in the boundary region.Test on the wear resistance of TiAl-based alloy showed that the friction coefficient of about 0.140 for the cast specimens under the condition of 50N/10min (the loading was 50N and the time span was 10min) and 100N/5min. For the HIPed ones, the friction coefficient increased to 0.158 when the tests were preformed at 50N/10min and 100N/3min. The increasement in friction coefficient attributed to the effect of HIP on the density, which was characterized by the elimination of micro-porosities and the microstructure transformation from fully laminar to duplex-structure.