Effects of the Surface Fine-grain Layer on the Mechanical Properties of Cast TiAl

摘要

Based on cast TiAl based alloy with the preferred orientation lamellar microstructure, three types of specimens with different microstructural morphologies on surface fine-grain layers were cast in three types of moulds with different thermal physical parameters,and effect of the surface fine-grain layer on the four-point bending strength was studied. The results indicated that the bending strengths increased after the surface fine-grain layer was removed, which implied that the surface fine-grain layer composed of randomly oriented colonies had an adverse effect on the bending strength; the specimen with the lamellar nearly parallel to the cast surface exhibited much higher bending strength than that with nearly perpendicular to the cast surf ace, which was attributed to the lamellar orientations of the colonies in the surface fine-grain layer. Decreasing the thickness and coverage ratio together with colony size and lamellar spacing of the surface fine-grain layer was helpful to reduce the adverse effect of surface fine-grain layer on the mechanical properties of titanium aluminide based alloys with this microstructure.