Microstructure evolution and mechanical properties of TiAl binary alloys added with SiC fibers

Abstract

Binary TiAl (Ti29.8Al and Ti33.3Al, weight percent, hereafter in wt.%) alloys with different SiC fibers contents were prepared by arc melting. Microstructure, phase transformation, mechanical properties and related mechanism were elaborately researched. For the microstructure of Ti29.8Al alloy, the matrix consisted of fully α2/γ lamellar colonies, the grain morphology changed from columnar to equiaxed when the SiC content reached 0.9%. For Ti33.3Al alloy, the matrix consisted of α2/γ lamellar colonies and γ phases, the columnar grains changed to equiaxed grains when the SiC content was more than 0.3%, and the grain size decreased from 150.9 to 69.3 μm with increasing SiC content. Ti5Si3 phases formed at the grain boundaries of both SiC-containing binary alloys. Ti2AlC particles would appear in the lamellar colonies when the SiC content was more than 0.9% in Ti29.8Al alloy and 0.3% in Ti33.3Al alloy, respectively. The formation of Ti5Si3 and Ti2AlC phases resulted from the reaction of SiC fibers and TiAl alloy. The solid solution of C element in α2 phase is higher than that in γ phase, Ti2AlC will be more easily formed in Ti33.3Al alloy due to less α2 phases and more γ phases comparing with Ti29.8Al alloy. Compressive testing results showed that the strength and the strain of SiC-containing Ti29.8Al alloy were almost unchanged until the SiC content was 0.9%, which were improved to 1383 MPa and 6.5%, respectively. A good combination of strength and ductility of SiC-containing Ti33.3Al alloy was obtained, the highest values of them were 2196 MPa and 27.5% when the SiC content was 0.5%. Improvement of mechanical properties is caused by the grain refinement, grain boundary strengthening of Ti5Si3 particles, load transfer strengthening of Ti2AlC particles and solid solution strengthening of C and Si atoms.