Microstructure Evolution of Rapidly Solidified TiAl Alloys with Various Nb Contents

摘要

TiAl alloy is a kind of attractive high temperature structural materials because of the low density, high strength,and good creep resistance and good oxidization resistance. However,the low ductility was the main obstacle for their extensive application. Rapid solidification technique is a method to solve this problem by refining and homogenizing the microstructure. The alloy ribbons with nominal composition of Ti-46Al-(2,4,6) Nb-(Cr, Y)(at. %) were used in this work, which were prepared by melt-spinning method. The results show that higher Nb content decreases both the thickness and width of ribbons. All the free surfaces exhibit dendrite structure with the secondary dendrite arms oriented 60 degree to the primary dendrite spines. Increasing Nb addition leads to a more flat free surface. The three alloys are composed of a_2+γ phases,and Nb addition does not alter the phase constitutions. The microstructure of the near roller contacted surface of the three alloys is composed of equiaxed grain and lamellar structure or massively transformed γ_m grain. The volume fraction of massively transformed γ_m grain increases with raising Nb content.