F.T. Kong

Effects of yttrium on microstructures and properties of Ti-17Al-27Nb alloy

The effects of rare earth yttrium on the microstructures and mechanical properties of Ti-17Al-27Nb alloy were studied. The as-cast microstructures of Ti-17Al-27Nb alloy with 0.85%Y(mole fraction) addition were refined and the tensile elongation also increased. Yttrium in the alloy exists as Y2Al according to the EPMA, XRD analysis and electronegativity differences. Y2Al distributes mainly on the grain boundary. Yttrium is found to improve the tensile strength of Ti-17Al-27Nb alloy due to the grain boundary strengthening. Furthermore, Y2Al distributing in the grain boundary leads to grain refinement by pinning grain growth. This fracture mode has been changed from intergranular fracture for Ti-17Al-27Nb alloy to a mixture of intergranular fracture and transgranular fracture for Ti-17Al-27Nb-0.85Y alloy. The dimples were observed distinctly. Therefore, this yttrium containing alloy shows an excellent plasticity.

Influence of yttrium on microstructure and properties of Ti-23Al-25Nb alloy after heat treatment

Abstract The existence of yttrium in Ti-23Al-25Nb alloy and its influence on the microstructure after heat treatment of Ti-23Al-25Nb alloy were investigated using thermal analysis(DTA), EPMA, XRD and SEM. The heat treatment was determined based on DTA measurements. The compression tests at room temperature were performed on a Instron-569 universal tester. The results show that yttrium exists as the Y 2 O 3 alloy. The addition of Y doesnt affect the characteristic phase transformation temperature. At lower quenching temperature, Y strengthens the XRD peaks of O phase by improving the decomposition of B 2 phase. Yttrium addition enhances the compression properties with the compression strength, yield strength and compression ratio increasing. The strengthening is attributed to the second phase strengthening of Y 2 O 3 particles and the grain refinement.

Production and characterization of TiAl ribbons with Y additions

Abstract Rapid solidification method was employed to produce TiAl based alloy ribbons and finally to produce TiAl based alloys with novel microstructure and properties. TiAl based alloys with nominal compositions of Ti-46Al-2Cr-2Nb (atomic ratio) and various yttrium additions (0, 0.5%, 1.0%, 1.5%, 2.0%, atom fraction) were produced using the melt spinning method. For comparison, cast alloys with the same compositions were prepared by argon arc melting as well. It is shown that the as cast microstructure of Y free alloy is lamellar. With addition of Y up to 1.5%, the microstructure of the alloy changes from lamellae to dendrites, while more addition of Y leads to a finer dendrite structure. For the rapidly solidified TiAl based alloy ribbon, refined microstructure is produced. The increase of Y addition modifies the phase constituents from pure γ-TiAl phase of Y free alloy gradually to γ-TiAl+α2-Ti3Al and γ-TiAl+α2-Ti3Al+small amount of Al2Y phase. Though the phase constituents on the two sides of ribbons, surface contacting roll and free surface, are essentially the same, the microstructure of the former one is much finer than that of the latter one.