The effect of imposed strain e, annealing temperature T A , and annealing time s on the static spheroidization behavior of Ti-6Al-2Sn-4Zr-2Mo-0.1Si having an initial lamellar microstructure was investigated. For this purpose, the samples were compressed isothermally at 1173 K (900°C) to e = 1.0 and subsequently annealed at 1228 K (955°C) £ T A £ 1253 K (980°C) for 10 minutes £ s £ 24 hours. For each test condition, metallography was performed to evaluate the change in aspect ratio (AR) and thus quantify the structural evolution from a lamellar to an equiaxed morphology. The average AR decreased rapidly during short annealing times as a result of sub-boundary-induced boundary splitting, but it decreased at a considerably slower rate during subsequent long-time, diffusion-controlled termination migration. The overall time to complete the static globularization was thus governed largely by termination migration. To model the observations, a kinetic equation describing the static spheroidization of two-phase titanium alloys was developed. A comparison of experimental results and predictions showed that the model can provide a reasonable prediction of the time required to complete diffusioncontrolled migration of the edges of thin lamellar fragments that are circular or elliptical in shape.

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Abstract:In this study, new high-entropy alloys (HEAs), which contain lightweight elements, namely Al and Ti, have been designed for intermediate temperature applications. Cr, Mo, and V were selected as the elements for the Al-Ti-containing HEAs by elemental screening using their binary phase diagrams. AlCrMoTi and AlCrMoTiV HEAs are confirmed as solid solutions with minor ordered B2 phases and have superb specific hardness when compared to that of commercial alloys. The present work demonstrates the desirable possibility for substitution of traditional materials that are applied at intermediate temperature to Al-Ti-containing lightweight HEAs.

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