The role of Kirkendall porosity in determining β → δ transformation types in Nb-Ti-Al alloys

The formation of Kirkendall porosity and its role in determining β → δ transformation types in Nb-Ti-Al alloys has been reported. The Kirkendall porosity appears in Nb-Ti-Al alloys due to the discrepancy in diffusion rates of Nb, Ti and Al atoms. It is proposed that Kirkendall porosity can serve as a criterion in judging the types of β → δ phase transformations: The appearance of Kirkendall porosity indicates the long-range diffusional transformation and excludes the massive transformation. Moreover, the criterion is also applicable in some other alloy systems in judging the phase transformation types. Besides, Kirkendall porosity in Nb-Ti-Al alloys with different hot-pressing durations exhibits different dimensions.