Subsequent growth and sequential twinning induced by the interaction of {332} twins in Ti-15Mo alloy

The mechanisms associated with the interaction of {332} twins are investigated in metastable Ti-15Mo alloy. There are 12 possible twin-twin junctions (TTJs) induced by {332} twins that can be classified into 5 types according to the crystallographic relation. Twin-twin interactions are accompanied with the formation of twintwin boundaries (TTBs) on the acute side and obtuse side. Experimental results based on transmission electron microscopy (TEM) and procession electron diffraction (PED) show that subsequent growth of the TTBs is asymmetric with the twin thickening preferred only on one side for each type. Besides, it is observed that the twin-twin interaction could stimulate sequential {332} twinning inside the primary twin with a specific twin variant promoted. To account for the subsequent growth of the TTBs and the preferred selection of the sequential twinning variant associated with twin-twin interactions, the elastic energy analysis of the resultant dislocations at TTBs indicates that the growth of the TTBs is energetically favorable only on one side. Displacement gradient based analysis shows that the active sequential twin variant could maximumly accommodate the accumulated strain induced by the twin-twin interaction. This work is useful for predicting the preferential growth of the interfaces and the associated accommodation mechanisms induced by the interactions of localized shear bands.