A novel multi-scale strategy to reveal martensitic transition and strengthening mechanism in Ti6Al4V alloy

Abstract

The preferred microstructure and formation of variants during martensitic transformation of titanium alloys are very important for understanding and optimizing the mechanical properties of alloys. However, the main contribution of variant selection in the past two decades mainly focused on the issues associated with the interfaces, and a comprehensive explanation at the micro atomic level is still lacking. In the current work, EBSD, TEM, and SEM were used to analyze the essence of variant selection in combination with the valence electron theory of alloys (VE-theory) and cellular automata (CA) modeling. The results show that the driving force and atom path can be demonstrated for the collective shear and rotation displacements of atoms in martensitic transition; the martensitic variant selection in Ti6Al4V alloy has greater randomness in three aspects, namely area ratio of martensitic variants, two variants formed by the same crystal plane of parent phase β, and the distribution ratios of five typical grain boundaries. The preferred selection of α' variant is mainly affected by atom interaction and element distribution, especially Al and V elements. The dislocation pile-up and the soft β phase in martensitic variants are two of the main factors to affect the hardness variation of lath martensite and acicular martensite.