Comparative research on Charpy impact behaviors of a novel TRIP Ti alloy with single β and α + β dual phase

A novel transformation induced plasticity (TRIP) Ti alloy with the composition of Ti-4.7Al-6.26Mo-2.85Cr was designed. The tensile and Charpy impact behaviors of the alloy with single β and α + β dual phase were comparably investigated. Compared to the single β microstructure, the α + β dual microstructure exhibited the higher yield strength (YS) and impact absorbed energy. This suggests the YS of the metastable β Ti alloys has a significant influence on the impact toughness, i.e., the disadvantage of the low YS in single β microstructure become more prominent in the impact deformation. Because the β matrix in the α + β dual microstructure was more stable than that in the single β microstructure due to the elemental partitioning effect, the primary impact deformation mechanism changed from the stress induced martensite in the single β microstructure to dislocation slip in the α + β dual microstructure. Correspondingly, the cracking mechanism changed from β/α” interface cracking to βretained/αlath interface cracking. These findings provide guidance for the simultaneous improvement of YS and Charpy impact absorbed energy of TRIP Ti alloys by microstructural regulation.