Influence of strength difference between soft and hard zones on hetero-deformation induced strengthening effect: Taking heterostructured β Ti alloy as an example

The large strength difference between soft and hard zones in heterostructured materials is a double-edged sword: on the one hand, the effective back (tau b) and forward stress (tau f) are generated to produce hetero-deformation induced (HDI) strengthening and strain hardening effect. On the other hand, the micro-cracks tend to initiate and propagate along the interface to cause premature failure. Here we prepared three different heterostructured Ti-4.8Al-5.6Mo-3V-1.5Cr-1.6Fe alloys to reveal the influence of magnitude of strength difference between soft primary alpha phase (alpha p) and hard beta matrix on its tensile strength and ductility. It demonstrates that only when the sum of applied stress (tau a) and tau f is greater than the yield strength of hard beta matrix (sigma yhard), i.e., tau a + tau f > sigma hard y , the alloy can obtain both high strength and ductility. Contrary, when tau a + tau f < sigma yhard, the alloy exhibits a highest strength but a lowest ductility. These findings are expected to help with designing heterostructured materials for superior mechanical properties.