Trifunctional nanoprecipitates ductilize and toughen a strong laminated metastable titanium alloy

Abstract

Metastability-engineering, e.g., transformation-induced plasticity (TRIP), can enhance the ductility of alloys, however it often comes at the expense of relatively low yield strength. Here, using a metastable Ti-1Al-8.5Mo-2.8Cr-2.7Zr (wt.%) alloy as a model material, we fabricate a heterogeneous laminated structure decorated by multiple-morphological α-nanoprecipitates. The hard α nanoprecipitate in our alloy acts not only as a strengthener to the material, but also as a local stress raiser to activate TRIP in the soft matrix for great uniform elongation and as a promoter to trigger interfacial delamination toughening for superior fracture resistance. By elaborately manipulating the activation sequence of lamellar-thickness-dependent deformation mechanisms in Ti-1Al-8.5Mo-2.8Cr-2.7Zr alloys, the yield strength of the present submicron-laminated alloy is twice that of equiaxed-coarse grained alloys with the same composition, yet without sacrificing the large uniform elongation. The desired mechanical properties enabled by this strategy combining the laminated metastable structure and trifunctional nanoprecipitates provide new insights into designing ultra-strong and ductile materials with great toughness.