Microstructure features of failure and mechanical properties of ultra-fine grained Ti–6AL–4V ELI alloy at 300–77 K

Experimental investigation of mechanical characteristics and failure regularities of the ultra-fine grained Ti–6Al–4V ELI alloy, produced by equal channel angular pressing (ECAP), have been carried out under the uniaxial tension at 300 and 77 K. These characteristics have been compared for the different structural states of the Ti–6Al–4V ELI alloy, distinguished by the average grain size and by the morphology of α and β phases. It has been established that the combination of the heat treatment, ECAP, and the extrusion of the Ti–6Al–4V ELI alloy leads to a considerable increase of the alloy’s strength in comparison with the initial state (54% at 300 K and 78% at 77 K) with preserving the reasonable values of the ductility (3–4% elongation to the neck beginning and 5–10% to the failure). For all investigated structural states of the Ti–6Al–4V ELI alloy only ductile failure was observed at 300 and 77 K. The fracture surface consists of regions failed under normal and shear stresses. In shear failure regions of fracture surface only elongated dimples were present.