The improved strength and fracture mechanism of additive manufactured Ti-6Al-4 V alloys compared with corresponding as-rolled alloys

The microstructure and tensile fracture mechanisms of as-rolled and additive manufactured Ti-6Al-4 V alloys were systematically investigated. The ultimate tensile strength and elongation of as-rolled Ti-6Al-4 V alloy are 856.27 MPa and 11.67%, respectively. The coarse grains with fewer grain boundaries relatively slightly hinder the dislocations slip and make dislocations easily bypass. And the ultimate tensile strength of as-printed Ti-6Al-4 V alloy reach to 1492.89 MPa with an elongation of 5.76%, which is attributed to the microstructure refinement of as-printed Ti-6Al-4 V alloy with some defects. The high percent of HAGB from as-printed alloy is also beneficial to improve strength. More cleavage facets appear on the fracture morphology fracture surface of as-printed Ti-6Al-4 V alloy, leading to strength enhancement and elongation decrease. The differences of mechanical properties and fracture mechanism between as-rolled and as-printed Ti-6Al-4 V alloys were discussed from grain boundary misorientation, Schmid factor and kernel average misorientation.