Microstructures and tensile mechanical properties of Ti-6Al-4V bar/disk fabricated by powder compact extrusion/forging

Ti-6Al-4V (wt%) bar and disk with a density close to 100%, a lamellar structure and oxygen content of 0.44 and 0.51 wt%, respectively, have been made by powder compact extrusion and powder compact forging of HDH Ti-6Al-4V powder respectively. Their microstructure, tensile mechanical properties at different strain rates in the range of 10−4-10−1 s−1 and the fracture surfaces and longitudinal sections of the tensile test specimens have been studied. It was found that the level of consolidation of the PE/Ti-6Al-4V bar and PF/Ti-6Al-4V disk was very high, as reflected by their high strength and good ductility, small untransformed interparticle boundaries (smaller than 3 μm in sizes), and low volume fraction of cavities (<1.5%) formed by separation of powder particles at the untransformed interparticle boundaries in the specimens tensile tested at a high strain rate of 10−2 s−1. The high level of consolidation achieved within a short time through induction heating and extrusion/forging of the Ti-6Al-4V powder compacts suggests that the rate of transforming interparticle boundaries to grain boundaries is very high, and the reasons for this might be formation of new powder particle surfaces through plastic deformation and rapid dissolution of the powder particle surface oxide films. The formation of cavities from the untransformed interparticle boundaries in the PE/Ti-6Al-4V bar and PF/Ti-6Al-4V disk is highly strain rate sensitive with the number and volume fraction of the cavities formed increases significantly with increasing the strain rate.