Influence of inhomogeneity on mechanical properties of commercially pure titanium processed by HPT

Already for fifteen years many researchers have been trying to discover metallic materials with unusual combinations of strength and ductility: with high strength and enhanced ductility. This combination may be achieved through different ways: alloying, nanostructuring, etc. This report is an attempt to analyze the influence of inhomogeneity of different types (structural, phase and space) on mechanical properties of commercially pure titanium (bulk and powder) subjected to high-pressure torsion. Experimental results for HPT bulk and powder titanium have demonstrated that mechanical behavior of CP titanium strongly depends on phase inhomogeneity (alpha + omega phases), structural inhomogeneity (bimodal grain size distribution) and space inhomogeneity (retained porosity) in case of cold consolidated Ti powder. High strength in HPT bulk titanium due to the formation of hard omega phase during HPT processing at room temperature was detected. The strong omega phase transforms back to nanograined alpha phase domains during short annealing at elevated temperature. HPT consolidation of titanium powder leads to the formation of brittle specimens showing high strength but almost zero plasticity