Compacts of Ti-4mass%Cr alloy with various porosity and oxygen content were produced from the mixture of crashed metallic Cr, atomized Ti and HDH Ti powders, and then sintered at 1473K for 3.6ks. Effects of pores and oxygen content on mechanical properties were examined in the sintered Ti-4mass%Cr alloy by means of optical microscopy, analysis of oxygen content, measurement of porosity and tensile tests.
The tensile strength of sintered compacts increases with increasing the volume fraction of HDH Ti powder, because the porosity of sintered compacts is decreased and the shape of pores becomes spherical due to the excellent sintering property of HDH powder. The oxygen content of sintered compacts also increases with increasing the volume fraction of HDH powder, owing to the higher oxygen content in HDH Ti powder than atomized Ti powder. Microstructures of sintered materials are of (a+β) two-phase characterized by fine platelet a phase. The phase ratio a/β and the microstructure of sintered materials don't depend on the volume fraction of HDH Ti powder in spite of having different oxygen content. Consequently, the strength of a sintered Ti-4mass%Cr alloy is greatly influenced by the solid solution of oxygen and by the shape and volume fraction of pores. Especially, when the shape of pores is angular, stress concentration at the corner of pores results in a significant decrease in the tensile strength and elongation.