Microstructure and mechanical properties of a high nitrogen titanium alloy

High nitrogen titanium alloy with the chemical composition of Ti-4%Cr-0.6%N was produced by solution nitriding to nitrogen-free Ti-4%Cr alloy, and then its microstructure was controlled to have fine (α + β) dual phase structure by aging treatment to improve the ductility. As solution-nitrided specimen has a platelet hcp-martensitic structure (α′) and is characterized by hard but brittle nature that has been produced by solid solution of 0.6% of nitrogen. On the following aging treatment, fine β phase formed along the original plate boundaries, resulting in a fine (α + β) dual phase microstructure. X-ray and EELS analyses revealed that nitrogen is greatly concentrated in the tempered α′ phase. Although the hardness of as-quenched material gradually decreases during the aging treatment with increasing volume fraction of β, the hardness can be kept much higher than that of the aged Ti-4%Cr alloy without nitrogen. As a result of tensile testing, it was found that the aged Ti-4%Cr-0.6%N alloy has high tensile strength over 1 GPa with moderate ductility.