Abstract
The effects of interstitial carbon solute and titanium carbide on the tensile and fatigue properties of an (α+β)-type titanium alloy, Ti–4.5Al–2.5Cr–1.2Fe–0.1C (KS Ti-531C), with bimodal and Widmanstätten α structures were investigated. In order to control the microstructures, this alloy was subjected to annealing at temperatures just below and just above the β-transus (531C-α+β annealed and 531C-β annealed, respectively). The microstructure of 531C-α+β annealed shows a bimodal structure and any titanium carbide is not observed, whereas that of 531C-β annealed shows a Widmanstätten α structure and some titanium carbides, which are considered to be Ti2C, are observed. The tensile strength and elongation of 531C-α+β annealed and 531C-β annealed are similar, but 0.2% proof stress is higher and further the reduction of area is much larger for 531C-α+β annealed than 531C-β annealed. Their tensile properties depend mainly on the type of microstructure and interstitial element partitioning because the titanium carbide is not observed on the fractured surfaces of both the alloys after tensile tests. Also, the fatigue properties of 531C-α+β annealed are better than those of 531C-β annealed. The titanium carbide is observed on the fractured surface of 531C-β annealed, but not observed on that of 531C-α+β annealed, after fatigue tests. Therefore, titanium carbide is considered to cause deterioration in the fatigue properties of 531C-β annealed compared to those of 531C-α+β annealed.
