チタン鋳物の機械的性質と耐食性

抄録

Castings in plate form of commercially pure titanium KS50 and three titanium alloys, Ti-5Al-2.5Sn, Ti-6Al-4V, Ti-15Mo-5Zr, were prepared by using graphite molds and an arc skull furnace which was of tilting pour type with consumable electrodes, as previously reported. Mechanical and corrosion resistant properties of these castings were studied and compared with those of forged materials. In the case of KS50 and the α alloy, Ti-5Al-2.5Sn, there was no significant difference ofmechanical properties between the as-cast and the annealed castings. However, the strength of the α + β alloy, Ti-6Al-4V, in which phase stabilization occured during annealing, was increased by annealing. The hardening and the reduction of ductility due to ω phase formation in the Ti-15Mo-5Zr alloy castings were suppressed by annealing. There was no large difference of mechanical properties between castings and forgings of KS50. However, the Ti-5Al-2.5Sn alloy castings showed significant decrease of strength, compared to the forged materials, while the Ti-6Al-4V alloy castings showed slight decrease of strength and large reduction of ductility. The inferior properties of the castings seemed to be due to the large grain size. The presence of pin holes in castings of 0.5mm in diameter had a negligibly small effect on the tensile and smooth rupture properties. Annealing of the KS50 and the Ti-15Mo-5Zr alloy castings showed a small effect on the corrosion resistant properties which were, thus, comparable to those of the forged materials. α precipitates due to dendritic micro-segregation were observed in the Ti-15Mo-5Zr alloy castings and were not eliminated by the annealing treatment.