浮遊溶解−減圧吸引鋳造した各種チタン合金鋳造材の機械的性質

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Properties of precision castings of Ti alloys were investigated in order to evaluate a newly developed casting process. This process is constituted of combination of levitation melting and counter-gravity low-pressure casting, named "LEVICAST". Cast specimens of commercial pure titanium (CP-Ti), Ti-6Al-4V and Ti-6Al-7Nb were prepared by LEVICAST process, and their mechanical properties and surface contamination were examined as compared with rolled and annealed bar. Sound surfaces of castings were obtained through LEVICAST process. Hard alpha case caused by oxygen contamination at surface of the cast specimens were very thin. Increases of carbon and nitrogen from melting atmosphere were negligible. Tensile properties of CP-Ti and Ti-6Al-4V in as-cast condition satisfied the specification of ASTM B367 C-2 and C-5 for ordinary cast use. HIP treatment improved ductility of the casts at the sacrifice of strength. Strength and ductility of HIPed Ti-6Al-7Nb casts were slightly lower than those of HIPed Ti-6Al-4V casts. Mechanical properties of the HIPed casts of both alloys satisfied the specification of ASTM F1108 of Ti-6Al-4V casts for surgical and implant use. Mechanical properties of the cast alloys were almost same as those of rolled and beta-annealed specimen which had coarse microstructures similar to cast one. This demonstrates that mechanical properties of the these alloys are essentially determined by microstructures such as prior beta grain size and lamellar spacing of alpha phases independent of production processes. It was confirmed that LEVICAST was a suitable precision casting process for Ti alloy casts which were free from contamination.
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浮遊溶解−減圧吸引鋳造した各種チタン合金鋳造材の機械的性質

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