Overcoming the strength-ductility trade-off by the combination of static recrystallization and low-temperature heat-treatment in Co-Cr-W-Ni alloy for stent application

MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING

卷:766

Article

Ueki, Kosuke¹  Yanagihara, Soh²  Ueda, Kyosuke²  Nakai, Masaaki¹  Nakano, Takayoshi³  Narushima, Takayuki² 

[1] Kindai Univ, Dept Mech Engn, 3-4-1 Kowakae, Higashiosaka, Osaka 5778502, Japan

[2] Tohoku Univ, Grad Sch Engn, Dept Mat Proc, Aoba Ku, 6-6-02 Aza Aoba, Sendai, Miyagi 9808579, Japan

[3] Osaka Univ, Grad Sch Engn, Div Mat Sci & Engn, 2-1 Yamada Oka, Suita, Osaka 5650871, Japan

关键词: Co-Cr-W-Ni alloy;    Static recrystallization;    Mechanical properties;    Plastic deformation;   

DOI  :  10.1016/j.msea.2019.138400

来源: Elsevier

【 摘 要 】

A process combining swaging, static recrystallization, and heat treatment at 873 K (low-temperature heat-treatment, LTHT) was developed for achieving both high ultimate strength and high ductility in Co-20Cr-15W-10Ni (mass%, CCWN) alloy for stent application. The alloys swaged to a sectional area reduction rate of 58.3% were annealed at 1373-1473 K for 30-300 s. Under annealing at 1373 K for 300 s, a fine grain structure with an average grain size of similar to 6 mu m formed, while under annealing at 1473 K, a structure with an average grain size of 12 mu m formed after 120 s. In the alloys annealed at 1373-1448 K, the formation of eta-phase precipitates (M6X-M12X type, M: metallic elements, X: C and/or N) was observed, while no precipitates were observed in the alloys annealed at 1473 K. The improvement in ultimate strength by grain refinement was confirmed. Alloys annealed at 1473 K showed higher ductility compared to those annealed at 1373-1448 K even if the grain size was similar. It is considered that the eta-phase precipitates deteriorated the ductility of the annealed alloys. LTHT suppressed the strain-induced martensitic gamma-to-epsilon transformation to improve the ductility of the fine-grained as well as coarse-grained alloys. Thus, regardless of the grain size, it is newly evidenced that LTHT effectively improves ductility in CCWN alloy. By combining high-temperature short-time annealing and LTHT, both the ultimate strength and ductility of Co-2OCr-15W-10Ni (mass%) alloy improved, and it was possible to provide properties suitable for next-generation balloon-expandable stents with Co-20Cr-15W-10Ni (mass%) alloy.

【 授权许可】

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