Synchronous improvement in strength and ductility of biomedical Co-Cr-Mo alloys by unique low-temperature heat treatment

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

卷:739

Article

Ueki, Kosuke¹  Abe, Mai²  Ueda, Kyosuke¹  Nakai, Masaaki³  Nakano, Takayoshi⁴  Narushima, Takayuki¹ 

[1] Tohoku Univ, Dept Mat Proc, Aoba Ku, 6-6-02 Aza Aoba, Sendai, Miyagi 9808579, Japan

[2] Tohoku Univ, Inst Multidisciplinary Res Adv Mat, Aoba Ku, 2-1-1 Katahira, Sendai, Miyagi 9808577, Japan

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

[4] Osaka Univ, Div Mat & Mfg Sci, 2-1 Yamada Oka, Suita, Osaka 5650871, Japan

关键词: Heat treatment;    Mechanical properties;    Plastic deformation;    Stacking fault;    Strain-induced martensitic transformation;   

DOI  :  10.1016/j.msea.2018.10.016

来源: Elsevier

【 摘 要 】

The microstructure and tensile properties of Co-27Cr-6Mo (mass%) alloys heat-treated at 673-1373 K were studied. Lower elongation was observed after heat treatment at 1073 K due to formation of carbonitride precipitates. In contrast, when low-temperature heat treatment (LTHT) was applied at 673-873 K, both the ultimate tensile strength and elongation synchronously improved compared with the solution-treated alloy. Electron backscatter diffraction analysis for plastic-strained alloys and in situ X-ray diffraction analysis under stress induced conditions revealed that the strain-induced martensitic transformation (SIMT) of the gamma(fcc)-phase to epsilon(hcp)-phase during plastic deformation was suppressed by the LTHT. Stacking faults (thin epsilon-phase) were observed to collide in the LTHT alloys. The following mechanisms for the synchronous improvement in the tensile strength and elongation after LHTH are proposed. First, stacking faults with multiple variants were formed during LTHT. Then, the epsilon-phase of a single variant formed by SIMT during plastic deformation collides with preexisting multi-variant stacking faults formed during LTHT, increasing the tensile strength. In addition, the SIMT during plastic deformation is suppressed in the high-plastic-strain region by the collision. This decreases the total amount of epsilon-phase formed during plastic deformation, which improves the ductility. We demonstrated that LTHT of Co-Cr-Mo alloys effectively improves the performance and mechanical safety of spinal fixation implants, which often fracture because of fatigue cracking.

【 授权许可】

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