Evolution of cold-rolled microstructures of biomedical Co-Cr-Mo alloys with and without N doping
Evolution of cold-rolled microstructures of biomedical Co-Cr-Mo alloys with and without N doping
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DOI：
10.1016/j.msea.2010.09.002
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发表时间：
2010-12
期刊：
影响因子：
6.4
通讯作者：
M. Mori;K. Yamanaka;H. Matsumoto;A. Chiba
中科院分区：
文献类型：
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作者：
M. Mori;K. Yamanaka;H. Matsumoto;A. Chiba
研究了氮掺杂对无镍Co-Cr-Mo合金冷轧过程中组织演变的影响。氮掺杂改善了该合金系统的冷加工性，虽然观察到的边缘裂纹的开始为30%的冷轧压下量的Co-29 Cr-6 Mo-0.17N（质量%）的合金，其中具有最高的氮含量的合金中使用的本研究。添加0.17%的氮可使γ相（面心立方结构）在室温下充分稳定，抑制固溶处理后冷却过程中的非热马氏体γ→马氏体相变，但变形机制仍以应变诱发马氏体相变（SIMT）为主。SIMT是负责有限的冷加工的Co-Cr-Mo合金与N添加和不添加。用透射电镜观察了冷轧初期γ基体马氏体片层的发展及随后裂纹附近剪切带的形成。在SB内部观察到沿剪切方向沿着伸长的细颗粒;这与其他具有低堆垛层错能的材料类似。在相对低的应变下的这种SB演变被认为源自由应变诱导的马氏体组成的层状显微组织，其导致裂纹在γ基体-马氏体边界处和沿着γ基体-马氏体边界扩展，在该边界处容易发生应力集中。
The effects of nitrogen doping on microstructural evolution during cold rolling of Ni free Co-Cr-Mo alloys have been investigated. Nitrogen doping improved the cold workability of this alloy system, although initiation of edge cracks was observed for a cold rolling reduction of 30% in a Co-29Cr-6Mo-0.17N (in mass%) alloy, which has the highest nitrogen content of the alloys used in the present study. Nitrogen addition of 0.17% sufficiently stabilizes the γ phase (fcc structure) at room temperature, suppressing the athermal martensitic γ→ɛ transformation during cooling after solution treating, while the primary deformation mechanism is still the strain-induced martensitic transformation (SIMT). The SIMT is responsible for the limited cold workability of Co-Cr-Mo alloys with and without N addition. The development of γ matrix –ɛ martensite lamellae in the initial stages of cold rolling and subsequent shear band (SB) formation in the vicinities of cracks was observed by transmission electron microscopy. Fine grains, which elongate along the shear direction, were observed inside SBs; this is similar to other materials with low stacking fault energies. Such a SB evolution at relatively low strain is thought to originate from the lamellar microstructure that consists of strain-induced ɛ martensites, which leads to crack initiation and propagation at and along γ matrix –ɛ martensite boundaries where stress concentrations readily occur.