The isothermal phase transformation behavior in a biomedical Co-29Cr-6Mo alloy without carbon or nitrogen was investigated during aging at temperatures between 973 K and 1273 K (700 °C and 1000 °C) for up to 90 ks. Transformation from the γ to the e phase did not occur at 1273 K (1000 °C) as the σ phase was more stable than the ε phase, and the r phase precipitated at the c grain boundaries. At 1173 K (900 °C), a σ →ε1 phase transformation occurred by massive precipitation. Prolonged annealing at 1173 K (900 °C) led to a lamellar structure of ε2 and σ phases at ε1/ε1 boundaries by a discontinuous/cellular reaction, expressed by the reaction equation ε1 → ε2+σ. After decreasing the aging temperature to 973 K (700 °C), transformation from the γ to the σ phase occurred mainly by isothermal martensitic transformation, but a lathlike massive e1 phase and ε2/σ lamellar colonies were also observed at the original γ-grain boundaries. It is likely that not adding carbon results in the promotion of the massive transformation and the precipitation of the r phase during isothermal aging in the Co-29Cr-6Mo alloy system, whose composition corresponds to the ASTM F75 standard for metallic materials for surgical implantation. The resultant isothermal transformation behavior of the present alloy is described on the basis of thermodynamic calculations using Thermo-Calc.
|Number of pages||13|
|Journal||Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science|
|Publication status||Published - 2010 Oct|
ASJC Scopus subject areas
- Condensed Matter Physics
- Mechanics of Materials
- Metals and Alloys