ホットプレス法により作製した生体用 Co-Cr-Mo 合金粉末焼結体の組織におよぼす窒素含有量の影響

Abstract

The gas atomized Co-29Cr-6Mo alloy powder was hot-pressed in Ar, Ar and N2 (Ar+N2), and N2 atmosphere at 1273 K and 80 MPa for 7.2 ks. Nitrogen content in the compacts can be controlled by the mixture ratio of Ar and N2 gases and the compacts contains nitrogen as high as 0.81 mass%. Microstructure and constituent phase of the compacts depends on the nitrogen content. In the compacts containing nitrogen less than 0.2%, the γ(fcc) ε (hcp) and σ phases coexist in the compacts. The volume fraction of σ phase decreases with increasing nitrogen content up to 0.2%. The γ phase is dominantly confirmed in the compacts with nitrogen content of approximately 0.2%. In the compacts containing nitrogen over 0.2%, Cr2N phases in addition to the γ and ε phases are detected in the compacts. This result suggests nitrogen suppress the σ phases formation and stabilize γ phase in the Co-29Cr-6Mo alloy. When the Co-29Cr-6Mo alloy compacts are hot-pressed with Cr2N powder as a nitrogen source, the σ and nitrides coexist and the microstructure is inhomogeneous. Therefore, it is found that controlling the mixture ratio of Ar and N2 gases during hot-pressing is effective methods to distribute nitrogen uniformly in the Co-Cr-Mo alloy compacts.