ホットプレス法により作製した生体用co-cr-mo合金粉末焼統体の絤織におよぼす窒素含有量の影響

摘要

Co-Cr-Mo合金は耐食性や耐摩耗性に優れるため，人工rn股関節などの整形外科材料として広く使用される．その成rn型品のはとんどは鋳造法により溶製されるが，鋳造材にはマrnイクロポアや偏析などの鋳造欠陥が含まれるため加工性に乏rnしい．このため塑性加工性を改善させるには欠陥を除去するrn必要がある．%The gas atomized Co-29Cr-6Mo alloy powder was hot-pressed in Ar, Ar and N_2 (Ar + N_2), and N_2 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 N_2 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 (hep) and σ phases coexist in the compacts. The volume fraction of a 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%, Cr_2N phases in addition to the γ and e 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 Cr_2N 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 N_2 gases during hot-pressing is effective methods to distribute nitrogen uniformly in the Co-Cr-Mo alloy compacts.