注镧Co-Cr合金表面氧化膜生长规律与微观结构表征

Growth kinetics and microstructure characterization of oxide film formed on La-implanted Co-Cr alloy

采用热重分析(TGA)方法研究了离子注镧对Co-40Cr合金在1000℃空气中的恒温氧化和循环氧化行为的影响.用扫描电镜(SEM)和透射电镜(TEM)对表面氧化膜的微观形貌和结构进行了研究.用二次离子质谱(SIMS)对合金表面元素铬结合能的变化情况以及氧化膜中元素镧的深度分布进行了测试,并用激光拉曼谱(Raman)对掺杂镧引起的氧化膜内应力改变进行了测量研究.结果表明,离子注镧后Co-40Cr合金在1000℃空气中的恒温氧化速率显著降低,表面Cr2O3氧化膜的抗开裂与抗剥落性能明显增强.原因主要是镧细化了Cr2O3氧化膜的晶粒尺寸、降低了氧化膜内应力水平并增加了氧化膜的高温塑性.稀土镧主要以La2O3和LaCrO3的形式存在于Cr2O3氧化膜的外侧,通过阻碍膜内阳离子扩散影响膜的生长规律,进而改善氧化膜的黏附性能.

The isothermal and cyclic oxidizing kinetics of Co-40Cr alloy and its lanthanum ion-implanted samples were studied at 1000℃ in air by thermal-gravimetric analysis （TGA）. Scanning electronic microscopy （SEM） and transmission electronic microscopy （TEM） were used to examine the morphology and structure of the oxide film after oxidation. Secondary ion mass spectrum （SIMS） method was used to examine the binding energy change of chromium caused by La-doping and its influence on formation of Cr2O3 film. Laser Raman spectrum was used to examine the stress changes within oxide films. It was found that lanthanum implantation remarkably reduces the isothermal oxidizing rate of Co-40Cr and improves the anti-cracking and anti- spalling properties of Cr2O3 oxide film. The reasons for the improvement were mainly that the implanted lanthanum reduces the grain size and internal stress of Cr2O3 oxide and increases the high temperature plasticity of oxide film. Lanthanum mainly exists in the outer surface of Cr2O3 oxide film in the forms of fine La2O3 and LaCrO3 spinel particles.