INFLUENCE OF RARE EARTH DOPING ON MECHANICAL PROPERTY AND MICRO-STRUCTURE OF CHROMIA OXIDE FILM

摘要

The isothermal oxidizing kinetics of Co-40Cr alloy and its yttrium ion-implanted samples arc studied at 1000℃in air by thermal-gravity analysis(TGA).Scanning electronic microscopy (SEM)is used to examine the Cr_2O_3 oxide film's morphology after oxidation.Acoustic emission(AE) method is used in situ for monitoring the cracking and spalling of oxide films formed on both samples during oxidizing and subsequent air-cooling stages.Theoretical model is proposed relating to the film fracture process and is used for analyzing the acoustic emission spectrum both on time domain and on AE-cvcnt number domain.It is found that yttrium implantation remarkably reduces the isothermal oxidizing rate of Co-40Cr and improves the anti-cracking and anti-spalling properties of Cr_2O_3 oxide film.The reasons for the improvement arc mainly that the implanted yttrium reduced the grain size of Cr_2O_3 oxide,increased the high temperature plasticity of oxide film,and remarkably reduced the number and size of Cr_2O_3/Co-40Cr interfacial defects.