Effect of Rare-earth Element La on Co-base Superalloy

The effect of La element on the mechanicalproperties and constitution nearby grain boundaryin a Co-base superalloy Co-22Ni-22Cr-14k during760℃ ageing has been investigated by AES andmaterial testing. Results show that elementLa can be in a state of solid solution andsegregates mainly at the vicinity of grainboundaries. The prior segregation of La atomscan affect segregation behaviour of otherelements, so that exerts influence onmicrostructure of the alloy, Particularlyincreasing of La content can decrease Pconcentration at the vicinity of grain boundariesbut not decrease S concentration. S togetherwith La produce cosegregation effect. Thecontent of La has no obvious effect on hightemperature strength. When the content of Lacomes up to 0.02wt-％, it can obviously improvethe high temperature ductility.