Microstructures and properties of dz40m co-based superalloy after long-term ageing at 850 °c

DZ40M is a newly developed directionally solidified Co-based superalloy. Its microstructural characteristics and mechanical properties at room and elevated temperatures after ageing for 100-1000 h at 850 °C were studied. The results showed that 100 h ageing at 850 °C results in a substantial increase of tensile strength at room temperature and stress-rupture life at elevated temperatures, serious decrease of ductility at room temperature and improvement for stress-rupture ductility. With increasing ageing time, stress-rupture life tends to decrease and the other properties keep at essential constant. During ageing, primary carbides M₇C₃ and MC decompose sluggishly, fine M₂₃C₆ precipitates copiously around them and M₆C forms on the surface of some M₇C₃. The increased strength of the aged alloy is attributed to a strong interaction between M₂₃C₆ and dislocations.