DZ40M, a newly developed directionally solidified
Co-base superalloy was agedat 950℃ for long term. Its microstructural charateristics
and mechanical properties at roomand elevated temperatures were studied. Long-term ageing results in substantial increase intensile strength and sharp reduction in ductility at room temperature. Its effect oil mechanicalprOPerties at elevated temperatures is dependent on eXperimental parameters. At 980℃ , 83 MPa,stress-rupture life is prolonged and at 816 ℃, 215 MPa, it is shortened. However, in all of thecases, the alloy possesses a high stress-rupture ductility. During ageing, primary carbide M7C3and MC decomposed sluggishly, fine M23C6 precipitated copiously around them and M6C formedon the surfaCe of some M7C3. Decomposition of the primary carbides promoted the precipitationof M23C6 by supplying carbon atoms and segregation of tungsten caused the
precipitation ofM6C. It is thought that the change of mechanical properties of the alloy is attributed to theM23C6 precipitation.