Abstract: The microstructure changed markedly with increasing solution temperature, i.e eutectic γ' phases and coarse primary γ' phase are redissolved continuously into matrix, which was finished at 1250-1260℃, and more and finer γ' phases are reprecipitated. The grain boundary morphology changed gradually to "fine line" form. The dendritic segregation of elements decreased. With raising solution temperature the longitudinal stress-rupture life at high and intermediate temperature were enhanced, but the transversal stress-rupture life at intermediate temperature decreased obviously. The incipient melting temperature of DZ22 alloy was measured to be 1230-1240℃ and may be increased by homogenization at 1150℃. In this paper the principle of determining solution temperature of DS alloys was discussed. It was suggested that the solution temperature of alloy DZ22 selected at 1200-1210℃ is appropri- ate.

Key words: directional solidification, stress-rupture, microstructure, solution temperature