Effect of fine-grained structure on the mechanical properties of superalloys K3 and K4169

The fine-grained structures of superalloys K3 and K4169 were achieved by the addition of refiners. Test bars for the determination of mechanical properties were cast under the chosen conditions to study the tensile properties at room and intermediate temperatures, and the stress rupture properties at intermediate temperatures. Results show that for alloy K3, the yield and tensile strengths of the fine-grained samples are superior to those of the conventional ones at room and intermediate temperatures, but there is little difference in tensile plasticity. The stress rupture life of the fine-grained sample is much longer than that of the conventional at 750 degrees C, whereas it has no remarkable change at 800 degrees C. For alloy K4169, the yield and tensile strengths of fine-grained samples are still superior to those of the conventional ones at room temperature and 760 degrees C. In addition, the stress rupture life of the fine-grained sample is 1.1 times longer than that of the conventional one at 760 degrees C. However, the permanent plasticity almost remains the same. The fracture of the samples was examined by scanning electron microscopy (SEM) and the fracture mechanisms were investigated. (C) 2001 Published by Elsevier Science Ltd.