RELATIONSHIP BETWEEN THE MICROSTRUCTURE, LOW CYCLE FATIGUE AND CREEP PROPERTIES OF A CAST AND WROUGHT Ni-Co BASE SUPERALLOY TMW-4M3 DISK

A series of cast and wrought (C&W) Ni-Co base superalloy TMW (TMW is a trademark of National Institute for Materials Science registerd in Japan.) alloys, was developed for applications of turbine disks and other components. TMW-4M3 has excellent creep resistance among the lineup of TMW alloys. A TMW-4M3 disk with increasing amounts of strengthening elements (Ti, B and Zr) was produced via improved hot-working process, starting from an ingot of industrial triple-melt (vacuum induction melting / electro-slag remelting / vacuum arc remelting). To investigate the effect of the microstructure on fatigue and creep properties, another TMW-4M3 disk with standard composition produced by previous trial (not improved) processes and an Alloy 720Li disk were also prepared as references. A TMW-4M3 disk via improved process had fine grains pinned by primary gamma' particles after solution heat-treatment at 1100 degrees C. ALA grain size of this disk was finer than that of a previous trial disk, though average grain sizes were similar. This TMW-4M3 disk having small ALA grain exhibited long fatigue life at 400 degrees C compared to other disks. In addition, creep rupture life at 725 degrees C of this TMW-4M3 disk was longer than those of a previous trial disk and Alloy 720Li disk due to larger amounts of Ti, B and Zr. Therefore, these results show that this improved TMW-4M3 disk had good low cycle fatigue properties and creep resistances.