Creep Rupture Properties of Ni-26 Cr-17 W Alloys with Small amount of B and/or Zr

Creep rupture tests were carried out at 1 000°C in air on the Ni-26Cr-W alloys containing small amount of B and/or Zr, and the effect of the minor elements addition on the creep rupture properties was investigated in relation to the microstructure. The results obtained were summarized as follows ; 1. A minimum creep rate was decreased remarkably through small addition of B. This is attributed to the uniform and fine dispersion of M23C6 in a grain during creep deformation. The state was kept at least up to 2 500 h. 2. A rupture ductility was improved by a small addition of Zr. This seems to result from the increase of the surface energy for cracking at the grain boundary through the Zr addition. 3. Owing to (1) and (2), the alloy containing a small amount of B and Zr showed better creep rupture properties than the alloys solely with B or Zr. Its rupture life was longer than that of 113MA (Ni-23Cr-18W) and the life difference was apt to become larger with decreasing in the applied stress.