EFFECTS OF MODE-I STRESSES ON THE OXIDATION AND FAILURE MECHANISMS OFNI-20CR AND NI-15CR-8FE ALLOYS IN SULFUR-DIOXIDE

Two alloys, Ni-20Cr and Ni-15Cr-8Fe, as wire specimens, were exposed t o sulfur dioxide between 325 and 800-degrees-C, with applied external stresses (mode I). Their mechanical properties have been investigated, and the variation of their radius has been precised by conductivity m easurements. For the Ni-20Cr alloy, below 550-degrees-C, the failure p rocess combines cracking and corrosion: Cr2S3 crystals formed at the t ip of the cracks facilitate their propagation. Above 550-degrees-C, no barrier effect is observed, and intergranular corrosion takes place. For the Ni-15Cr-8Fe alloy, mode-I stresses bolster intergranular corro sion.