Intergranular Sulfur Attack in Nickel and Nickel-base Alloys

The phenomenology of intergranular sulfur attack in nickel and nickel-base alloys and the resulting embrittlement on post-exposure tensile testing was investigated. Using Ni 270 as a model material, specimens were exposed at temperatures between 450°C and 800°C to Fgous sulfur e vironments with sulfur partial pressures ranging from atm. to 10' B atm. Increasing exposure temperature and increasing sulfur partial pressure increased the severity of the sulfur attack as measured by post-exposure tensile testing in air. Measurements of the maximum depth of intergranular fracture on room temperature tensile specimens were used to calculate the activation energy for the sulfur penetration as 74 KJ/mol. Auger analyses indicate that the level of sulfur on the grain boundaries increases with increasing temperature and increasing sulfur partial pressure. The implications of these data for nickel-base alloys are discussed. Superalloys 1988 Edited by S. Reichman, D.N. Duhl, G. Maurer, S. Antolovich and C. Lund The Metallurgical Society, 1988