Nickel-Copper Alloy K-500 products have exhibited rate-dependent, intergranular failure at temperatures as low as room temperature under ambient (low humidity), static load conditions. Failure probability has been correlated to the amount of grain boundary carbon precipitates existing in this alloy [1]. As part of an ongoing investigation to bound the service conditions of intergranular failure in nickel-copper alloy K-500 containing grain boundary precipitates of carbon, previously tested stress-rupture specimens were examined to document and characterize the deformation associated with grain boundary failures. Of particular interest was defining the role of the grain boundary carbon precipitates in the rate-dependent intergranular fracture process under ambient conditions. The failed creep/stress rupture specimens were sectioned perpendicular to the fracture surface and prepared for optical and electron microscopy of the microstructure adjacent to the primary fracture. High resolution microscopy revealed voids opened along the grain boundaries at carbon precipitate/nickel grain boundary interfaces. A diffusional-creep failure mechanism is postulated.