CREEP CRACK BEHAVIOR IN ALLOY C-263 USED FOR THICK-WALLED COMPONENTS

For safe operation of thick-walled components for Advanced Ultra Super Critical (A-USC) power plants, detailed knowledge of the creep crack initiation and growth behavior is essential. The high loading and high temperature conditions in an A-USC power plant require, in many cases, the employment of nickel base super alloys. Unfortunately, both manufacturing and non-destructive evaluation (NDE) of thick-walled components (> 50 mm) made of nickel base super alloys are quite challenging. In this paper, one candidate material for such applications, Alloy C-263, was tested for creep and creep crack behavior at 700 degrees C. Objective of the study was to determine a critical flaw size. In order to establish this size, the duration to achieve the 1%-strain limit at a given load is compared with the time to grow the initial flaw for Delta a = 0.5 mm when the component was loaded with the same given load. It will be shown that manufacturing parameters, e.g. heat treatment procedures, have a significant influence on the creep crack initiation and growth behavior and thus on component life. Decoration of grain boundaries with precipitates, for instance caused by the manufacturing process, can reduce the creep crack resistance and thus increase the risk for premature component failure.