Analysis of the fracture behaviour of an aluminide coating on a single-crystal superalloy under tensile conditions

The fracture behaviour of an aluminide coating applied to the single-crystal nickel-based superalloy SRR99 was studied under monotonic loading conditions. A set of tensile tests were carried out in order to determine the fracture strain of the coating as a function of the temperature. During testing, images of the sample surface were periodically captured by means of a video camera system. Analysis of the images has led to the establishment of a value of the coating fracture strain and to a simple method for examining displacements in the coating plane. The observed coating cracking is preceded by substrate yielding, hence the fracture behaviour of the coating has been rationalised in terms of substrate crystal orientation, its yielding behaviour and strain concentration.