Cold spray repair for gas turbine components

Gas turbine components are often facing hazardous conditions which lead to massive attack and materials loss. Therefore, repair technolgies especially for Nickel base alloys are needed and cold spray is often used for this application. While the introduced compressive stress in cold spray is in many cases advantegous, it might become detrimental for large repair volumes. Here the stored elastic energy might exceed the critical energy release rate leading to failure. Hence, a detailed understanding of the stress development during spray also on complex shaped parts is needed. Here the results of stress measurements by hole drilling method or by X ray diffraction for IN718 repair coatings deposited on different groove geometries will be presented.

Furthermore, an adjustment of the stress state by defined process technologies is highly desireable. It will be shown that by the variation of robot speed and feed rate an adjustment of the stress state is possible. With this concept even final tensile stress levels could be obtained. For the evaluation mainly the ICP sensor was used. This device allows the in-situ stress evaluation by measuring the bending of a beam during deposition. The results could be explained in a semi qunatitative way by a rather simple analytical model taking into account the temperature gradients during deposition.