Improved Cold Spray Repair for Nickel-based Superalloys

Nickel based superalloys are widely used for high temperature applications e.g. hot section parts in aviation engines and stationary gas turbines. The repair of worn or damaged parts is from an economic viewpoint desirable, however, usually difficult due to the poor weldability of these alloys. Cold gas spray has a great potential for the repair application of this type of alloys, since the deposited coatings are dense and free of oxides.

For an advanced repair of the nickel-based superalloy IN 738, different techniques were combined to optimize the adhesion, residual stress profiles and microstructure of the coating. The surface of the substrates prior to powder deposition was improved in matters of surface roughness using laser structuring. The porosity and residual stress profiles were enhanced using a heated sample holder and heat treatments were carried out with a hot isostatic press of the latest generation.

The residual stress profiles were measured with the hole drill and XRD-method. Adhesion tests of the coatings were performed. Detailed microstructural investigations were used to explain different mechanisms with scanning electron microscopy (SEM) using electron backscatter diffraction (EBSD), transmission electron microscopy (TEM) and image analysis for porosity measurements.