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The formation of cracks in single crystal (SX) turbine blades is a common problem for aero-engines. To repair cracks, which are located under the tip-area, a new method is to clad with single-crystal-technology. This technology use multi-layer cladding to replace the single crystal material. To regenerate cracked material it is necessary to remove the crack affected material. The used notch geometries to remove the crackaffected area must be weldable and also permit the material solidification in the same oriented plane as the original microstructure. To solidify in the original structure a thermal gradient has to be introduced in order to guide the grain growth. This required gradient can be established by inductive heating. To reduce the thermal effected zone, a laser source is used. In addition, it is also an efficient process to fill the notch. Also the small local heat input and controlled material supply support the epitaxial growth. However, there are requirements to achieve a SX structure without cracks and pores. Current achievements and further challenges are presented in this paper.

The objective of this work was to achieve a single crystalline (SX) clad on the tip of an SX turbine blade. It was assumed that remelting could extend the SX-height by resolidifying the misoriented volume of its clad tracks. Thus, remelting was used as a tool to ease the clad epitaxy. All tests were performed with SX Ni-based superalloys CMSX-4 or PWA 1426. To determine the remelting parameters, the following methodology was devised: An ideal energy input per unit was determined for each clad track shape by applying a variable laser power during the process while traveling steadily. The energy value was defined using a combination of cross-sectional analyses and different laser parameters, thereby reducing the number of required tests to find the effective track remelting parameters. This was then tested thoroughly on five differently shaped CMSX-4 clad tracks to evaluate its validity. Thereafter, the remelting parameters from one chosen CMSX-4 track were applied to a similarly shaped PWA 1426 track, resulting in a complete SX clad track. This SX track was used to form the SX deposition on top of the blade, which was also made of PWA 1426. The tests to evaluate the remelting methodology were carried out on (010)/[100] or (010)/[001] crystalline orientations, which are equivalent to the orientations found on a turbine blade tip.

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