Crack Repair of Single Crystal Turbine Blades Using Laser Cladding Technology

Abstract

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.

Grain-Boundary Interaction between Inconel 625 and WC during Laser Metal Deposition

“…Turbine blades are made of heat-resistant steel or nickel/cobalt-based superalloys. Because of the harsh environment and relatively short lifespan of the blades, any opportunity to regenerate damaged element is very attractive [6,7,8,9]. …”

Application of Directed Energy Deposition-Based Additive Manufacturing in Repair

“…High-pressure single-crystal turbine blades made of Ni-based superalloys have superior creep and fatigue properties with respect to the polycrystalline ones and, accordingly, they can sustain temperatures up to 1100 °C. However, as a consequence of the extreme conditions in the engine of High-pressure single-crystal turbine blades made of Ni-based superalloys have superior creep and fatigue properties with respect to the polycrystalline ones and, accordingly, they can sustain temperatures up to 1100 • C. However, as a consequence of the extreme conditions in the engine of commercial airplanes, they undergo erosion and cracking [90,99,100]. Kaierle et al demonstrated that the DED process had promising results in the building-up of a single crystal or directionally solidified structures, while laser remelting could be used to extend this monocrystalline height [99].…”

Prospects of Use of Laser Cladding Technology for Restoration of Compressor Blades of Gas Turbine Engines

“…Results of metallographic studies showed the existence of clear boundary between the base and built-up material, absence of defects and fine-needled structure of built-up layer indicating high cooling speeds. In respect to the advantages of used methods the authors also mentioned its adaptivity, тельным результатом стало наличие системы контроля геометрии наплавленных валиков с целью обеспечения минимального припу-ска на последующую механическую обработку, а так же оценки технологической возможно-сти "лечения" поверхностных трещин лопаток из никелевых сплавов при лазерной наплавке [21][22][23].…”

“…Also, authors mention the advantages of fiber laser in comparison with СО 2 laser. The positive result consisted in the presence of control system of weld bead geometry for the purpose of provision of minimum allowance for the further mechanical treatment; also the evaluations of technological capacity of "treatment" of surface cracks of the blades of nickel alloys during the laser cladding were mentioned in the papers [21][22][23].…”