During the last years gas turbine efficiency could be significantly improved throughrnincreasing firing temperature which has called for advanced turbine blade materials such asrnsingle crystal (SX) superalloys. At the same time sophisticated internal cooling features havernresulted in complex blade designs and increased component costs. New technologies for bladernrefurbishment are now emerging and allow a reduction of operating costs by offering thernoption to repair worn blades instead of replacing them.rnWe report on the use of Epitaxial Laser Metal Forming (E-LMF), a laser powder weldingrntechnique, for the restoration of damaged SX turbine blades. The process combines a fiberrncoupled diode laser, a robot and a coaxial powder nozzle with integrated on-line monitoringrncapability. With the robot-guided laser system repair or coating of complex shaped turbinernblades becomes possible by adding new material layer by layer.rnThe repair process is fully automated and therefore highly repeatable. With correct adjustmentrnof process parameters it is possible to refurbish costly single crystal components.rnThe E-LMF process has been successfully applied for the tip restoration of high-pressurernturbine blades from ALSTOM’s GT26 turbine. SX blades of two different designs were usedrnfor this demonstration. Prior to the real application the repair process was simulated andrnoptimized with new offline programming tools. This resulted in optimized quality of the lasergeneratedrnstructures and near net shape deposition with very little need for rework. It wasrnshown that precise control of laser power limits detrimental heat input to a surface layer ofrnless than 1mm thickness. Therefore, even turbine blades with film cooling holes in closernproximity to the blade tip can now be refurbished.
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