The primary objectives of this research project are to understand how defects in single crystals can be eliminated by localized melting and re-solidification using lasers, and subsequently use this basic information for repairing defects in single crystal turbine blades that are used in aerospace engines and power plants. The conditions, which lead to defect elimination during re-solidification in single crystals, are currently not clearly understood, and this has precluded successful repair. The approach to be taken in this research is interdisciplinary and involves students and faculty in Mechanical Engineering and Materials Engineering Departments working together to first establish how the single-crystal nature can be preserved under different solidification conditions. This fundamental research will lead to a physical and numerical model of single crystal solidification. This basic information will then be applied to control laser repair processes so that the melted area re-solidifies in a manner that removes the defect and restores the single crystal nature of the turbine blade.
If successful, the results of this research will provide an improved understanding of the mechanism of single crystal solidification and lead to the creation of physical and numerical models of single crystal solidification that are currently not available. In addition, application of these results for repair of single crystal turbine blades will lead to a substantial cost savings associated with manufacturing and replacement of turbine blades. For example, one turbine blade currently costs approximately $30,000 to manufacture, and one engine contains many blades. In some cases the blades cannot be used because of defects that formed during initial manufacturing. Once a defect-free blade is manufactured and placed into service, it must eventually be removed from service because of wear and replaced with a new blade. At present, most blades exhibiting manufacturing defects or service damage must be discarded because there is no reliable technique to repair these defects. The industrial partner of this program has determined that a successful repair method could result in savings of as much as $100,000 each time an engine is inspected and/or overhauled.