Single-crystal laser deposition of superalloys: processing–microstructure maps Original Research Article

In order to extend the life cycle of modern single-crystal (SX) high-pressure high-temperature gas turbine blades, repair of cracked or worn parts is of great interest. The success of the repair technique depends critically on a close process control in order to ensure SX repair. Based on solidification theory a process called epitaxial laser metal forming (E-LMF) has been developed. This paper presents the important concepts necessary for any process control for SX repair based on processing maps which relate the expected solidification microstructures and growth morphologies to the processing conditions. These maps are obtained in two steps. Firstly, the relationships between local solidification conditions and the resulting solidification microstructures, i.e. columnar or equiaxed, are formulated. Secondly, the local solidification conditions as a function of the laser processing parameters are calculated with an analytical heat flux model. By a combination of both approaches, processing–microstructure maps are obtained which define processing windows for SX generation and repair by laser deposition.