Crystalline controlled build-up repairing utilizing unidirectional solidification

Abstract

Ni-base single crystal superalloy CMSX-4 has been widely used for turbine blades and vanes. However, since they are used under severe environments, the blades sometime suffer from erosion. Therfore, it is of great interest to develop repairing techniques that allow the life of single crystal turbine blades and vanes to be extended. So, in this study, the applicability of repairing techniques of the eroded blades by directional solidification treatment was investigated. Ni-Cr-B and Ni-Cr-Si filler metals were used as built-up repairing for the eroded region of the blade. The built-up repairing treatment was developed by utilizing unidirectionally solidification of a repaierd region under temperature gradient using a vertical type furnace with a movable heater. Microstructure and crystal orientaion in the repaired regions under various heat treatment conditions were examined by SEM and EBSP. The microstructure of the repaired region could be classified into several zones; eutectic zone, normally solidified zone, isothermally solidified zone and substrate. The solidification morphology of the normally solidified zone changes from dendoritic to planar with decreasing the moving speed of the heater. The single-crystallization could be achieved in the isothermally solidified zone and the normally solidified zone when its solidification morphology was planar. The thickness of the built-up region of about 2590μm can be obtained when the moving speed of heater is 0.28μm/s using Ni-Cr-Si filler metal.