Recrystallization Behavior and Mechanical Properties of Surface-melted Region of Ni-base Single Crystal Superalloy

Recrystallization behavior in postheat treatment of the surface-melted regions of Ni-base single crystal superalloy CMSX-4 have been investigated. In, addition, mechanical properties of surface-melted regions after postheat treatment were evaluated. The surface melting was conducted using 2kW diode laser. The microstructure and crystal orientation in the melted regions were analyzed by using optical microscopy, scanning electron microscopy (SEM) and electron backscattered pattern analysis (EBSP). The effect of postheat treatment condition on microstructure was investigated using the specimens whose surface-melted regions were single-crystallized. The surface-melted regions were recrystallized when the temperature of postheat treatment was higher than 1513K. On the basis of this result, the partial solution treatment condition was proposed as 1493K×3.6ks to maintain single crystal structure without recrystallization in the surface-melted regions. Furthermore, the mechanical properties of surface-melted regions after partial solution treatment and subsequent aging were investigated by the creep rupture test. The creep rupture strength of surface-melted specimens was comparable to those of the base metal. It could be concluded that the crystalline controlled repairing technique would be applicable to the repair of single crystal superalloy turbine blades.