Microstructural degratation of the single-crystal superalloy CMSX-4-during annealing under load: Implementation of rafting kinetics in mechanical modelling.

• Applicants: Dr.-Ing. Thomas Link; Professor Dr.-Ing. Pedro Dolabella Portella
• Subject Area: Metallurgical, Thermal and Thermomechanical Treatment of Materials
• Term: from 2005 to 2009
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 16524572

During high temperature service the y/y -microstructure of nickel-base superalloys becomes unstable: the cuboidal y precipitates coalesce into expanded y -rafts. Mechanical properties strongly degrade due to rafting . It is proposed to include the effect of rafting into modelling the mechanical behaviour of superalloy CMSX-4 widely used in gas turbines. This will be done in three steps: investigation of the rafting kinetics, mathematical description of rafting as a function of the deformation/stress state and the temperature, implementation of this function into a mechanical model. The rafting kinetics will be investigated at low stresses over a wide temperature range 825-1050°C simulating the operating conditions of aircrafts and power gas turbines. A new specimen design (flat wedge shape) will be applied. Its advantages are: the flatness allows preparing the surface of the same specimen anew after multiple load-annealing tests for investigation of the microstructual change by SEM and XRD; the wedge shape provides a linear change of stresses along the specimen axis. The outcome of these investigations will be the identification of an evolution law for rafting. The resulting constitutive law will take into account the degradation of the mechanical properties due to rafting thus allowing the Finite Element analysis of blades under service conditions, where rafting occurs.

• DFG Programme: Research Grants