Fast-Acting Property Models for the Transient Constitutive Properties of Superalloys

Current alloy design or improvement efforts are typically based on the designer’s need for uniform increases in one or more mechanical properties, even though these properties may not be needed everywhere throughout a disk. Designers are now considering the use of dual microstructure turbine disks to obtain optimum local properties while minimizing component weight.  State-of-the-art dual microstructure disks utilize sophisticated tooling and furnace temperature profiles to tailor the mechanical properties of the rim and bore of the disk.  The build-up of residual stresses during heat treatment and subsequent relaxation following heat treatment are difficult to assess using intuition, engineering judgment, or empirical methods. Subtle changes in processing conditions and component geometry can significantly affect the magnitude and pattern of residual stresses.  The rapid cooling required to control microstructure evolution generates large temperature gradients and hence thermal stresses leading to the development of residual stresses which in turn can lead to in-process cracking, distortion during machining  and/or a reduced service life. While on-cooling tensile tests attempt to capture this microstructural effect it is unlikely that the resulting data fully covers the range of thermal history present within and between components, particularly given the highly non-linear nature of precipitation and its influence on flow stress.  Consequently, the further development of location-specific property technologies will require fast-acting validated modeling tools which can accurately and relatively easily provide constitutive properties for standard industry modeling packages such as DEFORM. To that end, we present results from the development of fast-acting property models to predict transient constitutive properties during quenching operations.