Effect of Thermomechanical Treatment on the Formation of Gradient Structure and Mechanical Properties in a Disk Made of Powder-Metallurgy Nickel-Based Superalloy

The process of obtaining a gradient structure by thermomechanical treatment (TMT) has been demonstrated using the example of a model disk workpiece made of the powder-metallurgy (PM) EP741NP nickel-based superalloy. The TMT included the main deformation leading to the development of recrystallization and the formation of a fine-grained microstructure, heat treatment in a gradient temperature field, additional deformation, and final strengthening heat treatment. In the disk workpiece after TMT, a gradient structure was obtained: a necklace structure in the peripheral part and a fine-grained microduplex structure in the center. The estimation of mechanical properties of samples cut out at different distances from the axis of symmetry of the disk workpiece showed that the central part of the disk is characterized by enhanced strength and ductility, and the peripheral part possesses enhanced high-temperature strength and impact toughness. The obtained results indicate that the approach used is promising for achieving a gradient structure and gradient mechanical properties in disks made of PM nickel based superalloys.