# Effect of Freckle Defects on Hot Deformation Behavior and Dynamic Recrystallization Structure Inheritance of an Iron–Nickel-Based Superalloy

## TL;DR

This study examines how freckle defects affect the hot deformation and recrystallization behavior of an iron-nickel-based superalloy.

## Contribution

The paper reveals how freckle defects alter dynamic recrystallization mechanisms in GH4706 alloy during hot deformation.

## Key findings

- Freckle-containing specimens show lower DRX degree and larger grain size compared to freckle-free ones.
- Freckle defects promote both DDRX and CDRX, while freckle-free specimens mainly show DDRX and PSN.
- MC carbides and Laves phases in freckles act as nucleation sites for PSN.

## Abstract

To study the influence of freckle defects on the hot deformation behavior and the inheritance of dynamic recrystallization (DRX) structure in GH4706 alloy, the microstructures of specimens with and without freckles and the evolution laws of hot-processing parameters were compared. Hot compression experiments were conducted on a thermal simulation testing machine at 950–1150 °C, strain rates of 0.001–1 s−1, and 55% deformation. Freckle-containing specimens were tested under DRX critical conditions. The flow stresses of both specimens increase with strain rate or with decreasing temperature. The power dissipation coefficient (η) and instability value (ξ) follow complex laws. Electron back-scattering diffraction (EBSD) was used to analyze DRX microstructures and nucleation mechanisms. The DRX degree of freckle-containing specimens is lower, with a larger average grain size. The DRX mechanism initiates preferentially in freckle-containing specimens, and its volume fraction changes in a complex manner. Grain coarsening occurs in freckle-containing specimens at high temperatures and low strain rates. Freckle defects lead to significant differences in the DRX mechanism of GH4706 alloy. Freckle-containing specimens exhibit both discontinuous dynamic recrystallization (DDRX) and continuous dynamic recrystallization (CDRX), whereas freckle-free specimens primarily display DDRX and second-phase particle-stimulated nucleation (PSN). The presence of MC carbides and Laves phases within freckle defects provides nucleation sites, further supporting a typical second-phase particle-stimulated nucleation mechanism.