Serrated Flow Behavior and Microstructural Response of FeCrAl APMT and Inconel 716 Under DSA Conditions

FeCrAl Kanthal® APMT and Inconel 718 (IN718) are advanced structural alloys used in nuclear and aerospace applications due to their excellent high-temperature strength and oxidation resistance. However, both materials exhibit dynamic strain aging (DSA) and serrated flow behavior under certain temperature and strain rate conditions, which can compromise mechanical reliability.

This study investigates the DSA behavior of FeCrAl APMT and IN718 through uniaxial tensile testing across a broad temperature range (298–973 K) and strain rates (10⁻³ to 10⁻⁵ s⁻¹). The onset and characteristics of serrated flow were mapped, and serration maps were constructed by correlating critical strain values with temperature and strain rate. Activation energies associated with serration regimes were calculated to identify underlying diffusion-controlled mechanisms.

Microstructural analysis provided further insight into the deformation behavior. Electron backscatter diffraction (EBSD) was used to examine grain structure and misorientation evolution, while transmission electron microscopy (TEM) revealed dislocation-solute interactions, slip behavior, and nanoscale clustering. Fracture surface analysis via scanning electron microscopy (SEM) highlighted void formation and crack propagation linked to strain localization and embrittlement.

Mechanical properties including yield strength, tensile strength, ductility, and work-hardening behavior were evaluated to assess the impact of DSA on performance. The study highlights key differences and similarities between the two alloys in terms of their susceptibility to DSA and deformation instability.

By integrating mechanical testing with multiscale microstructural characterization, this work provides a comparative framework for understanding DSA in FeCrAl APMT and IN718, supporting their development and optimization for service in extreme environments.