Interstitial-Free Bake Hardening Realized by Epsilon Martensite Reverse Transformation

Abstract

By investigating a metastable high-entropy alloy, we report a latent strengthening mechanism that is associated with the thermally-induced epsilon-martensite-to-austenite back-transformation. We show this reversion-assisted hardening effect can be achieved in the same time-scale and temperature range as conventional bake-hardening treatment, but leads to both improved strength and cumulative ductility. Key mechanisms are discussed considering transformation kinetics, kinematics, strengthening and ductilization modules.

Deformation faulting in a metastable CoCrNiW complex concentrated alloy: A case of negative intrinsic stacking fault energy?

“…Compared with the commercial solid-solution or precipitation strengthened superalloys [69] with similar chemical constitutions, as well as the latest metastable FeMnCoCr HEAs [62,70] where extensive mechanically-induced martensitic transformation takes place, a more improved strength-ductility is indeed achieved in the present CCA. Such intriguing mechanical properties render careful explorations of the underlying deformation micro-events, which will be detailed next, starting with post-mortem ECCI/EBSD analyses.…”

“…A quick-emerging scanning electron microscopy (SEM)-based technique, electron channeling contrast imaging (ECCI) [58,59], does manage to complement some of these limitations. With a comparatively wider view-of-field and a satisfactory spatial resolution (down to 50-80 nm) as well as the capability in excerpting crystallographic information once coupled with electron backscatter diffractometry (EBSD), ECCI has received increasing attention in revealing the defect substructural evolution associated with plastic deformation and/or phase transformations in a broad spectrum of metallic alloys [60][61][62][63][64].…”

Processing and Properties of Reversion-Treated Austenitic Stainless Steels

“…Singh [37] reported that the ε-martensite was stable up to 200 • C, and according to Santos and Andrade [128], it reverses in the temperature range 50-200 • C and between 150-400 • C according to Dryzek et al [129]. Very recently a latent strengthening mechanism, bake hardening without interstitials, due to the reversion of ε-martensite, has been reported in a metastable FCC high entropy alloy by Wei et al [133]. Annealing for 20 min at 200 • C was enough for complete reversion accomplished by a shear-assisted displacive mechanism.…”

Thermodynamic Behavior of Fe-Mn and Fe-Mn-Ag Powder Mixtures during Selective Laser Melting

“…The ε-martensite appeared only in the samples where the Mn content was low enough. The reason for the temperature differences in the ε-martensite's start could be the range of the chemical composition or the fact that the ε-martensite can occur athermically [31], which means that for the phase transformation, a change in the temperature is not required, but as a consequence of the phase transformation, a suppressed dislocation motion with stress delocalization is also present with the appearance of extensive phase boundaries. Problems with the vapor pressure differences and consequently the strong vapori tion of Mn bring major challenges with respect to achieving the desired chemical comp sition.…”