Deformation mechanisms in ultrahigh-strength and high-ductility nanostructured FeMnAlC alloy

Significance Statement

Scientists from National Chiao Tung University, Taiwan demonstrated a series of FeMnAlC alloys with unprecedented combination of yield strength and elongation, which has evidently exceeded the specifications posted by the Steel Market Development Institute, US Department of Energy and Pohang Steel Company (POSCO), Korea that are anticipated to be realized during the period of 2017-2025 for the next generation (the Third Generation Advanced High-Strength Steels, 3GAHSS) automobile industry applications. In this article, the authors further provided experimental evidence through detailed microstructural analyses that unveils a novel deformation mechanism dominated by bursting dislocations prevailing in the unique microstructure consisting of directional nano-sized (Fe,Mn)₃AlC carbides (k¢-carbides) and isolated austenite nano-channels bounded by the carbides. The coherent nano-sized k¢-carbides formed by spinodal decomposition during quenching had been identified to be the key for resulting in the unique microstructure after the subsequent aging treatment.

Figure legend: Unprecedented combination of yield strength and elongation exhibited in a series of ultrahigh-strength and high-ductility, light-weighted FeMnAlC alloys (indicated by symbols) and deformation mechanism manifested by bursting dislocations in the austenite nano-channels (TEM image).

Journal of Alloys and Compounds, Volume 586, 2014, Pages 616–620.

Chih-Lung Lin^a, Chuen-Guang Chao^a, Jenh-Yih Juang^b, Jenn-Ming Yang^c, Tzeng-Feng Liu^a

^a Department of Materials Science and Engineering, National Chiao Tung University, Hsinchu, Taiwan and

^b Department of Electrophysics, National Chiao Tung University, Hsinchu, Taiwan and

^c Department of Materials Science and Engineering, University of California, Los Angels, CA, USA.

Abstract

The deformation mechanisms of a bulk nanostructured Fe–30Mn–9.5Al–2.0C (in wt.%) alloy were investigated. After aging at 450 °C for 9–12 h, the alloy exhibits an exceptional strength-ductility combination (e.g. yield strength ∼1406 MPa with elongation ∼32%). The aged alloy exhibits a novel microstructure with isolated austenite nano-channels bounded by an extremely high volume fraction of directional nano-sized (Fe,Mn)₃AlC carbides (κ′-carbides). The plastic deformation was found to be dominated by bursting dislocation nucleation within the isolated austenite nano-channels.

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