Lightweight steels display microstructural configuration- and unit size-dependent mechanical properties, yet how can these factors be synergistically adjusted to achieve superior performance? In this study, two kinds of microstructural configurations are fabricated in the lightweight steel by thermo-mechanical processes: (i) heterogeneous structures with gradually optimized hetero-unit sizes; (ii) homogeneous structures, alongside partially/ non-recrystallized variants for comparison. The heterogeneous structure with optimized hetero-unit size achieves an exceptional mechanical synergy, delivering an excellent ductility of 36.1 % at an ultrahigh tensile strength of 1441 MPa. This synergy arises from a dual-improvement effect synergized by hetero-structural design and hetero-unit size optimization, in which the physical mechanism is ascribed to grain boundary strengthening and coupling-enhanced hetero-deformation induced (HDI) strengthening and hardening. A physical-based mechanical model is proposed to elucidate the coupling effect, jointly governed by volume fractions of hetero-zone boundary affected region and disparities of geometrically necessary dislocation density between hetero-boundaries and grain cores, theoretically confirming the ideal hetero-unit size. A mechanical comparison across massive configurations reveals that heterostructure designs reshape strength-ductility synergy, in which the size-optimized (approaching the ideal size) heterostructure is the optimal structural design. This work advances high-performance lightweight steel designs and enriches theories of HDI effects. (c) 2025 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.
The development of high-entropy alloys (HEAs) for hydrogen storage is hopeful for addressing critical limitations of conventional metal hydrides, such as high activation barriers, limited capacity, and poor cycling stability. Here, we report the novel AB(2)-type (A = Ti, Zr; B = Cr, Mn, Fe, Co, Ni) C14 Laves phase HEAs, namely TiZrCrFeCoNi, TiZrCrMnFeCo, and TiZrCrMnFeNi, integrating thermodynamic calculations, arc-melting synthesis, microstructural characterization, hydrogen storage testing, and first-principles calculations. It is shown TiZrCrFeCoNi has very low affinity for hydrogen, which is mainly attributed to the relatively small cell volume. TiZrCrMnFeCo is able to absorb and release 0.94 wt% hydrogen rapidly at room temperature after a 400 degrees C thermal activation. Replacing Co with Ni atoms has a significant effect of improving hydrogen storage capacity. Strikingly, TiZrCrMnFeNi alloy, with outstanding kinetic and excellent cycling performance, can reversibly absorb and desorb hydrogen at room temperature with a capacity of 1.66 wt% without any activation treatment. Additionally, the ground-state structural and electronic properties of AB(2)-type HEAs were clarified by firstprinciples calculations.
The inherent drawbacks of sluggish kinetics and excessive thermodynamic stability limit the practical deployment of Mg-based hydrogen storage materials. In this study, multi-component Mg90La2Ce2Ni3Al3-xBax (x = 0, 0.3, 0.6, 0.9, 1.2) alloys were fabricated. X-ray diffraction analyses reveal that Ba-containing alloys develop a multi-phase structure comprising Mg, La2Mg17, CeMg12, AlNi, and the Mg17Ba2 phase. The Mg17Ba2 induces a reversible transformation between Ba2Mg7H18 and Ba2MgH6, which occurs alongside the primary hydrogenation and dehydrogenation reactions of MgH2 and Mg. Importantly, the generated LaH3, CeH2.73, and Ba2Mg7H18/ Ba2MgH6 hydrides, in conjunction with the AlNi phase, introduce numerous phase boundaries within the alloys. This structural change creates numerous nucleation sites for MgH2/Mg and diffusion channels for hydrogen atoms. Consequently, the activation and hydrogen absorption and desorption properties of the alloys are significantly enhanced. Kinetic analysis using the Johnson-Mehl-Avrami-Kolmogorov model demonstrates that Ba doping accelerates the growth of MgH2 and facilitates the diffusion of hydrogen atoms during hydrogenation. Furthermore, both the calculated dehydrogenation activation energy and the peak dehydrogenation temperature of the alloys significantly decrease with the introduction of Ba element, confirming its pivotal role in enhancing the performance of Mg-based alloys.
Slow hydrogen absorption/desorption kinetics and high thermal stability are regarded as major setbacks for the real application of Mg-based hydrogen storage alloys. Overcoming these shortcomings, the Mg25-xYxNi10 (x = 0, 1, 3, 5, 7) alloys with nanocrystalline and amorphous structures were synthesized by melt spinning technology to improve their hydrogen absorption/desorption properties. The dehydrogenation activation energy of the alloy was estimated using the Arrhenius and Kissinger methods. The starting dehydrogenation temperature and thermodynamic parameters (Delta H, Delta S) of Y partially substituted Mg alloys prepared by melt spinning technique were significantly decreased. The partial substitution of Y for Mg is the main reason for the decrease in the hydrogen storage capacity of Mg-Y-Ni alloys, and the hydrogen absorption capacity increases in the beginning and then declines with the spinning rate rising. Partial substitution of Mg by Y and melt spinning resulted in a significant improvement in the dehydrogenation kinetics of the alloy along with a slight decrease in the hydrogen absorption kinetics. The dehydrogenation activation energy of the alloys decreased significantly with increasing Y content and spinning rate, when the spinning rate was increased from 0 m/s to 30 m/s, the Ede decreased from 68.61 kJ/mol to 53.84 kJ/mol, and when the Y content was increased from 0 to 7, the Edek-value of the alloy decreased from 65.96 kJ/mol to 48.86 kJ/mol. The decrease in dehydrogenation activation energy was also considered to be the main reason for the enhanced dehydrogenation kinetics of the alloys.
In this paper, the effects of microstructure changes on the hydrogen diffusion behavior and hydrogen embrittlement (HE) of X60 pipeline steel at different tempering temperatures were systematically investigated through slow strain rate tensile (SSRT) tests, gas phase hydrogen penetration tests and thermal desorption spectroscopy (TDS) tests, combined with scanning electron microscope (SEM), electron backscattering diffraction (EBSD), xray diffraction (XRD) and transmission electron microscope (TEM) characterization methods. The results show that with increasing tempering temperature, the IHEA of X60 pipeline steel in H2 gradually decreases, while the area of the ductile fracture zone on the fracture surface increases. This indicates that the HE of the steel decreases significantly with increasing tempering temperature. When the tempering temperature reaches 660 degrees C, the comprehensive mechanical properties and HE resistance of X60 steel reach the optimal value. As the tempering temperature increases, the effective grain size of the test steel does not change significantly, while the dislocation density decreases, and the degenerated pearlite (DP) decomposes. Meanwhile, Nb-V composite microalloying promotes the extensive precipitation of the nanoscale (Nb, V, Ti)C second phase particles during the high-temperature tempering. This results in a significant increase in the number of hydrogen traps (NT) in the steel and a substantial decrease in the apparent diffusion coefficient (Dapp). Essentially, this is attributed to the coupling effect of the reduction in reversible hydrogen traps and the increase in irreversible hydrogen traps.
