Abstract
Catastrophic accidents caused by fatigue failures often occur in engineering structures. Thus, a fundamental understanding of cyclic-deformation and fatigue-failure mechanisms is critical ...for the development of fatigue-resistant structural materials. Here we report a high-entropy alloy with enhanced fatigue life by ductile-transformable multicomponent B2 precipitates. Its cyclic-deformation mechanisms are revealed by real-time in-situ neutron diffraction, transmission-electron microscopy, crystal-plasticity modeling, and Monte-Carlo simulations. Multiple cyclic-deformation mechanisms, including dislocation slips, precipitation strengthening, deformation twinning, and reversible martensitic phase transformation, are observed in the studied high-entropy alloy. Its improved fatigue performance at low strain amplitudes, i.e., the high fatigue-crack-initiation resistance, is attributed to the high elasticity, plastic deformability, and martensitic transformation of the B2-strengthening phase. This study shows that fatigue-resistant alloys can be developed by incorporating strengthening ductile-transformable multicomponent intermetallic phases.
This work reports the low cycle fatigue behavior of a wrought 316LN stainless steel under different control modes at room temperature. Under symmetrical strain and stress cycling, the steel exhibits ...consistent loading-amplitude-dependent cyclic hardening/softening and fatigue life characteristics. Under asymmetrical stress cycling, the steel is significantly hardened due to mean stress, and the fatigue life at the same strain amplitude is significantly reduced due to ratcheting strain. With the increase of mean stress, though the ratcheting strain level is increased, the fatigue life is prolonged. The effect of mean-stress hardening and ratcheting strain on fatigue life is discussed in terms of strain amplitude and micro-crack initiation and propagation. The Smith-Walker-Topper (SWT) model and a newly proposed fatigue life model based on the Coffin-Manson equation were used to predict the fatigue life under mean stress, and the proposed model yields more robust predictions.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, SAZU, SBCE, UL, UPCLJ, UPUK
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•In-situ neutron diffraction measured the elastic properties of NbV, NbTiV, and MoNbV alloys, which are consistent with first-principles calculations.•Adding Ti elements into the NbV ...alloy results in the formation of the elastically isotropic NbTiV alloy.•This work provides valuable insights into the design of ductile and strong refractory high-entropy alloys by tuning the elastic properties.
Elastic properties are essential to the mechanical performance of materials, and therefore, can be tuned to design high-performance materials. In this study, the elastic constants of the equiatomic ternary refractory multi-principal-element alloys, NbTiV, and MoNbV, were investigated, using in-situ neutron diffraction and first-principles calculations. The experimentally measured and theoretically predicted elastic constants show a good agreement. The alloying effect of adding Ti and Mo into NbV base alloy on the elastic constants is studied. Particularly, adding Ti elements into the NbV alloy results in the increase of the Zener anisotropy ratio from 0.59 to 0.99, leading to the formation of the elastically isotropic NbTiV alloy, while the addition of Mo decreases the anisotropy ratio to 0.52. Pugh’s ratio (B/G), Cauchy pressure (C12-C44), and Poisson’s ratio (ν) are used to predict the brittle/ductile nature of the studied alloys, which is consistent with the mechanical results. The present work provides valuable insights into the design of ductile and strong refractory high-entropy alloys by tuning the elastic properties.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Neutron diffraction instruments offer a platform for materials science and engineering studies at extended temperature ranges far from ambient. As one of the widely used neutron sample environment ...types, cryogenic furnaces are usually bulky and complex, and they may need hours of beamtime overhead for installation, configuration, cooling, and sample change, etc. To reduce the overhead time and expedite experiments at the state-of-the-art high-flux neutron source, we developed a low-cost, miniature, and easy-to-use cryogenic environment (77–473 K) for in situ neutron diffraction. A travel-size mug serves for the environment where the samples sit inside. Immediate cooling and an isothermal dwell at 77 K are realized on the sample by direct contact with liquid N2 in the mug. The designed Al inserts serve as the holder of samples and heating elements, alleviate the thermal gradient, and clear neutron pathways. Both a single-sample continuous measurement and multi-sample high-throughput measurements are demonstrated in this environment. High-quality and refinable in situ neutron diffraction patterns are acquired on model materials. The results quantify the orthorhombic-to-cubic phase transformation process in LiMn2O4 and differentiate the anisotropic lattice thermal expansions and bond length evolutions between rhombohedral perovskite oxides with composition variation.
Zero thermal expansion (ZTE) alloys with high mechanical response are crucial for their practical usage. Yet, unifying the ZTE behavior and mechanical response in one material is a grand obstacle, ...especially in multicomponent ZTE alloys. Herein, we report a near isotropic zero thermal expansion (α
= 1.10 × 10
K
, 260-310 K) in the natural heterogeneous LaFe
Co
Si
alloy, which exhibits a super-high toughness of 277.8 ± 14.7 J cm
. Chemical partition, in the dual-phase structure, assumes the role of not only modulating thermal expansion through magnetic interaction but also enhancing mechanical properties via interface bonding. The comprehensive analysis reveals that the hierarchically synergistic enhancement among lattice, phase interface, and heterogeneous structure is significant for strong toughness. Our findings pave the way to tailor thermal expansion and obtain prominent mechanical properties in multicomponent alloys, which is essential to ultra-stable functional materials.
► Uniaxial ratcheting behaviors of Z2CND18.12N steel at room temperature were obtained by tests. ► A Visco-plastic constitutive model incorporated with isotropic hardening was developed. ► The ...parameter
m
i
of the Ohno–Wang model was developed to evolve with accumulated plastic strain.
Experimental results of monotonic uniaxial tensile tests at different strain rates and the reversed strain cycling test showed the characteristics of rate-dependence and cyclic hardening of Z2CND18.12N austenitic stainless steel at room temperature, respectively. Based on the Ohno–Wang kinematic hardening rule, a visco-plastic constitutive model incorporated with isotropic hardening was developed to describe the uniaxial ratcheting behavior of Z2CND18.12N steel under various stress-controlled loading conditions. Predicted results of the developed model agreed better with experimental results when the ratcheting strain level became higher, but the developed model overestimated the ratcheting deformation in other cases. A modified model was proposed to improve the prediction accuracy. In the modified model, the parameter
m
i
of the Ohno–Wang kinematic hardening rule was developed to evolve with the accumulated plastic strain. Simulation results of the modified model proved much better agreement with experiments.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Rapid progress in modern technologies demands zero thermal expansion (ZTE) materials with multi-property profiles to withstand harsh service conditions. Thus far, the majority of documented ZTE ...materials have shortcomings in different aspects that limit their practical utilization. Here, we report on a superior isotropic ZTE alloy with collective properties regarding wide operating temperature windows, high strength-stiffness, and cyclic thermal stability. A boron-migration-mediated solid-state reaction (BMSR) constructs a salient "plum pudding" structure in a dual-phase Er-Fe-B alloy, where the precursor ErFe
phase reacts with the migrated boron and transforms into the target Er
Fe
B (pudding) and α-Fe phases (plum). The formation of such microstructure helps to eliminate apparent crystallographic texture, tailor and form isotropic ZTE, and simultaneously enhance the strength and toughness of the alloy. These findings suggest a promising design paradigm for comprehensive performance ZTE alloys.
Deformation damage during tension and compression were revealed using in-situ neutron diffraction for a high manganese steel: (1) When the tensile stress is increased, an indication of damage is ...provided when the 111 and 422 lattice strains along the transverse direction give no more contraction or even expansion. This is because that the replacement of slip or twinning activities by crack propagation induces relaxation, which can outweigh contraction of the damaged slip or twinning planes. (2) For compression and also when the stress amplitude is decreased, the increase of the 111, 220, 311, 422 lattice strain amplitudes along the loading direction indicates damage. This is because micro-cracks can decrease the effective elastic modulus and crack propagation is not favored during compression. The identified damage grains for both cases belong to the same set. Distribution of the damaged grains in fractured samples is similar to that from grains featuring large Taylor factors. The cracks mainly distributed at the transverse surface. It is due to stronger deformation heterogeneity and ratcheting events at the surface rather than in the interior. During tension-compression fatigue loading, grain boundaries and the narrow deformation twins often correspond to different amplitudes of transversal contraction and expansion from those in other surface areas. This may trigger surface flaws as nuclei for cracks. The findings point to the important relations among damage, lattice strains, and plastic activities, as well as damage behavior differences between tension and compression.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
An equal-molar CoCrFeMnNi, face-centered-cubic high-entropy alloy system and a face-centered-cubic stainless steel described as a medium-entropy system, are measured by in situ neutron-diffraction ...experiments subjected to continuous tension at room and several elevated temperatures, respectively. With spallation neutron, the evolution of multiple diffraction peaks is collected simultaneously for lattice-elasticity study. Temperature variation of elastic stiffness of a single face-centered-cubic-phase Ni and a single face-centered-cubic-phase Fe are compared as low-entropy metals. The CoCrFeMnNi high-entropy alloy shows distinct lattice anisotropy.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
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