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To investigate the effects of hydrogen (H) on the mechanical properties of 316L austenitic stainless steel (316L) additively manufactured using laser-powder bed fusion (L-PBF), tensile, nanoindentation, and micropillar compression tests were performed on samples in both the as-built (AB) and H-charged (HC) conditions. Microstructural characterization revealed that the electrochemical H charging exerted marginal effects on grains, phases, and overall dislocation densities of L-PBF 316L. However, the dislocation networks inherent to L-PBF 316L appear to disentangle upon H charging and are distributed more homogeneously through the matrix. Mechanical test results showed that H charging results in a marginal reduction in hardness and strength, indicating H-induced softening, possibly due to the elastic shielding effects of H that weaken the interactions between dislocations. The elastic shielding effect and the enhanced slip planarity, facilitate the H accumulation along slip bands and twins, promote H-enhanced localized plasticity, resulting cracking when a critical H concentration is reached. This, in turn, aids in H embrittlement mechanism that results in a significant loss in ductility upon H charging. A detailed discussion of all these micromechanisms is presented. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract By adopting in situ nano-mechanical testing in transmission electron microscope, we reveal that nanoscale helium bubbles can simultaneously enhance strength and ductility in small-volume single-crystal Al-4Cu pillars, which breaks the paradox of trade-off between strength and ductility. Nanoscale helium bubbles serve as internal dislocation sources and shearable obstacles, which promote dislocation nucleation and storage, and give rise to higher flow stress, controllable plasticity and larger uniform deformation in Al-4Cu pillars. Nanoscale helium bubbles are rather stable under plastic straining. Bubble coarsening and coalescence are only observed at final localized deformation regime. Graphical abstract Unlabelled Image [ABSTRACT FROM AUTHOR]

To ascertain the role of the solidification cell structures on the mechanical performance of Al-Si-(Mg) alloys processed using the laser powder bed fusion (LPBF) technique, micropillar compression tests were performed on LPBF Al-10Si-0.3Mg (AlSi10Mg). The alloy's microstructure consists of submicron-scale cellular structures, dense dislocation networks, and dispersed nanoscale Si precipitates. The stress-strain responses of the micropillars are devoid of pronounced serrations and the yield strength and work hardening behaviors are size-independent. A comparison of the micropillar compression responses of the LPBF AlSi10Mg, 316 L stainless steel and Inconel 718 alloy, and nano-and micro-crystalline alloys is made. In LPBF AlSi10Mg, the combination of dislocation networks and shear-resistant Si particles resist the dislocation motion significantly and enhance dislocation storage. This results in the cellular structure dominating the strength and plastic flow. These results show a pathway for designing high strength alloys via additive manufacturing. [Display omitted] [ABSTRACT FROM AUTHOR]

Objectives: Osteoradionecrosis of the mandible is a late radiation-induced complication, which is a major concern in survivors of head and neck cancer.Study Design: In this study, we present a case of a patient with nasopharyngeal carcinoma who developed extensive bilateral osteoradionecrosis of the ascending ramus of the mandible. After preoperative virtual surgical planning, the obtained data were used to fabricate patient-specific cutting templates. The bilateral mandibular defects were reconstructed using 2 separate flaps prepared from a single fibula.Results: Both defects were successfully reconstructed, and satisfactory aesthetic and functional results were achieved.Conclusions: Bilateral mandibular osteoradionecrosis can be managed with virtual surgical planning, and the defects can be reconstructed using 2 separate flaps prepared from a single fibula. [ABSTRACT FROM AUTHOR]

Energetic electron beams (e-beams) are used in the welding, 3D printing and imaging of various materials. It is commonly accepted that the e-beam irradiation inside transmission electron microscope has a negligible effect on the intrinsic mechanical properties of small-volume metallic materials during in situ investigation. However, as small-volume Al is usually covered by a thin layer of native oxide, we show here that high-energy (200 keV) e-beam irradiation can dramatically alter the deformation behavior. E-beam irradiation can drastically rejuvenate the amorphous structure of the oxide layer, producing a defective interface/surface, and promoting the transition of the deformation mode from internal dislocation multiplication to interface-dominated dislocation nucleation mediated plasticity, as indicated by the enhanced strain rate sensitivity and reduced activation volume. Moreover, the amorphous oxide layer undergoes viscous flow under the e-beam irradiation, such that nanoscale single-crystal Al confined by a 29% volume fraction of native oxide shell exhibits more than 60% uniform elongation. [ABSTRACT FROM AUTHOR]

Mechanically robust nanoscale metallic materials are highly desirable in many miniaturized devices. However, the lack of strain hardening and controllable plasticity plagues such small-volume metals. Using Al-4Cu alloy as an example, here we show that a submicron-sized metallic material with ultrathin native oxide shell exhibits a high degree of deformation controllability, unprecedented strain hardening, size strengthening and toughness, in uniaxial tensile deformation. The metal/native oxide “composite” is easy to make, and the emergent properties extend well beyond the benchmark range known for metals in a normalized (i.e., dimensionless) strength-toughness plot. The origin of the combination of strengthening and plastic stability is that an intact ultrathin native oxide shell exerts a strong confinement on dislocation movement and annihilation, thereby breaking the envelope on dislocation storage and strain hardening achievable in small-volume metals. [ABSTRACT FROM AUTHOR]

Solidification cells and a high density of dislocations are two common features of additively manufactured (AM) alloys that are processed using techniques such as laser powder bed fusion (L-PBF) and directed energy deposition (DED). A critical assessment of their role in determining the plastic properties (yield strength, σ y , and work hardening behavior) was performed via the micropillar compression tests on the austenitic 316L stainless steel (316L) and the Inconel 718 (IN718) alloys manufactured using the L-PBF and DED techniques, and comparing the results obtained with those of the compression and tensile tests on bulk samples. While both the L-PBF alloys contain submicron-scale cells whose boundaries are decorated with the dislocation networks, the DED 316L consists of micron-scale cells (whose boundaries are enriched with elemental segregation) with a uniform distribution of dislocations within them. The variations in σ y with the pillar size are similar to those reported on pillars fabricated from pre-strained Ni but are opposite to those reported on pillars of micro/nano-crystalline alloys. The mechanical responses of the DED 316L pillars with and without cell boundaries (CBs) are similar. These observations suggest that the high density of dislocations (arranged in the network fashion or distributed uniformly) —and not the CBs—determine σ y of the AM alloys. The stress-strain responses of pillars and transmission electron micrographs obtained on the deformed bulk samples suggest that the dislocation networks significantly enhance dislocation storage, leading to bulk-like deformation behaviors and superior work hardening capability in the L-PBF pillars with larger diameters. [Display omitted] [ABSTRACT FROM AUTHOR]

Currently, the effects of different tillage modes on greenhouse gas (GHG) emissions, carbon footprint (CF), energy budget and net ecosystem economic efficiency (NEEE) in rice fields remain unclear. In the present study, three tillage modes were tested, including rice conventional cultivation with intensive till (CT), conventional flat cultivation with no-till (FNT) and ridge cultivation with no-till (RNT) in Dafasi town, Wuxue city, Hubei province, China. This study for the first time evaluates the effects of RNT on agricultural GHG emissions, grain yield, CF, energy budget and NEEE. Compared with CT and FNT, RNT reduced the soil CH 4 emissions by 29.5% and 9.9%, respectively. CT resulted in 15.8% and 23.1% lower total GHG emissions than FNT and RNT, respectively, due to lower soil CH 4 emissions. Moreover, RNT significant decreased the CF by 35.7% and 18.2% relative to CT and FNT, respectively. The net energy, energy efficiency and energy productivity under RNT were 41.2%, 25.0% and 26.7% higher than those under CT, respectively, while the specific energy under RNT was 24.7% lower than that under CT. The NEEE under RNT was 1.66 and 1.20 folds of that under CT and FNT, respectively. In conclusion, this study recommends that RNT is an environmentally safe tillage mode for reducing GHG emissions and CF, and improving energy use efficiency and NEEE for rice production in China and similar agro-eco-regions elsewhere in the world. [ABSTRACT FROM AUTHOR]

Coke powders in the coking wastewater generated by petroleum refining industry needs to be removed to achieve water reuse for lack of water resources. This study developed a decoking hydrocyclone in the closed coking wastewater circulation treatment system to remove coke powders, which was highly efficient and environmentally friendly. Computational Fluid Dynamics (CFD) method was carried out to study the tangential velocity distribution index n-value to guide design of decoking hydrocyclone and experiment was conducted to verify the coke powders removal effect. It was found that the increase of n-value is conducive to the improvement of coke powders separation efficiency. A decoking hydrocyclone with a cone angle of 15° and an inlet size of 4 × 6 mm is the optimum hydrocyclone and the recovery efficiency of coke powders is stable at more than 90%. It is the first time for hydrocyclone successfully applied to the removal of coke powders in coking wastewater in the decoking process of petroleum refining industry, in which the separation efficiency of coke powders is considerably improved. Unlabelled Image • Solid-liquid hydrocyclone is first applied to remove coke powders in coking wastewater. • CFD method and tangential velocity distribution index n-value is studied to optimize the hydrocyclone. • Coke powders recovery rate is stable above 90% in industry application. [ABSTRACT FROM AUTHOR]

Using a modified laser powder bed fusion (LPBF) technique, a compositionally graded Cu-Ni alloy was fabricated. Through microstructural and mechanical characterization on the samples extracted from it, the addition of 7.6 wt.% Ni to Cu is identified as the minimum required for obtaining a crack-free and nearly-fully-dense coupons using LPBF. Subsequently, 3 wt.% Al was added to the Cu-7.6 wt.% alloy to deplete the solute Ni atoms from the matrix through the precipitation of Ni 3 Al upon aging of the LPBF Cu-Ni-Al alloy, which simultaneously enhances the strength and electrical conductance of the alloy. Through this example, we demonstrate the potential of high-throughput screening of alloys suitable for LPBF through the fabrication of the compositionally graded alloys and subsequent alloy design for optimum property combinations. [Display omitted] [ABSTRACT FROM AUTHOR]

Numerous studies have reported effects of straws with microbial decaying agents on greenhouse gas emissions from rice fields. However, studies regarding the effects of microbial decaying agents on carbon footprint and economic profit under diverse water regimes remained unclear. A two-factor field experiment was adopted to assess effects of different straw treatments (straw returning alone abbreviated as S, and straw returning with microbial decaying agent abbreviated as SMD) on CH 4 and N 2 O emissions, rice yield, carbon footprint, economic profit and net ecosystem economic profit (NEEP) from paddy field under different water regimes (continuous flooding abbreviated as F, and alternation of wetting and drying abbreviated as AWD) in central China. Compared with S treatment, SMD treatment significantly enhanced the crop water productivity by 7.9%−8.4% and the rice yield by 7.3%−7.7%. Though SMD treatment increased the economic profit by 9.9%−18.5%, and the NEEP by 9.6%−18.0% relative to S treatment, it also resulted in higher the CH 4 emissions by 12.7%−32.4% and global warming potential by 11.2%−21.5% regardless of water regimes. Water regimes had significant effects on the crop water productivity, rice yield, CH 4 and N 2 O emissions, global warming potential, economic profit, NEEP and carbon footprint. Compared with F treatment, AWD treatment improved the crop water productivity by 51.7%−79.4%, maintained rice yield, increased N 2 O emissions by 17.7%−40.0%, and mitigated CH 4 emissions by 33.2%−75.1%, which therefore resulted in lower global warming potential by 31.5%−69.8% and carbon footprint by 32.7%−66.0%. Moreover, AWD treatment significantly increased the economic profit by 25.4%−41.9% and the NEEP by 28.8%−46.6% relative to F treatment. Overall, the straw incorporated with microbial decaying agents is not an environmental friendly practice for the tradeoff of mitigation of CH 4 emissions and increase in economic profit. It is necessary to further optimize straw treatment for mitigating CH 4 emissions in order to develop rice sustainable production. • AWD irrigation reduced carbon footprint while increased economic profit. • Straws with microbial decaying agents increased rice yield and economic profit. • Straws with microbial decaying agents did not affect carbon footprint. • Straws with microbial decaying agents boosted CH 4 emissions and GWP. [ABSTRACT FROM AUTHOR]