Robust Low-Friction and Low-Wear TiNbMoTaCr High-Entropy Film Enabled by Periodically Inserting Curved MoS2 Sheets.

The well-known integration of physical, chemical, and mechanical properties enables high-entropy alloys (HEAs) to be applied in various fields; however, refractory HEAs are brittle and susceptible to abrasive wear at high coefficients of friction (COF), resulting in insufficient mechanical durability against abrasion. Herein, curved MoS2 nanosheets are periodically introduced into the TiNbMoTaCr film for triggering the self-assembly mixed metal oxides @MoS2 nanoscrolls, which contain hard mixed metal oxides cores and the low-shearing lubricant MoS2 shells, during the friction in the air environment; such mixed metal oxides@MoS2 nanoscrolls in the friction interfaces can contribute to the robust low friction and low wear. Compared to the pure TiNbMoTaCr film (with high COF of ∼0.78, low abrasive durability identified by worn-out event), the periodic incorporation of 10 nm thickness curved MoS2 sheets can successfully achieve a low COF of ∼0.08 and low wear rate of ∼9.561 × 10-8 mm3/ Nm, much lower than the pure MoS2 film (COF = ∼ 0.21, wear rate = ∼ 1.03 × 10-6 mm3/ Nm). Such superior tribological properties originate from the cooperative interaction of TiNbMoTaCr nanolayers and curved MoS2 nanosheets, accompanied by the self-assembly of mixed metal oxides@MoS2 nanoscrolls. In these nanoscrolls, TiNbMoTaCr can act as an 'air-absorbing agent' to form high-loading mixed metal oxide cores and serve as an 'oxygen sacrificer,' preventing the low-shearing lubricant curved MoS2 nanosheets from oxidation. In addition, even with the soft MoS2, the hardness of the TiNbMoTaCr/MoS2 nanomultilayers can still be well maintained and increased above the calculated values by mixing law, further favoring superior mechanical durability. The synergetic effect of TiNbMoTaCr and curved MoS2 nanosheets during the friction in air can provide a route to design HEA films with enhanced tribological properties for better mechanical durability and broader application prospects.

Bamboo-like dual-phase nanostructured copper composite strengthened by amorphous boron framework.

Grain boundary engineering is a versatile tool for strengthening materials by tuning the composition and bonding structure at the interface of neighboring crystallites, and this method holds special significance for materials composed of small nanograins where the ultimate strength is dominated by grain boundary instead of dislocation motion. Here, we report a large strengthening of a nanocolumnar copper film that comprises columnar nanograins embedded in a bamboo-like boron framework synthesized by magnetron sputtering co-deposition, reaching the high nanoindentation hardness of 10.8 GPa among copper alloys. The boron framework surrounding copper nanograins stabilizes and strengthens the nanocolumnar copper film under indentation, benefiting from the high strength of the amorphous boron framework and the constrained deformation of copper nanocolumns confined by the boron grain boundary. These findings open a new avenue for strengthening metals via construction of dual-phase nanocomposites comprising metal nanograins embedded in a strong and confining light-element grain boundary framework.

Pt-induced atomic-level tailoring towards paracrystalline high-entropy alloy.

Paracrystalline state achieved in the diamond system guides a direction to explore the missing link between amorphous and crystalline states. However, such a state is still challenging to reach in alloy systems in a controlled manner. Here, based on the vast composition space and the complex atomic interactions in the high-entropy alloys (HEAs), we present an "atomic-level tailoring" strategy to create the paracrystalline HEA. The addition of atomic-level Pt with the large and negative mixing enthalpy induces the local atomic reshuffling around Pt atoms for the well-targeted local amorphization, which separates severe-distorted crystalline Zr-Nb-Hf-Ta-Mo HEA into the high-density crystalline MRO motifs on atomic-level. The paracrystalline HEA exhibits high hardness (16.6 GPa) and high yield strength (8.37 GPa) and deforms by nanoscale shear-banding and nanocrystallization modes. Such an enthalpy-guided strategy in HEAs can provide the atomic-level tailoring ability to purposefully regulate structural characteristics and desirable properties.

Biochar and Intercropping With Potato-Onion Enhanced the Growth and Yield Advantages of Tomato by Regulating the Soil Properties, Nutrient Uptake, and Soil Microbial Community.

The application of biochar stimulates the activities of microorganisms that affect soil quality and plant growth. However, studies on the impacts of biochar mainly focus on a monoculture, its effects on interspecific interactions are rarely reported. Here, we investigated the impacts of biochar on tomato/potato-onion intercropped (TO) in a pot experiment. Tomato monoculture (T) and TO were treated with no, 0.3, 0.6, and 1.2% biochar concentrations in a pot experiment. Microbial communities from tomato rhizosphere soil were analyzed by quantitative PCR and Illumina MiSeq. The results showed that compared with the tomato monoculture, 0.6%TO and 1.2%TO significantly increased tomato yield in 2018. TO and 1.2%TO significantly increased plant height and dry weight in 2018 and 2019. Biochar treatments increased soil pH, decreased NO 3 - -N and bulk density, and increased the absorption of N, P, and K by tomato. Bacterial and fungal abundances increased with an increase in biochar concentration, while Bacillus spp. and Pseudomonas spp. abundances showed an "increase-decrease-increase" trend. Biochar had a little effect on bacterial diversities but significantly lowered fungal diversities. TO, 0.6%TO, and 1.2%TO increased the potentially beneficial organisms (e.g., Pseudeurotium and Solirubrobacter) and lowered the potentially pathogenic organisms (e.g., Kribbella and Ilyonectria). Different concentrations of biochar affected the bacterial and fungal community structures. Redundancy analysis indicated that the bacterial community was strongly correlated with soil pH, NO 3 - -N, and EC, while the fungal community was closely related to soil NO 3 - -N and moisture. The network analysis showed that biochar and intercropping affected the symbiosis pattern of the microorganisms and increased the proportion of positive interactions and nitrifying microorganisms (Nitrospirae) in the microbial community. Overall, our results indicated that monoculture and intercropping with biochar improved soil physicochemical states and plant nutrient absorption, and regulated soil microbial communities, these were the main factors to promote tomato growth and increase tomato productivity.

Characteristics of annual N2O and NO fluxes from Chinese urban turfgrasses.

Urban turfgrass ecosystems are expected to increase at unprecedented rates in upcoming decades, due to the increasing population density and urban sprawl worldwide. However, so far urban turfgrasses are among the least understood of all terrestrial ecosystems concerning their impact on biogeochemical N cycling and associated nitrous oxide (N2O) and nitric oxide (NO) fluxes. In this study, we aimed to characterize and quantify annual N2O and NO fluxes from urban turfgrasses dominated by either C4, warm-season species or C3, cool-season and shade-enduring species, based on year-round field measurements in Beijing, China. Our results showed that soil N2O and NO fluxes varied substantially within the studied year, characterizing by higher emissions during the growing season and lower fluxes during the non-growing season. The regression model fitted by soil temperature and soil water content explained approximately 50%-70% and 31%-38% of the variance in N2O and NO fluxes, respectively. Annual cumulative emissions for all urban turfgrasses ranged from 0.75 to 1.27 kg N ha-1 yr-1 for N2O and from 0.30 to 0.46 kg N ha-1 yr-1 for NO, both are generally higher than those of Chinese natural grasslands. Non-growing season fluxes contributed 17%-37% and 23%-30% to the annual budgets of N2O and NO, respectively. Our results also showed that compared to the cool-season turfgrass, annual N2O and NO emissions were greatly reduced by the warm-season turfgrass, with the high root system limiting the availability of inorganic N substrates to soil microbial processes of nitrification and denitrification. This study indicates the importance of enhanced N retention of urban turfgrasses through the management of effective species for alleviating the potential environmental impacts of these rapidly expanding ecosystems.