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The viability of adapting HEAs or MEAs with single-phase structures, such as either FCC or BCC phases, for industrial applications is challenging due to the trade-offs in properties between different phases. Therefore, a novel high entropy alloy-medium entropy alloy composite coating based on a hard metal concept was designed using a CALPHAD approach, followed by experimental validation that included microstructural, mechanical and tribological analysis. A harder BCC/B2-based AlCoCrFeNi HEA powder was blended with a softer and more ductile FCC-based CoCrFeNi MEA to manufacture a composite coating using the HVOF process. The phase prediction, using Scheil simulation, which depicts non-equilibrium processing conditions experienced during the HVOF process, suggested the development of BCC, B2 and FCC phases, complementing XRD phase projections. The composite coating exhibited higher hardness than either single phase AlCoCrFeNi or CoCrFeNi coatings and achieved superior wear resistance under dry sliding conditions at elevated temperature, thereby, exhibiting potential for structural applications. Refereed/Peer-reviewed

Biochar amendments add persistent organic carbon to soil and can stabilize rhizodeposits and existing soil organic carbon (SOC), but effects of biochar on subsoil carbon stocks have been overlooked. We quantified changes in soil inorganic carbon (SIC) and SOC to 2 m depth 10 years after biochar application to calcareous soil. The total soil carbon (i.e., existing SOC, SIC, and biochar-C) increased by 71, 182, and 210% for B30, B60, and B90, respectively. Biochar application at 30, 60, and 90 t ha–1 rates significantly increased SIC by 10, 38, and 68 t ha–1, respectively, with accumulation mainly occurring in the subsoil (below 1 m). This huge increase of SIC (mainly CaCO3) is ∼100 times larger than the inorganic carbon present in the added biochar (0.3, 0.6, or 0.9 t ha–1). The benzene polycarboxylic acid method showed that the biochar-amended soil contained more black carbon particles (6.8 times higher than control soil) in the depth of 1.4–1.6 m, which provided the direct quantitative evidence for biochar migration into subsoil after a decade. Spectral and energy spectrum analysis also showed an obvious biochar structure in the biochar-amended subsoil, accompanied by a Ca/Mg carbonate cluster, which provided further evidence for downward migration of biochar after a decade. To explain SIC accumulation in subsoil with biochar amendment, the interacting mechanisms are proposed: (1) biochar amendment significantly increases subsoil pH (0.3–0.5 units) 10 years after biochar application, thus forming a favorable pH environment in the subsoil to precipitate HCO3–; and (2) the transported biochar in subsoil can act as nuclei to precipitate SIC. Biochar amendment enhanced SIC by up to 80%; thus, the effects on carbon stocks in subsoil must be understood to inform strategies for carbon dioxide removal through biochar application. Our study provided critical knowledge on the impact of biochar application to topsoil on carbon stocks in subsoil in the long term.

First reported in the early 2000s, a new generation of metals called ‘high-entropy alloys’ (HEAs) have the potential to outperform conventional alloys that rely on a primary base metal. The plethor...

The effect of lamellar orientation on the deformation behavior of eutectic high entropy alloy at the micrometer scale, and the roles of two rarely explored laminate orientations (i.e., the lamellar orientation at ∼ 0° and 45° angles with the loading direction) in regulating size-dependent plasticity were investigated using in-situ micropillar compression tests. The alloy, CoCrFeNiTa0.395, consists of alternating layers of Laves and FCC phases. It was found that the yield stress of the 0° pillars scaled inversely with the pillar diameters, in which the underlying deformation mode was observed to transform from pillar kinking or buckling to shear banding as the diameter decreased. In the case of the 45° pillars with diameters ranging from 0.4 to 3 μm, there exists a ‘weakest’ diameter of ∼ 1 μm, at which both constraint effect and dislocation starvation are ineffective. Irrespective of the lamellar orientations, the strain hardening rate decreased with decreasing pillar diameter due to the diminishing dislocation accumulation that originated from the softening nature of large shear bands in the 0° pillars, and the enhanced probability of dislocation annihilation at the increased free surfaces in the 45° pillars. The findings expand and deepen the understanding of the mechanical size effect in small-scale crystalline materials and, in so doing, provide a critical dimension for the development of high-performing materials used for nano- or microelectromechanical systems.

Cadmium pollution in the environment is ubiquitous and can be a serious health issue. Crop straw-based biochar is a promising adsorbent, yet few studies have systematically examined the effects of both feedstock and pyrolysis temperature on biochar efficacy for cadmium (Cd) sorption. Sorption-desorption experiments were conducted to explore the mechanisms of Cd sorption for biochars derived from wheat straw (WSB), rape straw (RASB), soybean straw (SSB), and peanut straw (PSB) feedstocks, which were produced by pyrolysis at 450 °C and 650 °C. For biochars pyrolyzed at 450 °C, the sorption capacities varied as PSB>SSB>RASB≈WSB, while the order changed as RASB≈WSB>PSB>SSB for 650 °C biochars. With the increase in pyrolysis temperature, for wheat straw biochar and rape straw biochars, Cd sorption capacities increased by 72% and 63%, while there were 61% and 63% decreases for peanut straw biochar and soybean straw biochar, respectively. Compared to the non-legume straw biochars (WSB and RASB), legume straw biochars (SSB and PSB) have higher sorption capacities for Cd. Peanut straw biochar (PSB) produced at 450 °C was found to be the most promising adsorbent for cadmium. Examination of the sorbed biochars using a range of analytical techniques indicated that 450 °C PSB immobilized cadmium by precipitation with non-electrostatic adsorption. The precipitation of Cd on 450 °C PSB was mainly induced by cation exchange between Cd with mineral cations, which caused Cd complexation with carboxyl functional groups.

Application of iron (Fe)- and silica (Si)-enhanced biochar compound fertilisers (BCF) stimulates rice yield by increasing plant uptake of mineral nutrients. With alterations of the nutrient status in roots, element homeostasis (e.g., Fe) in the biochar-treated rice root was related to the formation of biominerals on the plaque layer and in the cortex of roots. However, the in situ characteristics of formed biominerals at the micron and sub-micron scale remain unknown. In this study, rice seedlings (Oryza sativa L.) were grown in paddy soil treated with BCF and conventional fertilizer, respectively, for 30 days. The biochar-induced changes in nutrient accumulation in roots, and the elemental composition, distribution and speciation of the biomineral composites formed in the biochar-treated roots at the micron and sub-micron scale, were investigated by a range of techniques. Results of laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) showed that biochar treatment significantly increased concentrations of nutrients (e.g., Fe, Si, and P) inside the root. Raman mapping and vibrating sample magnetometry identified biochar particles and magnetic Fe nanoparticles associated with the roots. With Fe plaque formation, higher concentrations of FeOx− and FeOxH− anions on the root surface than the interior were detected by time-of-flight secondary ionization mass spectrometry (ToF-SIMS). Analysis of data from scanning electron microscopy energy-dispersive spectroscopy (SEM-EDS), and from scanning transmission electron microscopy (STEM) coupled with EDS or energy electron loss spectroscopy (EELS), determined that Fe(III) oxide nanoparticles were accumulated in the crystalline fraction of the plaque and were co-localized with Si and P on the root surface. Iron-rich nanoparticles (Fe–Si nanocomposites with mixed oxidation states of Fe and ferritin) in the root cortex were identified by using aberration-corrected STEM and in situ EELS analysis, confirming the biomineralization and storage of Fe in the rice root. The findings from this study highlight that the deposition of Fe-rich nanocomposites occurs with contrasting chemical speciation in the Fe plaque and cortex of the rice root. This provides an improved understanding of the element homeostasis in rice with biochar-mineral fertilization.

TiC nanoparticle-reinforced Mg−4Zn−0.5Ca matrix nanocomposites were processed by combining multidirectional forging (MDF) and extrusion (EX). The grain size of the nanocomposite after MDF+EX multi-step deformation was significantly decreased compared with that processed only by MDF. The average size of the recrystallized grains gradually increased after EX with increasing the number of MDF passes at 270 °C. However, the grain size significantly decreased by MDF processing at 310 °C. Both fine and coarse MgZn2 phases appeared in the (MDF+EX)-processed nanocomposites, and their volume fractions gradually increased with increasing the number of MDF passes before EX. Ultrahigh tensile properties (yield strength of ~404 MPa, ultimate tensile strength of ~450.3 MPa and elongation of ~5.2 %) were obtained in the nanocomposite after three MDF passes at 310 °C followed by EX. This was attributed to the refinement of the recrystallized grains, together with the improved Orowan strengthening provided by the precipitated MgZn2 particles that were generated by MDF+EX multi-step deformation.

The mechanical size effect of nanostructured, dual-phase CrCoNi medium-entropy alloy (MEA) was investigated by combining in-situ micro-compression testing with post-mortem electron microscopy analysis. The alloy possesses a superior yield strength up to ~4 GPa, primarily due to its hierarchical microstructure including column nanograins, preferred orientation, a high density of planar defects and the presence of the hexagonal close packed (HCP) phase. While the yield strength of the alloy has shown size-independency, the deformation behaviour was strongly dependent on the sample size. Specifically, with decreasing the pillar diameters, the dominant deformation mode changed from highly localized and catastrophic shear banding to apparently homogeneous deformation with appreciable plasticity. This transition is believed to be governed by the size-dependent critical stress required for a shear band traversing the pillar and mediated by the competition between shear-induced softening and subsequent hardening mechanisms. In addition, an unexpected phase transformation from HCP to face-centered cubic (FCC) was observed in the highly localized deformation zones, leading to strain softening that contributed to accommodating plasticity. These findings provide insights into the criticality of sample dimensions in influencing mechanical behaviors of nanostructured metallic materials used for nanoelectromechanical systems.

A new Mg-2.2 wt% Zn alloy containing 1.8 wt% Ca and 0.5 wt% Mn has been developed and subjected to extrusion under different extrusion parameters. The finest (~ 0.48 μm) recrystallized grain structures, containing both nano-sized MgZn2 precipitates and α-Mn nanoparticles, were obtained in the alloy extruded at 270 °C/0.01 mm s−1. In this alloy, the deformed coarse-grain region possessed a much stronger texture intensity (~ 32.49 mud) relative to the recrystallized fine-grain region (~ 13.99 mud). A positive work hardening rate in the third stage of work hardening curve was also evident in the alloy extruded at 270 °C, which was related to the sharp basal texture and which provided insufficient active slip systems. The high work hardening rate in the fourth stage contributed to the high ductility extruded at 270 °C/1 mm s−1. This alloy exhibited a weak texture, and the examination of fracture surface revealed highly dimpled surfaces. The optimum tensile strength was achieved in the alloy extruded at 270 °C/0.01 mm s−1, and the yield strength, ultimate tensile strength and elongation to failure were ~ 364.1 MPa, ~ 394.5 MPa and ~ 7.2%, respectively. Fine grain strengthening from the recrystallized fine-grain region played the greatest role in the strength increment of this alloy compared with Orowan strengthening and dislocation strengthening in the deformed coarse-grain regions.

In the present study, microstructural analysis was carried out to investigate the effect of substrate surface chemistry on splat formation. Ni powder was sprayed onto stainless steel substrates exhibiting two different surface conditions (polished and oxidized) by high-velocity oxy-fuel (HVOF) thermal spray. X-ray photoelectron spectroscopy (XPS) was employed to investigate the chemical state of the surfaces which indicated the presence of the adsorbates on the oxidized substrate. Single splats of different morphologies from both samples were examined using a range of characterization techniques including scanning electron microscopy (SEM), focused ion beam (FIB) microscopy and transmission electron microscopy (TEM) and energy-dispersive x-ray spectroscopy (EDS) interfaced to both SEM and TEM. This provided information on the particle solidification behavior and splat formation mechanism following impact on substrates with distinct surface conditions. The results showed the effect of oxidized surface adsorbates on splat morphology, pore formation and splat–substrate interactions. These microstructural findings, aided by theoretical models, revealed that a mixture of mechanical and metallurgical bonds exists between the splats and both substrates.

FeMnCoCrC high entropy alloy coatings were deposited onto high speed steel substrates using magnetron sputtering under a range of substrate bias voltages. These coatings exhibited a novel α-Mn crystal structure and highly refined columnar grains. Higher bias voltages promoted strong texture development through favouring (332)-oriented grains along the coating growth direction, as well as the formation of well-defined twin boundaries. The -80 V coating possessed a high hardness (~12.5 GPa), more than triple that of its fcc-structured bulk counterpart. This is attributed to the cumulative effects of the α-Mn structure, strong texture, grain refinement and the presence of twin boundaries.

To meet the needs of corrosion resistance and electrically conductivity for metallic bipolar plates that are employed in proton exchange membrane fuel cells (PEMFCs), a TiSiN nanocomposite coating was fabricated on to a Ti–6Al–4V substrate using reactive sputter-deposition through the double cathode glow discharge plasma technique. The microstructure of the TiSiN coating comprised nanocrystallite TiN grains embedded in an amorphous Si3N4 matrix. Electrochemical measurements were employed to investigate the corrosion behavior of the TiSiN coating in the simulated operating environments of a PEMFC, specifically 0.5 M H2SO4 solution containing different HF concentrations (namely 2, 4 and 6 ppm) at 70 °C pumped with H2 at the anode and air at the cathode. With increasing HF concentration, a higher corrosion current density and lower corrosion potential were observed from both the coating and the uncoated substrate, indicating that the addition of HF accelerated their corrosion rates under these conditions. Compared to the uncoated substrate, the TiSiN coating showed a markedly higher corrosion resistance at all HF concentrations. The passive film that formed on the TiSiN coating, with a resistance of the order of magnitude of ~107 Ω cm2, displayed good electrochemical stability and was less affected by changes in HF concentration. For the TiSiN coating, the values of interfacial contact resistance (ICR) were 14.7 mΩ cm−2 and 18.3 mΩ cm−2, respectively, before and after 2.5 h potentiostatic polarization with 6 ppm HF under cathodic conditions under a compaction pressure of 140 N cm−2. Both values are much lower than those for the bare substrate. Moreover, the TiSiN coating was shown to improve the hydrophobicity of Ti–6Al–4V that would help facilitate water management in the PEMFC operating environment. This coating, which exhibited excellent corrosion resistance, electro-conductivity and hydrophobicity, is therefore a promising material for protecting metallic bipolar plates from corrosive attack.

CeO2-x coatings were deposited under variable oxygen flow ratios (%fO2) onto Si substrates by reactive magnetron sputtering. Nanoindentation testing revealed an increase in the hardness, elastic modulus, H/E and H3/E2 ratio with increasing oxygen flow ratio, which in turn increased the adhesion and tribological performance of the coatings. Scratch testing yielded the highest critical load (LC2 = 28.8 N) and CPRS = 103 for the coating deposited with the highest oxygen flow ratio (57 %fO2). Cracking events during scratch testing were initiated by tensile forces behind the scratch stylus, which led to the formation of semi-circular ring cracks. As the normal load increased, transverse cracks emerged extending outwards from the scratch track towards the edge causing the exposure of substrate. Beyond LC2, severe spallation of the CeO2-x coatings led to coating failure. Furthermore, the specific wear rates of the CeO2-x coatings were determined to be within the ~10−15 m3/Nm range influenced by three-body abrasive wear. In-depth analyses from scratch and wear data indicates that these coatings possess good adhesion and durability.

The microstructure, texture and mechanical properties of a series of Mg–Zn–Ca–Mn alloys with three Zn/Ca ratios (2.63, 1.22 and 0.53, by weight ratio) were investigated. The dominant second phase changed from MgZn to Ca2Mg6Zn3 as the Zn/Ca ratio decreased from 2.63 to 1.22. With decreasing Zn/Ca ratio, the grain size of the as-cast alloys was significantly decreased, accompanied by an increase in the volume fraction of second phase. For as-extruded Mg–1.4Zn–2.6Ca–0.5Mn, the finest (~ 0.36 μm) recrystallized grain structures, containing both fine MgZn2 precipitates and α-Mn particles, were obtained at an extrusion speed of 0.01 mm/s. The texture of the deformed structure was more intense (~ 30.39 mud) relative to the recrystallized region (~ 8.33 mud). As the Zn/Ca ratio decreased, basal plane texture was weakened deriving from grain refinement following recrystallization. Superior mechanical properties with a yield strength of ~ 387.8 MPa and ultimate tensile strength of ~ 409.2 MPa were achieved in the Mg–1.4Zn–2.6Ca–0.5Mn alloy extruded at 270 °C at an extrusion speed of 0.01 mm/s. A number of factors were determined to contribute to strengthening including Hall–Petch effects from the fine recrystallized grains (contribution ~ 58.7%), dislocation strengthening of the deformed region (contribution ~ 29.3%) and Orowan strengthening (contribution ~ 12%).

The effect of chromium substrate preheating on the spreading behavior of plasma-sprayed nickel splats was characterized. The interfacial features along the splat-substrate interface were analyzed by focused ion beam (FIB) microscopy and transmission electron microscopy (TEM). In addition, the transient droplet spreading process was modelled in a simulation study. The results showed that the presence of a large fraction of surface moisture on the substrates induced splat fragmentation. However, splat fragmentation was completely constrained on chromium preheated to a low temperature (373 K) where a certain amount of surface moisture was still present. The high thermal conductivity of chromium substrates increased droplet solidification rates, decreasing the interaction time between the spreading droplet and the vaporized gas layer. Accordingly, splat fragmentation was suppressed and disk-shaped splats were formed. Fast solidification not only refined the final splat microstructure, but also promoted the formation of finger-splashed disk splats. In addition, the extent of elemental diffusion across the splat-substrate interface was decreased due to the low interfacial temperature.

Fe-modified biochar has been shown to have high sorption ability for cadmium (Cd), while Cd immobilization effects of Fe-modified biochars with Si-rich and S-rich feedstocks have been rarely addressed. To explore the effects of Fe-modified Si-rich and S-rich biochars on Cd translocation in the soil-rice system, a pot experiment was carried out with an acidic Cd-contaminated sandy loam paddy from central South China and a late season rice cultivate during July to November 2018. Rice straw and rice husk were chosen as Si-rich feedstocks, and rape straw was applied as S-rich feedstock, these feedstocks were further collected and pyrolyzed at 450 °C. Pristine and Fe-impregnated rice straw (BRS/BRS-Fe), rice husk (BRH/BRH-Fe) and rape straw (BRE/BRE-Fe) biochars were applied at 0 and 10 t/ha, respectively. The reductions in Cd concentrations in rice grains were 23.8%, 22.3% and 46.1% with treatments of BRE, BRS and BRH, respectively, compared to the control. Compared to other pristine biochars, BRH is more effective in Cd remediation in paddy soil. For Fe-modified biochars, BRE-Fe achieved the highest reductions in Cd concentrations in rice grains with 46.7% and 30.1%, compared with the control and BRE, respectively. BRE-Fe decreased Cd remobilization from leaves to grains. Only BRE-Fe enhanced the formation and Cd sorption capacity of iron plaque. BRS-Fe and BRH-Fe enhanced Fe content in rice plants, which might induce the reduction in iron plaque formation. Fe and S-contained complexes contents increased in the contaminated pristine biochar particles, but reduced in the contaminated BRE-Fe particles. Therefore, Fe modification could not enhance Cd immobilization effect of Si-rich biochar, while Fe modified S-rich biochar has promising potential for Cd remediation with enhancement in iron plaque formation and Cd fixation in rice leaves.

Biochar-based compound fertilisers (BCF) are gaining increasing attention as they are cost-effectiveness and improve soil fertility and crop yield. However, little is known about the mechanisms by which micron-size BCF particles enhance crop growth. In the present study, Wuyunjing7 rice seedlings were exposed to micron-size particles of wheat straw-based BCF (mBCF) diffused through a 25-μm nylon mesh. The control was fertilised with urea, diammonium phosphate, and potassium chloride to ensure that both treatments received comparables level of N, P, and K. The effects of mBCF on rice seedling growth were evaluated by determining the changes in nitrogen uptake and utilisation via nitrogen content measurements, short-term

The effect of Ag additions on the structural, mechanical and thermodynamic properties of α-Nb5Si3 is systematically investigated using the first-principles calculations based on density functional theory. The calculated formation enthalpies show that when Nb atoms in α-Nb5Si3 are replaced by one and two Ag atoms, Ag atoms prefer Nb4c sites rather than Nb16l sites. With increasing concentration of Ag atoms, the elastic moduli and theoretical Vickers hardness of the α-(Nb1-xAgx)5Si3 compounds decrease, while they become more ductile. Ag additions slightly raise the mechanical anisotropies of α-(Nb1-xAgx)5Si3 compounds and increases the linear thermal expansion coefficients of the α-(Nb1-xAgx)5Si3 compounds along the c and a axes, with a decrease in the αc/αa ratios. Finally, the anisotropy of acoustic velocities and Debye temperatures for the α-(Nb1-xAgx)5Si3 compounds were also calculated.