Search Results (477)

This paper reviews the fracture mechanics parameters associated with the variability in the crack growth curves associated with forty-two different tests that range from additively manufactured (AM) steels to cold spray additively manufactured (CSAM) 316L steel. As a result of this review, it is found that, to a first approximation, the effects of different building processes and R-ratios on the relationship between ΔK and the crack growth rate (da/dN) can be captured by allowing for changes in the fatigue threshold and the apparent cyclic toughness in the Schwalbe crack driving force (Δκ). Whilst this observation, when taken in conjunction with similar findings for AM Ti-6Al-4V, Inconel 718, Inconel 625, and Boeing Space Intelligence and Weapon Systems (BSI&WS) laser powder bed (LPBF)-built Scalmalloy^®, as well as for a range of CSAM pure metals, go a long way in making a point; it is NOT a mathematical proof. It is merely empirical evidence. As a result, this review highlights that for AM and CSAM materials, it is advisable to plot the crack growth rate (da/dN) against both ΔK and Δκ. The observation that, for the AM and CSAM steels examined in this study, the da/dN versus Δκ curves are similar, when coupled with similar observation for a range of other AM materials, supports a prior study that suggested using fracture toughness measurements in conjunction with the flight load spectrum and the operational life requirement to guide the choice of the building process for AM Ti-6Al-4V parts. The observations outlined in this study, when taken together with related findings given in the open literature for AM Ti-6Al-4V, AM Inconel 718, AM Inconel 625, and BSI&WS LPFB-built Scalmalloy^®, as well as for a range of CSAM-built pure metals, have implications for the implementation and certification of limited-life AM parts. Full article

Today, PHB and its copolymers—potential plastic substitutes—are produced by fermenting sugar, which is not scalable to the volumes of plastic consumption. PHB from CH₄ can offer a sustainable process route, with CH₄ potentially produced from a variety of waste biomass streams through anaerobic digestion, gasification, and methanation. The high molar mass (M_w) of PHB is a key determinant of its mechanical properties, and strain, culture conditions and downstream processing influence it. In this work, the strain Methylocystis sp. GB 25 (DSMZ 7674) was grown on natural gas as the sole carbon and energy source and air (1:1) in a loop reactor with 350 L active fermentation volume, at 35 °C and ambient pressure. After two days of continuous growth, the bacteria were limited in P and N for 1, 2, and 2.5 days to determine the optimal conditions for PHB accumulation and the highest Mw as the target. The biomass was then centrifuged and spray-dried. For downstream processing, chloroform solvent extraction and selected enzymatic treatment were deployed, yielding ~40% PHB from the biomass. The PHB obtained by solvent extraction exhibited high average weight molar masses of M_w ~1.1–1.5 × 10⁶ g mol⁻¹. The highest M_w was obtained after one day of limitation, whereas enzyme treatment resulted in partially degraded PHB. Cold chloroform maceration, interesting due to energy savings, did not achieve sufficient extraction efficiency because it was unable to extract high-molar-mass PHB fractions. The extracted PHB has a high molar mass, more than double that of standard commercial PHB, and was characterized by DSC, which showed a high degree of crystallinity of up to 70% with a melting temperature of close to 180 °C. Mechanical tensile properties measurements, as well as dynamic mechanical thermal analysis (DMTA), were performed. Degradation of the PHB by enzymes was also determined. Methanotrophic PHB is a promising bioplastics material. The high M_w can limit and delay polymer degradation in practical processing steps, making the material more versatile and robust. Full article

The impact and solidification of multiple molten droplets on a cold substrate critically influence the quality and performance of thermally sprayed coatings. We present a Smoothed Particle Hydrodynamics (SPH) model that couples fluid-solid interaction, wetting, heat transfer and phase change to simulate multi-droplet impact and freezing. The model is validated against benchmark cases, including the Young–Laplace relation, wetting dynamics, single-droplet impact and the Stefan solidification problem, showing good agreement. Using the validated model, we investigate two droplets—either centrally or off-centrally—impacting on a cold surface. Simulations reveal two distinct solidification patterns: convex pattern (CVP), which results in a mountain-like splat morphology, and concave pattern (CCP), which leads to a valley-like shape. The criterion for the two patterns is explored with two dimensionless numbers, the Reynolds number $Re$ and the Stefan number $Ste$. When $Re\le 17.8$, droplets tend to solidify in CVP; at higher Reynolds numbers $Re\ge 18.8$, they tend to solidify in CCP. The transition between the two patterns is primarily governed by $Re$, with $Ste$ exerting a secondary influence. For example, when droplets have $Re=9.9$ and $Ste=5.9$, they tend to solidify in a convex pattern, whereas at $Re=19.8$ and $Ste=5.9$, they tend to solidify in a concave pattern. Also, the solidification state of the first droplet greatly influences the subsequent spreading and solidification of the second droplet. A parametric study on CCP cases with varying vertical and horizontal offsets shows that larger vertical offsets accelerate solidification and reduce the maximum spreading factor. For small vertical distances, the solidification time increases with horizontal offset by more than 29%; for large vertical distances the change is minor. These results clarify how droplet interactions govern coating morphology and thermal evolution during thermal spraying. Full article

Frost accumulation on heat exchangers severely limits the efficiency and reliability of air-source heat pumps (ASHPs) in cold, humid environments. Superhydrophobic coatings fabricated via electrostatic spraying offer a promising energy-free strategy for frost suppression. In this study, a robust superhydrophobic coating was deposited on the heat exchanger of a residential ASHP using this scalable technique. Under low-temperature heating conditions (2/1 °C), the coated exchanger delayed frost completion by a factor of 2.83 and shortened defrosting time by 33.3% compared to a conventional hydrophilic counterpart. These improvements translated to a 6.24% increase in average heating capacity and a 2.83% gain in the coefficient of performance (COP). Although the thicker superhydrophobic coating resulted in a marginal 3.1% reduction in cooling capacity during free-cooling operation, the significant enhancements in frost resistance and heating performance underscore its practical value. This work demonstrates that electrostatic spraying is a viable and effective method for fabricating high-performance superhydrophobic heat exchangers, paving the way for more efficient and frost-resistant ASHPs. Full article

This work investigates the penetration behavior of SiC particles into Digital Light Processing (DLP)-printed thermoset substrates under low-pressure cold-spray conditions, aiming to enhance surface hardness and wear resistance. A coupled simulation framework was established in which particle acceleration was obtained from CFD using ANSYS Fluent, and high-speed impact and embedding were modeled through ANSYS Explicit Dynamics. Two particle diameters (25 μm and 60 μm) were examined across inlet pressures from 2 to 5 bar to evaluate both the continuous influence of pressure and the two-level effect of particle size. Mesh convergence was achieved at a resolution of d_p/20, ensuring numerical stability and computational efficiency. The results showed a strong dependence of penetration depth on pressure and particle size: for 25 μm particles, penetration increased from 0.76 d_p at 2 bar to 1.53 d_p at 5 bar, while 60 μm particles exhibited deeper absolute embedding due to their significantly higher kinetic energy. Response-surface analysis further revealed nonlinear pressure effects and a predominantly linear size-dependent shift. Experimental validation at 3 bar confirmed a penetration depth of approximately 1 d_p, demonstrating good agreement between simulation and physical observation. Overall, the validated workflow provides quantitative insight into particle–substrate interaction in thermoset polymers and offers a practical basis for controlled particle embedding as a surface-strengthening strategy in additive manufacturing. Full article

Many special structures such as pipeline, revolving gears, and tanks suffer from biofouling used in marine environment, which could induce serious results in the ship system such as blockage and stuck, consequently lead to failure of the mechanical system and power system. Generally, coatings with antifouling agents are used for protecting metal structures from biofouling, but coatings are not conveniently applicable in the high velocity flowing seawater and narrow space. Electrochlorination and electrolysis of copper and aluminum anode are usually used in these circumstances, but the electric power will lead to stray current corrosion to the component. For the sake of convenience and safety, Cu-Ti pseudo alloy antifouling anode was proposed in this work for antifouling in pipeline and other narrow spaces without external electric power. Four Cu-Ti pseudo alloy antifouling anodes with different Ti contents (mass fraction) of 0 wt.%, 5 wt.%, 10 wt.%, and 15 wt.% were investigated with computational method, and a 15 wt.% Ti content Cu-Ti pseudo alloy antifouling anode was prepared by cold spray, and the microstructure and composition of the anode were observed by scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS). Electrochemical tests were conducted to obtain the corrosion potential, potentiodynamic polarization curve, and micro zone electrochemical information in natural seawater, and the Cu ions releasing behavior were analyzed using inductively coupled plasma (ICP). The results indicated that in natural seawater, copper particles, and titanium particles on the surface of anode samples can form micro galvanic couples. With the increase in Ti mass fraction, the number of micro primary cells composed of copper particles and titanium particles increases, and the corrosion rate of Cu particles increased. When the Ti mass fraction is 15%, the corrosion rate is the fastest, and the copper ion release rate increases by nearly ten times, reaching 147 μg/(cm²·d). This method can effectively accelerate the releasing rate of Cu ions in Cu-Ti pseudo alloy anode and promote the antifouling effect. Full article

This study evaluated the effects of pre-harvest hexanal and post-harvest 1-methylcyclopropene (1-MCP) treatments on bitter pit incidence and fruit quality in ‘Arisoo’ apples during cold storage. Hexanal (0.02%) was sprayed on trees twice, 18 and 8 days before harvest, and 1-MCP (1 μL·L⁻¹) was applied by fumigation immediately after harvest. Treated apples were subsequently stored at 0.5 ± 1 °C for 5 months. At harvest, the control group showed an incidence rate of 20.6% and a severity score of 0.34, while the hexanal-treated group had a reduced incidence of 13.2% and a severity score of 0.18. Fruit quality parameters did not differ significantly between the control and hexanal-treated groups at harvest. During cold storage, spot incidence significantly increased in the control after 2 months and reached 60.5% after 5 months. In contrast, bitter pit incidence in the hexanal and 1-MCP-treated groups was lower after 5 months, at 46.6% and 47.1%, respectively. No significant difference in spot severity was observed between the hexanal and 1-MCP treatments. Polyphenol oxidase activity increased in all treatments during storage, but both hexanal and 1-MCP significantly inhibited this increase compared to the control. Total sugar and uronic acid contents decreased across all treatments during storage. However, the hexanal and 1-MCP treatments mitigated this reduction relative to the control. At the end of storage, apples treated with 1-MCP had lower internal ethylene concentrations and higher flesh firmness compared to both the control and hexanal-treated apples. In conclusion, pre-harvest hexanal application reduced the bitter pit incidence at harvest and during storage, while post-harvest 1-MCP provided a similar reduction effect and better preserved fruit quality during cold storage. Full article

This study employs numerical simulations and experiments to examine the cold spray deposition of nanostructured hydroxyapatite (Ca₁₀(PO4)₆(OH)₂, HA)/70wt.%Ti composite particles under different processing conditions, based on the features of nanocomposites that strengthen interfacial adhesion and improve coating interfacial strength. Using ABAQUS/CAE combined with LS-PrePost 4.9-x64 software, the deposition behavior of the composite particles during deposition under various impact velocities was analyzed, along with the stress of the HA and Ti particles within the composite particle. The deposition behavior of both single and multiple composite particles under different gas temperatures was studied through cold spray experiments, and composite coatings were fabricated. The microstructure and phase composition were analyzed using scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results showed that the numerical simulations were consistent with the experimental analyses. As the particle velocity or gas temperature increased, the degree of particle deformation upon deposition became more pronounced, accompanied by phenomena such as cracking or fragmentation and splashing rebound. At a gas temperature of 700 °C, both the bonding density of individual particles and the bonding effectiveness of multi-particle deposits were lower than those achieved at 500 °C. The coating prepared at a gas temperature of 500 °C exhibited a flatter surface, better overall bonding with the Ti interlayer, and higher internal density. Full article

Fresh figs are a highly perishable fruit with a very limited shelf life. Consequently, the development of innovative strategies at both the preharvest and postharvest stages is essential to enhance their quality and extend their shelf life. This study aimed to evaluate the postharvest performance of fresh figs (cv. Calabacita) treated preharvest with oxalic acid (OA) via foliar spraying at 1.2 L per tree at two concentrations (1 and 2 mM), applied either twice or three times. Figs were harvested at commercial maturity and stored for 10 days at 1 °C and 90% relative humidity in darkness, with sampling carried out at 0, 3, 7 and 10 days. At each sampling point, physiological, physicochemical, and bioactive parameters were assessed, and an analysis of variance was performed to determine differences among OA treatments. The findings showed that the effectiveness of OA depended on the number of applications, with two preharvest sprays providing the most favourable outcomes. OA at 2 mM significantly reduced weight loss, respiration rate, and ethylene production compared with controls and increased titratable acidity. Furthermore, all OA treatments enhanced the antioxidant activity of the fruit, improving both enzymatic and non-enzymatic antioxidant activity, as well as total phenolic content. This suggests improved stress tolerance supported by lower cell wall oxidation at the end of cold storage. In conclusion, two preharvest applications of oxalic acid effectively contribute to maintaining fruit quality and extending the storability of fresh figs during cold storage. Full article

We present a new finite element framework for modeling compressible, turbulent multiphase flows with heat transfer. For two-fluid systems with a free surface, the Volume of Fluid (VOF) method is implemented without the need for interface reconstruction, while turbulence is resolved using a dynamic Vreman large eddy simulation (LES) model. Unlike most two-phase VOF studies, which neglect heat transfer, the present approach incorporates energy transport equations within the VOF formulation to account for heat exchange, an effect particularly important in turbulent flows. Conjugate heat transfer is often challenging in finite volume methods, which require explicit specification of heat fluxes at the solid–fluid interface, limiting accuracy and predictive capability. By contrast, the finite element formulation does not require heat flux inputs, allowing more accurate and robust simulation of heat transfer between solids and fluids. The method is demonstrated through three representative cases. First, a two-fluid instability with a single-mode perturbation is simulated and validated against analytical growth rates. Second, conjugate heat transfer is examined in a high-temperature flow over a cold metal cylinder, with validation performed both quantitatively—via pressure coefficient comparisons with experimental data—and qualitatively using vector field topology. Finally, compressible spray injection and breakup are modeled, demonstrating the ability of the framework to capture interfacial dynamics and atomization under turbulent, high-speed conditions. In the compressible spray injection and breakup case, the results indicate that the finite element formulation achieved higher predictive accuracy and robustness than the finite-volume method. With the same mesh resolution, the FEM reduced the root mean square error (RMSE) and mean absolute percentage error (MAPE) from 6.96 mm and 26.0% (for the FVM) to 4.85 mm and 12.7%, respectively, demonstrating improved accuracy and robustness in capturing interfacial dynamics and heat transfer. The study also introduced vector field topology to visualize and interpret coherent flow structures and instabilities, offering insights beyond conventional scalar-field analyses. Full article

Cold-spray additive manufacturing (CSAM) is an emerging solid-state deposition technology that effectively mitigates common defects associated with conventional thermal processes, such as oxidation, phase transformation, and residual stresses. In this study, copper–titanium (Cu-Ti) composite coatings were fabricated via high-pressure CSAM using mixed powders with Ti contents of 3, 6, and 10 wt.%. The influence of Ti content and post-heat treatment (350–400 °C) on the tensile properties of the composites was systematically investigated. The results indicate that the ultimate tensile strength (UTS) remained consistently within the range of 265–285 MPa under all conditions, showing only a mild positive correlation with Ti content. In contrast, ductility was significantly influenced by Ti addition, with elongation decreasing markedly as the Ti content increased. Notably, the composite with 3 wt.% Ti heat-treated at 400 °C exhibited a well-balanced combination of tensile strength (270 MPa) and ductility (20% elongation). These findings demonstrate that CSAM-fabricated Cu-Ti composites possess attractive mechanical properties, which can be tailored through Ti content and heat treatment. Full article

Marine engineering equipment operates under extreme conditions such as high salinity, humidity, and flow velocity during marine resource exploration. These harsh environments impose strict requirements on surface performance, especially in terms of wear and corrosion resistance. Wear-resistant coatings are increasingly regarded as a crucial surface engineering approach to mitigate multi-mechanism degradation and improve the long-term reliability of marine equipment. In this review, the typical wear mechanisms in marine environments are systematically analyzed. Corresponding to different service scenarios, the main categories of coating materials, such as metal matrix composite coatings, cermet coatings, functionally graded coatings, and nanolayered coatings are summarized in terms of their structure and performance characteristics. Furthermore, mainstream fabrication techniques, including high-velocity oxy-fuel (HVOF), high-velocity air-fuel (HVAF), laser cladding, cold spray, and physical/chemical vapor deposition (PVD/CVD), are reviewed with respect to their influence on coating micro-structure and properties. Standardized evaluation methods for coating performance are also discussed. Finally, the current research challenges are identified, and future development trends are outlined, with an emphasis on multifunctional, intelligent, and environmentally friendly coating systems. This work aims to provide a systematic reference and theoretical basis for the design and application of wear-resistant coatings in marine environments. Full article

The increasing prominence of blade icing in wind power generation within cold regions has positioned anti-icing coating technology as a key research focus. This study synthesised phase-change microcapsules using bio-wax as the core material and isophorone diisocyanate as the shell material via interfacial polymerisation. These microcapsules were then compounded with polyurethane to form an anti-icing coating, whose properties and anti-icing performance were systematically investigated. Key findings indicate that a 1% emulsifier concentration yielded microcapsules with a concentrated particle size distribution (≈20 μm). Microcapsules with a core-to-shell ratio of 7:3 exhibited optimal thermal storage performance, characterised by a melting enthalpy of 49.73 J/g and an encapsulation efficiency of 78%, establishing this as the optimal formulation. Icing wind tunnel tests demonstrated enhanced anti-icing efficacy with increasing microcapsule concentration. At 36% concentration, the coating achieved an anti-icing efficiency of 65.80% under conditions of −15 °C and 3 m/s wind speed, and 64.05% at −10 °C and 6 m/s. The coating maintained its effectiveness under high wind speeds, though its performance diminished with increased water spray flux. The coating functioned by delaying ice formation through phase-change heat release. It consistently demonstrated an anti-icing efficiency exceeding 60% across operational conditions −15 °C to −5 °C and wind speeds of 3–9 m/s. This work provides an efficient and environmentally friendly anti-icing solution for wind turbine blades in cold regions. Full article

This study investigated the microstructure and corrosion behavior of 30MnB5 hot-stamped steel after applying a zinc coating using the cold-spraying method followed by heat treatment (HT). Al-10 wt%Si coating is essential for improving the high-temperature corrosion resistance of 30MnB5 steel during the hot-stamping process. Before HT, the coating layer primarily consisted of Al, whereas after HT, Fe–Al-based intermetallic compounds were formed throughout the layer. The Zn in the coating layer applied using the cold-spraying method was not uniformly distributed before HT. However, during HT, the low-melting-point Zn melted and re-solidified, allowing it to combine with Fe diffusing from the substrate. Consequently, Zn–Al–Fe-based intermetallic compounds were formed on the surface of the coating layer. In the Zn-coated specimens, the current density near the corrosion potential tends to be lower than that of the Al–Si-coated specimens because Zn corrodes preferentially owing to its sacrificial anode effect, thereby protecting the underlying Al–Si-coated layer and steel. Full article

As cold spray additive manufacturing matures, significant efforts are being made to develop spray conditions for more challenging materials, thereby expanding the technology’s range of applications. One main challenge while using commercially available equipment is that, even under optimized conditions, deposition efficiency remains low for some materials. Powder particles that do not adhere are wasted, which can severely affect the process economics, especially in a mass production context and/or when expensive feedstocks are used. Powder recovery and reuse is a logical solution to mitigate this problem, yet few studies evaluate its feasibility and its impact on powder characteristics and ultimately coating performance. In this work, powder recovery was investigated for two cases: a Ni powder and a NdFeB-Al powder mix, used respectively for repair applications and for the fabrication of permanent magnets. A prototype recovery system was built, achieving a recovery efficiency of up to 75%. The powders were recovered after up to four spray runs, and their morphology and size distribution were characterized. The magnetic properties of both powders and coatings were evaluated using hysteresis measurements. Although the process affects the particle size distribution and their magnetic properties, powders remain suitable for re-deposition for both materials. In particular, it was shown that NdFeB-Al mix maintains 97% of its initial magnetic performance under industrial operating conditions. Full article