Uncoated Material Research Articles

Ceramic-metal Composite Coating on Steel Using a Powder Compact Tool Electrode by the Electro-Discharge Coating Process

In this work, using a powder compact tool electrode prepared with TiC-Cu powder mixture a TiC-Cu composite coating was deposited on AISI 1020 steel by the electro-discharge coating (EDC) process. Among the different ratios of TiC and Cu in the tool electrode, it was found that the tool electrode with 60% TiC was capable of producing an acceptable quality coating. The effect of peak current and pulse duration on the deposition rate and surface characteristics of the coating was evaluated. Also, a detailed mechanical characterization of the coating was carried out through the measurement of microhardness and wear resistance of the coated surface. The results indicated up to ten times improvement in the hardness value and four times improvement in the wear resistance as compared to the uncoated substrate material. The microstructure of the deposited layer revealed some undulations on the coating surface specifically processed at higher current, which may affect the wear resistance of the coating. The experimental results revealed that within the processing range, peak current and pulse duration have a significant effect on the performance of the coating due to alteration in the deposition of the coating material.

Atomic layer deposition of nano-TiO2 thin films with enhanced biocompatibility and antimicrobial activity for orthopedic implants.

Titanium (Ti) and its alloys have been extensively used as implant materials in orthopedic applications. Nevertheless, implants may fail due to a lack of osseointegration and/or infection. The aim of this in vitro study was to endow an implant surface with favorable biological properties by the dual modification of surface chemistry and nanostructured topography. The application of a nanostructured titanium dioxide (TiO2) coating on Ti-based implants has been proposed as a potential way to enhance tissue-implant interactions while inhibiting bacterial colonization simultaneously due to its chemical stability, biocompatibility, and antimicrobial properties. In this paper, temperature-controlled atomic layer deposition (ALD) was introduced for the first time to provide unique nanostructured TiO2 coatings on Ti substrates. The effect of nano-TiO2 coatings with different morphology and structure on human osteoblast and fibroblast functions and bacterial activities was investigated. In vitro results indicated that the TiO2 coating stimulated osteoblast adhesion and proliferation while suppressing fibroblast adhesion and proliferation compared to uncoated materials. In addition, the introduction of nano-TiO2 coatings was shown to inhibit gram-positive bacteria (Staphylococcus aureus), gram-negative bacteria (Escherichia coli), and antibiotic-resistant bacteria (methicillin-resistant Staphylococcus aureus), all without resorting to the use of antibiotics. Our results suggest that the increase in nanoscale roughness and greater surface hydrophilicity (surface energy) together could contribute to increased protein adsorption selectively, which may affect the cellular and bacterial activities. It was found that ALD-grown TiO2-coated samples with a moderate surface energy at 38.79 mJ/m2 showed relatively promising antibacterial properties and desirable cellular functions. The ALD technique provides a novel and effective strategy to produce TiO2 coatings with delicate control of surface nanotopography and surface energy to enhance the interfacial biocompatibility and mitigate bacterial infection, and could potentially be used for improving numerous orthopedic implants.

Fundamental Study of Corrosion Preventive Compounds: Part II—Effects on Galvanic Corrosion of Coated Al Alloy Panels Coupled to Noble Fasteners

The effects of corrosion preventive compounds (CPCs) on galvanic corrosion of coated Al alloy panels coupled to noble material fasteners were studied using a test specimen consisting of a painted AA7075-T6 panel and uncoated through-hole noble material fasteners. This specimen provides accelerated degradation of multi-layered coatings through galvanic attack. Homemade hard film CPCs formulated based on the general composition of a commercial hard film CPC were applied on the test specimens. The galvanic current between the panel and each fastener was monitored using a zero-resistance ammeter during exposure of the test panels in an ASTM B117 chamber for 3 weeks. The corrosion morphology, depth, and volume of the test panels after exposure and removal of the coating systems were investigated using optical profilometry (OP). The equivalent mass losses determined by two means, OP analysis and charge calculations by integration of galvanic currents with exposure time, were compared. For comparison with the homemade CPCs, test specimens without CPC and with commercial hard and soft film CPCs were also studied. CPCs reduced the galvanic current to a large extent and correspondingly mitigated galvanic attack. In particular, the commercial CPCs and a homemade CPC without corrosion inhibitor exhibited the best performance. This homemade CPC was also applied on a pre-corroded test panel. The galvanic current decreased after the CPC was applied on the pre-corroded test panel, indicating that the homemade CPC inhibited both the initiation and growth of galvanic corrosion.

Metallized Nonwoven Electrospun Polyamide-6 Nanofibers for Energy Production and Storage

Nonwoven polymer materials based on polyamide-6 coated with stainless steel that are used as electrodes to produce energy and batteries to store it were investigated. Nanofibers were prepared by capillary-free electrospinning. The metal coating was applied using vacuum magnetron sputtering. Continuous metallized nonwoven material coated with sputtered stainless steel was formed after 4-10 min of magnetron sputtering. The resistance of the metallized nonwoven material was seven orders of magnitude less than that of uncoated material and five orders less than that of heat-treated nonwoven material. It was found that vacuum sputtering of the conducting stainless-steel coating reduced the nanofiber diameter by an average of 1.5 times due to evaporation of residual solvent.

Investigation of Influence of Quenching and Annealing on the Plane Fracture Toughness and Brittle to Ductile Transition Temperature of the Zinc Coated Structural Steel Materials

This article discusses that the variation in fracture toughness is exclusively due to the influence of coating on the surface of the material, depending upon the time interval that the specimen is immersed in the coating tub under a specific temperature. Parameters during the process of coating have shown their own influence on heat treatment, which has shown its own significance of the fracture toughness of coated and uncoated materials. Hence, to estimate this effect, EN 18 and AISI 1020 steels have been tested under different heat treatment processes, like annealing, oil-quenching and water-quenching. The results obtained under these conditions have clearly shown that the influence of heat treatment is significant on the fracture toughness of the materials. Compared to untreated materials, the annealed and quenched materials have shown much variation in fracture toughness.

Effect of Alloy Composition on the Oxidation Behaviour and Cr Vaporisation of High-Cr Steels for SOFC Cathode Air Preheater

Solid oxide fuel cell (SOFC) stacks require the inlet air to be pre-heated prior to entry into the fuel cell and produce exhaust gas containing a high level of thermal energy which can be recovered and transferred elsewhere within the system. The Cathode Air Preheater (CAPH) functions as a heat exchanger, recovering heat from the exhaust gas to heat air before it enters the fuel cell. The latest generation of the CAPH design uses an advanced alloy containing Cr to provide improved oxidation resistance under isothermal and cyclic conditions and provide good high temperature strength. However, reactive evaporation of Cr-species from high-Cr steels is a technical challenge for SOFC systems and other devices operating in high-temperature (>600 °C) oxidising environments. The vaporisation of Cr-rich volatile species from stainless steel materials is a major source of degradation that limits the lifetime of SOFC systems with metallic CAPH. For a more systematic approach, it is crucial to measure the oxidation rate and quantify the amount of evaporated Cr-species of coated and uncoated stainless steel materials. This study compares the oxidation performance of the aluminium containing Aluchrom 418 alloy and the nickel based Inconel 625 alloy at high temperature. Furthermore, the oxidation behaviour of uncoated stainless steel 309 is also compared with PVD aluminised version of same material. The materials have been researched with respect to oxidation rate and Cr evaporation. High temperature oxidation measurements have been implemented both isothermal and discontinuously in tubular furnaces at 850 °C, with 6 L/min airflow and 3% H2O to simulate the cathode atmosphere in SOFC. In addition to the oxidation test, the Cr evaporation tests have been performed by applying a developed denuder technique, which allows time-resolved and accurate quantification of Cr evaporation from alloys at high temperature. Chemical analysis of the formed oxide scales are subsequently studied by XRD and SEM/EDX. SEM results indicate that all the materials produce an oxide scale with an inner layer of Cr2O3 and a spinel layer on top. EDX analysis reveals that transitional alumina layer is formed for the Aluchrom 418 and the aluminised stainless steel 309. The Cr evaporation tests show that the aluminium containing alloys effectively decrease Cr evaporation by forming a stable and protective Al2O3 scale. Furthermore, the quantity of Cr evaporated from alloys increases with operating temperature and humidity. High temperature mechanical properties of these materials for application of CAPH in SOFC have been investigated with the tensile and creep tests. Tensile properties are evaluated at temperature of 850 °C. Creep properties are investigated by constant-load measurements at 850 °C. The nickle based 625 alloy shows the highest mechanical strength among all these materials, which could be ascribed to precipitation strengthening effect of the Laves phase with the addition of Nb and Ti elements.

Enhanced Electrochemical Capability of LiNi1/3Co1/3Mn1/3O2 Cathode Materials Coated with Fluoroborate Glass for Lithium‐Ion Batteries

AbstractA LiNi1/3Co1/3Mn1/3O2 (NCM) cathode material is coated with fluoroborate glass (xLi2O‐yB2O3‐zLiF) to improve the electrochemical performance of lithium‐ion batteries. An xLi2O‐yB2O3‐zLiF layer was successfully coated onto the surface of NCM by using a solution‐phase method. The resulting materials are characterized by using X‐ray diffraction, scanning electron microscopy, and transmission electron microscopy. The xLi2O‐yB2O3‐zLiF‐coated NCM exhibits a superior discharge capacity, rate capability, and cycling stability than those of the uncoated material. Notably, the initial discharge capacity of bare and 2Li2O‐B2O3‐LiF‐coated NCM were 182.1 and 207.5 mAhg−1, respectively, in the voltage range from 2.5 to 4.5 V. At a rate of 5C, the discharge capacity of Li2O‐B2O3‐LiF‐coated NCM is 144.4 mAhg−1, whereas that of bare NCM is 76.7 mAhg−1. After 50 cycles at a rate of 0.2C, the capacity retentions of Li2O‐B2O3‐LiF‐, 2Li2O‐B2O3‐LiF‐, Li2O‐2B2O3‐LiF‐, and Li2O‐B2O3‐2LiF‐coated NCM are 96.8, 97.2, 95.6, and 95.2%, respectively, whereas the capacity retention of bare NCM is 81.4%. Cyclic voltammetry and electrochemical impedance spectroscopy results indicate that the xLi2O‐yB2O3‐zLiF coating reduces electrode polarization and decreases charge‐transfer resistance at the electrolyte–electrode interface, further improving the electrochemical activity of the NCM cathode material.

Using the Charge-Discharge Cycling of Positive Electrode Symmetric Cells to Find Electrolyte/Electrode Combinations with Minimum Reactivity

The effects of solvents, salts, electrolyte additives and surface coatings on LiNi0.4Mn0.4Co0.2O2 (NMC442) or LiNi0.6Mn0.2Co0.2O2 (NMC622) have been probed using positive electrode Li-ion symmetric cells coupled with dV/dQ analysis. A robust symmetric cell design is presented which prevents hardware corrosion for over at least 800 hours of testing to 4.5 V vs. Li/Li+ at 40°C. Positive electrode symmetric cells using uncoated positive electrode materials and 1M LiPF6 EC:EMC 3:7 or 1M LiPF6 EMC electrolyte rapidly developed high impedance and showed poor capacity retention. However, if 1% pyridine boron trifluoride (PBF) was added to these electrolytes, cell performance was dramatically improved. Replacing LiPF6 by LiBF4 in the electrolytes above, with or without PBF, yielded positive electrode symmetric cells with good capacity retention. Two types of surface coatings were explored on NMC622 positive electrodes. Cells using surface-coated positive electrodes demonstrated better capacity retention for all electrolytes compared to cells without surface coatings. This work can be used as a guide by those attempting to find electrolyte/electrode pairs suitable for use in NMC/graphite cells that can operate with long lifetime to 4.5 V.

Colloidal Synthesis and Electrochemistry of Surface Coated Nano-LiNi0.80Co0.15Al0.05O2

Nano-crystalline LiNi0.80Co0.15Al0.05O2 with and without an electrochemically inactive “Al2O3” surface coating has been successfully prepared by a colloidal synthesis method followed by a chemical lithiation reaction. In situ high temperature X-ray diffraction studies evidenced the slowness of the lithiation reaction due to diffusion and suggested longer calcination holding times at temperatures below 500°C. At 550°C, lithiated compounds were obtained although calcinations to 750°C are necessary to obtain ordered layered structures. Ex situ XRD studies and cyclic voltammograms revealed a single-phase solid solution mechanism taking place during the first charge unlike the two-phase reaction “activation mechanism” seen for micron-sized material. While nano-crystalline LiNi0.80Co0.15Al0.05O2 exhibits cycle stability at 2.4 mA g−1 and a good rate capability even at 240 mA g−1 in the galvanostatic tests, the specific charge of the surface coated material fades more quickly. These results are caused by the material characteristics such as small particle size and significant amount of microstrains, high degree of cation mixing, and increased compositional inhomogeneity among the nano-particles, compared to the uncoated material.

Protective Properties of Various Coatings on CoSb3 Thermoelectric Material

In this study, various coatings including Mo, Ti, Y2O3-stabilized ZrO2 (YSZ)/Ti films were deposited on the CoSb3 substrate using magnetron sputtering to suppress the sublimation of antimony in CoSb3 during thermal aging tests. The microstructure and growth of films were observed using scanning electron and atomic force microscopes. The thermal aging behavior of CoSb3 coated with various films was investigated through an accelerated experiment at 923 K for 24 h. The weight loss of CoSb3 decreased with the thickness of coatings increasing. Among these films, the YSZ/Ti film can suppress the sublimation of antimony in CoSb3 more effectively. Compared with the uncoated CoSb3 material, the degradation of thermoelectric properties for coated CoSb3 samples decreased slowly after the accelerated thermal aging test.

Experimental studies on fly-ash erosion behavior of Ni-Cr based nanostructured thermal spray coating in boiler tubes

ABSTRACTErosion study was performed on the uncoated and coated SA210Gr-C boiler tube substrates. This study was performed in a view to reducing the scaling on boiler water-wall and super-heater tubes. In the present work, the High Velocity Oxygen Fuel (HVOF) coating process was used to deposit nanostructured and conventional coatings on the boiler tube substrates. Fly-ash produced after the combustion of coal in an Indian thermal power station was used as erodent. The erosion loss of coated and uncoated substrates was recorded at a regular interval of 30 minutes. The study was conducted at 30°, 60°, and 90° impingement angles and at two different operating temperatures (300°C, 550°C). Surface morphology of eroded samples was analyzed using macro and micro imaging techniques, and surface roughness was also recorded for the eroded samples. The phases present in the eroded substrates were indexed using the X-Ray diffraction (XRD) analysis. HRTEM images of nanostructured coated samples at 550°C with varying impingement angles were analyzed. The result reveals that the nanostructure in the coating was retained even after high-temperature erosion test. Comparative study was made with nanostructured and conventional coatings against the uncoated materials.

The erosion performance of particle reinforced metal matrix composite coatings produced by co-deposition cold gas dynamic spraying

This work reports on the erosion performance of three particle reinforced metal matrix composite coatings, co-deposited with an aluminium binder via cold-gas dynamic spraying. The deposition of ceramic particles is difficult to achieve with typical cold spray techniques due to the absence of particle deformation. This issue has been overcome in the present study by simultaneously spraying the reinforcing particles with a ductile metallic binder which has led to an increased level of ceramic/cermet particles deposited on the substrate with thick (>400μm) coatings produced. The aim of this investigation was to evaluate the erosion performance of the co-deposited coatings within a slurry environment. The study also incorporated standard metallographic characterisation techniques to evaluate the distribution of reinforcing particles within the aluminium matrix. All coatings exhibited poorer erosion performance than the uncoated material, both in terms of volume loss and mass loss. The Al2O3 reinforced coating sustained the greatest amount of damage following exposure to the slurry and recorded the greatest volume loss (approx. 2.8mm3) out of all of the examined coatings. Despite the poor erosion performance, the WC-CoCr reinforced coating demonstrated a considerable hardness increase over the as-received AA5083 (approx. 400%) and also exhibited the smallest free space length between adjacent particles. The findings of this study reveal that the removal of the AA5083 matrix by the impinging silicon carbide particles acts as the primary wear mechanism leading to the degradation of the coating. Analysis of the wear scar has demonstrated that the damage to the soft matrix alloy takes the form of ploughing and scoring which subsequently exposes carbide/oxide particles to the impinging slurry.

Corrosion and wear of PEO coated AZ91/SiC composites

In this work, corrosion and wear resistance of uncoated and PEO coated AZ91/SiC/0-10p composites manufactured by semisolid processing is evaluated by corrosion tests in saline solution and ball-on-disc tests. AZ91/SiC composites show a globular microstructure with SiC clusters located at the interglobular regions. PEO coatings reveal a trilayered structure with thicker, less porous and softer regions at the locations of SiC clusters. Corrosion rate increases with increasing the volume fraction of reinforcement, which shows a cathodic activity and disrupts the continuity of the β-phase network. PEO improves the corrosion resistance, but it is also negatively influenced by the presence of the reinforcement. Tribological tests show a positive effect of the reinforcement on uncoated materials, whereas an opposite effect is found on PEO coated materials, probably due to the detachment of SiC particles from the coating.

The continued development of reticulated vitreous carbon as a versatile electrode material: Structure, properties and applications

The limitations of two-dimensional electrodes can be overcome by using three-dimensional materials having sufficient porosity and active area while offering moderate mass transport rates and a relatively low pressure drop at controlled electrolyte flow rate. In concept, a wide variety of metal, ceramic and composite materials are possible but restrictions are imposed by the need to avoid materials degradation, while maintaining adequate electrical conductivity, sufficient robustness and the possibility of facile scale-up. Despite its fragility, one of the traditional electrode materials used as a porous, three-dimensional electrode is carbon foam, particularly in the 97% vol. porous form of reticulated vitreous carbon, RVC. A time-line indicates that the history of this material dates back over 50 years to the mid-1960s, when it was primarily used as an uncoated material in small-scale, laboratory electroanalysis. Surface modification and diverse coatings have considerably extended the use of RVC. Recent applications are found in sensors and monitors, electrosynthesis, environmental processing and energy conversion. This review highlights the fundamental structure and summarises the physicochemical properties of RVC. Fluid flow through various porosity grades of the material, their active electrochemical area and rates of mass transport are quantified. The diverse applications of RVC in energy conversion, environmental treatment and electrosynthesis are illustrated by selected examples from the authors’ laboratories and others over the last 30 years. Recent research on coated RVC, energy conversion environmental remediation and sensors is highlighted. Critical areas deserving further research and development are proposed.

Polydopamine-Coated Manganese Complex/Graphene Nanocomposite for Enhanced Electrocatalytic Activity Towards Oxygen Reduction.

Platinum electrodes are commonly used electrocatalysts for oxygen reduction reactions (ORR) in fuel cells. However, this material is not economical due to its high cost and scarcity. We prepared an Mn(III) catalyst supported on graphene and further coated with polydopamine, resulting in superior ORR activity compared to the uncoated PDA structures. During ORR, a peak potential at 0.433 V was recorded, which is a significant shift compared to the uncoated material’s −0.303 V (both versus SHE). All the materials reduced oxygen in a wide pH range via a four-electron pathway. Rotating disk electrode and rotating ring disk electrode studies of the polydopamine-coated material revealed ORR occurring via 4.14 and 4.00 electrons, respectively. A rate constant of 6.33 × 106 mol−1s−1 was observed for the polydopamine-coated material–over 4.5 times greater than the uncoated nanocomposite and superior to those reported for similar carbon-supported metal catalysts. Simply integrating an inexpensive bioinspired polymer coating onto the Mn-graphene nanocomposite increased ORR performance significantly, with a peak potential shift of over +730 mV. This indicates that the material can reduce oxygen at a higher rate but with lower energy usage, revealing its excellent potential as an ORR electrocatalyst in fuel cells.

Influence of plasma electrolytic oxidation coatings on fatigue performance of AZ31 Mg alloy

Magnesium and its alloys are attractive for lightweight construction, but suffer often from poor corrosion resistance. Plasma electrolytic oxidation is a promising surface treatment to overcome these limitations. Recently, introduction of particles to the PEO electrolyte has been explored as new strategy to provide a wider range of compositions and new functionalities for PEO coatings. However, this surface treatment can have negative impact on the fatigue strength. In the present study, the influence of PEO coatings with and without particle addition on the corrosion fatigue behavior of AZ31 Mg alloy is investigated. The corrosion fatigue behavior is investigated in load increase tests and constant amplitude tests in 0.5% NaCl solutions. Results are correlated with the corrosion behavior evaluated in polarization and electrochemical impedance spectroscopy measurements. Corrosion tests show significant improvement of the corrosion resistances of PEO‐coated specimens. However, the uncoated material exhibits the highest corrosion fatigue strength, whereas a reduction of 7% for the PEO‐coated specimen without particles and 27% for the PEO‐coated specimen with particles is found.

Synthesis and high-temperature oxidation of a polymer-derived Mo-SiN based ceramic composite

Si3N4 ceramics strengthened with molybdenum silicides seem to be potential candidates for (ultra-)high temperature applications. While Mo5Si3 exhibits a higher melting point and a better creep resistance than MoSi2, its oxidation resistance is inferior due to accelerated pest oxidation at 700°C in air.In order to protect Mo5Si3/Si3N4 ceramic composites from pesting, in this work a composite material was developed using the inorganic precursor PHPS loaded with Mo particles as active filler. After pyrolysis, the resulting ceramic composite was coated with PHPS to generate a protective SiO2 layer before the oxidation of Mo5Si3 starts.The results demonstrated the in-situ formation of the silicide phase during pyrolysis at temperatures up to 1500°C via solid-state reaction of the formed amorphous SiN phase and the Mo particles. As intended, the coated Mo5Si3/Si3N4 ceramic composites exhibit a remarkably increased oxidation resistance up to 700°C compared to the uncoated material.

Modification of Ni-Rich FCG NMC and NCA Cathodes by Atomic Layer Deposition: Preventing Surface Phase Transitions for High-Voltage Lithium-Ion Batteries.

The energy density of current lithium-ion batteries (LIBs) based on layered LiMO2 cathodes (M = Ni, Mn, Co: NMC; M = Ni, Co, Al: NCA) needs to be improved significantly in order to compete with internal combustion engines and allow for widespread implementation of electric vehicles (EVs). In this report, we show that atomic layer deposition (ALD) of titania (TiO2) and alumina (Al2O3) on Ni-rich FCG NMC and NCA active material particles could substantially improve LIB performance and allow for increased upper cutoff voltage (UCV) during charging, which delivers significantly increased specific energy utilization. Our results show that Al2O3 coating improved the NMC cycling performance by 40% and the NCA cycling performance by 34% at 1 C/−1 C with respectively 4.35 V and 4.4 V UCV in 2 Ah pouch cells. High resolution TEM/SAED structural characterization revealed that Al2O3 coatings prevented surface-initiated layered-to-spinel phase transitions in coated materials which were prevalent in uncoated materials. EIS confirmed that Al2O3-coated materials had significantly lower increase in the charge transfer component of impedance during cycling. The ability to mitigate degradation mechanisms for Ni-rich NMC and NCA illustrated in this report provides insight into a method to enable the performance of high-voltage LIBs.

Atomic Layer Deposited Fluoride Coatings for Li-Ion Battery Cathodes

Atomic layer deposition (ALD)1, 2 of AlF3 coatings for the Li-ion battery cathode LiNi0.5Mn0.3Co0.2O2 (NMC)3, 4 was investigated using a combination of trimethylaluminum and TaF5 precursors. ALD growth mode was dictated by a competition between temperature-limited desorption of Ta reaction byproducts and temperature-driven conversion of these byproducts into nonvolatile TaC. At T ≥ 200°C, decomposition to TaC occurred, leading to continuous deposition and high concentrations of TaC in the resulting films. A self-limited ALD growth mode was found to occur when deposition temperature was reduced to 125 °C, and the TaF5 exposures were followed by an extended purge. During ALD growth, vapor-surface ligand exchange reactions lead to formation of Ta(CH3)xF5-x and AlF3. Ta(CH3)xF5-x desorbs from the surface or it decomposes via an intermolecular α-hydrogen abstraction,5,6 eventually forming TaC. The extended purge times and lower temperatures reduce decomposition, while also allowing more time for Ta(CH3)xF5-x desorption. NMC cathode powders were coated using these optimized conditions, and coin cells employing these coated cathode particles were characterized using electrochemical impedance spectroscopy and by cycle performance testing, which demonstrated significant improvements in charge capacity fade at high discharge rates as compared to uncoated materials (Figure 1). These improvements at high C-rates are attributed to the reduction of undesirable electrode-electrolyte reactions by protection of the cathode surface with the ALD coating through which fast Li-ion transport occurs.7-9 Figure 1: Averaged gravimetric capacity of coin cells versus discharge cycle number during a rate test. Black squares (■) fluoride ALD coated, red circles (●) uncoated.

Enhancement of open cell aluminum foams through thermal evaporating Zn film

Relatively low mechanical properties of open cell aluminum foams have become a restrictive factor to their applications in engineering fields. To overcome this shortcoming, a surface enhancing method was investigated in the present study to coat a zinc film on the cell strut surface through thermal evaporating technology. The results show that the coated film obviously makes the foam enhanced and the compression yield strength is increased one order of magnitude higher than that of uncoated material. On the other hand, the mechanical characteristics of the foam has changed from ductile to brittle after the coating, represented by pronouncedly serrated stress-strain curves. This demonstrates that the mechanical behavior of the coated foam is to a great degree dominated by the film and the surface coating does be an effective way to modify the overall mechanical behavior of aluminum foams.