Comparison of the effects of pre-activators on morphology and corrosion resistance of phosphate conversion coating on magnesium alloy

In this study, Mg–6.0Zn–3.0Sn–0.5Mn(ZTM630) magnesium alloy was pre-activated by colloidal Ti, oxalic acid, and phosphoric acid,and a phosphate conversion coating(PCC) was prepared on the alloy surface. The morphology and corrosion resistance of the prepared PCCs were investigated. Surface morphology studies showed that the phosphate crystals that formed the coating were the smallest for the sample pre-activated by phosphoric acid. The coating on the colloidal Ti and the phosphoric acid samples had the largest and the smallest thickness and surface roughness, respectively. The reason for the discrepancy was analyzed by comparing the surface morphologies of alloy samples immediately after the pre-activation treatment and various phosphating treatments. X-ray diffraction analysis revealed that all three PCCs contained the same compounds. The corrosion resistance time from the copper sulfate drop test and the electrochemical data from the potentiodynamic polarization curves showed that the coating pre-activated by phosphoric acid had the best corrosion resistance. Finally, the 1500 h neutral salt spray corrosion test confirmed that the phosphating treated magnesium alloy, which was pre-activated by phosphoric acid,exhibited excellent corrosion resistance and behavior.

Effect of Pulsed Laser on the Structure and Morphology of Alumina-Zirconia Coatings

The effect of excimer laser annealing on the structure and morphology of ceramic coatings were investigated. Alumina-40% zirconia (AZ-40) coatings were sprayed with a water-stabilized plasma spray gun. The coated surface was treated by excimer laser having a wavelength of 248 nm and pulse duration of 24 ns. The surface structure of the treated coating was examined by field emission scanning electron microscope (FESEM) and X-ray diffraction (XRD). A detailed parametric study was performed to investigate the effects of different parameters such as laser energy density (fluence), pulse repetition rate (PRR), and the number of shots on the mechanical properties, surface morphology, and microstructure of the coatings. The results of this study indicated that laser energy and pulse repetition rate have significant effects on surface morphology, porosity, and microstructure of the coating.

Morphology and texture of high speed galvanized coatings on interstitial free steel sheet

The morphology and texture of zinc coatings deposited on interstitial free （IF） steel sheets were investigated by means of scanning electron microscopy （SEM） and orientation distribution function. It was shown that the microstructure of the coatings consisted of thin hexagonal platelets tilted with respect to the substrate surface. Zinc coatings exhibited low angle pyramidal {11.5} nonfiber texture component resulting from epitaxial growth via two-dimensional （2D） nucleation. The 2D nucleation was attributed to severe zinc hydroxide adsorption on the substrate surface during the nucleation stage, which can inhibit three-dimensional （3D） nucleation and promote nonfiber texture. The pyramidal texture was beneficial for plastic deformation of zinc coatings because a significant amount of resolved shear stress can be obtained when the uniaxial stress is applied.

Preparation of Al_2O_3/Au nano-laminated composite coatings and their oxidation resistance on stainless steel

Al2O3/Au nano-laminated composite coatings were prepared by means of magnetron sputtering. The coating was compact and comprised of nano-laminated Al2O3 and Au layers. High temperature cyclic oxidation test was employed to investigate the oxidation resistance of the composite coatings. The results revealed that the applied Al2O3/Au nano-laminated composite coatings improved the oxidation and spallation resistance of the stainless steel substrate significantly. The mechanism accounting for oxidation resistance was related with the suppression of inward oxygen diffusion and selective oxidation of Cr in the substrate. The mechanism accounting for spallation resistance was attributed to the relaxation of thermal stress by the nano-laminated structure.

The Effect of Chemical Composition and Thermal Sprayed Method on the Chromium and Tungsten Carbides Coatings Microstructure

The microstructure, phase consistence and microhardness of thermal sprayed coatings were investigated. The tungsten and chromium carbide coatings and also composite NiCrSiB coating were analyzed. The microstructure of coatings were observed by using optical microscopy (MO), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Almost equiaxial carbide particles settled inside the surrounded material of coating were found. The cracks propagating thorough the particles and along boundaries between the particles and surrounded material were observed. This phenomenon was connected with the porosity of coatings. The decarburization process was detected in coatings by phase composition investigation using X-ray method. The decarburization process was the reason due to which beside initial Cr3C2 the Cr7C3 and Cr23C6 particles were found. In the tungsten coatings beside the initial WC carbides the W2Cones were found.

Biochar amendment modulates xylem ionic constituents and ABA signaling:Its implications in enhancing water-use efficiency of maize(Zea mays L.)under reduced irrigation regimes

While biochar amendment enhances plant productivity and water-use efficiency(WUE),particularly under waterlimited conditions,the specific mechanisms driving these benefits remain unclear.Thus,the present study aims to elucidate the synergistic effects of biochar and reduced irrigation on maize(Zea mays L.)plants,focusing on xylem composition,root-to-shoot signaling,stomatal behavior,and WUE.Maize plants were cultivated in splitroot pots filled with clay loam soil,amended by either wheat-straw biochar(WSB)or softwood biochar(SWB)at 2%(w/w).Plants received full irrigation(FI),deficit irrigation(DI),or partial root-zone drying rrigation(PRD)from the 4-leaf to the grain-filling stage.Our results revealed that the WSB amendment significantly enhanced plant water status,biomass accumulation,and WUE under reduced irrigation,particularly when combined with PRD.Although reduced irrigation inhibited photosynthesis,it enhanced WUE by modulating stomatal morphology and conductance.Biochar amendment combined with reduced rrigation significantly increased xylem K^(+),Ca^(2+),Mg^(2+),NO_(3)^(-),Cl^(-),PO_(4)^(3-),and SO_(4)^(2-)-but decreased Na+,which in turn lowered xylem pH.Moreover,biochar amendment and especially WSB amendment further increased abscisic acid(ABA)contents in both leaf and xylem sap under reduced irrigation conditions due to changes in xylem ionic constituents and pH.The synergistic interactions between xylem components and ABA led to refined adjustments in stomatal size and density,thereby affecting stomatal conductance and ultimately improving the WUE of maize plants at different scales.The combined application of WSB and PRD can,therefore,emerge as a promising approach for improving the overall plant performance of maize plants with increased stomatal adaptations and WUE,especially under water-limited conditions.

Improvement strategy on thermophysical properties of A_(2)B_(2)O_(7)-type rare earth zirconates for thermal barrier coatings applications:A review

The A_(2)B_(2)O_(7)-type rare earth zirconate compounds have been considered as promising candidates for thermal barrier coating(TBC) materials because of their low sintering rate,improved phase stability,and reduced thermal conductivity in contrast with the currently used yttria-partially stabilized zirconia (YSZ) in high operating temperature environments.This review summarizes the recent progress on rare earth zirconates for TBCs that insulate high-temperature gas from hot-section components in gas turbines.Based on the first principles,molecular dynamics,and new data-driven calculation approaches,doping and high-entropy strategies have now been adopted in advanced TBC materials design.In this paper,the solid-state heat transfer mechanism of TBCs is explained from two aspects,including heat conduction over the full operating temperature range and thermal radiation at medium and high temperature.This paper also provides new insights into design considerations of adaptive TBC materials,and the challenges and potential breakthroughs are further highlighted for extreme environmental applications.Strategies for improving thermophysical performance are proposed in two approaches:defect engineering and material compositing.

Storage and Preservation of Carica papaya Using Composite Fungicidal Coatings

[Objectives]The paper was to investigate a method for the storage and preservation of Carica papaya utilizing chemical fungicides and composite biological coatings.[Methods]C.papaya fruits with red pulp sourced from Lianjiang were utilized as test materials.The fruit epidermis was subjected to treatment with composite fungicidal coatings at ambient temperature,and the nutritional and physiological indicators of the fruits were measured at regular intervals.[Results]Under ambient temperature conditions,a chemical fungicide composite consisting of 300 mg/L fludioxonil and 250 mg/L propiconazole was employed to soak the fruits for a duration of 2 min.Subsequently,a composite biological coating formulated with 8 g/L KGM and 1.0%Zein at a pH of 7.0 was applied to the fruits.This treatment effectively inhibited the decline in the content of total soluble solids(TSS)and vitamin C(V C)in C.papaya,reduced the weight loss rate and the decay index,and enhanced the yellow ripening index.[Conclusions]This study establishes a foundation for the advancement of additional methods and techniques for the storage and preservation of C.papaya.

Microstructure and mechanical properties of Ni-based composite coatings reinforced by in situ synthesized TiB_2 + TiC by laser cladding

A Ni-based composite coating reinforced by in situ synthesized TiB2 and TiC particles was fabricated on Ti6A14V by laser cladding. An attempt was made to correlate the thermodynamic predictions and experimental observation. The micro- structure and the microhardness profile across the coating were investigated by means of X-ray diffraction （XRD）, scanning electron microscopy （SEM）, energy dispersive spectroscopy （EDS）, and a hardness tester. It is found that the coating mainly consists of a large number of reinforcements （black blocky TiB2, flower-like or equiaxial TiC, and fine acicular CrB） and the 7 matrix. The hardness of TiB2, TiC, and CrB reinforcements is much higher than that of the 7 matrix. The dispersive distribu- tion of such high hardness reinforcements causes the increase in hardness of the whole coating. The average value of the hard- ness is approximately Hv0.2 700 in the coating. The hardness of the coating is obviously higher than that of the substrate due to the dispersion strengthening of reinforcements.

Synthesis and Deposition of TiC-Fe Coatings by Oxygen-acetylene Flame Spraying

A simpler and more convenient method for producing wear-resistant, TiC-reinforced coatings were investigated in this study. It consists of the simultaneous synthesis and deposition of TiC-Fe materials by oxyacetylene flame spraying. Solid reagents bound together to form a single particle are injected into the flame stream where an in-situ reaction occurs. The reaction products are propelled onto a substrate to form a coating. Microstructural analyses reveal that TiC and Fe are the dominant phases in the coatings. The reaction between Ti and C happens step by step along with the reactive spray powder flight, and TiC-Fe materials were mainly synthesized where the spray distance is 125-170 mm. The TiC-Fe coatings are composed of alternate TiC-rich and TiC-poor lamellae with different microhardness of 11.9-13.7 and 3.0-6.0 GPa, respectively. Submicron and round TiC particles are dispersed within a ductile metal matrix. The peculiar microstructure is thought to be responsible for its good wear resistance, which is better nearly five times than WC-reinforced cermet coatings obtained by traditional oxyacetylene flame spray.

Predicted interfacial thermal conductance and thermal conductivity of diamond/Al composites with various interfacial coatings

The interfacial thermal conductance （ITC） and thermal conductivity （TC） of diamond/Al composites with various coatings were theoretically studied and discussed. A series of predictions and numerical analyses were performed to investigate the effect of thickness, sound velocity, and other parameters of coating layers on the ITC and TC. It is found that both the ITC and TC decline with increasing coating thickness, especially for the coatings with relatively low thermal conductivity. Nevertheless, if the coating thickness is close to zero, or quite a small value, the ITC and TC are mainly determined by the constants of the coating material. Under this condition, coatings such as Ni, TiC, Mo 2 C, SiC, and Si can significantly improve the ITC and TC of diamond/Al composites. By contrast, coatings like Ag will exert the negative effect. Taking the optimization of interfacial bonding into account, conductive carbides such as TiC or Mo 2 C with low thickness can be the most suitable coatings for diamond/Al composites.

Effect of Laser Power on the Microstructure and Mechanical Properties of TiN/Ti_3Al Composite Coatings on Ti6Al4V

Laser nitriding is one of the effective techniques to improve the surface properties of titanium alloys and has potential application in the life extension of last-stage steam turbine blades. However, cracking of surface coating is a common problem due to heat concentration in laser nitriding process. Conventionally, the cracks can be avoided through heat treatment, which may have an important influence on the mechanical properties of coating. Crack-free TiN/Ti3Al IMC coatings on Ti6Al4V are prepared by plasma spraying and laser nitriding. The microstructures, phase constitutes and compositions of the coating are observed and analyzed with scanning electron microscopy(SEM), X-ray diffraction(XRD) and X-ray energy-dispersive spectroscopy(EDS). Microhardness, elastic modulus, fracture toughness of the coating are measured. The results show that the crackand pore-free IMC coatings can be made through the proposed method; with increasing laser power, the amount and density of TiN phase in the coating first increased and then decreased, leading to the similar trend of microhardness and elastic modulus and the reverse trend of fracture toughness of the coating. Both the average microhardness and elastic modulus of the coating increase three times higher than those of the substrate. The volume fraction of the TiN reinforced phase in composite can be controlled by varying the laser power and the cracking problem in laser nitriding process is successfully solved.

Morphology and Phase Compositions of Hydroxyapatite Powder Particles Plasma-sprayed into Water

Hydroxyapatite powder particles were plasma sprayed into water, their inner structures and phase compositions were studied by using scanning electron microscope(SEM) and X-ray diffractometer. The results show that the molten HA particles have a central hollow morphology and high crystallinity. The hollow morphology was caused by sublimated P2O5 and H2O, which will have an effect on surface morphology, cohesive and adhesive strength as well as dissolution and degradation of coating. The high crystallinity is attributed to lower cooling speed in water.

Microstructure and properties of in situ synthesized TiB_2+WC reinforced composite coatings

Nickel-based composite coatings reinforced by in situ synthesized TiB2 and WC particles were deposited on stainless steel by laser cladding, and their microstmcture and mechanical properties were investigated. The results show that the coatings are mainly composed of 7-Ni cellular dendrites and dispersed spherical/strip/network shaped TiB2 and equiaxial WC particles. The initial WC particles are dissolved to become fine and mostly dispersed within Y-Ni cellular dendrites. The coating prepared at a special laser energy of 0.225 kJ@mm^-2 is uniform, continuous, and free of pores and cracks. With the decrease in special energy density, TiB2 phase changes from fine spherical particles which cluster together to strip shape with different morphologies and further crystallizes to form network structure, and the dispersion zone also gradually changes from intragranular to intergranular phase. The coating possesses a higher microhardness compared with the substrate, and it has a good metallurgical bond with the substrate and excellent cracking resistance.

Preparation and characterization of molybdenum powders with copper coating by the electroless plating technique

Molybdenum powders with a diameter of approximately 3 μn were coated with copper using the electroless plating technique in the pH 12.5-13 and temperature range of 55-75℃. The optimization of the electroless copper bath was evaluated through the combination of process parameters like pH and temperature. The optimized values ofpH and temperature were found to be 12.5 and 60℃, respectively, which attributes to the bright maroon color of the coating with an increase in weight of 46%. The uncoated and coated powders were subjected to microstructural studies using scanning electron microscope （SEM） and the phases were analyzed using X-my diffrction （XRD）. An attempt was made to understand the growth mechanism of the coating. The diffusion-shrinkage autocatalytic model was suggested for copper growth on the molybdenum surface.

Effect of electromagnetic stirring on the microstructure and wear behavior of iron-based composite coatings

The effect of electromagnetic stirring on the microstructure and wear behavior of coatings has been investigated. A series of iron-based coatings were fabricated by the plasma-transferred arc cladding process by applying different magnetic field currents. The microstructure and wear resistance of the composite coatings were characterized by scanning electron microscope （SEM）, en- ergy dispersive X-ray analysis （EDAX）, X-ray diffraction （XRD）, and wet sand rubber wheel abrasion tester. The experimental results showed that the microstructure of the coatings was mainly the γ-Fe matrix and （Cr, Fe）7C3 carbide reinforced phase. The coatings were metallurgically bonded to the substrate. With increasing magnetic field current, the amount of the block-like （Cr, Fe）TC3 carbide reinforced phase increased at first, reached a local maximum, and then decreased sharply. When the magnetic field current reached 3 A, the block-like （Cr, Fe）TC3 carbides with high volume fraction were uniformly distributed in the matrix and the coating displayed a high microhardness and an excellent wear resistance under the wear test condition.

ZIF-8-based micro-arc oxidation composite coatings enhanced the corrosion resistance and superhydrophobicity of a Mg alloy

Mg alloys are considered the most promising engineering materials because of their unique properties.However,the uncontrolled corrosion rate of these alloys limits their applications.Therefore,in this study,a micro-arc oxidation layer was used as a transition layer to“directly”grow a zinc-based metal-organic framework(MOF)composite coating on the surface of a Mg alloy(AZ91D).Herein,the two zeolitic imidazolate framework(ZIF-8)coatings with different morphologies were separately prepared by homologous metal oxide induction and a one-step in-situ growth method.The superhydrophobic composite coating showed strong hydrophobicity and self-cleaning properties,which could prevent the penetration of water and corrosive ions(Cl^(−))into the surface of AZ91D.Electrochemical tests demonstrated that the super-hydrophobic composite coatings greatly enhanced the corrosion resistance of AZ91D,and the corrosion current density decreased from 10^(−5)to 10^(−9)A/cm^(2).These results indicate that the ZIF-8 coatings are beneficial for improving the hydrophobicity and enhancing the corrosion resistance of Mg alloys.Therefore,MOF composite coatings provide a new strategy that can be used to prepare multifunctional anticorrosion coatings on metal substrates.

SYNTHESIS, CROSSLINKING MECHANISM AND PROPERTIES OF A POLYACRYLATE/POLYURETHANE COMPOSITE COATING

A polyacrylate/polyurethane (P(A)/P(U)) composite coating has been prepared by crosslinking an acetoacetylated polyacrylate with a vinylic group terminated polyurethane at room temperature. A model Michael reaction between ethyl acetoacetate (EAA) and methyl acrylate (MA) was designed to study the crosslinking mechanism. It was found that the two active hydrogen atoms in acetoacetyl group can both add to vinylic groups and the yield of mono-and bis-adducts are much affected by the molar ratio of acetoacetyl to vinylic groups. Higher crosslinking degree and better properties could be obtained with decreasing the molar ratio of the two active groups from 1/1 to 0.6/1 in the composite coatings.

Morphology and tribological properties of Ni/n-SiO_2 composite coatings by pulse-reverse current brush-plating

Ni/n-SiO2 composite coating was electrodeposited by brush-plating with pulse-reverse current（RC）. The morphology, hardness, and tribological properties of the coating were investigated and compared with those of Ni and composite coatings electrodeposited with direct current（DC）. The results indicate that Ni/n-SiO2 composite coating electrodeposited by RC, because of RC and the nano powders, has denser coating, finer crystal grains, higher hardness（HV650.0, nearly 1.5 times higher than that of Ni coating electrodeposited by DC） and lower friction coefficient（nearly 0.62）, as a result, in the wearing experiment, the Ni/n-SiO2 composite coating electrodeposited by RC has the least worn loss. So this kind of coating has better wear resistance. And RC electro brush-plating can be used as a new technology of brush-plating in the area of wear resistance.

The Surface Morphologies and Spectroscopy Analysis of VC Coatings on the Substrate of Cr12MoV Prepared by TD Process after Salt Spray

The normal temperature corrosion of VC coating on the substrate of Cr12MoV prepared by TD process was tested in 5% NaCl aqueous solution, its surface morphologies and corrosion components after salt spray were observed with SEM and EDS, respectively, and the effects of salt spray on micro-structures of VC coating were analyzed. Moreover, the invalidation mechanism of VC coating after salt spray and its effect on substrate material were discussed. The experimental results shown that the uniformity and integrity of VC coating surface are destroyed by salt spray for 120 h, a large number of the pits are produced on the coating surface, and the coating falls off, which speeds corrosion breakage of its substrate; the oxidated film on its surface becomes rougher, broken and discontinuous, and falls off easily, which reduce the ability of resistance salt spray; the failure modes of VC coating after salt spray are expressed with falling off of oxidated film, stress concentration and pore effect and so on, the corrosion breakage of oxidated film is the corrosion result of deoxidization corrosion from oxygen and HCl produced by NaCl and vapor.