化学镀镍对碳纤维增强聚酰亚胺表面WC/Co涂层抗热震性能的影响

在航空发动机涡轮叶片用碳纤维增强聚酰亚胺(C/PMR15)复合材料表面喷涂WC/Co涂层可以提高其抗氧化耐冲刷性能,采用整体热震法能够评定涂层与基体的结合力.研究了在C/PMR15基体上化学镀镍作为粘结底层对WC/Co喷涂层抗热震性能的影响,并与喷涂PMR15粉末作为过渡层的方法进行了比较.结果表明,在PMR15过渡层上不能得到完整的后续涂层,在化学镀镍粘结底层上可得到连续致密的镍基合金层和WC/Co涂层,镀镍层大幅度提高了基体抗氧化能力,缓和了WC/Co涂层和基体界面位置的热应力,涂层抗热震性提高.     

Facile electroless copper plating on diamond particles without conventional sensitization and activation

Conventional electroless plating of copper on diamond particles needs SnCl₂ sensitization and PdCl₂ activation pretreatments, which needs noble metal and consumes a large amount of reducing agent. In this paper, metallic tungsten coatings were first plated onto diamond particles by microwave-heating salt-bath plating (MHSBP) method, and then copper layer was directly plated onto the out surface of the tungsten layer by an electroless plating method with no need of SnCl₂ sensitization and PdCl₂ activation pretreatments. Composition and morphology of the coatings was analyzed by XRD, SEM, and EDS. The results show that the copper coating on the diamond surfaces can be adjusted by control the concentration of CuSO₄·5H₂O and plating temperature, and a full copper coating is achieved with content of CuSO₄·5H₂O of 19.6 g/L in the plating solution at 60 °C. The bending strength of the coated diamond/Cu composites is as high as 630 MPa, which increases 93.3% than the uncoated composites. This work presents an electroless plating of copper can directly on the surfaces of diamond particles with no need of conventional sensitization and activation, and a strong interface combination between coated diamond and copper.     

The Effect of Variable Binder Content and Sintering Temperature on the Mechanical Properties of WC–Co–VC/Cr3C2 Nanocomposites

WC powders with an average crystallite size of 10 nm were successfully prepared by ball milling of micron-sized tungsten carbide powders. Grain growth inhibitors (VC and Cr₃C₂) with concentrations of 0.6 wt% each were added to nanocomposites of WC–9Co and WC–12Co, in both as-received and milled WC. Powder mixtures were then consolidated using spark plasma sintering technique at 1200 and 1300 °C for 10 min under high vacuum and pressure of 50 MPa. The influence of WC crystallite size, Co content, and sintering temperature over microstructure and mechanical properties of the resulting composites were studied through XRD and FESEM. Densification and attained grain sizes of the sintered products were measured by Archimedes principle and Scherrer procedure, respectively. Moreover, microhardness (H_v30) and fracture toughness were measured and compared for each composition to comparatively assess the individual effect. It was observed that the addition of VC and Cr₃C₂ resulted in decreased densification of the synthesized composites. These grain growth inhibitors were found to limit grain sizes to 131 nm with an average hardness of 1592 H_v30 and fracture toughness of 9.23 Mpam^1/2.     

Fabrication and characterization of NiTi shape memory alloy synthesized by Ni electroless plating of titanium powder

In this work NiTi shape memory alloy was fabricated from mixed elemental powders, Ni plated titanium powder and Ni heated/plated titanium powder by Ar-sintering. Electroless plating process was utilized to fabricate Ni plated titanium powder. For this purpose titanium powder was plated in an electroless Ni bath for 225?min and hydrazine hydrate was used as a reductant to deposit pure nickel on the titanium particles. Ni plated titanium powder was heat treated under an argon atmosphere at 1000?°C to prepare Ni heated/plated titanium powder. Finally, the three sample powders were pressed by CIP followed by sintering at 980?°C for 8?h to manufacture NiTi shape memory alloy. The prepared powders, as well as sintered samples, were characterized by scanning electronic microscopy (SEM), energy dispersive spectrometer analysis (EDS), X-ray fluorescence (XRF), X-ray diffraction (XRD) and differential scanning calorimetric (DSC). The results indicated the presence of NiTi phase and also non-transformable phases (NiTi₂ and Ni₃Ti) in the heated/plated Ti powder and sintered samples. NiTi compound was dominated phase in the heated/plated sintered sample. All three sintered samples, as well as heated/plated powder, showed one-step phase transformation (B2???B19′).     

A study on the synthesis of nanostructured WC–10 wt% Co particles from WO<Subscript>3</Subscript>, Co<Subscript>3</Subscript>O<Subscript>4</Subscript>, and graphite

The formation of the nanostructured WC–10 wt% Co powder from WO₃, Co₃O₄, and graphite is studied. The effects of the processing parameters of high-energy ball milling, reduction in H₂ atmosphere, and carburization in Ar/CO atmosphere are investigated. The crystallite size of the as-synthesized WC is 30–40 and 40–50 nm for 900 and 1000 °C carburized powders, respectively. The powder is agglomerated with the size of the primary particles ranging from 50 to 700 nm. High-energy ball milling of WO₃–Co₃O₄–C powder mixtures leads to finer particle and crystallite sizes with larger surface area. Such milled powders can be reduced to nanostructured W at 570 °C and carburized to form WC at temperatures as low as 900 °C. Crystal growth has taken place during carburization, particularly at 1000 °C, which results in the formation of truncated triangular prisms and nanoplates of WC at 1000 °C.     

Efficacy of Novel Electroless Plating Process for Dense Pd/Cr2O3/PSS Membrane Fabrication

This work addresses the role of chromia diffusion barrier on the combinatorial plating characteristics of Pd plating baths during fabrication of dense Pd/Cr₂O₃/porous stainless steel (PSS) composite membranes and is compared with those obtained during fabrication of Pd/PSS membranes. Cr₂O₃ was deposited by electroplating technique followed with oxidation at 700°C and Pd films were deposited using a novel Pd electroless plating process that provides optimal performance. Apart from providing similar process characteristics, the Pd/Cr₂O₃/PSS membrane provided 15.2% lower Pd film thickness in comparison with Pd/PSS membrane for similar pore densification values.     

The preparation of Al/Fe composite powders by electroless plating

The core–shell Al/Fe composite powders were synthesised by electroless plating. The effects of concentration of FeSO₄·7H₂O, pre-treatment method of aluminium powders, and secondary plating on the preparation of core–shell Al/Fe composite powders were studied. The composite powders were analysed by the X-ray diffraction, a scanning electron microscope, and an energy-dispersive spectrometer. The results indicate that the content of iron in the composite powders could be effectively controlled by adjusting the concentration of FeSO₄·7H₂O in the plating solution. The pre-treatment of the raw aluminium powders is also a key factor to form a uniform iron layer on the surface of aluminium particles. Furthermore, the density and iron content of the composite powders prepared by secondary plating have been improved.     

Use of Ti in hard metal alloys – Part II: mechanical properties

WC‐Co hard metal is a material of high hardness, high compressive strength and wear resistance while maintaining good toughness and thermal stability. Samples of nanosized WC powders with 10 wt% Co, WC‐10 wt% Ti, WC‐9 wt% Ti‐1 wt% Co were cold pressed at 200 MPa and sintered at 1500°C during 1 hour under vacuum of 10^–2 mbar. The characterization of the sintered materials was performed by the measurements of densification, HV30 hardness, fracture toughness and compression strength. The results showed that it is possible to process a hard metal through a Powder Metallurgical conventional route from nanoscaled WC grains, using Ti (or a Ti‐Co mixture) as a binder phase, with good mechanical properties.     

Preparation of AlN-Cu composite powders by electroless plating of controlled oxidized nitride particles to prevent degradation by hydrolysis

The present work describes the preparation of AlN-Cu composite powders by electroless plating. Initially, the hydrolysis reaction of the ceramic particles in the electroless solution was studied as a reference element for the design of a protective surface barrier that enabled the coating process, with no ceramic phase degradation. The metal source of the electrolytic bath was copper sulfate, with formaldehyde as the reducing agent, under alkaline conditions of pH 12. The microstructural characterization indicated the formation and growth of aluminum hydroxides from AlN particles, inhibiting the coating of Cu by increasing the OH⁻ ions in the solution. As the exposure time increased, the ellipsoidal bayerite grew from AlN and transformed into prismatic particles of the thermodynamically more stable gibbsite phase. To prevent the degradation of AlN, a controlled oxidation stage was implemented to form a protective barrier of non-reactive alumina on the surface through thermal treatment in oxidizing atmospheres. An atmosphere of dry air was found to be more appropriate than pure oxygen for the formation of a continuous and dense layer of crack-free alumina on nitride surfaces, and a temperature of 1000 °C for 1 h enabled the formation of 3.9 by weight of α-Al₂O₃, capable of reducing the hydrolysis reaction of AlN. The process of autocatalytic deposition on the passivated particles, applied in three consecutive steps of metallization, led to AlN-Cu composite powders with 29 wt% Cu. Finally, the coated powders were treated in a hydrogen-reducing atmosphere at 400 °C to remove traces of the Al(OH)₃ phase encountered, as well as to improve the adhesion of the nanostructured deposit of the cauliflower-like structure to the AlN surfaces, obtaining AlN-Cu composite powders suitable for the preparation of metal/ceramic composites.     

Investigation on a Non-cyanide Plating Process of Ni-P Coating on Magnesium Alloy AZ91D

In this research we presented a non-cyanide plating process of Ni-P alloy coating on Mg alloy AZ91D. By applying a new process flow of electroless nickel plating in which zinc coating is used as transition of Ni-P coating on Mg alloy AZ91D, the process of copper transition coating plated in the cyanides bath can be replaced. A new bath composed of NiSO4 was established by orthogonal test. The results show that zinc transition coating can increase the adhesion and pH 4.0 and 95℃, respectively. The present process flow is composed of ultrasonic cleaning→alkaline cleaning→acid pickling→activation→double immersing zinc→electroplating zinc→electroless nickel plating→passivation treatment.The present non-cyanide process of electroless nickel plating is harmless to our surroundings and Ni-P coating on Mg alloy AZ91D produced by present process possesses good adhesion and corrosion resistance.     

Preparation of high-purity and ultrafine WC-Co composite powder by a simple two-step process

In this study, high-purity and ultrafine WC-6%Co composite crystallites was synthesized by a simple two-step process consisting of the precursor-formation of the mixture of blue tungsten oxide (WO_2.9) and cobaltic oxide (Co₂O₃) and the following deep reduction and carburization with CH₄-H₂ mixed gases. The experimental results revealed that after the first carbothermic reduction stage at 1050 or 1150 °C, a mixture of W, WO₂ and Co₇W₆ was obtained, which was further carburized to the WC and Co phases by CH₄-H₂ mixed gases at 900 °C. With the increase of C/WO_2.9 molar ratio, the particle sizes of first-stage precursor and carbonized product were both decreased. The particle sizes of final products are mainly determined by C/WO_2.9 ratio and reaction temperature at the first stage. When the C/WO_2.9 ratio was in the range of 2.3–2.7, the high-purity WC-6%Co composite powder with the average particle sizes of 160–410 nm could be obtained.     

Fabrication of conductive copper-coated glass fibers through electroless plating process

A simple electroless copper plating process was employed to prepare copper-coated glass fibers with excellent conductivity. The glass fibers were pretreated by etching, sensitizing, and activating procedures. Disodium ethylenediamine tetra acetate (EDTA-2Na) and hydrazine hydrate (N₂H₄·H₂O) were employed as complex reagent and reductant, respectively. It was found that the copper deposition was greatly influenced by dosage of EDTA-2Na, concentration of sodium hydroxide (NaOH), temperature, and volume of N₂H₄·H₂O. The optimal temperature for electroless copper plating ranged from 40 to 60 °C. The composites were characterized by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy techniques. The result showed that the minimum volume resistivity of 0.0010 Ω cm was obtained for the sample with perfect copper coatings on the surface of glass fibers. This method is simple, low-cost, and large production, and can be extended to fabricate other metal-coated glass fibers with distinct conductivity.     

Use of Ti in hard metal alloys – Part I: structural and microstructural analysis

Nanosized WC, and binders Co, Ti and Ti‐Co, are used to process hardmetals. Titanium (Ti) was proposed to reduce and even replace the Co in these composites, verifying the effectiveness of the new binders. Samples of nanosized WC with 10 wt% Co, 9 wt% WC 1 wt% Ti – Co, WC‐10 wt% Ti were cold compacted at 200 MPa and sintered at 1500°C during 1 hour under vacuum of 10^–2 mbar for the processing of hardmetal were performed. The structural characterization by X‐ray diffraction and microstructure by scanning electron microscopy (SEM) and EDS microanalysis of the sintered material. We observed the presence of the W₂C phase in the sintered samples, and Co₃W phases in the samples with Co content and a good distribution of binder phase, leading to formation of small “pool” of Co and Ti and small porosity and well distributed. It was proved that using Ti as binder phase, the neta phase formation was avoided.     

Combinatorial Electroless Plating Characteristics for Dense Pd–PSS Composite Membrane Fabrication

Emphasizing upon a process–product combinatorial perspective, this article addresses the role of rate enhanced electroless plating baths for the fabrication of dense Pd/porous stainless steel composite membranes. Adopting phasewise contacting pattern of the reducing agent, plating experiments have been carried out with variegated Pd electroless plating baths at a palladium solution concentration of 0.005 M with a loading ratio of 203 cm²/L for the plating time of 2–6 h. Amongst all processes, surfactant and sonication coupled electroless plating baths provided optimal combinations of combinatorial plating process characteristics for dense Pd composite membrane fabrication.     

Determination of oxygen in W-C-Co nanopowders

The oxygen content of W-C-Co nanopowders produced by plasma reduction of WO₃, followed by low-temperature carburization in hydrogen has been determined by carrier gas hot extraction. The oxygen in adsorbed water, carbon-oxygen complexes weakly bound to the surface, and surface oxides (WO _x and CoO _x ) has been determined separately. Freshly prepared, passivated WC and WC + 8% Co powders with a specific surface area of 6–11 m²/g were found to contain 0.03–0.07 μg/cm² of oxygen, not counting adsorbed water. Strongly bound oxygen in the form of surface oxides accounts for at least 80% of the total oxygen. These oxygen contents are equivalent to surface coverages from 1.2 to 2.5 oxygen monolayers (monolayer density of 10¹⁵ at/cm²). The water content varies from 0.15 to 0.3%, which corresponds to a water film no thicker than a monolayer. All of the water is physisorbed. The products of the plasma reduction of WO₃ have a complex phase composition (W₂C, WC_{1 ? x} , W, α-WC) and a specific surface area from 21 to 24 m²/g. In spite of the high content of the readily oxidizable phases W and W₂C, the plasma-synthesized mixtures have submonolayer surface coverages with oxygen. They are protected from air oxidation by thin (one to three monolayers) pyrolytic carbon films, while the small amount of oxygen present originates from unreacted particles. In dry air, the powders oxidize insignificantly. At 100% humidity, stoichiometric WC powders are the most stable, while WC + 8% Co shows the lowest stability. The oxidation rate of W-C powders is proportional to the overall content of W and W₂C.     

基于微观结构的热喷涂WC/Co涂层裂纹生长模拟

涂层微观结构特征直接影响涂层的寿命,基于涂层微观结构研究涂层裂纹扩展特征成为评价热喷涂层性能的重要问题.本文基于WC/Co涂层微观结构建立了有限元模型,并采用XFEM方法研究了单应力状态预存裂纹行了模拟,获得了涂层微观裂纹扩展的损伤规律.研究表明:在拉应力作用下,沿着WC-Co边界产生的应力集中是涂层裂纹产生的根源;WC/Co涂层浅表面(0.125b,b为涂层厚度)的水平裂纹对垂直拉应力敏感、吸收能量快,0.78b处的裂纹扩展后对应力响应迅速,因此0.125b与0.78b是WC/Co涂层裂纹生长的关键深度;在0.78b处,当初始裂纹角度0°～45°时,扩展位移逐渐减小,扩展偏转角增大,45°时存在能量积累导致角度快速偏转.在周期应力作用时,WC/Co涂层的疲劳周期随应变幅值增加而减小;应变幅值相同时,WC/Co涂层的疲劳周期随频率增加而增加.     

Synthesis of WC hard materials using coated powders

Nickel and cobalt were used as binder materials for tungsten carbide powders (WC) hard materials. Ni and Co binder were added individually to the WC powder by two different methods namely, mechanical mixing and chemical electroless coating. In this study WC powders of grain sizes 0.3–1.0 μm were electroless coated with either nickel or cobalt. The loading of either Ni or Co coating was 13 wt.%. The electroless-coating method conditions of both Ni and Co on WC powders are described. The coated powders were cold compacted and sintered in vacuum at different sintering temperatures. For comparison, identical materials compositions were prepared by mixing the powders constituents mechanically, compacted and sintered under the same conditions.The prepared powders and sintered materials were investigated using X-ray diffraction (XRD) and scanning electron microscope (SEM). The results revealed that coated WC materials have smaller values of porosity and more homogeneous microstructure while other properties, such as transverse rupture strength, and hardness exhibit greater values than those produced using mixing elemental powders. It is possible to outline the benefits of coated powder approach in the following: high homogeneity and better distribution of binder materials within WC hard materials, higher density and good interfacial bonding, capability of using fine powders, and possibility of using small alloying and/or reinforcement additions in a more uniform manner.     

Combustion synthesis of WC powder in the presence of alkali salts

This paper deals with the formation of tungsten carbide sub-micrometer powders from WO₃ + Mg + C + sodium salts (NaCl, Na₂CO₃) system by combustion synthesis technique. The powders were characterized by XRD and FESEM. X-ray data demonstrate the superiority of the NaCl + Na₂CO₃ combined mixture in the WC formation process. Single phase, sub-micrometer WC powders were synthesized at temperatures as low as 1600 °C. The roles of sodium salts in combustion process were discussed and chemical mechanism of WC formation was proposed. WC powder produced by salt-assisted combustion synthesis technique has a size 0.2–3 μm, crystalline shape and low agglomeration degree.     

Wettability and spreading kinetics of molten aluminum on copper-coated ceramics

The purpose of this study was to investigate the influence of Cu-coating on the spreading kinetics and equilibrium contact angles of aluminum on ceramics using a sessile drop technique. Al₂O₃ and SiC plates were coated by electroless plating. The copper film overcomes the low wetting of the uncoated samples by dissolution in the drop at 800 °C in argon, showing an intrinsically favorable effect on the adhesion energy. Just after 2 min, the contact angle decreased to 12.6° and 26°for Al/Cu–Al₂O₃ and Al/Cu–SiC, respectively. However, a de-wetting behavior was observed, reaching equilibrium contact angles of 58.3° and 45.5° for the couples. The dissolution reaction rate at the triple junction was so high that the spreading process was controlled by local diffusion rather than chemical reaction kinetics.     

Microstructure and thermal decomposition property of Ni-P/Cr2N composite powder by electroless plating

Cr₂N is the most promising blowing agent for the preparation of steel foam using melt foaming method. In this work, to obtain a blowing agent with suitable density and gas decomposition characteristics for steel melt foaming, Ni-P/Cr₂N composite powder was prepared by electroless plating. The surface morphology, phase, coating thickness, density and decomposition characteristics of Ni-P/Cr₂N composite powder were analyzed. The results indicate that the surface of Ni-P/Cr₂N composite coating powder is covered by the high nickel and low phosphorus layer which has a dense and uniform cell structure. The decomposition rate of the Ni-P/Cr₂N composite powder is 7.46?mW/mg slower than that of the uncoated Cr₂N powder at 1107.4?°C. When the plating time is 30?min, the thickness of Ni-P layer reaches 2.86?μm, the density of the Ni-P/Cr₂N composite powder is 7.45?g/cm³, and maximal decomposition rate temperature reaches 1500?°C. These findings suggested that Ni-P/Cr₂N composite powder meets the requirements of decomposition temperature and density of the blowing agent used to produce steel foam with a uniform pore structure by the melt foaming method.