Fabrication and machining of ceramic composites — A review on current scenario

Ceramic matrix composites (CMCs) are the best-suited material for various engineering application due to their superior properties. The different processing methods involved in the fabrication and machining of these CMCs are a center for attraction to researchers and industrial society. This review article primarily focuses on the development of different processing methods and machining methods for ceramic matrix composites since the last few years. Out of these fabrication methods, powder metallurgy emerged as a most promising and cost-effective technique. In addition, electric discharge machining (EDM) has proved to be time saving, cost effective, and capable of machining complex shapes in composites. At the end, challenges in the processing and machining of ceramic matrix composites have been identified from the literature, and further benefits of microwave sintering and electric discharge machining of materials have been addressed in the paper.     

The physicochemical parameters during dry heating strongly influence the gelling properties of whey proteins

In this study we determined the composition (proportion of native proteins, soluble and insoluble aggregates) and quantified the gelling properties (gel strength and water holding capacity) of pre-texturized whey proteins by dry heating under controlled physicochemical conditions. For this purpose, a commercial whey protein isolate was dry heated at 80 °C (up to 6 days), 100 °C (up to 24 h) and 120 °C (up to 3 h) under controlled pH (2.5, 4.5 or 6.5) and water activity (0.23, 0.32, or 0.52). Gelling properties were quantified on heat-set gels prepared from reconstituted pre-texturized proteins at 10% and pH 7.0. The formation of dry-heat soluble aggregates enhanced the gelling properties of whey proteins. The maximal gelling properties was achieved earlier by increasing pH and water activity of powders subjected to dry heating. An optimized combination of the dry heating parameters will help to achieve better gelling properties for dry heated whey proteins.     

Aluminum diffusion in aluminide coatings deposited by the CVD method on pure nickel

The aluminum diffusion in aluminide coatings deposited on nickel by the CVD method was investigated. The microstructure, chemical and phase compositions of coatings were examined by SEM, EDS and XRD techniques. The triple zone structure was revealed. The β-NiAl phase was on the surface of the coatings, whereas γ-(Ni) and γ′-Ni₃Al formed deeper parts of the coatings. Diffusion coefficients were calculated from the concentration profiles in coatings deposited for various times (15 min, 1 h, 4 h and 8 h) at 1000 °C and 1050 °C. The procedure was based on the classic finite difference method (FDM). Diffusion coefficients in three phases were calculated simultaneously and the influence of diffusivity in one phase on the diffusivity in the neighboring phase was taken into account. The results of the calculation agree with the literature data obtained for each of the analyzed phases separately.     

Structural and optical behavior of electrodeposited black chrome‐graphite encapsulated FeCo nanoparticles composite coatings

Black chrome‐graphite encapsulated FeCo nanoparticles (BC‐GEFeCo NPs) composite coatings were electrodeposited on substrates such as stainless steel, Cu, and Ni‐coated Cu. The major content of the deposited film is contributed by Cr, Fe‐Cr, Fe₂AlCr, and FeCr_0.29Ni_0.16C_0.06 as deduced from X‐ray diffraction. The root‐mean‐square roughness value of black chrome on Ni‐coated Cu employing PbSb anode is measured by atomic force microscopy (nanoindentation) studies as 57.176 nm, which is in satisfactory agreement with the literature value of 53.83 nm. With the addition of GEFeCo Nps, the root‐mean‐square roughness value for BC‐GEFeCo composite coatings on Ni‐coated Cu increases approximately 6.1 times that of black chrome surface. Copyright © 2016 John Wiley & Sons, Ltd.     

Influence of various surface treated silica nanoparticles on the electrochemical properties of SiO2/polyurethane nanocoatings

Various organosilane-treated SiO₂ nanoparticles were dispersed in a 2-pack polyurethane coating. The influence of surface modification and silica content on the electrochemical behaviour of the resultant nanocoatings was investigated. Electrochemical impedance spectroscopy (EIS) and open circuit potential (OCP) variations were examined. The surface chemistry of nanoparticles and its effect on the resultant nanocoating morphology were also studied utilising FTIR, and TEM analyses. The results reveal that the presence of more hydrophobic groups and longer-lengthed hydrophobic chains on the surface of nanoparticles, greatly improves the interfacial interactions at the polymer/filler interfaces resulting in a better corrosion performance.     

Cu-Fe基金刚石复合材料的制备工艺及性能

采用真空热压烧结工艺制备了Cu-Fe基粉末金刚石复合材料磨头,通过金相、XRD及硬度测试等实验方法,研究了不同烧结温度下制得的合金材料的显微组织特性和性能。结果表明,在实验条件下,烧结体中各元素之间产生了冶金结合,且合金化程度随着温度的升高而增大;930℃时,烧结体中金刚石与基体结合性较好,金刚石无石墨化现象,烧结体的硬度最高,达到160HB。     

Evolution of thermal stress in a coating/substrate system during the cooling process of fabrication

An analytical model is established for the thermal stress evolution in a film/substrate system during the cooling process of fabrication. Herein, heat transfer characteristics are incorporated which is critical for thermal spray coatings. The in situ temperature field solution is used to derive the instantaneous thermal stress field. Since the loss of thermal energy is account for, the new model may provide the basis for a more realistic prediction of the in situ thermal stress the fabrication process. The magnitude of thermal stress derived from the present model is lower than that of the classic one. The thermal stress is generated quickly and significantly during the initial seconds of the cooling process, and stabilizes later. The effects of several spray factors, such as the pre-heat temperature and the thicknesses of coating and substrate, are discussed and compared with a parallel experiment.     

A micro-ultrasonic powder moulding method to fabricate Sn–Bi alloy micro parts

The Sn–Bi eutectic alloy powder in the micro-cavity was melted by ultrasonic vibration and rapidly cooled to form micro parts; no subsequent sintering process was required. Three kinds of Sn–Bi alloy micro gears were successfully fabricated, which verified the feasibility of the micro-ultrasonic powder moulding method. The effect of ultrasonic exposure time on the microstructure and mechanical properties of the micro parts was investigated respectively by metallographic analysis, XRD and tensile testing. Reasonable process parameters for this method were determined, which were sonotrode pressure of 63.5 MPa, ultrasonic output power of 2475 W and ultrasonic exposure time of 1.5 s.     

Iodide substitution in lithium borohydride, LiBH4-LiI

The new concept, anion substitution, is explored for possible improvement of hydrogen storage properties in the system LiBH₄-LiI. The structural chemistry and the substitution mechanism are analyzed using Rietveld refinement of in situ synchrotron radiation powder X-ray diffraction (SR-PXD) data, attenuated total reflectance infrared spectroscopy (ATR-IR), differential scanning calorimetry (DSC) and Sieverts measurements. Anion substitution is observed as formation of two solid solutions of Li(BH₄)_1−xI_x, which merge into one upon heating. The solid solutions have hexagonal structures (space group P6₃mc) similar to the structures of h-LiBH₄ and β-LiI. The solid solutions have iodide contents in the range ∼0-62 mol% and are stable from below room temperature to the melting point at 330 °C. Thus the stability of the solid solutions is higher as compared to that of the orthorhombic and hexagonal polymorphs of LiBH₄ and α- and β-LiI. Furthermore, the rehydrogenation properties of the iodide substituted solid solution Li(BH₄)_1−xI_x, measured by the Sieverts method, are improved as compared to those of LiBH₄. After four cycles of hydrogen release and uptake the Li(BH₄)_1−xI_x solid solution maintains 68% of the calculated hydrogen storage capacity in contrast to LiBH₄, which maintains only 25% of the storage capacity after two cycles under identical conditions.     

采用泡沫铜改进ZrCo合金吸放氢性能研究

采用孔隙率大于90％的泡沫铜装填ZrCo合金粉末，测试分析了泡沫铜填充ZrCo合金粉末的吸放氢性能和充放氢抗破坏性能。结果表明：通过泡沫铜填充法制备贮氢块的传热性能比自然堆积状态的粉末有很大提高，因此采用泡沫铜装填的贮氢反应容器吸、放氢速率比自然堆积粉末有明显改善，并显著提高了充放氢抗破坏能力，利用该方法改进贮氢粉末的装填方式是可行的。