LaPO4 coating on alumina-based fiber: Strength retention of fiber and improvement of interfacial performances

The characteristics of the interface are the key factors that determine the mechanical properties and fracture behavior of fiber-reinforced ceramic matrix composites. Design and preparation of coatings which can preserve fiber strength and maintain appropriate interfacial bonding strength are of great challenges. LaPO₄ coating is a promising weak interface coating for oxide fiber reinforced oxide ceramic matrix composites. Through this coating, the toughening mechanism of the composite such as fiber pulling out and fiber debonding is triggered. The LaPO₄ coating was deposited on the surface of alumina-based fibers by a solution precursor heterogeneous precipitation method. The effects of different precursors and different deposition temperatures on fiber strength were studied, and the mechanism of the strength degradation of the coated fiber was analyzed. It was found that the fibers coated with phytic acid precursor and deposited at 90 °C had the highest tensile strength compared to other coated fibers. The retention of strength is attributed to its loosely stacked coating. Besides, a single fiber pullout test was carried out to evaluate the effect of the coating on the interface of the composites. The results show that the composites coated by depositing citric acid precursor and phytic acid precursor at 90 °C can reduce the interfacial bonding strength by 32.5% and 46.7%, respectively compared to uncoated composites. This study has potential application value in the preparation of ceramic matrix composites used in oxidation and high temperature environments.     

Strength degradation of SiC fibers with a porous ZrB2-SiC coating: Role of the coating porous structure

ZrB₂-SiC coatings with varied porous structures were deposited on SiC fiber tows using the sol-gel method and cured at 1400 ℃ in vacuum. Tensile strength of the coated SiC fibers were much lower than that of the uncoated fibers. The bimodal distribution in the Weibull plot of the coated SiC fibers demonstrated that the fracture of the coated fiber can be attributed to two types of defects: the porous structure of the coating and the fiber defects. Detailed morphology and microstructure characterization of the coating and fiber combined with strength calculation were carried out to investigate the individual contribution of the fiber defects and the porous coating layer respectively. The results revealed that apart from the fiber damage during the coating process the porous structure of the fiber coating has a non-negligible effect on the fiber strength, presumably due to a relatively strong bonding between the fiber and coating.     

UV-Light Absorption Properties of Cr-Doped Polyethyleneglycol (PEG)/γ-Glycidoxypropyltrimethoxysilane (GPTMS)/Chelated-Titanium Coating Materials Prepared by the Sol–Gel Process

New hybrid inorganic–organic glass coating materials, which contain polyethyleneglycol/γ-glycidoxypropyltrimethoxysilane/titanium(IV)-n-propoxide(2-methoxyethylacetoacetate)/chromium(III)nitrate [PEG/GPTMS/Ti(OR)(2-MEAA)/Cr³⁺] have been developed for UV-light absorption by using the sol–gel process. The effect of agitation time and temperature on UV-light absorption was investigated. The titanium complex was characterized by ¹H-NMR and FTIR spectroscopies. UV–Vis spectroscopy was used to investigate the optical properties of the coating materials. The results show that the coated glass has very low transmission in the UV region (300–400 nm) compared to the uncoated glass, especially at 150, 200, 250 and 300°C treatment temperatures after 1- and 18-hour agitation times. The UV-light transmission of the coated glass was not different from the uncoated glass between 80–100°C and 350–500°C.     

On the shock-based determination of the adhesive strength at a substrate-coating interface

Evaluating the bonding strength at the interface between two layers is an issue of considerable practical interest for a wide variety of engineering applications involving coatings, such as thermal protective ceramics coated on engine blades. Spallation under laser driven shock loading is one of the experimental means to test interface debonding. However, numerical simulations are usually needed to infer a quantitative value of the bonding strength from such tests, where the coating free surface velocity is usually the only measurable variable. In this paper, the analysis of the propagation and interactions of compression and release waves leading to spall fracture in a shock-loaded material is detailed, then it is extended to a substrate-coating system. Different cases are considered, depending on the acoustic impedances of the substrate and coating materials and on the duration of the loading pressure pulse with respect to the wave transit time through the coating thickness. In each case, the interfacial strength can be analytically estimated from the velocity variations without resorting to numerical models.     

Titania-Coated Magnetite and Ni-Ferrite Nanocomposite-Based RADAR Absorbing Materials for Camouflaging Application

A novel core–shell-structured nanocomposite material based on titanium dioxide-coated magnetite and Ni-ferrite has been prepared for RADAR absorbing application in a X-band region. The coating of magnetic particles with TiO₂ was carried out by in situ hydrolysis of titanium tetrabutoxide, and the composite absorber sheets were prepared with epoxy resin. The morphological characterization of the magnetic particles was studied with field emission scanning electron microscope, transmission electron microscope, X-ray diffraction, and vibrating sample magnetometer analysis techniques. The measurement results confirmed the coating of magnetic particles with TiO₂ and reduction of the magnetization of magnetite and Ni-ferrite nanoparticles compared with the uncoated ferrite nanoparticles. Distribution of particle inside the matrix was studied with scanning electron microscope. Microwave absorption study in X-band (8–12 GHz) region was carried out with vector network analyzer. Results showed reflection loss values of ?26.5 db at 9.08 GHz for the magnetite coated with titanium dioxide/conducting carbon black containing sample which increased to ?45.7 db at 9.13 GHz for the Ni-ferrite coated with TiO₂/conducting carbon black formulation. It was observed that coating of magnetic particles resulted in the improvement in the microwave absorption.     

The effect of nano-structured alumina coating on the bond strength of resin-modified glass ionomer cements to zirconia ceramics

The purpose of this study was to evaluate the effect of Y-TZP ceramic surface functionalization with a nano-structured alumina coating on bond strength of the resin modified glass ionomer dental cement. A total of 160 disc-shaped specimens were produced and randomly divided into two groups of 80. Half of the discs in each group received an alumina coating which was fabricated by exploiting the hydrolysis of aluminum nitride (AlN) powder. The shear bond strengths of the resin-modified glass ionomer cement FUJI+ (GC Japan) and the composite resin luting agent RelyX Unicem (3M ESPE, USA) were then studied for the coated and uncoated surfaces The SEM analyses revealed that the application of an alumina coating to the Y-TZP ceramics created a highly retentive surface for bonding. The bond strengths for the coated groups in both cements were significantly higher than the uncoated groups.     

Active metal brazing of graphite foam-to-titanium joints made with SiC-Coated foam

Medium-density, high-conductivity carbon foams were joined to titanium using a two-step process that first exposed foam to SiO vapor at 1450 °C for 30 min. under vacuum followed by vacuum brazing Ti using Cusil-ABA to the sides of prismatic foam pieces along the ‘with-rise’ (WR) or foaming direction and the ‘against rise’ (AR) or transvers direction. Well-bonded joints with braze-infiltrated foam and Ti-rich interfaces formed along WR and AR. The un-bonded foam was stronger along WR (785 kPa) than along AR (277 kPa) as were the joints made using coated and uncoated foams. Foam thickness minimally affected joint strength along WR but along AR, joints with thick foam were 58 % stronger. The coating marginally (9 %) lowered joint strength along WR but led to a nearly 50 % strength drop along AR. The experimental foam is more robust and amenable to coating and joining along foaming direction than transverse to it.     

超临界流体快速膨胀法粒子包覆技术喷嘴的设计

改进了RESS法粒子包覆技术中喷嘴的结构。改进后的喷嘴,其喷孔可调,克服了传统毛细喷嘴易堵管、喷出效率低及包覆不紧密的缺点;采用laval管作送粉喷管,使被包覆粒子以超音速喷出,极大的加强了被包覆粒子和包覆剂粒子的碰撞力度;通过添加内外反向旋流器,使被包覆粒子和包覆剂粒子在喷嘴出口处高速反向旋转碰撞,实现粒子的均匀包覆。     

Attrition strength of different coated agglomerates

The goal of this paper is to test the strength against attrition of coated particles. What is the influence of different coating materials on different particles? To answer this question, two different core materials are coated with four different water-soluble polymers. The core materials are micro-crystalline cellulose (MCC) and sodium benzoate granules in the size range between 850 and . The coated granules are attrition tested in the repeated impact tester (RIT). During attrition testing the uncoated MCC granules do not show any attrition. When the MCC granules are coated, all the attrition observed is due to the failure of the coating. When the sodium benzoate (Purox-S) granules are attrition tested, significant attrition is observed. Coating the sodium benzoate granules with the polymers increases the strength against attrition. During attrition three typical failure modes are distinguished viz. the peeling mechanism, the erosion mechanism and the layer fatigue mechanism. For the four different coatings different attrition mechanisms are observed indicating that the polymer mechanical properties play an important role. For example, a higher molecular mass for poly(ethylene glycol) increases the mechanical stability of the granules. It is now important to study the mechanical polymer properties in more detail, to explain further the observed failure modes. With the RIT it is possible to select the optimal settings in the coating process, to optimize the coating material or composition and finally to optimize the coating thickness.     

TiB2涂层刀具制备及干铣削Ti-6Al-4V磨损行为研究?

由于切削过程中产生高温、刀具粘结与氧化严重,钛合金切削尤其是干切削,一直是刀具行业的重大挑战之一,而在刀具表面添加涂层是提高钛合金切削刀具寿命的有效途径。利用脉冲磁控溅射技术制备了TiB2涂层刀具,以相同基体的无涂层刀具为对照,干铣削Ti-6Al-4V钛合金,切削速度从30~100 m/min变化,研究TiB2涂层刀具的切削性能与失效机理。所制备的TiB2涂层具有(100)择优取向的六方晶体结构,组织致密。涂层硬度可高达4000 HV。切削实验发现,在30 m/min的低速时,TiB2涂层刀具的切削寿命超过无涂层刀具57%之多,当切削速度加倍到60 m/min时,刀具寿命未见下降。当切削速度增加到100 m/min时,TiB2涂层刀具与无涂层刀具切削寿命相当。TiB2涂层刀具表面氧化所产生的B2O3液化膜,起自润滑作用,可充分减少钛合金的粘结,降低摩擦力。因此,在TiB2或B2O3消失之前,TiB2涂层刀具均有良好表现。在100 m/min时,切削高温造成B2O3强烈挥发,且TiB2被氧化为多孔疏松的TiO2,刀具寿命急剧下降到无涂层刀具的水平。     

Boosting bonding strength of hydroxyapatite coating for carbon/carbon composites via applying tree-planting interface structure

Hydroxyapatite (HA) coated carbon/carbon composites (CC) is a potential material for orthopedic application because of the combination of good biocompatibility and mechanical properties. In this work, we synthesize a tree-planting interface which is composed of holes formed by micro-oxidized CC substrates and carbon nanotubes (CNTs) to achieve a high bonding strength of HA coating. The holes include annular gaps between carbon fiber and pyrolytic carbon, as well as irregular holes formed by oxidized pyrolytic carbon. The CNTs can grow inside the holes and extend into the HA coating. As a result, the bonding strength of HA coating with tree-planting interface achieves 11.14 ± 0.78 MPa. It increases by 181.3% comparing with the HA coating on CC without interface (3.96 ± 0.30 MPa). The in-vitro bioactivity evaluated by the response of mesenchymal stem cells (MSCs) shows promotions of cell proliferation and cell activity with increasing culture time. After applied with tree-planting interface, the HA coating with strong bonding and good bioactivity may be applied in orthopedic field in the future.     

A novel method for preparing nanoparticle‐coated additives used in polypropylene composites

A novel simultaneous, in situ milling and coating method carried out in a fluid energy mill (FEM) is applied for the first time to prepare nanoparticle‐coated CaCO₃ (CC) additives for polymer composite materials. Simply milled (without coating) CC particles and as‐received CC particles were used as references for comparison. The effects of the grinding pressure and the fraction of the nanoparticles on the size and flowability of CC particles were studied. The composites made with polypropylene (PP) and this specially prepared CC have higher elongation at break, elastic modulus, and impact strength, compared with the PP filled with uncoated CC. The thermal and thermo‐oxidative stabilities of PP are improved as well by introducing the milled and nanoparticle‐coated CC. POLYM. ENG. SCI., 2012. © 2011 Society of Plastics Engineers     

High performance reaction-induced quasi-ceramic silicone conversion coating for corrosion protection of aluminium alloys

Regulations posed by the Environmental Protection Agency on the use of chromate conversion coatings have triggered the need to find alternative materials for the corrosion protection of aluminium and its alloys. A simple four-step process of creating a quasi-ceramic coating has been developed. The coating, which is made of environmentally safe chemicals, should be easily and safely manufactured for bulk production. Here, we describe the synthesis, characterization and evaluation of a silicone conversion coating for aluminium metal and its alloys. The spectroscopic techniques utilised in this study have shown the mode of the bonding mechanism between the metal and the coating. Thermal analysis of the material was conducted to evaluate its stability, while nano-mechanical properties were determined and correlated with the surface morphology of the coating. Results obtained from FTIR and XPS spectroscopic techniques suggested that the coating adhered to the metal substrates through active surface functionalities, and thermal analysis showed that the coatings contained volatile solvents including water that evaporated at lower temperatures. Nano-mechanical tests suggested that the coating had elastic properties. Accelerated corrosion and immersion tests were also performed on coated and uncoated aluminium alloys. Coated and uncoated aluminium alloys were also exposed to soil containing sulphate-reducing bacteria. Coated coupons showed excellent corrosion protection and antifouling characteristics indicating that the coatings were impervious and of high integrity.     

Hard coatings on elastomers for reduced permeability and increased wear resistance

Abstract

In this study, three different elastomers, namely hydrogenated nitrile butadiene rubber, fluoroelastomer and silicone, have been subjected to two different hard metallised coatings by ion implantation process. The three different elastomers are commonly used in various seal applications, where reduced wear and gas permeability are essential in maintaining seal performance and functionality. Samples of these rubbers have been coated with chromium coating in one set of tests. In the second set of tests, samples of elastomers have been coated with tungsten carbide coating being deposited on all the three different elastomers. Wear, gas permeability and mechanical behaviour of the coated samples were compared with each other and with the control uncoated elastomers. All the coated samples showed good reduction in gas permeability. With the use of metallised coatings, there has been improved resistance to wear in all the coated samples. Adhesion strength and effect of coating on the elastomer have been investigated by mechanical testing. Mechanical tests revealed good adhesion of metal coatings on all the rubber samples, and there was no detrimental effect on the mechanical properties after coating.     

冰冻海水环境下混凝土表面涂层长期暴露试验研究

本文通过对暴露长达10年的表面涂层混凝土试件和青岛市胶州湾大桥实体结构进行涂层粘结强度、氯离子浓度等测试,对涂层应用在混凝土结构上的长期防护效果进行了研究。结果表明:在冰冻海水环境暴露10年后,大气区、浪溅区和水变区混凝土表面涂层的粘结强度均超过1.5 MPa,符合现行规范要求;在浪溅区和大气区环境下,涂层对海工混凝土的长期防护效果较好,但在水变区环境下涂层的防护效果相对较差;有涂层混凝土试件的表观氯离子扩散系数与无涂层混凝土在水变区环境下已无明显差别;大桥实体结构中有涂层混凝土的表面氯离子浓度较无涂层混凝土降低了2.3~3.9倍,且涂层对于实体结构的抗氯离子长期侵蚀效果稍弱于小尺寸混凝土试件。     

钛合金表面TiO2-FHA-HA梯度生物陶瓷涂层的制备

采用溶胶-凝胶工艺在经过微弧氧化预处理的钛基体表面制备二氧化钛(TiO2)-含氟羟基磷灰石(FHA)-羟基磷灰石(HA)梯度结构的生物陶瓷涂层.采用X射线衍射检测了涂层的相组成,采用扫描显微镜观察了梯度涂层的形貌,采用划痕法测定了涂基结合力,结果表明:所制备的涂层是均匀和致密的具有梯度结构的TiO2-FHA-HA涂层;与单一的HA涂层相比梯度的引入显著提高了涂基结合力.生物溶解性实验结果显示了溶解速度FHA小于HA,这就表明了可以通过梯度设计来提高涂层的植入寿命.     

Enhancement of mechanical properties of hydroxyapatite coating prepared by electrophoretic deposition method

The addition of bio-inert ceramics such as alumina and zirconia can significantly improve the mechanical properties of hydroxyapatite bioactive coatings and increase their biocompatibility. In the present study, the surface of a titanium substrate was coated by the electrophoretic deposition method (EPD). Moreover, the reaction bonding process has been used to precipitate the nanocomposite containing the hydroxyapatite (HA), alumina, yitteria-stabilized zirconia (YSZ). The coating process was performed by an electrical power supply and a suspension of hydroxyapatite, aluminum, and YSZ nanopowders. For preparing a suspension consisting of 50% isopropanol and 50% acetone, 0.6 g/L of iodine was used as a stabilizer. Green and sintered coatings were analyzed by FE-SEM and XRD. In addition, the mechanical properties such as bonding strength, hardness, and toughness were measured. The hardness, bonding strength, and toughness of the HA coating were 107 ± 10.3 HV, 10.8 ± 3.2MPa, and 0.72MPa√m, respectively, while those of the HA-Al₂O₃-YSZ nanocomposite coating were 213 ± 1.8 HV, 35 ± 1.6MPa, and 1.6MPa√m, respectively.     

Novel bi-layered nanostructured SiO2/Ag-FHAp coating on biodegradable magnesium alloy for biomedical applications

In this study, a novel bi-layered nanostructured silica (SiO₂)/ silver-doped fluorohydroxyapatite (Ag-FHAp) coating was deposited on biodegradable Mg-1.2Ca-4.5Zn alloy via physical vapor deposition (PVD) combined with electrodeposition (ED). The nano-SiO₂ underlayer had a compact columnar microstructure with thickness of around 1 µm while the Ag-FHAp overlayer presented large plate-like crystals accompanied with small rounded particles with thickness about 10 µm. Potentiodynamic polarization test exhibited that the double layer SiO₂/Ag-FHAp coated Mg alloy has superior corrosion resistance compared to uncoated and single layer SiO₂ coated samples. Contact angle measurement showed that Ag-FHAp coating over nano-SiO₂ layers significantly increased surface wettability which is favorable for the attachment of cells. Cytotoxicity tests indicated that the nanostructured SiO₂/Ag-FHAp coating enabled higher cell viability compared to nano-SiO₂ coating and uncoated samples. In addition, bi-layer and single-layer coatings considerably improved the ability of cell attachment than that of the uncoated samples. The cell viability of coated and uncoated samples increased with increasing incubation time. The double layer SiO₂/Ag-FHAp coated biodegradable Mg alloy possessed high corrosion resistance and cytocompatibility and can be considered as a promising material for implant applications.     

涂层对速凝3D打印水泥砂浆力学性能的影响

3D打印砂浆普遍存在层间界面粘结较弱、抗折强度较低的问题,而膨胀水泥浆涂层涂覆于砂浆表面可产生表层压应力,进而提升其抗折强度,作为界面剂涂覆于层间可同时增强其界面粘结强度。本文通过将硫铝酸盐水泥与膨胀剂混合而成的涂层涂覆于速凝3D打印砂浆的表面与层间,研究了该涂层对不掺纤维及掺0.5%(体积分数)玄武岩纤维3D打印砂浆试件力学性能的影响规律。结果表明,涂覆层间涂层对无纤维与掺纤维速凝3D打印砂浆的层间界面粘结强度提升率分别为21.4%、12.2%,同时对其抗压强度也有一定提升作用。仅涂覆表面涂层与仅涂覆层间涂层对3D打印砂浆的抗折强度提升效果相当;同时涂覆表面及层间涂层对3D打印砂浆的抗折强度提升效果最显著,与无纤维、掺纤维的无涂层试件相比,提升率最高分别可达44.2%、23.2%。涂层对于无纤维3D打印试件层间粘结强度及抗折强度的提升效果优于掺纤维试件。     

Performance of polyurethane-coated concrete in sewer environment

Polyurethane-based coatings are used to protect concrete facilities against corrosive environments. The performances of two commercially available polyurethane coatings were evaluated under sulfuric acid environment (representing sewer condition) for over 5 years. Both dry (representing new construction) and wet (representing rehabilitation) concretes were used in this study. A combination of the full-scale hydrostatic test, bonding test, and chemical resistance tests were performed to evaluate the coatings to protect concrete structures below ground water. The full-scale hydrostatic test was used to evaluate the application and performance of coatings under hydrostatic pressure to simulate underground concrete structures below ground water. Visual inspections and in situ bonding tests were performed on coated concrete under a hydrostatic pressure of 105 kPa. Test results showed that bonding strength of one coating was affected by the moisture condition and hydrostatic water pressure in the full-scale test. Coated cement concrete specimens with pinholes were used to study the chemical resistance of the coated concrete in sulfuric acid to represent the worst sewer condition. Change in weight of coated concrete specimens was measured at regular intervals. Types of failures in coated concrete under acidic environment have been identified. Test results showed that the performance of the two coatings were noticeably different and one coating with pinholes extended the service life of concrete by 14 times while the other coating extended the service life of concrete by 57 times. There was no direct correlation between bonding strength and chemical resistance of the polyurethane-coated concrete. Although both coatings were polyurethane-based, their performances were different under the testing conditions adopted in the study.