Adhesion of Ceramic Coating on Thin and Smooth Metal Substrate: A Novel Approach with a Nanostructured Ceramic Interlayer

The adhesion of plasma-sprayed coating is, to a large extent, controlled by the cleanness and roughness of the surface on which the coating is deposited. So, most of the plasma spray procedures involve surface pretreatment by grit-blasting to adapt the roughness of the surface to the size of the impacting particles. This preparation process brings about compressive stresses that make it inappropriate for thin substrates. The present works aim to elaborate a thick ceramic coating (about 0.5?mm thick) on a thin metal substrate (1?mm thick) with a smooth surface (Ra of about 0.4???m). The coating system is intended for use in a Generation-IV nuclear energy system. It must exhibit a good adhesion between the ceramic topcoat and the smooth metal substrate to meet the specifications of the application. Our approach consisted of depositing the ceramic topcoat by air plasma spraying on a few micrometers thick ceramic layer made by suspension plasma spraying. This nanostructured layer played the role of a bond coat for the topcoat and made it possible to deposit it on the as-received substrate. The adhesion of the nanostructured layer was measured by the Vickers indentation cracking technique and that of the ceramic duplex coating system by tensile test.     

MECHANICAL ANALYSIS AND NUMERICAL CALCULATION OF BONDING STRENGTH MEASUREMENT BY INTERFACIAL INDENTATION METHOD

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熔融模拟灰在h-BN基陶瓷涂层表面的粘附特性

针对锅炉燃烧劣质煤过程中存在的结渣问题,采用料浆法在20G钢材表面制备了h-BN基陶瓷涂层,对熔融模拟灰在钢片及涂层表面的接触角、铺展系数、粘附功等参数进行研究,进而分析熔融模拟灰在两种试样表面的粘附特性。结果表明：涂层表面较为致密,且与基材嵌合紧密,涂层附着力等级为0级,耐冲蚀性能较好,不易脱落。熔融模拟灰在涂层表面的接触角较大、粘附功较小。熔融模拟灰在涂层表面铺展系数较小,而且随着温度升高,熔融灰在涂层和钢片表面铺展系数的差值逐渐增大,在倾斜放置的试样表面,涂层和钢片铺展系数差值随着角度的增加而增大。通过对试样片截面的SEM/EDS分析可知,涂层对熔渣具有化学不亲和性,能有效阻止Pb的扩散,表明在钢片表面喷涂涂层能减弱熔融灰的润湿性和结合强度,提高其防结渣性能。     

Improvement of the adhesion of a ceramic coating on a ceramic substrate

The structure and adhesion of an alumina coating on a ceramic substrate with NiCrAlY alloy bond coating was investigated by heating at 1573 and 1673 K in the air. Phases of NiO, NiCrO₃, NiAl₂O₄, αAl₂O₃, and Ni were revealed in a 100 μm thick bond coating on heating at 1573 and 1673 K. A veined structure was also detected in the coating heated at 1573 K. The adhesion strength of the coating was improved and reached approximately 20 MPa on heating at 1573 and 1673 K for 14.4 ks in air although the strength of the as-sprayed coating was only 2 MPa. The improvement of adhesion strength may arise from the formation of NiAl₂O₄ with a spinel structure at the interfaces of the top coating/bond coating/substrate coating system. The adhesion strength of the coating improved on decreasing the bond coating thickness and reached approximately 45 MPa for a 20 μm thick bond coating which was heated at 1673 K. Only NiAl₂O₄ oxide was formed in the bond coating.     

3D打印-激光烧结制备导体和介质厚膜的显微结构与性能

为拓展3D打印技术在厚膜混合集成电路制备领域的应用,提高厚膜浆料烧结效率,采用3D直写+激光烧结制备三种导体浆料厚膜和一种介质浆料厚膜,并与常规的丝网印刷+高温炉烧结厚膜进行显微结构与性能的对比研究。结果表明,常规丝网印刷+高温炉烧结的导体及介质厚膜具有良好的显微结构与性能。相比而言,3D直写+激光烧结制备的导体厚膜平整连续、厚度均匀,焊接性能良好,但结构不够致密,部分导体厚膜存在膜层附着力不足,方阻偏大的问题;介质厚膜激光烧结后的致密性较导体厚膜更低,绝缘性能不满足要求。3D直写制备导体或介质浆料厚膜具有可行性,但激光烧结工艺参数有待优化,以实现厚膜的烧结致密化,提高厚膜与基板的结合强度。     

Adhesion of YSZ suspension plasma-sprayed coating on smooth and thin substrates

The design concept of the gas-cooled fast reactor which is a 4th generation nuclear reactor, requires protective coatings able to operate at 850 °C and protect the underlying structure in case of sudden increase of the functional temperature up to 1250 °C and depressurization from 0.70 MPa to atmospheric pressure. The parts to be covered are made of 1-mm thick materials resistant to heat and erosion and exhibiting high mechanical properties at high temperatures, such as the Haynes® 230 nickel-based alloy. In this study, the use of suspension plasma spraying to manufacture zirconia coatings is explored. The spraying conditions were optimized for the elaboration of coatings on stainless steel AISI 304L substrates and then adapted for Haynes 230 substrates. A special attention was paid to coating adhesion that was investigated by using a Vickers indentation cracking method.     

Design of novel plasma sprayed hydroxyapatite-bond coat bioceramic systems

Bond coats based on bioinert ceramic materials such as titania and zirconia were developed to increase the adhesion strength of the coating system hydroxyapatite-bond coat to Ti-6Al-4V alloy surfaces used for hip endoprostheses and dental root implants. The bond coats improved the adhesion strength, measured by a modified ASTM D 3167-76 peel test, by up to 100% and also the resorption resistance as determined by in vitro leaching in simulated protein-free body fluid for up to 28 days.     

Optimized HVOF titania coatings

A series of spray parameters was tested for a titania (TiO₂) feedstock, and the in-flight particle temperature was measured for each setting combination. The parameter set that resulted in the highest particle temperature was selected for producing coatings for further study and analysis. With this parameter set, the majority of the sprayed particles had temperatures (at least superficially) above that of the melting point of titania. The hardness (H), elastic modulus (E), and elasticity index (H/E ratio) on the cross section and top surface of these HVOF-sprayed titania coatings were evaluated using the Knoop technique and Vickers hardness measurements. The distribution of elastic modulus and hardness values was analyzed via Weibull statistics. The coating microstructure and phase composition were evaluated using scanning electron microscopy (SEM) and x-ray diffraction (XRD) analysis, respectively. The porosity level was determined via image analysis. It was observed that the coatings were uniform and very dense, consisting of rutile as the major phase. The optimized spray conditions allowed the production of thick coatings (∼740 μm), which were shown to be in a state of residual compressive stress using Almen strip measurements.     

CeO2对ZrH1.8表面微弧氧化复合陶瓷层结构的影响

目的利用微弧氧化表面处理技术,通过改变电解液成分,在ZrH_(1.8)表面原位制得一层致密的复合陶瓷层。方法通过在电解液中添加CeO_2颗粒,采用恒压模式对氢化锆(ZrH_(1.8))表面进行微弧氧化处理,利用扫描电子显微镜(SEM)、X射线衍射仪(XRD)、涂层测厚仪、涂层附着力自动划痕仪,分析陶瓷层表面和截面形貌、相结构、厚度及其与基体的结合力,通过Archimedes排水法对所制备陶瓷层的致密性进行定量分析。结果 CeO_2颗粒的添加有利于陶瓷层的生长,与不添加CeO_2颗粒所制得的陶瓷层相比,加入CeO_2后,陶瓷层的厚度有所增加,陶瓷层与基体的结合力由81 N增大至104 N。XRD分析表明,陶瓷层中出现CeO_2特征峰,可知CeO_2在微弧氧化过程中成功地吸附在陶瓷层表面。不添加CeO_2时,陶瓷层的孔隙率为14.22%;添加CeO_2后,陶瓷层的孔隙率降低至5.79%。结论 CeO_2颗粒的加入可有效提高基体ZrH_(1.8)与陶瓷层的结合力,降低了陶瓷层的孔隙率,使氢化锆表面微弧氧化陶瓷层的致密性得到改善。     

Wear behavior of Al2O3-TiCN composite ceramic sliding on stainless steel

It is well known that austenitic stainless steel AISI302 is relatively difficult to cut. In order to investigate the wear behavior of Al₂O₃-TiCN composite ceramic when machining austenitic stainless steels, a blockon-ring tribometer was used to simulate a real machining process. The test results showed that the wear of both the ceramic and the stainless steel increased rapidly with increasing load and speed. The boundary lubrication actions of water and oil used in this test could not reduce the wear of the rubbing materials. Scanning electron microscopy and energy-dispersive x-ray spectroscopy analyses identified material transferred between the ceramic and the stainless steel surfaces in rubbing process. On the one hand, stainless steel transferred on the ceramic surface because of adhesion; on the other, some ceramic fragments caused by microfracture of the ceramic were found to be embedded in the worn stainless steel surface. The wear of Al₂O₃-TiCN ceramic sliding against stainless steel was caused primarily by adhesion between the rubbing surfaces and the microfracture of the ceramic.     

Deposition of thick TiAlN coatings on 2024 Al/SiCp substrate by Arc ion plating

Aluminum-matrix composites with particulate SiC ceramic reinforcements (Al/SiC_p) have received much attention for space and aircraft propulsion applications. It is imperative to deposit thick hard coatings on these composites for protection. TiAlN coatings with a Ti interlayer were deposited by arc ion plating (AIP) on 2024 Al/SiC_p substrates at various nitrogen flow rates. It was found that when the nitrogen flow rate is increased from 100 sccm to 250 sccm, the deposition rate decreases, the coating hardness increases and the adhesion strength decreases. Based on the above results and the principle of gradient materials, the thick gradient TiAlN coatings with a Ti interlayer were successfully deposited on a 2024 Al/SiC_p substrate to a thickness of 60 μm by continuously increasing the nitrogen flow rate during deposition. Such an achievement can be attributed to the gradient distribution of elements, hardness, and stresses across the coating thickness.     

Fundamentals of adhesion of thermal spray coatings: Adhesion of single splats

Indentation experiments were performed inside a scanning electron microscope to measure adhesive strength of individual alumina splats on a steel substrate. The in situ nature of experimental evaluations made characterization of interfacial crack propagation possible by direct observation. The increase in the strain energy of brittle alumina splats originating from indentation deformation was correlated to the strain energy release rate through the characterization of interfacial crack propagation. An analytical model previously reported and evaluated in studies of the adhesive strength of thin films was employed. An average calculated strain energy release rate of 80 J m⁻² was found for single splats. This high value suggests that splat adhesion can make a significant contribution to the adhesion of thermal sprayed coatings.     

等离子喷涂ZrO2层经激光再熔后的组织变化

本文研究了等离子喷涂ZrO_2陶瓷层的激光再熔化处理经激光再熔化处理的ZrO_2涂层致密、无孔隙,但熔化层有裂纹在ZrO_2中添加适量的SiO_2,降低了熔化层在冷却时的热应力,有效抑制裂纹的产生经激光再熔化处理后的陶瓷展和粘结层之间的结合为冶金结合;粘结尾和基材的冶金结合层厚度明显增加;随着激光功率的增加,陶瓷层、粘结层以及一定厚度的基材发生熔化,陶瓷层和粘结层之间产生Zr_6Fe_3O反应相     

纯钛材与大变形纯钛材微弧氧化-水热合成复合陶瓷膜层的细胞相容性研究

采用微弧氧化-水热法分别在纯钛材及大变形纯钛材表面制备了TiO_2/HA复合陶瓷膜层,从细胞毒性实验、细胞增殖实验、细胞黏附实验等方面评价膜层的细胞相容性。结果表明:纯钛材与大变形纯钛材微弧复合陶瓷膜层均无细胞毒性。与纯钛材微弧复合陶瓷膜层相比,大变形纯钛材微弧复合陶瓷膜层表面粗糙度更适宜,结晶形核的HA晶粒的形状及Ca/P比更接近人骨HA,更能有效促进成骨细胞的黏附和铺展,随着培养时间的延长,成骨细胞双层重叠生长结构更为明显。成骨细胞在大变形纯钛材微弧复合陶瓷膜层表面各时间点的吸光度值均更高,细胞相容性更好。     

纯铝微弧氧化陶瓷膜组织及耐腐蚀性能

利用微弧氧化技术,在碱性硅酸盐电解液中对纯铝进行表面改性处理,制备均匀致密的陶瓷膜。利用扫描电子显微镜(SEM)观察氧化陶瓷膜表面形貌及横截面组织结构,利用纳米压入硬度测试仪测量陶瓷膜的显微硬度和杨氏模量的分布,运用电化学方法测量陶瓷膜的耐腐蚀性能。结果表明,铝合金微弧氧化陶瓷膜的表面硬度高达25.3GPa,纳米硬度和杨氏模量在陶瓷膜的横截面分布相似,从膜基结合处向膜层表面呈下降趋势。从极化曲线中的腐蚀电势和腐蚀电流来看,微弧氧化处理后,纯铝的抗腐蚀能力得到很大的提高。     

Anti-corrosion microarc oxidation coatings on SiCP/AZ31 magnesium matrix composite

The corrosion-resistant ceramic coatings up to 80 μm thick were fabricated on SiC_P/AZ31 magnesium matrix composite by microarc oxidation (MAO) technique in Na₃PO₄ + KOH + NaF solution. The microstructure, composition and phase constituent of ceramic coatings were analyzed by SEM and XRD, and the electrochemical corrosion behaviour of coatings was evaluated by the electrochemical polarization method. The thicker coating is compact and displays a good adhesion to the composite substrate. The ceramic coatings consist of MgO, Mg₂SiO₄, MgF₂, Mg₃(PO₄)₂, furthermore, a few residual SiC phases were also found in the coatings by means of SEM observation and EDX analysis. Most of SiC reinforced particles in the oxidized composite substrate have transformed into the oxides under microarc discharge sintering, but a few residual SiC reinforcements in the MAO coatings have not disrupted the continuity of coatings. So the corrosion resistance of the SiC_P/AZ31 composite is greatly improved by MAO surface treatment, however, the corrosion resistance of coated composite also depends on the coating thickness.     

High-power hybrid plasma spraying of large yttria-stabilized zirconia powder

To testify to the advantage of large ceramic powder spraying, numerical simulations and experimental studies on the behavior of large yttria-stabilized zirconia (YSZ) powder in a high-power hybrid plasma spraying process have been carried out. Numeric predictions and experimental results showed that, with the high radio frequency (RF) input power of 100 kW, the most refractory YSZ powder with particle sizes as large as 88 μm could be fully melted and well-flattened splats could be formed. A large degree of flattening (ξ) of 4.7 has been achieved. The improved adhesive strength between the large splat and the substrate was confirmed based on the measurement of the crack density inside of the splats. A thick YSZ coating >300 μm was successfully deposited on a large CoNiCrAlY-coated Inconel substrate (50×50×4 mm in size). The ultradense microstructure without clear boundaries between the splats and the clean and crack-free interface between the top-coat and the bond-coat also indicate the good adhesion. These results showed that highpower hybrid plasma spraying of large ceramic powder is a very promising process for deposition of highquality coatings, especially in the application of thermal barrier coatings (TBCs).     

Columnar grain growth of yttria-stabilized-zirconia in inductively coupled plasma spraying

Yttria-stabilized-zirconia (YSZ) was deposited 7 mm thick by inductively coupled plasma spraying (ICP) and a theory of nucleation and solidification of YSZ was introduced. The concentration was homogeneous within a particle, but different from particle to particle. The solute rejection by diffusion occurred in a layer during solidification, but the interface condition of (dT _q/dz)_z=0 > m(dC/dz)_z=0 led columnar grains to facilitate. The microstructure of the bottom part showed small equiaxed grains. In the middle part, large columnar grains, about 100 μm thick and 300 μm long, were developed through the layers with strong adhesion. Heat of droplets, latent heat of solidification, small pore array in the splat boundaries, and low thermal conductivity retard the heat transfer, and thus thick and long columnar grains could be facilitated. The long columnar grain growth through the layers was supposed to be possible when the previously solidified surface of the deposit acts as seed.     

陶瓷基板化学镀铜预处理的研究

为提高封装基板铜导体层与陶瓷基板的结合强度，研究了在氧化铝和氮化铝的基板上进行化学镀铜，对表面进行粗化和改性，经过优化工艺条件后，氧化铝与镀层的结合强度可以达到27MPa，氮化铝与镀层的结合强度可以达到22MPa。     

重力分离SHS法制备钢管陶瓷内衬的研究

用铝热-重力SHS法制备钢管陶瓷内衬，分析了不同钢管直径对反应过程的影响，并用SEM、能谱仪以及X射线衍射等手段研究了钢管内衬的微观组织。研究表明：内径小和管壁厚的钢管易发生堵塞现象；陶瓷内衬中弥散着黑色圆球主要是铁元素，同时混有少量的铬、硅元素，其平均硬度比铁素体大189HV。