Indentation method for fracture resistance determination of metal/ceramic interfaces in thick TBCs

The indentation technique has been used to measure the adhesion of plasma- sprayed ceramic coatings on metals intended for thick thermal barrier coating ( TTBC) applications. This approach provides the adhesion value as the critical strain energy release rate,Gc, of the interface, which also takes into account any residual stresses. The theoretical background of the method is outlined, and specific examples are reported with respect to the effect of substrate temperature on the metal/ceramic adhesion of thick TBCs.     

Mechanism and prediction of failure of diamond films deposited on various substrates by HFCVD

Diamond films were deposited on the WC-Co cemented carbide and Si3N4 ceramic cutting tool substrates by hot-filament-assisted chemical vapour deposition. The adherence property of diamond films was estimated using the critical load (Pcr) in the indentation test. The adhesive strength of diamond films is related to the intermediate layer between the film and the substrate. Poor adhesion of diamond films to polished cemented carbide substrate is owing to the formation of graphite phase in the interface. The adhesion of diamond films deposited on acid etched cemented carbide substrate is improved, and the peeling-off of the films often happens in the loosen layer of WC particles where the cobalt element is nearly removed. The diamond films' adhesion to cemented carbide substrate whose surface layer is decarbonizated is strengthened dramatically because WC phase forms by reaction between the deposited carbon and tungsten in the surface layer of substrates during the deposition of diamond, which results in chemical combination in the film-substrate interface. The adhesion of diamond films to silicon nitride substrate is the firmest due to the formation of chemical combination of the SiC intermediate layer in the interfaces. In the piston-turning application, the diamond-coated Si3N4 ceramic and the cemented carbide cutting tools usually fail in the form of collapsing of edge and cracking or flaking respectively. They have no built-up edge(BUE) as long as coating is intact.As it wears through, BUE develops and the cutting force on it increases 1 - 3 times than that prior to failure. This can predict the failure of diamond-coated cutting tools.     

Ceramic coating on ceramic with metallic bond coating

The change in structure and adhesion strength of the interface by heating in air has been investigated for a plasma- sprayed alumina coating on a ceramic substrate with a 50Ni- 50Cr alloy bond coating. A veined structure composed of NiO, NiCr ₂O₄, and NiAl₂O₄ oxides grew from the bond coating into cracks or pores in the top coating and the alumina substrate after heating at 1273 K for 20 h in air. The NiAl₂O₄ spinel may have formed by the oxidization of nickel, which subsequently reacted with the alumina coating or the substrate. The mechanism of the penetration of the spinel oxides into the cracks or pores is not clear. The adhesion strength of the coating is increased to about 15 MPa after heating at 1273 K for 20 h in air, compared to an as- sprayed coating strength of only 1.5 MPa.     

真空渗硼预处理在CVD金刚石-硬质合金涂层工具中的应用

采用固体粉末真空渗硼工艺，研究了硬质合金工具表面真空渗硼预处理对金刚石涂层附着力的影响，研究结果表明，硬质合金工具通过固定粉末真空渗硼处理，表面生成具有较高稳定性的以CoWB、CoB为主的渗层，经过长时间的金刚石涂层后，硬质合金工具表面出现Co3B和W2Co21B6相，没有单质Co相出现，克服了金刚石沉积中硬质合金表面钴的不利影响，使标志金刚石涂层附着力的压痕测试的临界载荷达到了1500N，并且有着较好的重现性。     

镁合金化学镀镍层的结合机理

镁合金在直接化学镀前的活化处理时，表面生成一层氟化物保护膜，溶解度计算及XPS分析表明，氟化物膜在镀液中可稳定存在，用SEM，XPS，SAM考察了初始沉积Ni，镀层横截面以及开裂后的断面形貌与成分，发现在镀层与基体之间存在着氟化物，镀液成分与Ni的混杂层，这一混杂层是镀层与基体结合的最薄弱环节，镀层开裂通常首先发生在此混杂层内。     

Molybdenum and tungsten coatings for x- ray targets obtained through the low-pressure plasma spraying process

Low-pressure plasma spraying under an argon atmosphere was employed to deposit molybdenum and tungsten coatings on different metallic, ceramic, and composite substrates. Molybdenum coatings ob-tained through this technique presented a homogeneous structure with an average porosity of about 17 %. These coatings exhibited adhesion greater than 40 MPa on molybdenum and grey cast iron (FT25) substrates. No adhesion was observed on an A1N surface regardless of the preheating temperature and/or surface preparation. Adhesion on AIN-Mo (AM25) composite substrate, containing 25 % dispersed metal-lic phase by volume, showed intermediate results. Tungsten coatings exhibited porosity between 10 to 12% and a typical lamellar structure. The adhesion of tungsten coatings on molybdenum and FT25 sub-strates was around 40 MPa.     

化学粗化对塑料表面镀层结合力的影响

化学粗化是影响塑料与镀层结合力最重要的因素之一。本文考察了铬酐-硫酸型粗化液的组成,粗化温度和时间与镀层结合力的关系。结果表明:在铬酐浓度为400g/L,硫酸浓度为200mL/L,粗化温度60～70℃,粗化温度10分钟的条件下,ABS塑料与镀层的结合力较好。并用扫描电子显微镜对粗化后的ABS塑料表面和断面进行了观察。     

Technical note: Plasma-sprayed ceramic thermal barrier coatings for smooth intermetallic alloys

A durable ceramic thermal barrier coating is applied directly to a smooth, highly oxidation resistant intermetallic alloy in two layers. The first layer of ceramic is applied by low pressure plasma spraying and the second layer is applied by conventional atmospheric pressure plasma spraying. This approach would allow the use of plasma sprayed ceramic coatings in applications where a metallic bond coat is not desirable.     

The influence of platinum on the maintenance of α-Al2O3 as a protective scale

The influence of externally located platinum on the isothermal stability of -Al₂O₃ scales formed at high temperatures has been examined. It has been observed that a nickel-base alloy forms an external scale of -Al₂O₃ during oxidation at 1200°C, but this scale breaks down isothermally, enabling a faster-growing Cr₂O₃-rich scale to develop. However, in the presence of platinum metal alongside the specimen in the furnace hot zone, the breakdown of the -Al₂O₃ scale is postponed for a substantial period of time. It appears that platinum, as the volatile species PtO₂, is incorporated into the growing -Al₂O₃ scale where it either influences the stress relief mechanism at temperature or reduces oxidation growth stress generation and thus significantly enhances the isothermal stability of the scale.     

硬质合金金刚石涂层工具基体前处理有效方法探讨

利用两种溶液浸蚀硬质合金表面，分别选择性刻蚀WC和Co.这不仅强粗化了硬质合金表面，而且，还能抑制CO在金刚石沉积过程中的负作用，从,而，提高了金刚石薄膜的质量和涂层的附着力。