Thermal modeling of plasma spray deposition of nanostructured ceramics

A thermal model for plasma spray deposition of ceramic materials onto metallic substrates has been developed. The enthalpy-based control volume formulation of the heat transfer processes has been used to study the temperature evolution in a two-dimensional substrate and in the coating as it is grown. In this paper, additional melting of ceramic splats after deposition is examined, with a view to predicting the retention of nanostructures in a spray consisting of agglomerated, nanometer-sized particles. Initial results for thin coatings indicate that when the mean temperature of the incoming particles is close to the fusion point of the ceramic material, the nanostructure distribution in the coating is largely determined by the composition of the spray. However, with thicker coatings, additional melting due to prolonged plasma gas heating combined with increased thermal resistance in the underlying coating leads to a loss of nanostructure.     

Air plasma-sprayed Y2O3 coatings for Al2O3/Al2O3 ceramic matrix composites

Al₂O₃/Al₂O₃ ceramic matrix composites (CMC) are candidate materials for hot-gas leading components of gas turbines. Since Al₂O₃/Al₂O₃ CMC are prone to hot-corrosion in combustion environments, the development of environmental barrier coatings (EBC) is mandatory. Owing to its favorable chemical stability and thermal properties, Y₂O₃ is considered a candidate EBC material for Al₂O₃/Al₂O₃ CMC. Up to 1 mm thick Y₂O₃ coatings were deposited by means of air plasma spraying (APS) on Al₂O₃/Al₂O₃ CMC with a reaction-bonded Al₂O₃ bond-coat (RBAO). APS Y₂O₃ coatings exhibit a good adherence in the as-deposited state as well as upon isothermal annealing up to 1400 °C. Moreover, furnace cyclic testing performed at 1200 °C revealed an excellent durability. This is explained by the formation of a continuous, approximately 1 μm thick reaction zone at the APS Y₂O₃/RBAO interface. The reaction zone between Y₂O₃ and Al₂O₃ comprises three layers of thermodynamically stable yttrium-aluminates exhibiting strong bonding, respectively.     

水性陶瓷涂料特点及应用前景

概述了水性陶瓷涂料的发展状况,化学反应基本原理,产品突出的性能特点,节能、环保优势,取代高温氟碳涂料和搪瓷钢板的可能性,产品应用及市场推广前景。     

Microstructure,adhesion, and tribological properties of conventional plasma-sprayed coatings on steel substrate

A variety of metallic and oxide coatings were deposited under various conditions on 1020 mild steel substrate by conventional plasma spraying. The coating thickness, microhardness, cohesion and adhesion failure loads, friction coefficient, and abrasive wear resistance were evaluated. The coatings were classified as follows, in order of decreasing microhardness and wear resistance: alumina, chromia, 316 stainless steel, Ni-5% Al, elemental aluminum and aluminum-polyester. Wear resistance increased with increasing microhardness and decreasing friction coefficient. The microhardness and wear resistance of high-velocity oxy-fuel (HVOF) diamond jet (DJ)-sprayed aluminum were found to be superior to those of plasma-sprayed aluminum. Plasma or flame-sprayed metallic coatings adhered well to the substrate. The cohesion, adhesion, microhardness, and wear resistance of alumina coatings exceeded those of equally thick chromia coatings.     

A design perspective on thermal barrier coatings

This article addresses the challenges for maximizing the benefit of thermal barrier coatings for turbine engine applications. The perspective is from the viewpoint of a customer, a turbine airfoil designer who is continuously challenged to increase the turbine inlet temperature capability for new products while maintaining cooling flow levels or even reducing them. This is a fundamental requirement for achieving increased engine thrust levels. Developing advanced material systems for the turbine flowpath airfoils, such as high-temperature nickel-base superalloys or thermal barrier coatings to insulate the metal airfoils from the hot flowpath environment, is one approach to solve this challenge. The second approach is to increase the cooling performance of the turbine airfoil, which enables increased flowpath temperatures and reduced cooling flow levels. Thermal barrier coatings have been employed in jet engine applications for almost 30 years. The initial application was on augmentor liners to provide thermal protection during afterburner operation. However, the production use of thermal barrier coatings in the turbine section has only occurred in the past 15 years. The application was limited to stationary parts and only recently incorporated on the rotating turbine blades. This lack of endorsement of thermal barrier coatings resulted from the poor initial duratbility of these coatings in high heat flux environments. Significant improvements have been made to enhance spallation resistance and erosion resistance, which has resulted in increased reliability of these coatings in turbine applications.     

Properties of ZnO coatings obtained by mechanoactivated oxidation

In this work a new method based on the mechanoactivated oxidation has been applied for obtaining thin nanostructured transparent ZnO coatings on glass. Zn has been transferred onto a glass substrate at room temperature using a quickly rotating steel wire brush. Afterwards by subsequent annealing it is modified into a transparent ZnO coating. The temperature range in which formation of the needle-like (whiskers) structure and transition to the fine-grained structure occurs has been determined. The interrelation between physical properties and the change of microstructure of the ZnO coatings has been shown.     

Low-temperature atomic layer deposition of Al2O3 thin coatings for corrosion protection of steel: Surface and electrochemical analysis

ToF-SIMS, XPS, voltammetry and EIS investigation of the anti-corrosion properties of thin (10, 50 and 100 nm) alumina coatings grown by atomic layer deposition at 160 °C on steel is reported. Surface analysis shows a thickness-independent Al₂O₃ stoichiometry of the coating and trace contamination by the growth precursors. The buried coating/alloy interface has iron oxide formed in ambient air and/or resulting from the growth of spurious traces in the initial stages of deposition. Electrochemical analysis yields an exponential decay of the coating porosity over four orders of magnitude with increasing thickness, achieved by sealing of the more defective first deposited 10 nm.     

聚氨酯粉末涂料用羟基聚酯树脂的合成

介绍了聚氨酯粉末涂料用羟基聚酯树脂的合成,简单地讨论了催化剂、多元酸和多元醇对合成反应的影响,并对聚氨酯粉末涂料的性能进行了测试。     

Study on the surface roughness of ceramic shells and castings in the ceramic shell casting process based on expandable pattern

A method to form a thin smooth film of wax on the surface of the foam pattern was proposed by introducing the molten wax in this work. Organic smoothing coatings for the foam pattern were also prepared and their effects on the surface roughness of the foam patterns, shells and castings were investigated. Effects of the facecoat slurry used to fabricate ceramic shells on the surface roughness of the shells and castings were studied. The analysis of results indicates that the surface smoothing coatings and the wax smoothing film both greatly decreased the surface roughness of ceramic shells and castings from 3.2-6.3 μm to 0.8-2.5 μm (Ra), and the surface roughness of shells and castings would be improved if the facecoat slurry is prepared with finer filler materials.     

Corrosion and corrosion protection of support structures for offshore wind energy devices (OWEA)

The paper provides a review about the corrosion and corrosion protection of offshore wind energy devices (OWEA). Firstly, special features resulting from location and operation of OWEA are being discussed. Secondly, types of corrosion and corrosion phenomena are summarized in a systematic way. Finally, practical solutions to the corrosion protection of OWEA, including steel allowances, cathodic protection and coatings and linings, are discussed.