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Inkjet printing was applied to manufacture silica-based gas separation membranes, which were coated on a pore-graduated alumina substrate with a mesoporous γ-alumina interlayer. A silica sol diluted by 1-propanol was used to print the membrane layer followed by thermal treatment in a rapid thermal processing furnace. The membrane thickness was varied between 30 and 110 nm by conducting one, two, and three coating steps. In the latter case, H2 permeance in the range of 2.0 × 10−8-3.3 × 10−8 mol/s·m2·Pa combined with H2/CO2 selectivities in the range of 15-25 were achieved, proving the concept that inorganic gas separation membranes can be successfully processed by inkjet printing. [ABSTRACT FROM AUTHOR]

Thermal spray coatings from liquid feedstock such as suspensions and solution precursors have received increasing interest due to the unique coating properties obtainable by these processes. Several research groups are working on the basis of plasma as well as on high-velocity oxy-fuel approaches to manufacture advanced nanostructured and nanophased materials. These activities are reflected in various recent publications and conference presentations about feedstock preparation, equipment and process design, modeling techniques, in-process diagnostics, coating characterization, and emerging applications. This article will review these recent developments to give an up-to-date overview and to trace the current trends. [ABSTRACT FROM AUTHOR]

Powder injection parameters such as gas flow, injection angle, and injector position strongly influence the particle beam and thus coating properties. The interaction of the injection conditions on particle properties based on DPV-2000 measurements using the single-cathode F4 torch is presented. Furthermore, the investigation of the plasma plume by emission computer tomography is described when operating the three-cathode TriplexPro™ torch. By this imaging technology, the three-dimensional shape of the radiating plasma jet is reproduced based on images achieved from three CCD cameras rotating around the plume axis. It is shown how the formation of the plasma jet changes with plasma parameters and how this knowledge can be used to optimize particle injection. [ABSTRACT FROM AUTHOR]

The very low-pressure plasma Spray (VLPPS) process has been developed with the aim of depositing uniform and thin coatings with coverage of a large area by plasma spraying. At typical pressures of 100-200 Pa, the characteristics of the plasma jet change compared to conventional low-pressure plasma-spraying processes (LPPS) operating at 5-20 kPa. The combination of plasma spraying at low pressures with enhanced electrical input power has led to the development of the LPPS-TF process (TF = thin film). At appropriate parameters, it is possible to evaporate the powder feedstock material providing advanced microstructures of the deposits. This technique offers new possibilities for the manufacturing of thermal barrier coatings (TBCs). Besides the material composition, the microstructure is an important key to reduce thermal conductivity and to increase strain tolerance. In this regard, columnar microstructures deposited from the vapor phase show considerable advantages. Therefore, physical vapor deposition by electron beam evaporation (EB-PVD) is applied to achieve such columnar-structured TBCs. However, the deposition rate is low, and the line-of-sight nature of the process involves specific restrictions. In this article, the deposition of TBCs by the LPPS-TF process is shown. How the evaporation of the feedstock powder could be improved and to what extent the deposition rates could be increased were investigated. [ABSTRACT FROM AUTHOR]

Abradable coatings in compressor and high-pressure stages of gas turbines must provide specific hardness and porosity values to achieve an optimal cut-in of the blade tips. A fractional factorial experimental plan was designed to investigate the influence of the plasma spraying parameters argon flow rate, current, spraying distance and powder feed rate on these properties of magnesia spinel. Based on the results, magnesia spinel coatings with low (~400 HV0.5), medium (~600 HV0.5) and high hardness (~800 HV0.5) could be reliably manufactured. Further incursion rig tests confirmed the dependence of the rub-in behavior and abradability on the coating characteristics and process parameters, respectively. Process monitoring was also applied during plasma spraying of magnesia spinel abradables on batches of turbine components. The recorded particle characteristics and coating properties showed a good reproducibility of the spraying process. [ABSTRACT FROM AUTHOR]

Atmospherically sprayed thermal barrier coatings (TBCs) are nowadays an essential part in modern gas turbines. However, a design integrated use of these coatings is only possible with reliable lifetime models. In this paper, a model is outlined which describes the major failure in TBCs associated with the growth of a thermally grown oxide (TGO) on the bond coat (BC). An essential part of the model is a simplified description of the crack growth as a result of thermal cycling and TGO growth. In addition, the energy release rate for the system is calculated and compared to an estimated critical energy release rate reduced by the crack growth. If both are equal, failure is assumed. The results of the modeling are compared to thermal cycling experiments partly applying a thermal gradient. BC temperatures and also microstructures of the ceramic topcoat have been varied and the influence on the cyclic life studied. [ABSTRACT FROM AUTHOR]

The occurrence of monoclinic zirconia phase has an important impact on the performance of thermal barrier coatings (TBC) of yttria-stabilized zirconia (YSZ). Therefore, a reliable method is needed to detect its contents and to investigate also its spatial distribution within the parent microstructure. This was the motivation to apply cathodoluminescence (CL) spectroscopy. YSZ coatings with different porosities were manufactured by atmospheric plasma spraying. CL analysis yielded monoclinic phase contents of 5.2 ± 1.6% for the high-porous sample and 3.4 ± 0.5% for the low-porous sample. The results were qualitatively confirmed by x-ray diffraction (XRD). However, due to its lower detection sensitivity the XRD results are quantitatively on lower level. Owing to its synthesis method, the applied powder feedstock showed a considerable content of monoclinic phase. The lower the particle temperatures were the larger fraction of monoclinic phase remained untransformed. This has to be considered when spraying high-porous TBCs. [ABSTRACT FROM AUTHOR]

Abstract: An approach to measure and assess the oxygen contents of vacuum plasma spraying process atmospheres is introduced. Hereby it is envisaged to monitor vacuum plasma spraying processes and to control the uptake of oxygen in metal alloy coatings. Coating experiments were performed with Ni–Co–Cr–Al alloy bondcoat powders to proof the effectiveness of this approach. Additional experimental coatings made of NiTi powders show the benefit of controlling the oxygen contents especially for metallic alloys being highly affine to oxygen. [Copyright &y& Elsevier]

Abstract: A carbon-fibre-reinforced carbon (C/C) composite filled with silicon carbide (SiC) particles was produced, using the winding technique. A porous matrix consisting of glassy carbon, SiC particles and small pores in homogeneous distribution was produced, ensuring a damage-tolerant fracture behaviour. Neither fibre coatings nor further infiltration steps were necessary for the preparation of the composite, which makes this a low-cost process making no limitations on wall thickness. The microstructure and homogeneity of the material is shown using micrographs, mercury porosimetry and BET measurements. Bending tests, as well as single-edge notch beam (SENB) tests point to high values for the bending strength and formal fracture toughness. A damage-tolerant fracture behaviour is demonstrated by the load–displacement curves and fracture surfaces. [Copyright &y& Elsevier]