The gas turbine industry is continuously developing and testing new materials and manufacturing methods to improve the performance and durability of hot section components, which are subjected to extreme conditions. SiAlON and Inconel 718 are especially desirable for turbomachinery applications due to their high strength and high temperature capabilities. To demonstrate the viability of additive manufacturing for small scale turbomachinery for 300W scale microturbines, a monolithic rotor with a design speed of 450,000 RPM containing radial turbine and compressor was developed considering additive manufacturing constraints. The geometry was manufactured from SiAlON and Inconel 718 using lithographic ceramic manufacturing and selective laser melting, respectively. The additive manufacturing and thermal process parameters as well as material characterization are described in detail. Surface and computerized tomography scans were conducted for both rotors. While the metallic rotor showed undesirable printing artefacts and a large number of defects, the ceramic part achieved a level of relative precision and surface quality similar to large-scale production via casting. To compare turbomachinery performance, an aerodynamic test facility was developed allowing to measure pressure ratios and efficiency of small compressors. The rotors were tested in engine realistic speeds, achieving a compressor rotor pressure ratio of 2.2. The ceramic part showed superior efficiency and pressure ratio compared to the Inconel rotor. This can be explained with lower profile and incidence losses due to a higher fidelity physical representation of the model geometry and better surface finish.

Porous Si3N4 materials in tubular geometry are prepared by slip casting before partial sintering. A variety of material- and process-specific variables and their respective effects on densification and resulting pore morphology are systematically evaluated, focusing on starting powder type, amount of sintering additives, and sintering parameters including temperature and time. An increased beta-Si3N4 content in the starting powder was found to promote the formation of a network of elongated grains exhibiting increased pore diameters, as opposed to a more finely featured pore network obtained from starting materials consisting of alpha-Si3N4. Following an iterative evaluation of processing variables, materials exhibiting a characteristic diametral compression strength (C-ring test) of 163 MPa and a Darcian permeability of 4.7 . 10(-15) m(2) at a total porosity of 41% were obtained, corresponding to an increase of over 40% in strength and of over 600% in permeability in comparison to materials obtained by alpha-Si3N4 powders at comparable porosities. These results demonstrate that the composition of Si3N4 powders significantly affects the resulting pore structure, and by combining the respective selection of starting materials with finely tuned sintering parameters, materials with superior performance in terms of mechanical properties as well as permeability characteristics are accessible.

Due to the high level of light absorption and light scattering of dark colored powders connected with the high refractive indices of ceramic particles, the majority of ceramics studied via stereolithography (SLA) have been light in color, including ceramics such as alumina, zirconia and tricalcium phosphate. This article focuses on a lithography-based ceramic manufacturing (LCM) method for β-SiAlON ceramics that are derived from silicon nitride and have excellent material properties for high temperature applications. This study demonstrates the general feasibility of manufacturing of silicon nitride-based ceramic parts by LCM for the first time and combines the advantages of SLA, such as the achievable complexity and low surface roughness (Ra = 0.50 µm), with the typical properties of conventionally manufactured silicon nitride-based ceramics, such as high relative density (99.8%), biaxial strength (σf = 764 MPa), and hardness (HV10 = 1500).

Die additive Fertigung von Schneidstoffen bietet die Chance, leistungsfähigere Zerspanungswerkzeuge herzustellen. Vorgestellt wird zum einen das Lithography-based Ceramic-Manufacturing-(LCM)-Verfahren und zum anderen die Entwicklung damit gefertigter Wendeschneidplatten (WSP). Die Funktionstauglichkeit dieser keramischen WSP wird in Außenlängsdrehversuchen an vermicularem Gusseisen untersucht.

A green and scalable one-pot hydrothermal synthesis generates polyimide/silica hybrid materials, which can be processed by green, solvent-free sintering.

A processing technique for the preparation of porous, silicon carbonitride-based ceramics in tubular geometry derived from a liquid polysilazane precursor is presented. After casting of polysilazane/polymer-microbead dispersions, cross-linking, and subsequent pyrolytic conversion and selective removal of polymer templates, specimens with an inner and outer diameter of 6 and 10 mm, respectively, and a length of up to 65mm were obtained. Porosity was controlled by sacrificial template content and reached values up to 48% after pyrolytic conversion, at average pore opening radii of 1 mu m. The tubular specimens exhibited diametral compression strengths (C-ring test) between 24 +/- 6 and 36 +/- 4 MPa. Darcian permeability constants of up to 1.7.10(-14)m(2) were found by gas permeability testing. The results demonstrate that this methodology facilitates the straightforward generation of complex-shaped porous specimens, further allowing for a control of strength and permeability in a specific range. Potential applications for the tubular, porous structures developed can be anticipated in the fields of separation or catalysis. (C) 2016 The Ceramic Society of Japan. All rights reserved.