A modification of the conventional inert gas condensation apparatus for making nanostructured powders, wherein as evaporative source is replaced by a chemical source, is described. The new chemical synthetic process, called chemical vapor condensation(CVC), combines rapid thermal decomposition and expansion of a precursor/carrier gas stream in a hot tubular reactor with rapid condensation of the product particle species on a cold substrate under a reduced inert gas pressure of 1-50 mbar. The process has been used to synthesize loosely agglomerated nanoparticles (6 to 10 nm) of n-SiCxNy, starting from hexamethyldisilazane (HMDS) as precursor compound. The phase, morphology, and composition of n-SiCxNy powders can be modified by heat treatment. ß-SiC particles with grain size less than 10 nm form after annealing at 1300°C in flowing Ar. In a 1:1 NH3/H2 mixture n-SiCxNy powders transform into a-Si3N4 whiskers, with [100] growth direction.

The Fused Deposition of Ceramics (FDC) process is an extrusion based layered manufacturing technique. In this study, the microstructural and property homogeneity of GS44-Si3N4 parts made by FDC is examined. The feedstock, green, and sintered parts were examined using characterization techniques such as optical and scanning electron microscopy, x-ray radiography, and x-ray diffraction. In addition, mechanical properties (σf, and Klc), shrinkage, and warpage results were used to characterize the FDC parts. It was found that by using proper build parameters and tool paths, dense, homogenous, near-net-shape GS44-Si3N4 parts can be fabricated. While the mechanical properties of these parts are shown to be isotropic, there is some degree of texturing detected with XRD. Si3N4 filament feedstock intentionally textured with 5.5 vol% of β-seed particles has also been made.

Contrary to the generally observed behavior in ceramic-ceramic composites, Nextel™312 fiber- BN -Blackglas™ matrix composites show no loss in flexural strength, an increase in failure strain and increased fibrous failure after oxidation at 600°C for 100 hours. In order to understand this phenomenon, the interfaces of the ammonia treated Nextel™312 fiber — BN -Blackglas™ matrix composites were evaluated in the as prepared condition and after oxidation at 600°C for 5, 24, 100, 200 and 1000 hours. The combined effect of stress and temperature was evaluated on pre-oxidized samples (oxidized at 600°C for 100 hours) stressed to failure at 566°C. In the as prepared composites a smooth interface between the fiber and the matrix was observed. No reaction was observed between the BN rich surface of the fiber and the Blackglas™ matrix. Similar observations were made on samples oxidized for 5, 24, 200 and 1000 hours. Samples oxidized for 200 hours showed matrix regions that were depleted in carbon. Long term oxidation (1000 hours) resulted in almost complete depletion of carbon from the matrix. Samples tested under stress again did not show a reaction zone between the fiber and the matrix, however precipitates were observed in the Blackglas™ matrix. Based on the observations of the long term oxidized and creep samples the observed changes in mechanical properties most likely can attributed to changes occurring in the matrix chemistry.

Ceramic matrix composites based on a Blackglas™ matrix reinforced with Nextel™ 312 fibers with a BN rich surface layer are being investigated for gas turbine engine applications in a temperature range of 500–600°C. Previous work has shown that the flexural properties of the Nextel™ 312/BN/Blackglas™ composites improved after exposure to flowing air at 600°C up to 100h. The creep properties of pre-oxidized specimens (600°C for 100h) were investigated at 566°C. The stress levels were varied between 25-67 MPa. The temperature and stress levels were selected based on the actual component requirements. The creep curve exhibited a large primary region and a flat steady state region with an overall creep rate of approximately 10−10 s1 over 750 hours. The primary region is believed to be due to a) fibers straightening out, and b) load shifting to the fibers due to the effects of oxidation on the matrix. The total creep strains were observed to be about 0.25% after exposure to creep stresses for 850h, which is less than the maximum allowable design strain limits for the component. The creep failure stress of 67 MPa over 750 hours is lower than the fracture strength at temperature.

The inherent strength, thermal shock resistance, and high temperature creep and oxidation resistance of silicon nitride make it one of the most promising materials for high temperature structural applications.

One of the major goals of this research is to develop a seamless, desktop, intelligent, computer-aided design environment to fabricate functional parts using a multi-material fused deposition manufacturing machine. The current research project has already developed tools for multi-material toolpath and virtual simulation of a layered fabrication [3,4]. A three-dimensional video microscopy is used to collect experimental data. The parts are fabricated using PZT, PMN-PT, silicone nitride and metals. Design of Experiment, DOE is being performed to quantify and predict void creation and elimination. Using our approach, a designer now could design, fabricate and verify the goals and alter both computation and fabrication parameters quickly. The design cycle has the potential to become faster and more creative.

Gas-phase reactions were initiated by laser energy sources in a manner that caused homogeneous nucleation and growth. Resulting Si, Si3, N4, and SiC powders have ideal characteristics for consolidation into dense ceramic pieces. The particles are small, uniform in size, round, pure, and appear loosely agglomerated. Silicon powders were sintered to controlled densities without using sintering aids and then nitrided to completion. Sintering and nitriding kinetics were both rapid because of the small Si particle size. The nitrided microstructure retained the fine features of the green Si. There is some evidence that the Si3N4 powders densified locally without the use of sintering aids.

We present processing (green and sintered), part shrinkage and warping, microstructural characterization, and mechanical properties of Si3N4 made by fused deposition of ceramics (FDC), using optical microscopy, scanning electron microscopy, and X‐ray diffraction. The mechanical properties (fracture strength, fracture toughness, and Weibull modulus) are also reported. Proper FDC build parameters resulted in dense, homogeneous, near‐net‐shape Si3N4, with microstructures and mechanical properties similar to conventionally processed material. Mechanical properties are shown to be isotropic, while there is some degree of microstructural texturing (preferred β‐Si3N4 grain orientation) in sintered components.

stainless steel is known to provide an attractive combination of high strength and corrosion resistance. In this research, the feasibility of SFF fabrication of high density parts using PH powder is examined. A part can be fabricated using both indirect and direct methods. The indirect method includes making a negative RTV mold, making compounded material using ECG binder and stearic acid with the metal powder, and pouring the compounded material to get a green part. This is followed by binder bum out(BBO) and sintering cycles. The direct method uses Fused Deposition of Metals(FDMet). In FDMet, the 17-4PH powder is compounded with a binder and extruded into filaments, followed by part building, BBO and sintering. The initial results of the indirect method of fabrication produced 91 % theoretical density of 17-4 PH parts with Vickers hardness of 223.

Blackglas™/BN/Nicalon™ Composites were fabricated under two different pyroiysis temperatures (900° and 1200°C) and infiltration cycles (5x and 8x). Some specimens were oxidized at 600°C in flowing air for 100 and 1000 hours in air. The tensile results show that the strength of the composites are reduced almost 60% of as-prepared composites after 1000 hours of oxidation. In general, pyroiysis temperatures and infiltration cycles had little effect on composite's long term oxidation behavior, but manifest themselves in the short term oxidation (100 hours). In this case, 1200°C pyroiysis seems to slow down the oxidation and the composites maintained the ultimate strength when compared to as prepared composites.

Fused Deposition of Ceramics (FDC) is a novel ceramics manufacturing process for the production of complex geometry parts. Computational thermal models have been developed to gain understanding and predictive ability for FDC, due to the fundamental role played by heat transfer in all manufacturing steps. The numerical model developed has been used to investigate the mechanisms of bonding deficiency generation, for different process parameters.

Chapter 29 Colloidal Processing of a SiC Whisker-Reaction Bonded Si3N4 Composite Fumio Takao, Fumio Takao Dept. of Ceramics, Rutgers The State University of New Jersey P.O. Box 909 Piscataway, NJ 08854Search for more papers by this authorW. Roger Cannon, W. Roger Cannon Dept. of Ceramics, Rutgers The State University of New Jersey P.O. Box 909 Piscataway, NJ 08854Search for more papers by this authorStephen C. Danforth, Stephen C. Danforth Dept. of Ceramics, Rutgers The State University of New Jersey P.O. Box 909 Piscataway, NJ 08854Search for more papers by this author Fumio Takao, Fumio Takao Dept. of Ceramics, Rutgers The State University of New Jersey P.O. Box 909 Piscataway, NJ 08854Search for more papers by this authorW. Roger Cannon, W. Roger Cannon Dept. of Ceramics, Rutgers The State University of New Jersey P.O. Box 909 Piscataway, NJ 08854Search for more papers by this authorStephen C. Danforth, Stephen C. Danforth Dept. of Ceramics, Rutgers The State University of New Jersey P.O. Box 909 Piscataway, NJ 08854Search for more papers by this author Book Editor(s):William Smothers, William SmothersSearch for more papers by this author First published: 01 January 1986 https://doi.org/10.1002/9780470320341.ch29Citations: 5Book Series:Ceramic Engineering and Science Proceedings AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Citing Literature 10th Annual Conference on Composites and Advanced Ceramic Materials: Ceramic Engineering and Science Proceedings, Volume 7 RelatedInformation

Nicalon fabric-reinforced 2-D ceramic composites were fabricated and tested using a CVD boron nitride (BN) interface coating at two thickness' (0.3 and 0.6 micron) with a silicon oxycarbide matrix (Blackglas™). The 0.6 micron thick BN coatings gave the most extensive fibrous fracture with flexure strengths and strains of 280 MPa and 0.65%. Oxidation at 600°C for 100 hours reduced the composite strength and strain (200 MPa and 0.57%) but maintained fibrous failure with no embrittlement. Oxidation at 800°C produced low strength (100 MPa), low strain (0.22%) failure in the embrittled composite. Microstructural analysis of the fibers and the composites showed a uniform, adherent boron nitride coating, resistant to 600°C oxidation.

SiC whisker-reinforced reaction bonded silicon nitride composites were fabricated by processing submicron Si powder and SiC whiskers in ethanol with the addition of a polyethoxylated amine. Potentiometric titration estimated that the equivalent weight of the amine additive was 1531 g/equiv. Adsorption of the additive did occur on the Si powder surface and it was Langmuirian in nature; the additive did not adsorb onto the SiC whisker surface. Rheologkal data for the Si-SiC whisker composite systems will be reported. Sedimentation studies determined that whisker packing densities in ethanol were 70% better than in aqueous systems. Composites formed by colloidal filtration were characterized for percentage of nitridation and for flexural strength.

Chapter 27 Rheological Behavior of SiC Whiskers in a Model Injection Molding System E. Krug, E. Krug Dept. of Ceramic Engineering, Rutgers The State University of New Jersey Piscataway, NJ 08855–0909Search for more papers by this authorS. C. Danforth, S. C. Danforth Dept. of Ceramic Engineering, Rutgers The State University of New Jersey Piscataway, NJ 08855–0909Search for more papers by this author E. Krug, E. Krug Dept. of Ceramic Engineering, Rutgers The State University of New Jersey Piscataway, NJ 08855–0909Search for more papers by this authorS. C. Danforth, S. C. Danforth Dept. of Ceramic Engineering, Rutgers The State University of New Jersey Piscataway, NJ 08855–0909Search for more papers by this author Book Editor(s):William Smothers, William SmothersSearch for more papers by this author First published: 01 January 1987 https://doi.org/10.1002/9780470320402.ch27Citations: 2Book Series:Ceramic Engineering and Science Proceedings AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Citing Literature 11th Annual Conference on Composites and Advanced Ceramic Materials: Ceramic Engineering and Science Proceedings, Volume 8 RelatedInformation