Fabrication process development of SiC/superalloy composite sheet for exhaust system components

A chemical compatibility study was conducted between SiC filament and the following P/M matrix alloys: Waspaloy, Hastelloy-X, NiCrAlY, Ha-188, S-57, FeCrAlY, and Incoloy 800. None of the couples demonstrated sufficient chemical compatibility to withstand the minimum HIP consolidation temperatures (996 C) or intended application temperature of the composite (982 C). However, Waspaloy, Haynes 188, and Hastelloy-X were the least reactive with SiC of the candidate alloys. Chemical vapor deposited tungsten was shown to be an effective diffusion barrier between the superalloy matrix and SiC filament providing a defect-free coating of sufficient thickness. However, the coating breaks down when the tungsten is converted into intermetallic compounds by interdiffusion with matrix constituents. Waspaloy was demonstrated to be the most effective matrix alloy candidate in contact with the CVD tungsten barrier because of its relatively low growth rate constant of the intermediate compound and the lack of formation of Kirkendall voids at the matrix-barrier interface. Fabrication methods were developed for producing panels of uniaxial and angle ply composites utilizing CVD tungsten coated filament

Characterization, shaping, and joining of SiC/superalloy sheet for exhaust system components

Hafnium carbide was shown to be virtually inert when in contact with silicon carbide and Waspaloy for at least 200 hr at 1093 C (2000 F). Extensive interaction was noted with other superalloys such as HA-188. A continuous CVD HfC deposition process was developed for deposition of up to 8 microns on .14 mm (.0056 in.) SiC tungsten core filament at rates as high as .6 m/min. The rate can be increased by increasing the length of the reactor and the output of the power supply used in resistive heating of the filament substrate. The strength of HfC coated filament varies with thickness in a Griffith-like manner. This strength reduction was greater for HfC coatings than for tungsten coatings, presumably because of the greater ductility of tungsten

Relating the South African soil taxonomy to the World Reference Base for soil resources

The South African Taxonomic soil classification system (SAT) is well established and utilised in South Africa. However, it is not internationally well known and therefore the need arose to provide a tool by which South African soil taxonomists can convert South African soil classifications and profile descriptions to the international classifications of the World Reference Base (WRB) for soil resources. The diagnostics and tacit knowledge presented in this publication are therefore based on the SAT and the WRB. When necessary, further substantiation was derived from the Land Type Survey of South Africa. The adopted procedure is effective in providing a reasonable classification based on the South African soil forms and families, while excluding certain WRB soil groups and qualifiers, because these are irrelevant to South African taxonomy. Lastly, this publication also highlights some peculiarities, omissions and inconsistencies observed between the SAT and WRB

Instrumentos climáticos para el sector transporte: Consideraciones para el régimen climático post-2012

En la comunidad internacional que se ocupa del cambio climático y el desarrollo se están debatiendo los instrumentos climáticos existentes y futuros. El estudio Instrumentos Climáticos para el Sector Transporte (CITS), comisionado por el Banco Asiático de Desarrollo (ADB) y el Banco Interamericano de Desarrollo (BID), evalúa la situación actual con relación al impacto del Mecanismo de Desarrollo Limpio (MDL), el Fondo para el Medio Ambiente Mundial (GEF) y elFondo de Tecnología Limpia (CTF) para el sector transporte en países en vías de desarrollo. Con base en análisis y estudios de caso en ciudades asiáticas y latinoamericanas, este estudio también ofrece recomendaciones para lograr la replicación a mayor escala del financiamiento climático y el desarrollo de la capacidad institucional en el sector transporte, particularmente mediante el uso de acciones de mitigación apropiadas a nivel nacional (las NAMA), un nuevo mecanismo de financiación que está siendo desarrollado bajo la Convención Marco de las Naciones Unidas sobre el Cambio Climático (CMNUCC).Servicios públicos domiciliarios, Infraestructura y transporte, Cambio climático, Polución, transporte sustentable, transporte sostenible, contaminación urbana

Fracture Analysis of Particulate Reinforced Metal Matrix Composites

A fracture analysis of highly loaded particulate reinforced composites was performed using laser moire interferometry to measure the displacements within the plastic zone at the tip of an advancing crack. Ten castings were made of five different particulate reinforcement-aluminum alloy combinations. Each casting included net-shape specimens which were used for the evaluation of fracture toughness, tensile properties, and flexure properties resulting in an extensive materials properties data. Measured fracture toughness range from 14.1 MPa for an alumina reinforced 356 aluminum alloy to 23.9 MPa for a silicon carbide reinforced 2214 aluminum alloy. For the combination of these K(sub Ic) values and the measured tensile strengths, the compact tension specimens were too thin to yield true plane strain K(sub Ic) values. All materials exhibited brittle behavior characterized by very small tensile ductility suggesting that successful application of these materials requires that the design stresses be below the elastic limit. Probabilistic design principles similar to those used with ceramics are recommended when using these materials. Such principles would include the use of experimentally determined design allowables. In the absence of thorough testing, a design allowable stress of 60 percent of the measured ultimate tensile stress is recommended

Thermal properties of metal matrix composites with planar distribution of carbon fibres

High thermal conductivity (TC) and a tunable coefficient of thermal expansion are essential properties for heat management materials operating in a wide temperature range. We combine both properties in a composite with a low‐density metal matrix reinforced with pitch‐based carbon fibres. The thermal conductivity of the metal matrix was increased by 50%, the thermal expansion coefficient was reduced by a factor of five. The samples were produced by powder metallurgy and have a planar random distribution of fibres, leading to high performance in two dimensions

E. Sachs

Introduction 1.1 Motivation. Two needs which are key to industrial productivity and competitiveness are the reduction in time to market for new products and the flexible manufacture of products in small quantities. This work targets a critical subset of the problems that must be overcome in order to achieve shorter product development cycles and flexible manufacturing for mechanical parts. The problems addressed are rapid prototyping, rapid fabrication of tooling, and the low cost manufacture of tooling. A major contributor to the time to market for new products is the time required to fabricate prototypes. Rapid prototyping can shorten the product development cycle and improve the design process by providing rapid and effective feedback to the designer. Some applications require rapid prototyping of nonfunctional parts for use in assessing the aesthetic aspect of a design or the fit and assembly of a design. Other applications require functional parts. Often, it is advantageous if the functional part is fabricated by the same process that will be used in production. A second major contributor to the time to market is the time required to develop tooling, such as molds and dies. For some types of tooling, such as injection molding dies, the turnaround time for the design and fabrication of a tool routinely extends to several months. The long lead times are due to the fact that tooling is generally one of a kind and can be extremely complex, requiring a great deal of human attention to detail

Online Social Networking, Interactions, and Relations: Students at the University of the Free State, Bloemfontein

Online social networking (OSN) is an activity performed through social network sites (SNS) such as Facebook, Twitter, WhatsApp, and Instagram. OSN has become a dominant interaction mechanism within contemporary society. Online platforms are woven inextricably into the fabric of individuals’ everyday lives, especially those of young adults. We present a mixed-methods study—conducted at the University of the Free State in Bloemfontein—that analyzes how students reflect on their everyday experiences of OSN. The key theoretical frameworks guiding this research are phenomenology, existentialism, and reflexive sociology. These theoretical lenses collectively assist in broadening our understanding of the students’ experiences that reveal the complexities associated with their interactions and social relations via SNS. From their narratives we learn how the students make sense of their engagements on SNS, how these engagements have an impact on their social interactions, and how OSN affects their self-presentation.Dziekan Wydziału Ekonomiczno-Socjologicznego (B18112CZAS1175.01; MPK: 2122524000)

Processing Aluminum Nitride-Silicon Carbide Composites via Polymer Infiltration and Pyrolysis of Polymethylsilane, a Precursor to Stoichiometric Silicon Carbide

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/65973/1/j.1151-2916.1999.tb01846.x.pd