|Prof. Antonio Pedro Novaes de Oliveira; Dr.-Ing. Rolf Janßen
|Seyed M. Goushegir; M.Sc. Paula O. Guglielmi
Fiber reinforced glass and glass-ceramic composite materials have been studied due to their good properties such as high temperature capability, light weight, high chemical resistance and thermomechanical stability. They can be used in relatively high temperature, high stress level and aggressive environments, like in gas turbine, automotive brake and gear system, energy conversion systems, aerospace sector, etc.
Glass-ceramic materials, as the matrix of the above mentioned composites, are a relatively new class of materials that combines good engineering properties such as high bending strength, high hardness and abrasion resistance, as well as high chemical resistance with a wide range of coefficient of thermal expansion, which makes them very interesting candidates in different applications.
These materials consist of crystals with residual glassy phase which are controllable by modifying the material’s chemical composition and the heat treatment process. The nature of the crystalline and glassy phases, as well as their size and distribution, have a great effect on the resultant properties. The glass-ceramics can be produced from glass powders, which can be shaped through different processing routs such as extrusion, injection moulding and tape casting, followed by sintering and crystallization.
A sintered LZS (Li2O-ZrO2-SiO2) glass-ceramic system has been studied by Oliveira et. al. and have shown good mechanical properties and chemical resistance. A major drawback of the system is its high coefficient of thermal expansion (CTE) for applications which thermal shock is an important issue. Due to this fact, Montedo et. al., modified LZS glass-ceramic by partially substituted ZrO2 by Al2O3, which led to a new system called LZSA (Li2O-ZrO2-SiO2-Al2O3). This system presents a wide range of CTE from as low as nearly zero.
The use of hard particles as reinforcement for glass-ceramic materials has already been investigated in some research. In this work, natural amorphous silica short fibers (NASSF) will be used to improve mechanical properties of the LZSA glass-ceramic. These kind of fibers are a natural product that have been found in Brazil and are good candidates to replace short glass fibers due to their similarity in morphology. The advantages of NASSF over short glass fibers are lower density and lighter products, harder materials and cost competitive. In general, their length lies in the range of 200-600 µm, diameter is about 10 µm, and they have tubular shape with a hole of less than 1 µm diameter. Their density is ca. 1.7 g.cm-3 which is much lower than commercial glass fibers’ density (2.59 g.cm-3).
The main objective of this project is production of the NASSF reinforced LZSA glass-ceramic composite as dense as possible with desirable mechanical properties. A very good attention should be paid to some important topics such as sintering and crystallization behavior of the matrix and fibers, fiber orientation within matrix and the interface phenomena between matrix and fibers.
Natural amorphous silica short fibers (NASSF)
Alumina fibers (NextelTM 610, from 3MTM) will also be investigated later on in this study as reinforcement for the LZSA matrix