Neutron Diffraction Measurements of Residual Stress and Mechanical Testing of Pressure Sintered Metal-Ceramic Composite Systems

Abstract

Abstract. Functionally graded materials (FGMs) are composite materials which vary in phase composition, microstructure and properties over one or more dimensions. They are a good potential choice for nuclear reactor components as they can be engineered to effectively resist corrosion and radiation damage. In the case of a metal-ceramic FGM, they can mate the strength and ductility of a metal with the hardness and toughness of a ceramic. A series of composite samples of variable metal-ceramic ratios was manufactured by hot uniaxial pressing in cylinders. Bulk uniform samples of a certain composition were manufactured as a more efficient way of studying FGMs without the extreme gradient required in practical applications. Thermally and mechanically generated stresses, inherent in composites, frequently create conditions for micro-cracking development, depending on the material's micro-structural characteristics and the thermomechanical processing route. Bulk stress measurements in the prepared samples were carried out on the Kowari diffractometer on the OPAL reactor at ANSTO. Both phases -metal matrix and ceramic inclusions -were measured in both axial and lateral directions for full characterisation of the composite stress state. When compared against analytical evaluation, experimental results, for some samples, demonstrated significant stress relaxation with micro-cracking being the main suspect. IntroductionFunctionally graded materials (FGMs) were first proposed as an advanced engineering material in 1972, and have been actively pursued since then. They are proposed in areas such as biomaterials, aerospace, chemical plants, mining and building material commodities [1,2]. Within the nuclear industry FGMs can be engineered to effectively resist corrosion, radiation and be used as potential nuclear reactor components; first wall for fusion reactors and fuel pellets. They have been proposed as potential plasma facing components (PFCs) in which the ideal PFC would gradually vary from a refractory material (e.g. tungsten, plasma face) to a heat sink material (e.g. copper). In the case of a metal-ceramic FGM, the composite can be engineered to mate the strength and ductility of a metal with the hardness and toughness of a ceramic [3][4][5]. FGMs have been successfully fabricated using various methods to produced thin film/interfacial FGMs or bulk FGMs (layered/continuous) [3].