Francois Boland

Tensile flow properties of Al-based matrix composites reinforced with a random planar network of continuous metallic fibres

Squeeze casting was used for processing two new types of composites: pure Al matrix composites reinforced with fibres of Inconel 601, and AS13 (Al-12% Si) matrix composites reinforced with fibres of Inconel 601 or stainless steel 316L. The fibres are continuous a with a diameter of 12 mu m and their volume fraction in the composites varied from 20 to 80%. The processing conditions were such that no trace of interfacial reaction compound or of matrix precipitate resulting from the dissolution of elements of the fibres could be detected. The quality of the process was attested by Youngs modulus and electrical conductivity measurements. Tensile tests were carried out from room temperature up to 300 degrees C. The composites with the pure Al matrix present a remarkable tensile ductility. They thus constitute convenient materials for assessing continuum plasticity models for composites. Properties of composites with the AS13 matrix are much affected by interface adhesion strength

Mechanical properties of aluminium/Inconel 601 composite wires formed by swaging

This work investigates the formability of a composite made of a pure aluminium matrix reinforced with an Inconel fibre network. Composites were formed into wires by swaging, to a true strain ɛtrue = 2.7. Thermal expansion, Youngs modulus and tensile properties of these wires were measured. Youngs modulus of the wires is slightly larger than that of the as-cast composites, indicating that no significant porosity is present in the composite after deformation. Tensile strength and ductility are found to decrease with increasing reduction of diameter. Scanning electron microscope (SEM) observations show that fibres align during swaging and that fibre fragmentation occurs beyond a certain strain. Fibre fragments reach a critical aspect ratio of about 7 after a swaging true strain of 1.5. Qualitatively, the evolution of the properties is explained by a combination of fibre fragmentation and fibre alignment effects. Properties of the wires are discussed using the Clyne model and the Nardone and Prewo model (modified shear lag models).

Comparison of fibres for creep strengthening of zinc-aluminium foundry alloys

A comparative evaluation is made of a variety of possible fibrous reinforcements for strengthening zinc-aluminium foundry alloys. The composites are processed by squeeze casting, using preforms of alumina, carbon, stainless steel or low carbon steel fibres. A drastic improvement of the creep strength is achieved with the use of alumina or steel fibres. However, an acceptable level of fracture toughness is maintained only in the composites reinforced with steel fibres. This property results from the low interface adhesion which allows bridging of the crack. by the fibres. Low carbon steel fibres do not exhibit more interface reaction than stainless steel fibres. It is concluded that low carbon steel fibres provide a better compromise when taking into account the creep strength, the fracture toughness and the cost of the composite.

On the control of interface reaction in squeeze cast aluminium matrix composites

The processing parameters for achieving proper control of the kinetics of interface reaction even in very reactive systems are discussed. The work concentrates on composites consisting of a pure Al matrix reinforced by continuous fibres of Inconel 601. Use is made of a low thermal inertia squeeze casting set-up equipped with monitoring of the sample temperature. Microstructural characterization and DTA analysis allow to elucidate some aspects of the reaction mechanisms. A model based on a parabolic growth law is developed for ranking the severity of processing conditions.