Catherine Salmon

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).

Oxidation behaviour in air of thin alloy 601 fibres

Abstract The oxidation behaviour in air of 12 μm diameter continuous alloy 601 fibres has been studied using thermo-gravimetric analysis (TGA) for kinetics identification and transmission electron microscopy (TEM) for determination of the nature of the oxide layers. The TGA allows two stages in the formation of the oxide layer to be distinguished: the first stage corresponds to the growth of a continuous layer of NiO above a discontinuous sub-layer of Cr2O3 whereas the second stage is attributed to the parabolic growth of the Cr2O3 sub-layer, from the time it becomes continuous. A third stage can be observed for high oxidation temperatures. The TEM observations of oxide layers formed after 30 min at 650, 750 and 900°C confirm these results. One common characteristic of these 3 oxidation conditions is the appearance of large cavities under the oxide layer. These cavities seem to be the consequence of the oxidation mechanism of Cr and of the particular morphology of the material (i.e. small diameter cylinders).

Strengthening of Al/Ni-based composites by in situ growth of intermetallic particles

Squeeze cast Al matrix composites reinforced with continuous fibers of Inconel 601 were submitted to different annealing treatments aiming at tuning the amount of reaction at the fiber/matrix interface. The reaction develops in the form of intermetallic nodules growing onto the fibers. The tensile flow stress of the composites increases with increasing nodule volume fraction at the expense of a progressive loss of ductility. This loss of ductility is due both to the low cohesion of the oxide layer separating the matrix from the nodules and to brittle cracking at the root of attachment of the nodules onto the fibers. Damage development is evaluated from the evolution of strain hardening. The nodules grow underneath the oxide barrier layer that protects the fibers from reacting with Al during squeeze casting. Their mechanism of growth involves the partial reduction of the oxide layer by Al, followed by diffusion of Al and Ni through the Cr-rich oxide layer

Neutron diffraction analysis of the evolution of phase stresses during plastic straining of aluminium matrix composites reinforced with a continuous, random planar network of fibres

Composites consisting of a pure Al matrix reinforced with a continuous network of 20 or 30 vol % of continuous fibres of Inconel 601 exhibit a tensile ductility of more than 10%, The fibre orientation distribution presents transverse isotropy with low misorientation with respect to the isotropy plane. The evolution of phase stresses during in-plane tensile testing was investigated by neutron diffraction, using Al-111 signal for the matrix and Ni-111 signal for the fibres. The phase stresses were obtained using computed diffraction elastic constants. Analysis of the variation of the fibre stresses as a function of composite strain allowed distinguishing four successive regimes corresponding to different straining behaviours of the phases.