INTERFACE REACTIONS AND FRACTURE-BEHAVIOR OF FIBER-REINFORCED MG AL ALLOYS/

In the composite system carbon fibre/magnesium alloy the interface rea ctivity was varied over a wide range by adding different amounts of th e alloying element aluminium (alloys: AM20, AZ91) and by using carbon fibres of different surface properties (fibres: M40J, T300J). The stru cture and composition of interlayers in these composites down to the a tomic scale as well as their effect on the mechanical properties were studied systematically by the combination of high-voltage electron mic roscopy, high-resolution electron microscopy, energy-dispersive X-ray spectroscopy and electron energy-loss spectroscopy with scanning elect ron microscope in situ bending tests, As resulting microstructure and nanochemistry correlate with the micromechanical fracture behaviour of the metal matrix composites, the interface reactivity can be used as a parameter governing the composite properties, In addition to precipi tates of aluminium carbide, strongly influencing the fracture behaviou r, there are also graphitic carbon ribbons and layers of nanocrystalli ne magnesium oxide at the fibre/matrix interface. Increasing the react ivity of the composite system, three characteristic modes of fracture behaviour are observed: single fibre pullout, bundle fracture (the opt imum composite) and brittle failure.