MECHANICAL-PROPERTIES OF ZBLAN GLASSES

Elastic moduli (E, G, K, nu) of various ZBLAN glass compositions have been determined using pulse echo ultrasonic technique. Vickers microhardness, H(v), was measured under 100 g load and also determined systematically as a function of the load (30-125 g) for a ZBLAN11.6 composition submitted to different surface treatments such as storage in dry and wet atmosphere and optical polishing. In all cases, H(v) increases with load until reaching an almost constant value H(v) congruent-to 200 kg/mm2 for load > 100 g. The hardness variation with load is similar for as-prepared glasses stored in dry or wet atmosphere but is more pronounced for samples with a polished surface. The results are explained by a model which assumes that H(v) is determined by the weighted average of plastically deformed volumes in a surface layer and in the bulk. The model allows one to estimate their microhardness and the thickness of the surface layer.