Mechanical properties of selected glasscrystal composites

Abstract

Desirable physical properties not provided by single-phase materials are often conveniently attained by multiphase composites. This paper is concerned with the variation of the mechanical properties of bulk glass through the incorporation of a crystalline oxide phase. Glass-Al₂O₃ and glass-ZrO₂ composites containing 20 and 40 vol % spherical, crystalline inclusions, 125 to 150 μrn in diameter, were prepared by hot pressing. The effects of internal stress and elastic properties of the crystalline inclusion on composite mechanical properties were studied. Experimental elastic-property values agreed well with theoretical values calculated from Hashin's equations. Flexural strength tests of all composite compositions revealed that the fracture path rarely traversed the crystalline oxide inclusions. The Al₂O₃ and ZrO₂ additions strengthened the glass considerably, except when internal stresses were of sufficient magnitude to cause cracking of the glassy matrix upon cooling and before flexural testing. Glass-Al₂O₃ composites were consistently stronger than the glass-ZrO₂ counterparts. This strength difference is attributed to the higher elastic moduli of the Al₂O₃ composites. Hypotheses which postulate strengthening as a result of restricted flaw size are apparently not applicable to these materials.