Yield stress of a composite consisting of amorphous Ni 78Si 10B 12 and μm sized WC particles

Abstract

The yield strength and elastic modulus of amorphous Ni 78Si 10B 12 alloys, dispersed with 4–5 μm sized particles of WC, was measured as a function of the volume fraction ( V f ). Within experimental error, Young's modulus ( E c ) measured by an ultrasonic method, increased linearly with V f according to the rule of mixtures: E c = E m (1 − V f ) + E p V f , where E m and E p are Young's modulus of the matrix and the second phase, respectively. The yield stress ( σ yc ) of the composite, measured in bending, was found to increase linearly with V f . For V f = 18.2%, the highest volume fraction investigated, σ yc was 2.2 times higher than the yield stress ( σ ym ) of the nondispersed matrix material. Experimentally, the ratio of E c to σ yc was found to be independent of V f and to be approximately 60. Thus, the yield stress, σ yc of the dispersed alloy various with volume fraction approximately as: σ yc = σ ym {1 + V f ( E p / E m − 1)}. The above dependence of the yield stress on V f corresponds to a rule of mixture in which the yield stress of the second phase must exceed the value of σ ym ( E p / E m ) or about 1000 kg/mm 2. Comparison with the experimentally measured value for the compressive yield stress of sintered 3% Co-WC indicate that elastic stresses in excess of 1000 kg/mm 2 might be reached in small WC particles.