The effect of partial crystallization on elevated temperature flow stress and room temperature handness of a bulk amorphous Mg₆₀Cu₃₀Y₁₀ alloy

Partially crystallized samples of the bulk amorphous alloy Mg60Cu30Y10 were prepared by annealing amorphous samples slightly above Tg. After partial crystallization, the alloy is a nanocomposite consisting of equiaxed Mg2Cu crystallites with an average diameter of 100 nm homogeneously distributed in an amorphous matrix.

The flow stress of the nanocomposites was measured as a function of strain rate above Tg. For fixed strain rate, the flow stress increases monotonically as a function of degree of crystallinity, increasing most rapidly for low degrees of crystallinity. A variety of models describing the rheological properties of composites are compared with the flow stress measurements.

In all cases, a significant discrepancy is found between the model predictions and experimental observations. A linear relationship was also found between hardness at room temperature and the degree of crystallinity, consistent with a recently proposed model.