Mechanically alloyed Zr55Al10Cu30Ni5 metallic glass composites containing nanocrystalline W particles

Composites based on the Zr55Al10Cu30Ni5 bulk metallic glass forming alloy, containing up to 17.5 vol % W particles were synthesized by mechanical alloying. Milling produces a metallic glass matrix with a homogeneous dispersion of nanoscale W particles. The composites exhibit almost the same thermal stability and no reduction of the supercooled liquid region compared to the particle-free metallic glass despite some small amount of dissolution of W into the glassy matrix. The viscosity in the supercooled liquid increases with increasing volume fraction of particles. This will be discussed with respect to the contribution of the particles as well as to changes in matrix composition and in the free volume of the material in the framework of the free volume model for viscous flow. Independent of the W content, the samples behave as moderately strong glasses. The viscous flow of the supercooled liquid is used to consolidate dense bulk samples. The Vickers hardness, H-V, of the composites increases with increasing volume fraction of particles. It is suggested that both the matrix and the nanocrystalline particles contribute to the overall hardness of the composites. (C) 1999 American Institute of Physics. [S0021-8979(99)04010-4].