Locally fluctuating cooling rate as possible reason for non-crystalline plasticity in metallic glasses

The preparation process of a CuZrAl metallic glass is simulated by molecular dynamics. Different temperatures of the initial liquid state and variation of the cooling rate over five decades are considered. Elastic moduli, mass density and frequency of icosahedral clusters follow a power-law scaling with the cooling rate. The ratio of shear to bulk modulus is most sensitive to changes of the cooling rate. Assuming local fluctuations of the cooling rate occurring during the preparation process, regions characterized by comparably low values of shear modulus, mass density and frequency of icosahedral clusters can be proposed as atomistic realizations of flow defects, at which non-crystalline plastic deformation is initiated

Short-range order of Cu-Zr metallic glasses

The atomic structure of Cu$_{35}$Zr$_{65}$, Cu50Zr50, and Cu$_{65}$Zr$_{35}$ (at.%) metallic glasses was investigated by means of high-energy X-ray diffraction, neutron diffraction and extended X-ray absorption fine structure spectroscopy. Three-dimensional structure models were developed by applying the reverse Monte-Carlo method and analyzed in terms of the local atomic arrangements. The geometric short-range order of Cu–Zr glasses is characterized by a variety of polyhedra. The atomic sites of the nearest neighbourhood around a Cu or Zr atom are statistically occupied by Cu or Zr atoms. The composition dependence of the short- and the medium-range order in the Cu–Zr glasses points to a statistical replacement of Cu and Zr atoms in the whole composition range. No indications were observed for the existence of a dominant structural arrangement in the Cu–Zr glasses

Atomic structure and formation of CuZrAl bulk metallic glasses and composites

Cu$_{47.5}$Zr$_{47.5}$Al$_{5}$ metallic glass is studied experimentally by high-energy X-ray diffraction, neutron diffraction with isotopic substitution, electron diffraction and X-ray absorption spectroscopy. The atomic structure of the glass is modeled by reverse Monte-Carlo and molecular dynamics simulations. RMC modeling of seven experimental datasets enabled reliable separation of all partial pair distribution functions for Cu$_{47.5}$Zr$_{47.5}$Al$_{5}$ metallic glass. A peculiar structural feature of the ternary alloy is formation of the strong Al–Zr bonds, which are supposed to determine its high viscosity and enhanced bulk glass formation. Analysis of the local atomic order in Cu$_{47.5}$Zr$_{47.5}$Al$_{5}$ glass and Cu$_{10}$Zr$_{7}$, CuZr$_{2}$ and CuZr B2 crystalline structures elucidates their similarities and differences explaining the phase formation sequence by devitrification of the glass