Study on Cu₄₈Zr₄₃Al₉ and Cu₅₄Zr₄₀Al₆ Amorphous Matrix Alloys by Mechanical Spectroscopy

Abstract

Anelastic properties of Bulk Metallic Glasses (BMG) were studied by mechanical spectroscopy using a flexural vibration apparatus. BMG’s samples, with nominal composition Cu48Zr43Al9and Cu54Zr40Al6, were produced by skull push-pull casting technique in rectangular cavity cooper mold. In both samples, the differential scanning calorimeter patterns have evidenced the presence of amorphous structure, although the X-ray diffraction for Cu48Zr43Al9composition has shown a heterogeneous microstructure embedded in the amorphous matrix. Anelastic relaxation spectra were obtained using an acoustic elastometer system with vibration frequency in the kilohertz bandwidth, a heating rate of 1 K/min, vacuum greater than 10-5mBar in the temperature range of 300 K to 620 K. In the flexural apparatus, an acoustic elastometer system, the internal friction (energy loss) and the elastic modulus were obtained by free decay of vibrations and by the squared of the oscilation frequency, respectively. Internal friction spectra were not reproducible among the measurements, which may imply atomic rearrangement in the samples due to consecutive heating. Normalized elastic modulus data showed distinct behavior from the first to the other measurements evidencing irreversible microstructural alterations in the samples possibly associated with mechanical relaxation due to the motion of atoms or clusters in the glassy state.