Effect of isothermal annealing on microstructure evolution and mechanical properties of Zr50Cu34Al8Ag8 amorphous alloy

Abstract

In this paper, Zr50Cu34Al8Ag8 amorphous alloy bars were prepared by copper-mold suction casting. The compressive mechanical properties of the as-cast samples and the alloy samples isothermally annealed for different times were tested by a universal testing machine, and the hardness values of the samples were measured by an automatic microhardness measurement system. The microstructure and thermodynamic properties of the alloy samples were analyzed by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and differential scanning calorimetry. The experimental results show that both annealing temperature and annealing time have significant effects on the microstructure and properties of the amorphous alloys. At an isothermal annealing temperature of 430 °C, the incubation time was 100.6 min, which decreased to 5.4 min when the temperature was increased to 460 °C. With prolonged isothermal annealing time, the width of the supercooled liquid region of the alloy samples became narrower and the stability decreased. After isothermal annealing at 440 °C for 20 min, the volume fraction of the crystalline phase in the alloy sample reached 45.2%, and the hardness of the alloy sample reached the maximum value of 526.5 HV. The compressive mechanical properties of the as-cast samples were the best with a compressive strength and ultimate strain of 1856.8 MPa and 3.57%, respectively. When increasing the isothermal annealing time, the compressive mechanical properties of the alloy samples decreased sharply, and the fracture mode changed from shear fracture to brittle fracture. The precipitation of hexagonal Al2Zr and tetragonal AgZr phases inside the alloy samples was the main reason for the decrease in the compressive mechanical properties and the increase in the hardness.