Ultrasonic Nondestructive Evaluation Of Elastic Properties For Cu-Zr-Al System Cu-based Bulk Metallic Glasses

Metallic glass is a metastable state with the short-range order and long-range disorder arrangement of atoms. It shows that the metallic glasses have superior physical, chemical and mechanical performance by the investigations on thermal, electricity, magnetic and mechanics. As a kind of new material, Cu-based metallic glasses have higher glass formation ability and lower cost. Remarkably, it not only has super strength but also definite ductility, (Tensile strength is more than 2000 MPa, elongation is greater than 2%)which even the Zr-based metallic glasses with the best glass formation ability cannot compare with. As an important mechanical performance parameter-elastic moduli which represent the elastic deformation resistance ability has attracted broad attention. Based on the basic theory of ultrasonic, elastic moduli are closely related with velocities, elastic moduli can be calculated by measuring longitudinal and shear velocities.Bulk metallic glasses(BMGs) Cu_58.1Zr_35.9Al₆ (Cu₈Zr₅ cluster structure) and (Cu_0.56Zr_0.44)_100-xAl_x (x=3.5,5,8) (Cu₆Zr₅ cluster structure) series were prepared by copper mould suction casting method. Structure of BMGs was analyzed by using X-ray diffraction and Optical microscope to confirm the nature of single amorphous. The glass formation ability (GFA) and thermal stability were studied by Differential scanning calorimeter and Differential thermal analysis. Longitudinal (V₁) and shear velocities (V_s) were measured by using ultrasonic water-immersion focusing method and the elastic property parameters such as elastic modulus and Debye temperature were deduced according to christoffel equation. The relativity between elastic property and inner structure of sample was analyzed by means of thermal analysis and XRD. The variation regularity of elastic property parameters during annealing process of Cu_58.1Zr_35.9Al₆ at different temperatures was observed.The results of DSC show that the regularity of GFA and thermal stability from strong to weak is Cu_58.1Zr_35.9Al₆,Cu_51.5Zr_40.5Al₈,Cu_53.2Zr_41.8Al₅ and Cu₅₄Zr_42.5Al_3.5.The GFA and thermal stability elevate with increase of the content of component Al for the same cluster structure Cu₆Zr₅. The order of the velocity and elastic modulus measured by ultrasonic method from maximum to minimum is Cu_58.1Zr_35.9Al₆,Cu_51.5Zr_40.5Al₈,Cu_53.2Zr_41.8Al₅ and Cu₅₄Zr_42.5Al_3.5, which keeps identical with the variation order of GFA as well as the chemical...