Effects of Additional Hf on the Thermal Stability and Mechanical Properties of Cu-Zr-Ag Bulk Glassy Alloys

Abstract

The thermal stability, crystallization behavior and mechanical properties of the Cu45Zr45� xHfxAg10 (x ¼ 0 to 45 at%) glassy alloys have been investigated. The glass transition temperature (Tg), crystallization temperature (Tx), liquidus temperature (Tl) and the supercooled liquid regionTx (¼ TxTg) increase with increasing Hf content. The reduced glass transition temperature (Tg=Tl) values are in the range from 0.54 to 0.59. The Vicker's hardness (HV ), Young's modulus (E) and compressive fracture strength (� c,f) of the Cu45Zr45� xHfxAg10 (x ¼ 0 to 25 at%) bulk glassy alloys increase linearly with increasing Hf content and reach the maximum values of 554, 123 GPa and 2020 MPa, respectively, for Cu45Zr20Hf25Ag10 alloy. A different crystallization behavior is observed for Cu45Zr45Ag10 and Cu45Hf45Ag10 glassy alloys. (doi:10.2320/matertrans.47.1922) the thermal stability and mechanical properties of Cu-based Cu-Zr-Ag bulk glassy alloys. This paper presents the thermal stability, density and mechanical properties of the Cu-Zr-Hf- Ag glassy alloys. The effectiveness of substitution of Hf for Zr is also investigated. 2. Experimental Procedure Multi-component Cu-(Zr, Hf)-Ag alloy ingots with nom- inal compositions were prepared from the mixtures of pure Cu, Zr, Hf and Ag metals by arc melting in a Ti-gettered argon atmosphere. The purity of metals was over 99.9 mass%. Alloy ingots were re-melted four times to ensure chemical homogeneity. The glassy alloys in a ribbon form with a cross section of 0:02 � 1:5 mm 2 and in a cylindrical rod form with diameters up to 2.0 mm were prepared by melt spinning and copper mold casting, respectively. The glassy structure was identified by X-ray diffraction and the thermal stability associated with glass transition temperature (Tg) and crystallization temperature (Tx) was examined by differential scanning calorimetry (DSC) at a heating rate of 0.67 K/s. The liquidus temperature (Tl) was measured by differential thermal analyzer (DTA) at a heating rate of 0.33 K/s. The density was measured by Archimedes's principle by weigh- ing ingots in tetrabromoethane and in air. Vicker's hardness was measured using a microhardness tester. Mechanical properties were measured under a compressive load with an Instron testing machine. The gauge dimension of specimens was 2.0 mm in diameter and 4.0 mm in height and the strain rate was 5 � 10 � 4 s � 1 .