Improvement of Mechanical Properties of Zr-Based Bulk Amorphous Alloys by High Temperature Heat Treatment

Abstract

Zr-based bulk amorphous alloys which were heat-treated from 673 to 1073 K were investigated, and compressive fracture mechanisms related with improvement of mechanical properties were investigated by observing how the type, size and volume fraction of crystalline particles which is generated during the heat treatment affected the fracture mode. The Zr-based bulk amorphous alloys contained nano-sized crystalline particles showed excellent mechanical properties of compressive fracture strength over 2.0 GPa and compressive plastic strain of approximately 1%. The fracture modes of the alloys are changed depending on the heat treatment temperature and their microstructure. When the alloy is heat-treated at 673 K, the nano-sized Zr2Cu particles are generated in amorphous matrix. According to the observation of fractured specimens, in the alloy heat-treated at 673 K, the fine and elongated vein patterns were well developed. The heat treatment temperature increased above Tx, the Zr2Cu particles as well as complex crystalline particles are consist in the heat-treated alloy, which lead to the brittle fracture and the alloy show the low strength of 605 MPa. In the fractured surface of the alloy, large cleavage facets were evenly developed. When the heat treatment temperature up near Tm, the size of Zr2Cu and complex crystalline particles increased to approximately 1 μm and the volume fraction of complex crystalline particles increased up to 52.3%. As the size of crystalline particles change, the size of facet decreased similarly to the size of crystalline particles. Zr-based bulk amorphous alloys which were heat-treated from 673 to 1073 K were investigated, and compressive fracture mechanisms related with improvement of mechanical properties were investigated by observing how the type and size of crystalline particles which is generated during the heat treatment affected the fracture mode. The fracture modes of the alloys are changed depending on the heat treatment temperature and their microstructure. When the alloy is heattreated at 673 K, the nano-sized Zr2Cu particles are generated in amorphous matrix. According to the observation of fractured specimens, in the alloy heat-treated at 673 K, the fine and elongated vein patterns were well developed. The heat treatment temperature increased near Tg, the Zr2Cu particles as well as complex crystalline particles are consist in the heat-treated alloy, which lead to the brittle fracture and the alloy show the low strength of 605 MPa. In the fractured surface of the alloy, large cleavage facets were evenly developed. When the heat treatment temperature up near Tm, the size of Zr2Cu and complex crystalline particles increased to approximately 1 μm.