Phase transformation and mechanical properties of Zr-base bulk glass-forming alloys

Zr60Ti5Cu15Ni10Al10 and Zr57Ti4.75CU14.15Ni9.5Al9.5Ta5 glass-forming alloys are investigated regarding their phase formation, as-cast microstructure, thermal stability and transformation behavior, mechanical properties and fracture features. Zr60Ti5Cu15Ni10Al10 exhibits a glass transition temperature 7, of 635 K and a supercooled liquid region AT, of 64 K. The melt-spun glassy phase presents a two stage phase transformation sequence corresponding to glass-to-quasicrystal transformation at about 699 K and quasicrvstal-to-Zr2Cu + Zr4Al3 + Zr2Ni (tetragonal) transformation at about 753 K. With addition of 5 at.% Ta, T-g increases to 663 K and AT, is reduced to 52 K. The melt-spun glassy ribbons primarily precipitates cubic-Zr2Ni upon heating to about 715-755 K. The residual glassy phase transforms into Zr3Al and Zr2Ni (tetragonal) at about 798-873 K. As-cast Zr60Ti5Cu15Ni10Al10 3 mm diameter cylinders exhibit an ultimate compression stress sigma(f) of 1752 MPa and Young's modulus E of 100 GPa. The 5 at.% Ta addition leads to a reduction of of to 1534 MPa. None of the alloys exhibits yielding behavior or plastic deformation. Rock-layers and deformation bands are found on the fracture surface for Zr60Ti5Cu15Ni10Al10. A honeycomb-like morphology and deformation bands are also exhibited on the fracture surface of Zr57Ti4.75Cu14.25Ni9.5Al9.5Ta5. The remelting phenomenon observed for both alloys is attributed to the high strength, large elastic energy and low melting temperature of the alloys. (C) 2002 Elsevier Science B.V. All rights reserved.