Density, thermal stability and mechanical properties of Zr-Ti-Al-Cu-Ni bulk amorphous alloys with high Al plus Ti concentrations

Abstract

Bulk amorphous Zr70-x-yTixAlyCu20Ni10 alloys with a thickness of 2.5 mm were formed in a wide composition range of 0 to 10 at%Ti and 7.5 to 15 at%Al by a squeeze casting process. The bulk amorphous alloys containing 0 to 5%Ti and 12.5 to 15%Al exhibit good combined properties of high tensile fracture strength above 1850 MPa, high specific strength of 28.4 × 105 N·m/kg and high Tg/Tm above 0.60 which have not been obtained for the Zr-based amorphous alloys reported hitherto. These bulk amorphous alloys have small difference in density of 0.3 to 0.6% between ascast amorphous and crystallized states. The high dense random packing fraction in the multicomponent amorphous structure seems to cause the high glass-forming ability and the high thermal stability of the supercooled liquid region by the decrease in atomic mobility. Furthermore, the crystallized phases change from NiZr2+CuZr+Zr3Al in the range of 5 to 15%Al and 0 to 2.5%Ti to NiZr+CuZr2+Zr3Al in the range of 5 to 15%Al and 2.5 to 7.5%Ti. The melting temperatures (Tm) of these crystallized compounds increase in the order of ZrNi>Zr2Ni>Zr2Cu>ZrCu and hence the crystallized structure of the 5%Ti-containing alloys is composed of ZrNi and Zr2Cu with higher Tm. The change in the amorphous structure leading to the precipitation of the compounds with higher Tm may be the reason for the higher mechanical strength in the higher Al and Ti contents.