High-strength bulk nanocrystalline alloys containing compound and amorphous phases

Partial crystallization of cast bulk amorphous alloys in Zr-Al-Cu-Pd and Zr-Al-Cu-Pd-Fe systems was found to cause bulk nanocrystalline alloys with high tensile strength (sigma(f)). The nanostructure alloys consist of nanoscale bct- Zr-2(Cu, Pd) surrounded by the remaining amorphous phase. The crystallization of a ternary Zr60Al10Cu30 amorphous alloy occurs by the simultaneous precipitation of Zr2Cu and Zr2Al phases with large particle sizes of 400 to 500 nm and hence the addition of Pd is essential for formation of the nanostructure. The Pd has much larger negative heats of mixing against Zr and the resulting Zr-Pd atomic pair seems to act as preferential nucleation sites leading to the precipitation,of Zr,(Cu, Pd). The nanostructure alloys in the cast cylinder of 4 to 5 mm in diameter keep good ductility in the volume fraction (Vf) range of the compound below 30 to 40 %. (C)1999 Acta Metallurgica Inc.