High-Strength Bulk Nanostructure Alloys Consisting of Compound and Amorphous Phases

Bulk nanocrystalline alloys with good ductility and high tensile strength (σ f) in Zr-Al-Cu- Pd and Zr-Al-Cu-Ni-Ti systems were formed by partial crystallization of cast bulk amorphous alloys. The nanostructure alloys consist of Zr2(Cu, Pd) or (Zr, Ti)2Al surrounded by the remaining amorphous phase. The particle size and interparticle spacing of their compounds are less than 10 and 2 nm, respectively. The crystallization of a Zr60Al10Cu30 amorphous alloy occurs by the simultaneous precipitation of Zr2Al and Zr2Cu with a large particle size of 500 nm and hence the addition of Pd or Ti is effective for formation of the nanostructure. The Pd or Ti has much larger negative heats of mixing against Zr or Al, respectively, and the Zr-Pd or Ti-Al atomic pair seems to act as preferential nucleation sites leading to the primary precipitation of Zr2(Cu, Pd) or (Zr, Ti) 2Al. The nanostructure alloy cylinders of 2 to 3 mm in diameter keep good ductility in the volume fraction (Vf) range of the compounds below 40 %. The σ f and Young's modulus (E) increase from 1760 MPa and 81.5 GPa, respectively, at Vf=40 % to 1880 MPa and 89.5 Gpa, respectively, at Vf =40 % for the Zr60Al10Cu20Pd10 alloy and from 1830 MPa and 89.0 GPa, respectively, at Vf =0 % to 1940 MPa and 95.2 GPa, respectively, at Vf =28 % for the Zr53Al12Cu20Ni10Ti5 alloy. The formation of the bulk nanostructure alloys with high σ f is presumably due to the reentrance of free volumes into the remaining amorphous phase caused by quenching from the supercooled liquid region.