Improvement of Mechanical Properties by Precipitation of Nanoscale Compound Particles in Zr–Cu–Pd–Al Amorphous Alloys

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Abstract
The replacement of Cu by 10 at%Pd for an amorphous Zr60Cu30Al10 alloy was found to change the crystallization process from the single stage of amorphous (Am)→Zr2Cu+Zr2Al to the two stages of Am→Am′+Zr2(Cu, Pd)→Zr2(Cu, Pd)+Zr3(Al, Pd)2 in the maintenance of the wide supercooled liquid region before crystallization. After the melt-spun amorphous alloys were annealed for 1.2 ks at 726 K and the volume fraction (Vf) of compound reached as large as 75%, the particle size and interparticle spacing of the compound particles in the amorphous matrix were 10 and 1.5 nm, respectively. The residual amorphous phase enabled the maintenance of the nanoscale compound particles. The nanoscale mixed phase alloy remains good bending ductility even at Vf=75% and exhibits high tensile strength (σf) of 1910 MPa which is higher than that (1640 MPa) for the amorphous single phase. The increase of the thermal stability of the remaining amorphous phase is presumably due to the generation of the strong bonding pair mainly among Zr, Pd and Al. The good ductility of the mixed phase alloy is due to the suppression of embrittlement for the remaining amorphous phase because the partial crystallization is made in the supercooled liquid region. The first achievement of high σf and good ductility for the mixed phase alloy with nanoscale Zr2(Cu, Pd) phase surrounded by the amorphous phase is important for future progress of high-strength nanocrystalline bulk alloys.