Multicomponent alloys of Zr50M50, Zr50(M,Ag)50 and Zr50(M,Pd)50 (M = Fe,Co,Ni,Cu) can be melt-spun to obtain amorphous ribbons. The maximum thickness for fully amorphous ribbons varies with composition in the range 34‒53 μm. In contrast, fully amorphous ribbons are not obtainable for binary Zr50Ni50 or ternary Zr50(Ni,Cu)50 alloys. Heating-induced crystallization occurs through: two stages of amorphous [am] →[am′ + B2] → [B2 + B33] for Zr50M50; and [am] → [am′ + B2] → [B2 + AgZr] for Zr50(M,Ag)50; and a single stage of [am] → [B2] for Zr50(M,Pd)50, while no B2 phase is formed for the binary and ternary Zr50Q50 (Q = Ni or/and Cu) alloys. As-spun amorphous ribbons have good bending plasticity. Remarkably, Zr50M50 ribbons in tension show 0.22‒0.28% plastic elongation and work-hardening (the yield stress is ∼820 MPa, the fracture stress is ∼1200 MPa). When cold-rolled at room temperature to 30% reduction in thickness, Zr50M50 ribbons show 10% increase in hardness, while retaining good bending plasticity. Cold-rolling induces precipitation of spheroidal B2 and irregular B33 particles, while deformation in tension induces B2, B33 and also plate-like monoclinic precipitates. The B2 and B33 particles form by polymorphic transformation, and include a high density of internal defects. This novel deformation-induced precipitation has not been recognized for any Zr50Q50 binary or ternary alloys. The new multicomponent systems are encouraging for future progress as structural amorphous alloys.
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A (Ho 0.17 Ba 0.33 Cu 0.5 ) 50 Ag 50 alloy ribbon with a non-equilibrium structure was produced by melt-spinning. Heating of the alloy ribbon in air brought about the structural change to a stable metallic phase at about 610 K, followed by the formation of Ho 1 Ba 2 Cu 3 O 6.7 and Ag in the range of 630 to 740 K. The mixed materials of Ho 1 Ba 2 Cu 3 O 6.7 and Ag produced by oxidization of the melt-spun ribbon exhibited high- T c superconductivity with onset at 90 K and zero resistance at 80 K. It is notable that the mixture of Ag enables us to produce an alloy ribbon by melt-spinning even in the Ho-Ba-Cu alloy system with large miscibility gap.
An attempt has been made to investigate the microstructure and soft magnetic properties of Fe-Al alloys produced by a rapid solidification technique, with the aim of estimating their aptitude as core elements in rotating machinery. Examinations by optical and transmission electron microscopy revealed that the specimen containing aluminium up to about 23 at. % consists of ductile ferrite, whereas further addition of aluminium gives rise to embrittlement by the formation of an ordered b.c.c. compound. Furthermore, the rapidly solidified alloys exhibited high saturation induction values, more than 1.88 T in the alloys with aluminium content below 10 at.%. For the coercivity behaviour and core loss at 50 Hz, notable improvement was achieved after annealing at elevated temperatures. It was thus concluded that the present alloys have potential for practical use as magnetic core materials in rotating machinery.
A finely mixed structure consisting of nanoscale icosahedral (I) particles embedded in an fcc-Al phase was formed in rapidly solidified Al92Mn6Ln2 (Ln=Y, La, Ce, Nd or Gd) alloys. The particle size and interparticle spacing of the I phase are about 50 to 100 and 5 to 25 nm, respectively, for the Al92Mn6La2 and Al92Mn6Ce2 alloys. Furthermore, the individual I-particle contains a high density of phason defects and approximant phases. These mixed phase alloys have good bending ductility and the Al–Mn–Ln alloys except Ln=Nd exhibit high tensile fracture strengths (σf) exceeding 700 MPa. The highest σf value reaches as high as 1320 MPa for the Al92Mn6Ce2 alloy. The simultaneous achievement of high σf and good ductility is obtained for the alloys containing the I-phase as a main phase. The good mechanical properties are presumed to result from the simultaneous achievement of the following structural effects: (1) the homogeneous distribution of nanoscale I-particles in the Al matrix, (2) the lower solute content in the I-particles as compared with the stoichiometric composition, and (3) further refinement of the nanoscale I-particles into the coexistent icosahedral and periodic approximant regions resulting from the generation of a high density of phasons. It is thus concluded that the unique structural modification of the I-phase is effective for the achievement of high σf and good ductility, though the stoichiometric I-phase itself has an extremely brittle nature.
Time-resolved fluorescence spectra were measured for pyrene and for the pyrene-N,N-dimethylaniline system in the range from 3 nsec to 150 nsec after the excitation by a nitrogen gas laser. By the aid of the spectra, we could follow the formation and decay processes of the pyrene excimer or the pyrene-N,N-dimethlaniline exciplex. The rate constants were determined for the exciplex formation and decay processes.
Change in the primary crystallization from a single icosahedral quasicrystalline phase into the fcc Zr2Ni phase by mechanical disordering was investigated in a melt-spun Zr65Al7.5Ni10Cu12.5Pd5 glassy alloy. The transition of the primary phase is attributed to the mechanical strain induced in the icosahedral local structure in the glassy state.
The glass-forming ability (GFA), thermal stability and mechanical properties of new Zr-rich Zr70–76Al7–7.5Ni15–20Ag2–2.5 alloys are assessed. Melt-spinning gives a glass (G) for 70–74 at%Zr and [G + β-Zr + ω-Zr] phases for 76 at%Zr. Crystallization occurs in stages: G → [G + icosahedral quasicrystal (IQ)] → [Zr2Ni + Zr2Ag + Zr5Al3] for 70Zr, G → [G + IQ + β-Zr + ω-Zr] → [α-Zr + Zr2Ni + Zr2Ag + Zr5Al3] for 72Zr, and G → [G + β-Zr + ω-Zr] → [β-Zr + ω-Zr + Zr2Ni + Zr2Ag] → [α-Zr + Zr2Ni + Zr2Ag + Zr5Al3] for 74–76Zr. Annealed ribbons with G, [G + IQ] or [G + β-Zr + ω-Zr] phases have good bending plasticity. The IQ and [β-Zr + ω-Zr] phases are spheroidal with diameters 15–28 and 20–35 nm, respectively. As-cast 1.5-mm-diameter rods contain a single glassy phase for 70–72Zr and [G + β-Zr + ω-Zr] phases for 74–76Zr. The rods exhibit high strength and plastic strain: 1499 MPa & 6.3% for 70Zr, 1475 MPa & 9.2% for 72Zr, 1458 MPa & 3.8% for 74Zr, and 1610 MPa & 2.7% for annealed 70Zr with [G + IQ] phases, respectively. These plastic strains exceeding 2% are unprecedented for [G + IQ] and [G + β-Zr + ω-Zr], indicating strengthening by precipitate dispersions. The formation of plastic [G + IQ] and [G + β-Zr + ω-Zr] bulk composites is expected to increase the engineering importance of Zr-based BMGs.
The microstructural features of NdsFe76.sCosB6Cuo.sNbl nanocomposite magnet have been studied by a three-dimensional atom probe (JDAP) and transmission electron microscopy (TEM). The as-melt- spun microstructure is composed of a-Fe, NdzFe14B and a large fraction of intergranular amorphous phase. The annealed microstructure with optimum magnetic properties contains the same constituent phases as those in the as-quenched state, but the volume fraction of the NdzFelrB grains is increased by partial crystallization of the remaing amorphous phase. Nb and B are found to be enriched in the remaining amorphous phase. Unlike Fe3B/Nd2Fe14B nanocomposite, Cu additions are not effective in refining the grain size in this system. Index Termea-FelNd2Fe14B, amorphous, nanocompo- site magnet, exchange spring magnet
An icosahedral quasicrystalline (IQ) phase forms in the as-spun ribbons as well as as-cast bulk rods with a diameter of 2 mm for the Ti39Zr39Ni20Ag2 and Ti39Zr39Ni20Cu2 alloys. The Ti39Zr39Ni20Ag2 alloy ribbon consists of a mostly amorphous phase containing a small amount of IQ phases and exhibits good bending plasticity. The decomposition of their metastable phases occurs accompanying exothermic peaks at 694 K and 890 K, followed by an endothermic peak at 991 K. The former two peaks are due to the transitions from amorphous to IQ + cF96-(Ti, Zr)2Ni phases, and to C14-TiZrNi Laves phase, respectively. The latter endothermic peak originates from the change of IQ to C14-TiZrNi Laves and β-(Ti, Zr) phases. Compared with the complex phase decomposition behavior of the quaternary alloys, the decomposition of the metastable phase of the Ti40Zr40Ni20 alloy ribbon occurs accompanying only an endothermic peak at a peak temperature of 952 K, followed by a melting peak. For the quaternary alloys, the as-cast rods consist of an IQ single phase, in contrast to three phases of IQ, C14-TiZrNi Laves and β-(Ti, Zr) phases for the Ti40Zr40Ni20 rod. The ternary alloy rod fractures in the quasi-cleavage fracture mode, while the fracture mode of the quaternary alloy rod is cleavage fracture. In the Ti39Zr39Ni20Ag2 rod, IQ phase displays a spherical morphology with an average diameter of approximately 0.27 μm. The formation of the bulk IQ rod as well as the enhancement of amorphous phase formability for the Ag/Cu-containing IQ alloys are presumably due to the stabilization of supercooled liquid caused by the development of more dense-packed atomic configurations resulting from the sequent atomic size change of Zr > Ti > Ag/Cu > Ni as well as by the necessity of the separation to Ti-Zr-Ni and Ti-Zr-Ag/Cu atomic pairs resulting from the positive heats of mixing for Ni-Ag and Ni-Cu pairs.
