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Abstract: The composition dependence of glass-forming ability (GFA) of Ni–P binary alloys was systematically examined by fabricating ribbons of different thicknesses, and the microhardness of the glassy ribbon was measured. The eutectic alloy Ni80.4P19.6 has the best GFA and the highest microhardness in glassy state. As the alloy composition is deviated from the eutectic composition, both GFA and microhardness decrease, accompanied with an increasing full width at half maximum of the main broad peak in the X-ray diffraction spectrum of the glassy ribbon. All these results indicate a close correlation among microstructure, GFA and microhardness for the metallic glass. [Copyright &y& Elsevier]

Abstract: Three Co–Sn alloys with compositions around the eutectic point were undercooled to different degrees below the equilibrium liquidus temperature and the solidification behaviors were investigated by monitoring the temperature recalescence and examing the solidification structure. It is revealed that the primary phase during rapid solidification changes complexly with the increasing undercooling in the off-eutectic alloys, while coupled eutectic growth takes place at all undercoolings in the eutectic alloy. Two types of anomalous eutectics form in the alloys: one evolving from coupled eutectics and the other from single phase dendrites or seaweeds. The crystallographic orientation of eutectic phases in the anomalous eutectic is dependent on which type their precursors belong to. [Copyright &y& Elsevier]

Anomalous eutectics are argued to form due to the remelting of the primary solid during solidification of deeply undercooled eutectic alloy melts. As an indicator of the tendency for anomalous eutectic formation, the remelted fraction of the primary eutectic was analyzed systematically based on the eutectic dendrite growth theory. For eutectic alloys with either larger equilibrium solute distribution coefficients or gentle liquidus slopes, the primary eutectic is highly supersaturated with solute and more prone to remelting. When the eutectic composition is set to different values, (e.g. the eutectic point is closer to one phase of the eutectic), the two eutectic phases under rapid growth change their compositions simultaneously, but their remelted fractions during temperature recalescence do not vary significantly. Three representative binary eutectic alloys Ag–39.9 at.%Cu, Ni–19.6 at.%P and Pd–16.0 at.%P – their eutectic products are solid solution–solid solution, solid solution–stoichiometric intermetallic compound and stoichiometric intermetallic compound–stoichiometric intermetallic compound, respectively, were solidified at large undercooling. Anomalous eutectics were observed in the first two eutectic alloys whose eutectic structure consists of at least one solid solution phase, whereby the stoichiometric intermetallic compound phase remained highly oriented whereas the solid solution phase had a near random distribution of orientations. For the Pd–16.0 at.%P alloy, however, the primary eutectic retained its original morphology as the final solidification structure regardless of the degree of undercooling. All these experimental results validate the argument that anomalous eutectics result from the remelting of the primary solid. [ABSTRACT FROM AUTHOR]

Abstract: Garnet peridotite, interlayered with lesser amounts of dunite and olivine websterite and interwoven with garnet pyroxenite dikes, makes up a 0.5km2 massif near Lüliangshan in the North Qaidam ultrahigh-pressure (UHP) metamorphic belt, Northern Tibetan Plateau. Previous studies have suggested that the garnet peridotites represent Alaskan-style magmatic cumulates or oceanic serpentinites that were subducted to depths of >200km. Re–Os isotopic data provide new constraints on the origin and formation of the peridotites. Most dunites (Mg# 92–>95) have high Os contents (2.90–4.25ppb) and low 187Os/188Os (minimum 0.1108), while garnet pyroxenites have high 187Os/188Os (up to 0.2847) and low Os contents (0.03–1ppb); garnet lherzolites lie between these extremes. The Archean model ages (TRD=2.6Ga, TMA=2.8Ga) of the most refractory dunites represent minimum estimates for the age of the original melt depletion. In an Os–187Os/188Os plot, almost all garnet peridotites fall along two mixing lines: one is defined by mixing between the most refractory dunite and a garnet-rich pyroxenite, and the other by mixing between the dunite and a garnet-poor pyroxenite. The extremely depleted nature of the dunites, the high Ca and Al contents of the lherzolites, the variable enrichment in incompatible elements, and the Re–Os isotopic data suggest that the Lüliangshan garnet peridotites represent a fragment of subcontinental mantle, in which ancient residues after melt extraction (e.g. dunite) were refertilised by mafic melts similar to the garnet pyroxenites. Modelling of the garnet peridotite data suggests that at least some of the metasomatism is Paleoproterozoic in age; Re also may have been introduced into some of the garnet peridotites during the Paleozoic UHP Qaidam orogeny. The Lüliangshan peridotites are interpreted as refertilised Archean subcontinental lithospheric mantle, probably derived from beneath the North China Craton and entrained in the surrounding gneisses during their subduction into the mantle; the garnet peridotite assemblages may have formed during the original refertilisation event, or during the subduction. [Copyright &y& Elsevier]