Influence of Similar Atom Substitution on Glass Formation in (La–Ce)–Al–Co Bulk Metallic Glasses

Department of Materials Science and Engineering, Beijing University of Aeronautics and Astronautics, Beijing 100083, China
Acta Materialia (Impact Factor: 4.47). 06/2007; 55(11):3719-3726. DOI: 10.1016/j.actamat.2007.02.026
Source: arXiv


The glass-formation range of bulk metallic glasses (BMGs) based on lanthanum and cerium was pinpointed in the La–Al–Co, Ce–Al–Co and pseudo-ternary (La–Ce)–Al–Co systems, respectively, by copper mold casting. Through the stepwise substitution of La for solvent Ce in (LaxCe1−x)65Al10Co25 alloys (0 < x < 1), the fully glassy rods of the (La0.7Ce0.3)65Al10Co25 alloy can be successfully produced up to 25 mm in diameter by tilt-pour casting. Compared with the glass-forming ability (GFA) of single-lanthanide-based alloys, La65Al10Co25 and Ce65Al10Co25, the coexistence of La and Ce with similar atomic size and various valence electronic structure obviously improves the GFA of (LaxCe1−x)65Al10Co25 BMGs, and this cannot be explained by the conventional GFA criteria for BMGs, e.g. atomic size mismatch and negative heats of mixing. A thermodynamic model was proposed to evaluate this substitution effect, which gives a reasonable explanation for the obvious improvement of GFA induced by the coexistence of similar atoms.

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Available from: Chaoli Ma, Nov 13, 2014
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    • "x Ce 1 − x ) 65 Al 10 Co 25 (x = 0.3, 0.4, 0.5, 0.6, 0.7, and 0.8) and Fe 72 − x Mo x Y 6 B 22 (x = 1, 2, 3, 4, 5, and 6) BMGs, which are taken from Refs. [24] "
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    ABSTRACT: Based on the Anderson's theory and Mott–CFO model for the electrical transport properties of disordered materials, an empirical criterion has been proposed for predicting the glass-forming ability (GFA) of amorphous alloys, which is termed as the relative electrical resistivity difference between the amorphous and fully crystallized states at room temperature (RT), i.e., Δρ = (ρamorRT − ρcrysRT)/ρcrysRT, ρamorRT and ρcrysRT denote the room-temperature electrical resistivities of an amorphous alloy and its corresponding crystal, respectively. A higher ∆ρ value of an alloy always correlates with a better GFA, which has been unambiguously confirmed by a large number of results in the Cu–Zr–Al–Ag, La–Ce–Al–Co, and Fe–Mo–Y–B alloy systems. Compared with the widely used criteria the reduced glass transition temperature Trg, the supercooled liquid range ∆Tx, and the parameter γ, in which the glass transition temperature Tg is necessary and its determination is sometimes arbitrary with inaccuracy for some amorphous alloys, ∆ρ can be quite easily and more exactly obtained, and is more consistent with the GFA. The empirical criterion is very useful especially for optimizing the compositions and pinpointing the best glass former with less cost in a given system.
    Full-text · Article · Jul 2015 · Journal of Non-Crystalline Solids
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    • "It is well known that the eutectic solidification is greatly beneficial for glass formation of the most of multi-component alloys[25]. A few alloys like (LaeCe)e Ale(CoeCu) with high GFA also exhibit the multi-peak melting behaviors[9,11]. The significant difference in solidification behaviors during between rapid solidification process and DSC measurement at a relatively low cooling rate might be responsible for the deviation. "
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    ABSTRACT: Glass formation, thermal stability, elastic moduli and mechanical properties of La–Al–C bulk metallic glasses (BMGs) were investigated. The BMGs of La57.5Al32.5C10, La60Al30C10, and La62.5Al27.5C10 with the maximal diameters up to 3 mm can be synthesized. Compared with other La-based glassy systems, like La–Al–(Co, Ni, Cu), the La–Al–C BMGs with the similar La concentration exhibit higher glass transition temperatures (507–577 K) and elastic constants. The La–Al–C BMGs with the unusual Tg and elastic moduli fill a gap in thermal and elastic properties between light rare-earth-based BMGs and heavy rare-earth-based ones. The compressive yield strength of La57.5Al32.5C10 BMG reaches to ∼1.1 GPa, higher than that of other reported La-based BMGs. The ternary BMGs with simple element constituent, high glass-forming ability and superior mechanical properties are significant for fundamental research as model materials.
    Full-text · Article · Sep 2014 · Intermetallics
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    • "As the Al content in the alloys is increased to 40–45 at.%, formation of the Al2(La,Ce) phase was further promoted, resulting in an increment in the critical cooling rate and a reduction in the maximum attainable rod diameter for fully glass formation35, as demonstrated by Rc-glass in Fig. 8b. During cooling, the Al2(La,Ce) phase still precipitated first, nevertheless, the remaining liquid still contained a relatively high Al content. "
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    ABSTRACT: The long-standing challenge for forming Al-based BMGs and their matrix composites with a critical size larger than 1 mm have not been answered over the past three decades. In this paper, we reported formation of a series of BMG matrix composites which contain a high Al content up to 55 at.%. These composites can be cast at extraordinarily low cooling rates, compatible with maximum rod diameters of over a centimetre in copper mold casting. Our results indicate that proper additions of transition element Fe which have a positive heat of mixing with the main constituents La and Ce can appreciably improve the formability of the BMG matrix composites by suppressing the precipitation of Al(La,Ce) phase resulted from occurrence of the phase separation. However, the optimum content of Fe addition is strongly dependant on the total amount of the Al content in the Al-(CoCu)-(La,Ce) alloys.
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