Enhancement Of Glass-forming Ability Research Articles

The outstanding effect and mechanism of non-inert casting atmospheres on glass forming ability of P-containing Fe-based soft magnetic bulk metallic glasses

Generally, amorphous alloys are fabricated in an inert atmosphere—Ar to avoid crystallization and gain high glass forming ability (GFA). In this work, the effect of non-inert casting atmospheres (N2, air and O2) on the GFA of Fe76Si9B10P5, Fe76Si8B10P5Mo1, Fe77Mo2P10C4B4Si3 and [(Fe0.8Co0.2)0.75B0.2Si0.05]96Nb4 soft magnetic bulk metallic glasses (BMGs) was systematically investigated. Surprisingly, contrary to existing experience, while the GFA of [(Fe0.8Co0.2)0.75B0.2Si0.05]96Nb4 alloy remains the same as cast in Ar, it was found that the non-inert casting atmospheres can dramatically improve the GFA of P-containing Fe-based BMGs, especially in oxidizing casting atmosphere, with no influence in their thermal properties and magnetic properties. The results also indicated the surface composition of the P-containing Fe-based BMGs varied much with the casting atmospheres whilst the bulk composition remain unchanged. Moreover, plausible reasons were eliminated and underlying mechanism was elucidated. The decreased surface tension resulted from the segregation of P element of the P-containing Fe-based liquids during the melting process leads to the crystallization occurring in the surface layer rather than in the central area. At last, the enhancement of GFA by non-inert casting atmospheres were mainly ascribed to the increased surface tension resulting from the elimination of oxygen element for the oxidizing (air and O2) atmosphere and the alloying effect of nitrogen element for the N2 atmosphere, respectively. The new understanding about the non-inert atmosphere and metallic amorphous formation is expected to benefit the composition design of amorphous materials with better GFA and advances in the manufacture of amorphous alloys.

Microstructure and mechanical properties of wedge-shaped CuZrAlNd metallic glass ingots

In this study, (Cu43Zr48Al9)100-xNdx (x = 1, 2, 3, or 4 at. %) bulk metallic glasses (BMGs) were successfully prepared by casting in wedge-shaped copper moulds. We studied the effect of rare-earth neodymium (Nd) addition on the glass forming ability (GFA) and mechanical properties of (Cu43Zr48Al9)100-xNdx. The enhancement of GFA in Cu–Zr–Al BMGs with Nd addition could be well explained by the atomic size difference δ, electronegativity difference Δx and negative mixing enthalpy ΔHmix. Of the alloys investigated, the (Cu43Zr48Al9)97Nd3 BMG exhibited the best GFA, with a high compressive strength of 2045 MPa. To prepare the wedge-shaped cast, the melt was subjected to a wide range of cooling rates that allow investigation of the transformed microstructure and dynamics. A U-shaped crystal-to-glass phase transition boundary was obtained. Based on the microstructural analysis of (Cu43Zr48Al9)97Nd3, we found that the equilibrium microstructure of this alloy consists of [CuZr + Cu10Zr7 + CuZr2].

Enhancement of glass-forming ability and thermal stability of a soft magnetic Co75B25 metallic glass by micro-alloying Y and Nb

Soft magnetic Co-based Co–Y–Nb–B bulk metallic glasses (BMGs) without Fe have been developed by micro-alloying Y and Nb into a Co75B25 alloy. First, addition of 3–4 at.% Y promotes the occurrence of glass transition and increases the supercooled liquid stability and magnetic softness. Co71.5Y3.5B25 metallic glass possesses a large supercooled liquid region (ΔTx) of 33 K and low coercivity (Hc) of 1.5 A/m. Subsequent alloying 2–4 at.% Nb into Co71.5Y3.5B25 alloy further enlarges ΔTx to 50 K, lowers Hc to 0.9 A/m, and enables the formation of BMGs with a critical sample diameter up to 2.0 mm. The alloying Nb causes the formation of complex (Co, Nb, Y)23B6 competing phase during crystallization and widens the melt undercooling during solidification, which improves the supercooled liquid stability and glass-forming ability, respectively. Co–Y–Nb–B BMGs also exhibit good soft magnetic and mechanical properties, i.e., low Hc of 0.9–1.2 A/m, relatively high saturation magnetic flux density of 0.36–0.57 T, high yielding strength of 3877–3930 MPa with plastic strain of 0.2%–0.3%, and high Vickers hardness of 1156–1201. The developed soft magnetic Co-based BMGs are promising for applications as structural and functional materials.

Enhancement of glass-forming ability and plasticity via alloying the elements having positive heat of mixing with Cu in Cu48Zr48Al4 bulk metallic glass

Limited glass-forming ability (GFA) and room-temperature brittleness are currently critical challenges for the field of bulk metallic glasses (BMGs). Simultaneously enhancing GFA and plasticity is a central yet important research theme in this area. In contrast to the traditional wisdom, herein we report that addition of the elements with positive heat of mixing (PHM) into Cu-Zr-Al BMGs not only facilitated glass formation but also enhanced plasticity. It was found that the elements with a smaller PHM value have a larger optimal dose and are more effective in enhancing GFA due to stabilization of the liquid phase with an enhanced packing density and destabilization of the crystalline phase by slowing down the atomic rearrangement. Moreover, addition of the elements with a medium PHM value is beneficial for plastic deformation because of the enhanced structural heterogeneity. The established composition-GFA-properties relationship is useful for designing novel BMGs with both enhanced GFA and plasticity via alloying the PHM elements.

Correlation between local structure and glass forming ability enhanced by similar element substitution in (La-Ce)-Co-Al bulk metallic glasses

Similar element substitution is an effective strategy to develop bulk metallic glasses (BMGs) with high glass forming ability (GFA). However, the relationship between the local structure and the GFA enhancement has not been clarified when similar element is introduced. In this paper, the local structures of the ternary La65Co25Al10 and pseudo-ternary (La0.7Ce0.3)65Co25Al10 BMGs were studied by ab-initio molecular dynamics. Partial pair correlation function, bond angle distribution, coordination number, solute-solute avoidance, Voronoi polyhedron, and free volume were used to characterize the local structure. After partial substitution of Ce for La, the (La0.7Ce0.3)65Co25Al10 BMG exhibited higher degree of solute-solute avoidance, more icosahedral-like Voronoi polyhedrons, and less free volume, which may be the structural origin of the higher GFA induced by similar element substitution.

Effects of lutetium addition on formation, oxidation and tribological properties of a Zr-based bulk metallic glass

Enhancement of glass-forming ability (GFA) and surface properties are important for the application of Zr-based bulk metallic glasses (BMGs), and surface oxidation is an effective strategy for surface strengthening. In this paper, the effects of rare earth element Lu addition on GFA and oxidation properties of a Zr50Ti2Cu38Al10 bulk metallic glass were studied. The tribological properties of Lu-free and Lu-doping BMGs before and after oxidation were also investigated. It is found that 2 at.% Lu addition in this alloy significantly enhance the critical diameter (dc) from 5 mm to 20 mm. The oxidation rate of 2 at.% Lu-doping alloy is higher than Lu-free alloy, indicating that the addition of Lu facilitates the formation of oxidized scale on the surface of Zr50Ti2Cu38Al10 alloy. Moreover, surface oxidation treatment remarkably improves the wear resistance of Zr50Ti2Cu38Al10 and (Zr0.5Ti0.02Cu0.38Al0.1)98Lu2. This study is beneficial for the improvement of surface properties and further application of Zr-based BMGs.

Enhancement of glass-forming ability and mechanical property of Zr-based Zr-Al-Ni bulk metallic glasses with addition of Pd

The effects of partial substitution of Ni by Pd in the high-Zr-based Zr65Al10Ni25-xPdx (at.%, x = 0, 5 and 10) alloys on their glass-forming ability (GFA), crystallization kinetics and mechanical property were investigated. The critical diameter for glass formation is increased from 3 mm for Zr65Al10Ni25 alloy to 5 mm for Zr65Al10Ni15Pd10. An icosahedral quasicrystal phase precipitates in the amorphous matrix in the first crystallization step of Zr-Al-Ni-Pd BMGs, implying that strong icosahedral short/medium-range order (IS/MRO) may exist in the Pd-containing alloys. In additional, Pd-bearing Zr-based BMGs present a lower Avrami exponent n indicating the higher stabilization of the supercooled liquid. Moreover, the Zr-Al-Ni-Pd BMGs exhibit larger compressive plasticity, higher notch toughness and Poisson's ratio than those of Zr65Al10Ni25 alloy, which can be correlated with the existence of strong IS/MRO clusters in amorphous phase.

Glass-forming ability, thermal stability of B2 CuZr phase, and crystallization kinetics for rapidly solidified Cu–Zr–Zn alloys

The glass-forming ability (GFA) of (Cu0.5Zr0.5)100-xZnx (x = 1.5, 2.5, 4.5, 7, 10, and 14 at %) metallic glasses (MGs) was studied. With increasing Zn content, the GFA of CuZr-based MGs gradually increases, enabling the fabrication of Cu–Zr–Zn bulk metallic glasses (BMGs) and metallic glass matrix composites. The enhancement of GFA with Zn addition to the CuZr binary alloy is well explained by considering topological instability and electronic criteria. Upon annealing of Cu–Zr–Zn MGs Cu10Zr7 and subsequent CuZr2 crystals precipitate in the glassy matrix, being followed by the nucleation of B2 CuZr crystals. It is shown that Zn addition can effectively stabilize B2 CuZr phase to lower temperatures. Analysis of the crystallization kinetics of Cu–Zr–Zn MGs under isothermal conditions shows that the dominated crystallization mechanism is the interface-controlled two- or three-dimensional growth with different nucleation rates.

Influence of mutual substitution between La and Gd on the glass-forming ability of Al–Ni–La–Gd alloys

A series of Al100–a–bNia(La1–xGdx)b alloys, where a=9–10, b=4.5–5.5 and x=0–1, were suction cast under identical conditions into a wedge-shaped copper mold for investigating the compositional dependence of glass-forming ability (GFA). The GFA of the ternary alloys, except for the optimal glass former (Al85.5Ni9.5La(Gd)5), is enhanced when a given rare earth element (La or Gd) is partially substituted by the other. The mutual substitution content between La and Gd for the optimal GFA increases with a decrease in Ni content. The enhancement of GFA by the mutual substitution between La and Gd was interpreted based on Miracle’s model of atom packing efficiency.

Enhancement of glass-forming ability and mechanical behavior of zirconium–lanthanide two-phase bulk metallic glasses

Development of the two-phase bulk metallic glasses (BMGs) is essentially retarded due to difficulties in finding of phase-separated (immiscible) alloys with high glass-forming ability (GFA) of coexistent phases. Referring to the concept of solute partitioning and minimization of free energy, in this work we present an idea that a metallic liquid system containing two liquids with individual self-assembled eutectic composition may yield two-phase BMGs upon casting. The formation of the two-glass structure is discussed and a strategy of partial substitution of chemically similar elements for overcoming the drawback of low GFA is proposed. A family of two-phase zirconium–lanthanide based metallic glasses in bulk form is developed. The mechanical behavior of the two-phase BMGs with different ratio of zirconium-rich to lanthanide-rich glassy phase is studied for the first time. This work provides a new concept for fabrication of two-phase BMGs and reveals the role of constituent phases in determining the mechanical properties of the whole glass.

Formation of Bulk Metallic Glasses from Cu-Zr Based Alloys with Yttrium Addition

Abstract Cu46Zr46Al8 bulk metallic glass (BMG) was prepared by low purity sponge zirconium instead of high purity crystal bar zirconium, and via the microalloying of adding a small amount of yttrium. The results show that the glass forming ability (GFA) and the thermal stability of the Cu46Zr46Al8 alloy are improved by yttrium addition. When the addition amount of Y is 2at% and 3at%, the enhancement of GFA is most significant. The compressive fracture strength of Y microalloyed BMG is more than 2 GPa, which is much higher than that of BMG alloy produced with high purity raw materials, but its plasticity deteriorates obviously.

Enhancement of glass-forming ability and plasticity of Cu-rich Cu–Zr–Al bulk metallic glasses by minor addition of Dy

Abstract

Effects of C Addition on Glass-Forming in FeCPSiBMoMn Bulk Metallic with Good Soft-Magnetic Properties

The effect of C substitution on the glass forming ability (GFA) and soft magnetic properties of Fe-based bulk metallic glasses (BMG) Fe79.4-xCxSi3.5B5.1P8.9Mo3Mn0.1(x = 4.2, 5.2, and 7.0) alloys have been investigated. It is revealed that fully glassy alloy rods with diameters up to 4 mm can be prepared by conventional copper mold casting method even using the low-cost industrial Fe-P master alloy. Properly substituting of Fe by C gives rise to an enhancement of GFA. Moreover, all the samples exhibit good soft magnetic properties with high saturation magnetization up to 1.16 T and low coercivity of 204 A/m.

Enhancement of glass-forming ability and corrosion resistance of Zr-based Zr-Ni-Al bulk metallic glasses with minor addition of Nb

Cu-free Zr-based bulk metallic glasses (BMGs) with high glass-forming ability (GFA) have been discovered in the Zr-Ni-Al-Nb system. The GFA of Zr-Ni-Al alloys can be significantly enhanced by the minor addition of Nb, which increases the glass transition temperature, and lowers the melting and liquidus temperatures. The Zr-Ni-Al-Nb BMGs have critical sample diameters of 15–20 mm as verified by a copper mold casting. They exhibit excellent corrosion resistance in chloride-ion-containing solutions, which is considerably better than that of other known Zr-based BMGs with superhigh GFA. It was revealed that the formation of highly protective Zr-, Al-, and Nb-enriched surface film is responsible for the high corrosion resistance. The BMGs also possess high compressive yield strength of 1786–1847 MPa, large plastic strain of 1.6–3.2%, and a high Poisson’s ratio of 0.365–0.371.

Enhanced glass forming ability of Fe-based alloys with minor additions

Minor Fe and Yof Fe71.2B24Y4.8 bulk metallic glass (BMG) are replaced by Ni, Nd, and Ge, respectively, and glass-forming ability (GFA) influenced by these similar element substitutions are studied. Except Ge, Ni and Nd can both improve the critical diameter of base BMG from 2 to 3 mm. Therefore, substitutions with chemical similar elements are more effective on GFA enhancement than those with atom size similar elements.

Enhancement of the glass forming ability of La–Al–Cu glassy alloys by partial substitution of Al by Mg

Partial substitution of Al by Mg was studied to reveal the influence of the neighboring element for glass forming ability (GFA) of La 62Al 14Cu 24 alloy. A series of quaternary La 62Al 14− x Mg x Cu 24 ( x = 2.8, 3.2, 3.5, 4.2, 5.0) alloys were cast by copper mold casting. As a result, the La–Al–Mg–Cu alloys with full glassy rods of 10 mm in diameter were achieved, suggesting that partial substitution of Al by Mg dramatically enhances the GFA. The enhancement of GFA can be mainly attributed to the large atomic size ratios among these constituent elements.

Enhancement of glass-forming ability and bio-corrosion resistance of Zr–Co–Al bulk metallic glasses by the addition of Ag

A novel Ni and Cu-free Zr-based bulk metallic glass (BMG) system with enhancement of glass-forming ability (GFA) and bio-corrosion resistance was prepared by copper mold casting by the addition of Ag. It was found that the addition of Ag can considerably enhance the glass-forming ability, as indicated by the increase of the critical glass dimension from 3 mm diameter of the ternary system to over 10 mm in the alloy of Zr 53Co 18.5Al 23.5Ag 5. The bio-corrosion behaviors of the Zr-based BMGs in phosphate buffered solution (PBS) were investigated by electrochemical polarization at 310 K. It was found that the addition of appropriate amount of Ag can enhance the corrosion resistance of the BMGs. The X-ray photoelectron spectroscopy (XPS) indicated that the formation of an Al 2O 3-enriched passive film is mainly responsible for the high corrosion resistance of Ag-bearing alloy in phosphate buffered solution.

Effect of Co concentration on thermal stability and magnetic properties of (Fe,Co)–Nb–Gd–B glassy alloys

A two-stage-like glass transition phenomenon attenuated gradually with an increase in Co content in (Fe 1− y Co y ) 67.5Nb 4Gd 3.5B 25 ( y = 0.1–0.5) glassy alloys, and disappeared for the alloy with y = 0.5, resulting in a large supercooled liquid region of 102 K. As the Co content increases, the liquidus temperature decreases gradually, and the reduced glass transition temperature increases, indicating the enhancement of glass-forming ability (GFA). The best GFA was obtained for alloy with y = 0.5, and the full glassy sample with a diameter of 5 mm could be fabricated by copper mold casting. The (Fe,Co)–Nb–Gd–B glassy alloys exhibited good soft magnetic properties, i.e., rather high saturation magnetization of 0.86–0.91 T, low coercive force below 5.0 A/m, and low saturated magnetostriction of 6–13 × 10 −6. In addition, the glassy alloys also possessed very high compressive fracture strength of 3821–4112 MPa and high Vickers hardness of 1028–1065.

Inhomogeneous structure and glass-forming ability in Zr-based bulk metallic glasses

Recently, a series of quaternary Zr-based bulk metallic glasses (BMGs), i.e., Zr 53Cu 18.7Ni 12Al 16.3, Zr 51.9Cu 23.3Ni 10.5Al 14.3 and Zr 50.7Cu 28Ni 9Al 12.3, have been developed and their glass-forming ability (GFA) increases with Cu concentration. In this work, atomic structures of the three BMGs were rebuilt by reverse Monte Carlo simulations based on the reduced pair distribution functions measured by high energy X-ray diffraction. The results show that a certain amount of substitution of short Zr–Cu, Cu–Cu pairs with long Zr–Zr and Zr–Al pairs enhances the local denser packing of Kasper polyhedral centered by Zr and Al atoms. A cell sub-divided method is proposed to describe the fluctuation of local number density which is found to follow the normal distribution function. The largest possible free volume in the three alloys is found to approaches to 3.8 Å. For the three alloys, the enhancement of GFA with increasing Cu content is due to the increase in the fluctuation degree of local density instead of the dense packing.

Effect of Al on the local structure and stability of Zr-based metallic glasses

The effect of Al addition on the local structure and the thermal stability in the Zr–Ni-based metallic glass is investigated. It is well known that Al is a very effective element on the enhancement of glass-forming ability (GFA), i.e., stability of supercooled liquid state in the alloy system. We have found that the dominant local structure is icosahedral-like in the Zr 70Al 10Ni 20 metallic glass and the tetragonal Zr 2Ni-like local in the Zr 70Ni 30 amorphous alloy. It is concluded that the change in the dominant local structure contributes to the enhancement of the stability of supercooled liquid state in the alloy.