Glass-forming Ability Of Cu Research Articles

Composition dependence in glass-forming ability of Cu–Ag binary alloys

Alloys around eutectic points are thought to be good glass formers. However, the glass-forming ability (GFA) as a function of composition from pure metals to the eutectic alloy has not been quantified and the underlying microstructural and dynamical origins are unclear. In this work, the GFA of Cu–Ag alloys at various compositions was thoroughly investigated by using molecular dynamics simulations. According to the results, the critical cooling rate for glass formation Rc (K/s) varies with solute content x′ (at%), following Rc ≈ Aexp(kx′) where A = 4.61 × 1012 and k = -0.25 on the Cu side and A = 4.43 × 1012 and k = -0.19 on the Ag side. The Rc of the eutectic alloy is about 5 orders of magnitude lower than that of the pure metals. Structurally, the number of densely packed icosahedral-like clusters in Cu–Ag metallic glasses increases with increasing solute content, resulting in the most densely packed structure at the eutectic composition. The dynamical properties of Cu–Ag melts are basically independent on composition at high temperatures, but obviously change with composition at low temperature. Besides the largest reduced glass transition temperature, the highest five-fold symmetry (FFS) local structure and more importantly the retarded dynamics of liquid atoms below the liquidus temperature around the eutectic composition impart the eutectic alloy with the best glass-forming ability.

Icosahedral clusters in Cu100-xZrx (x=32,34,36,38.2,40 at.%) metallic glasses near the peak of glass-forming ability (x=36): A balance between population and encaging strength

Understanding the origin of glass-forming ability (GFA) is important for the discovery or development of new metallic glasses (MGs). It is well known that the GFA in Cu–Zr binary MGs is sensitive to the composition and possesses a peak around Cu64Zr36 (at.%). The reason for this, however, is still not fully understood due to the complexity of the physics behind glass formation. Here, we use molecular dynamics simulations and statistics to study the structure and particularly the atomic energy state of the supercooled liquid and glass phases in the Cu100-xZrx (x = 32, 34, 36, 38.2, 40 at.%) alloy series. We show that the shell atoms of icosahedral clusters (the most dominant cluster type) in all these alloys have significantly lower (by > 1 eV/atom) potential energy than the core atoms. With rising Zr-content, the core–shell energy difference of the icosahedral clusters increases, making these clusters more strongly encaged and harder to break before or during crystallization. This effect counteracts the decrease in the population of the icosahedral clusters that has been noticed in previous studies. The net result of the interplay between these two factors can be represented by the product of the fraction of icosahedral shell-atoms and the core-shell energy difference, which exhibits a maximum at 36% Zr where the highest GFA has been observed. These findings provide new insights into the origin and peaking behavior of the GFA in this important binary bulk MG system, which could facilitate the search for the best glass-forming compositions in other alloy systems.

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].

Effect of Titanium Additions on the Thermophysical Properties of Glass-Forming Cu50Zr50 Alloy

Differential scanning calorimetry, laser flash method, and dilatometry were used to study the thermophysical properties of quenched Cu50Zr50–xTix (x = 0, 2, 4, 6, 8) alloys in the temperature range from room temperature to 1100 K. Data obtained on the heat capacity, thermal diffusivity, and density have been used to calculate the coefficient of thermal conductivity. Temperatures corresponding to the stability of martensite CuZr phase, its eutectoid decomposition, and formation in Cu50Zr50–xTix alloys with different Ti contents upon heating have been determined. It has been found that the thermal diffusivity and thermal conductivity of the studied alloys are low and a typical of metallic systems. As the titanium content increases, the coefficients of thermal conductivity and thermal diffusivity vary slightly. It has been shown that the low values of thermophysical characteristics correspond to the better capability of amorphization and can be a criterion for the glass-forming ability of Cu–Zr-based alloys.

Correlation between atomic-level structure, packing efficiency and glass-forming ability in Cu–Zr metallic glasses

The local structure and atomic packing in CuxZr100−x (46≤x≤70) alloys have been investigated using classical molecular dynamics. We convincingly demonstrate that the atomic packing efficiency of the polytetrahedral clusters strongly correlates with the glass-forming ability. It is found that the full-icosahedra (<0,0,12,0>), which is considered to be a key local structural feature associated with the glass formation in metallic alloys, alone cannot explain the compositional dependence of glass-forming ability. We suggest that the population of the so-called defected icosahedra (<0,2,8,2>), apart from the full-icosahedra, could be crucial to account for the observed high atomic packing efficiency in the best glass-forming compositions.

Roles of alloying additions on local structure and glass-forming ability of Cu–Zr metallic glasses

To identify the structural role of alloying element M (M = Ti, Ga, Co, Fe) on the glass-forming ability (GFA) of Cu50Zr50 base alloy, the atomic structures of the binary and ternary metallic glasses were examined by extended X-ray absorption fine structure (EXAFS) spectroscopy. The EXAFS curve-fitting analysis indicates that the main structural difference among the metallic glasses is in the atomic packing density of Cu-centered clusters. The relative shortening of the Cu–M distance is closely related to the heat of mixing between Cu and M: the more negative the heat of mixing, the larger is the shortening of the Cu–M distance. Based on a systematic analysis of the component properties and GFA data for Cu–Zr based alloys, it is suggested that alloying elements that bring a more uniform distribution of atomic size and possess strong chemical interactions with the main components should be selected in developing large-size bulk metallic glasses.

Non-isothermal crystallization kinetics and glass-forming ability of Cu–Zr–Ti–In bulk metallic glasses

In this paper, bulk metallic glasses with the compositions of Cu55−zZr37Ti8Inz (z=1, 3 and 5at.%) have been evaluated from the viewpoint of thermodynamics and kinetics. The activation energies corresponding to the characteristic temperatures have been calculated and the results show that the as-cast alloys have a good stability in thermodynamics. The difficulty of each crystallization step was discussed with activation energy. Furthermore, crystallization mechanism of each as-cast alloy was studied by phase transformation and local Avrami exponent. Depending on the fragility index, Cu54Zr37Ti8In1 can be classified to “strong glasses” and Cu52Zr37Ti8In3 and Cu50Zr37Ti8In5 should be considered as “intermediate glasses”. In addition, glass-forming ability of each alloy was discussed thoroughly. The results demonstrate that glass-forming ability increases with content of In element.

Effect of adding elements on glass-forming ability of (Cu47Ti34Zr11Ni8)99M (M=Al, Be, Si, Nb, Fe and Co) bulk amorphous alloys

Bulk amorphous alloys (Cu 47 Ti 34 Zr 11 Ni 8 ) 99 M (M = Al, Be, Si, Nb, Fe and Co) were prepared by arc melting and suction casting. The effect of the addition of alloying elements on the glass-forming ability and thermal stability of Cu 47 Ti 34 Zr 11 Ni 8 was studied. With the addition of Si, the glass-forming ability of the Cu 47 Ti 34 Zr 11 Ni 8 alloy is improved, which is evidenced by the increase of supercooled liquid region Δ T x , the reduced glass transition temperature T rg , γ parameter, K H stability parameter. With the addition of Al, Be, Co, Fe and Nb, the glass-forming ability of the alloys is decreased. Calculation of the formation enthalpies of amorphous alloys by using Miedema’s theory, show that the glass-forming ability of the (Cu 47 Ti 34 Zr 11 Ni 8 ) 99 M decreases with increasing formation enthalpy of the amorphous phase except in the case of Cu 47 Ti 34 Zr 11 Ni 8 . The glass transition activation energy linearly increases with increasing atom size parameter δ .

Prediction of the glass forming ability in Cu–Zr binary and Cu–Zr–Ti ternary alloys

By combining CALPHAD technique with kinetic approach, we evaluated the glass forming ability(GFA) of nine compositions of Cu–Zr and thirteen of Cu–Zr–Ti alloys in terms of critical cooling rate and fragility. The driving forces for crystallization from the undercooled liquid alloys were calculated by using Turnbull and Thompson–Spaepen (TS) Gibbs free energy approximate equations, respectively. Time–temperature-transformation (TTT) curves of these alloys were obtained with Davies–Uhlmann kinetic equations based on classical nucleation theory. With Turnbull and TS equations, the critical cooling rates are calculated to be in the range of 9.78 × 10 3–8.23 × 10 5 K/s and 4.32 × 10 2–3.63 × 10 4 K/s, respectively, for Cu–Zr alloys, and 1.38 × 10 2–7.34 × 10 5 K/s and 0.64–1.36 × 10 4 K/s, respectively, for Cu–Zr–Ti alloys. The calculated fragility parameters are in the range of 6.32–9.3 for Cu–Zr binary and 5.7–8.24 ternary alloys, respectively. The comparison of the calculated results to the experimental data indicates that the cooling rate obtained with TS equation is more valid than that with Turnbull equation, and that obtained by other researchers for the evaluation of GFA. The fragility be used as parameter to evaluate relatively the GFA in an alloy system. This work suggests that the combined thermodynamic and kinetic modeling may provide an effective method for the prediction of GFA in Cu–Zr and Cu–Zr–Ti alloys.

Corrosion behavior and glass-forming ability of Cu–Zr–Al–Nb alloys

Amorphous Cu50−xZr45Al5Nbx (x=0, 1, 3 and 5at.%) samples with critical diameters of 1.54–2.05mm were formed by copper-mold suction casting. The effects of Nb on the glass formation ability were evaluated with differential scanning calorimetry and the corrosion resistances of the alloys with the addition of Nb were evaluated in 1N HCl, 3% NaCl and 0.5N H2SO4 solutions, respectively, by weight loss and polarization curve measurements. The samples surfaces were examined after the corrosion test with SEM. It was found that the addition of Nb causes a decrease of ΔTx of Cu50−xZr45Al5Nbx alloy from 54K to 45K. On the other hand, the corrosion resistances in various solutions were improved with the addition of Nb.

Formation and thermal stability of Cu-Zr-Al-Er bulk metallic glasses with high glass-forming ability

The formation and thermal stabilities of Cu 46.25Zr 46.25- x Al 7.5Er x , ( x=0 to 8) bulk metallic glasses (BMGs) were investigated. The addition of a small amount of Er (2at%) for replacing Zr effectively improves the glass-forming ability of Cu 46.25Zr 46.25Al 7.5 alloy, and the glassy rod with a diameter of at least 12 mm can be formed. The glass transition temperature ( T g), temperature interval of supercooled liquid region Δ T x (= T x − T g, and reduced glass transition temperature T rg (= T g/T 1) of Cu 46.25Zr 44.25Al 7.5Er 2 glassy alloy are 699 K, 62 K and 0.607, respectively.

Devitrification behavior and glass-forming ability of Cu–Zr–Ag alloys

This paper presents an influence of Ag addition on the glass-forming ability and devitrification behavior of Cu–Zr glassy alloys on heating. The crystallization kinetics and structure changes in Cu 45Zr 45Ag 10 and Cu 35Zr 45Ag 20 glassy alloys on heating were studied by X-ray diffraction, transmission electron microscopy, differential scanning and isothermal calorimetry methods. Based on the results obtained one can assume that the improvement of the glass-forming ability of the Cu–Zr alloys by the addition of Ag is connected with a particular crystallization mechanism and a higher reduced glass-transition temperature of the Cu 45Zr 45Ag 10 ternary alloy compared to the binary Cu 55Zr 45 counterpart. As observed in the present work crystallization of the Cu–Zr–Ag alloys is found to cause embitterment of the samples and should be avoided as these alloys are considered to be used as structural materials. The Cu 35Zr 45Ag 20 alloy shows possible submicron-scale phase separation upon annealing.

Effects of additional Ag on the thermal stability and glass-forming ability of Cu–Zr binary glassy alloys

Thermal stability and glass-forming ability (GFA) of (Cu 0.5Zr 0.5) 100− x Ag x ( x = 0–16) glassy alloys have been studied. Both of the supercooled liquid region (Δ T x ) and the GFA greatly increase with increasing Ag content. The largest Δ T x of 80 K and the critical diameter ( d c) of 6.0 mm were obtained for x = 12 and 10 alloys, respectively, and then decrease with further increasing Ag content. The substitution of Hf for Zr in Cu 45Zr 45Ag 10 glassy alloy increases the stability of supercooled liquid and fracture strength, though the GFA decreases. The substitution of Al for Ag in Cu 45Zr 45Ag 10 alloy is effective for the increase in Δ T x as well as GFA. The largest Δ T x of 86 K and d c of 9.0 mm were obtained for Cu 45Zr 45Al 5Ag 5 alloy. The GFA of the Cu–Zr-based alloys has better correlation with reduced glass transition temperature and γ value. The new bulk glassy alloys exhibit high fracture strength of 1774–2000 MPa with distinct plastic strains of 0.002–0.014.

The effect of Gd addition on the glass-forming ability of Cu–Zr–Al alloy

A new Cu-based bulk metallic glass of 10 mm diameter was successfully prepared by a conventional copper mold casting method using alloy Cu 46 Zr 45 Al 7 Gd 2 . The addition of Gd effectively alleviates the harmful effects of oxygen in the melt by the preferential formation of gadolinium oxide and significantly increases the glass-forming ability. The T rg = T g / T m reaches a maximum value of 0.694 for the Cu 46 Zr 45 Al 7 Gd 2 alloy, which is consistent with the experimental results.

Metallographic analysis of Cu–Zr–Al bulk amorphous alloys with yttrium addition

Abstract Minor yttrium addition can improve the glass-forming ability of Cu–Zr–Al ternary alloys via suppression of the growth of eutectic clusters. Yttrium addition also makes the room temperature ductility of the alloys decrease, and both the compressive strength and elastic strain limits increase slightly.

Formation and Mechanical Properties of Cu&amp;ndash;Zr&amp;ndash;Al&amp;ndash;Sn Bulk Metallic Glasses

Formation and mechanical properties of Cu-Zr-Al-Sn bulk metallic glasses were investigated. The glass-forming ability of Cu 50 Zr 50 alloy is significantly improved with addition of Al, and the critical diameter for glass formation increases from 2 to 7 mm for Cu 46.25 Zr 46.25 Al 7.5 alloy. Furthermore, the critical diameter is slightly increased to 8 mm by substituting 1 at% Sn for Zr of Cu 46.25 Zr 46.25 Al 7.5 alloy. The bulk glassy Cu 46.25 Zr 46.25 Al 7.5 alloy exhibits a limited plasticity of about 1.2% to failure under compression and the plasticity is effectively enhanced due to the addition of Sn, about 4.1% for bulk glassy Cu 46.25 Zr 45.25 Al 7.5 Sn 1 alloy.

The effect of Sn addition on the glass-forming ability of Cu–Ti–Zr–Ni–Si metallic glass alloys

The effect of Sn substitution for Ni on the glass-forming ability was studied in Cu 47Ti 33Zr 11Ni 8− x Sn x Si 1 ( x=0,2,4,6,8) alloys by using thermal analysis and X-ray diffractometry. With increasing x from 0 to 8, the glass transition temperature, T g, of melt-spun Cu 47Ti 33Zr 11Ni 8− x Sn x Si 1 alloys increased gradually from 720 to 737 K. On the other hand, the crystallization temperature, T x, increased from 757 K at x=0 to 765 K at x=2, being nearly same with further increase of x. Partial substitution of Ni by Sn in Cu 47Ti 33Zr 11Ni 8Si 1 promotes the glass formation. Both amorphous Cu 47Ti 33Zr 11Ni 8− x Sn x Si 1 alloys prepared by melt spinning and injection casting showed similar crystallization process during continuous heating in DSC. Temperature range of undercooled liquid region exhibits good correlation with the critical diameter for the formation of an amorphous phase in injection casting.