Formation and mechanical properties of Ni-free Zr-based bulk metallic glasses

Glass formation and mechanical properties of Zr–Al–Co–Cu–Ag bulk metallic glasses (BMGs) were investigated. The glass-forming ability (GFA) of Zr₅₅Al₂₀Co₂₀Cu₅ alloy is significantly improved with minor addition of Ag, indicating by the impressive increase of the critical diameter of glass formation from 5 mm for Zr₅₅Al₂₀Co₂₀Cu₅ to 16 mm for (Zr_0.55Al_0.20Co_0.20Cu_0.05)₉₇Ag₃ and (Zr_0.55Al_0.20Co_0.20Cu_0.05)₉₅Ag₅ alloys. The Zr–Al–Co–Cu–Ag BMGs exhibit high compressive strength of 2160–2280 MPa and distinct plasticity of 0.6–2.5%. The Zr-based BMGs with outstanding GFA and mechanical properties as well as low-level cytotoxicity elements are expectative for industrial and biological applications.     

High-strength Cu-based bulk glassy alloys in Cu–Zr–Ti and Cu–Hf–Ti ternary systems

New Cu-based bulk glassy alloys were formed in Cu–Zr–Ti and Cu–Hf–Ti systems by the copper mold casting method. The critical diameter is 4 mm for the Cu₆₀Zr₃₀Ti₁₀ and Cu₆₀Hf₂₅Ti₁₅ alloys which are larger than 1 mm for the Cu₆₀Zr₄₀ and Cu₆₀Hf₄₀ glassy alloys. The substitution of Zr or Hf for Ti causes an increase in the glass-forming ability (GFA). As the Ti content increases, the glass transition temperature (T_g), crystallization temperature (T_x), and the supercooled liquid region ΔT_x(=T_x−T_g) decrease for both Cu₆₀Zr_40−xTi_x and Cu₆₀Hf_40−xTi_x alloys. In contrast, the liquid temperature (T_l) has a minimum value of 1127 K for the Cu₆₀Zr₂₀Ti₂₀ alloy and 1175 K for the Cu₆₀Hf₂₀Ti₂₀ alloy, resulting in a maximum T_g/T_l of 0.63 and 0.62, respectively. The alloys with the highest T_g/T_l value showed the highest GFA for these Cu-based alloys. The bulk glassy alloys exhibit high tensile fracture strength of 2000–2160 MPa, compressive fracture strength of 2060–2150 MPa and compressive plastic elongations of 0.8–1.7%. The finding of the new Cu-based bulk glassy alloys with high GFA, high fracture strength above 2000 MPa and distinct plastic elongation is encouraging for the future development of a new type of bulk glassy alloy which can be used for structural materials.     

Effects of rare-earth elements on the glass-forming ability and mechanical properties of Cu46Zr47-xA17Mx （M = Ce, Pr, Tb, and Gd） bulk metallic glasses

Cu₄₆Zr_47−x Al₇M _x (M = Ce, Pr, Tb, and Gd) bulk metallic glassy (BMG) alloys were prepared by copper-mold vacuum suction casting. The effects of rare-earth elements on the glass-forming ability (GFA), thermal stability, and mechanical properties of Cu₄₆Zr_47−x Al₇M _x were investigated. The GFA of Cu₄₆Zr_47−x Al₇M _x (M = Ce, Pr) alloys is dependent on the content of Ce and Pr, and the optimal content is 4 at.%. Cu₄₆Zr_47−x Al₇Tb _x (x = 2, 4, and 5) amorphous alloys with a diameter of 5 mm can be prepared. The GFA of Cu₄₆Zr_47−x Al₇Gd _x (x = 2, 4, and 5) increases with increasing Gd. T _x and T _p of all decrease. T _g is dependent on the rare-earth element and its content. ΔT _x for most of these alloys decreases except the Cu₄₆Zr₄₂Al₇Gd₅ alloy. The activation energies ΔE _g, ΔE _x, and ΔE _p for the Cu₄₆Zr₄₂Al₇Gd₅ BMG alloy with Kissinger equations are 340.7, 211.3, and 211.3 kJ/mol, respectively. These values with Ozawa equations are 334.8, 210.3, and 210.3 kJ/mol, respectively. The Cu₄₆Zr₄₅Al₇Tb₂ alloy presents the highest microhardness, Hv 590, while the Cu₄₆Zr₄₃Al₇Pr₄ alloy presents the least, Hv 479. The compressive strength (σ _c.f.) of the Cu₄₆Zr₄₃Al₇Gd₄ BMG alloy is higher than that of the Cu₄₆Zr₄₃Al₇Tb₄ BMG alloy.     

Glass-forming ability of RE–Al–TM alloys (RE=Sm,Y; TM=Fe,Co, Cu)

The glass-forming ability (GFA) of RE–Al–TM (RE=Sm, Y; TM=Fe, Co, Cu) upon melt-spinning and die-casting into a copper mold has been studied. Melt-spun ribbons for both Sm- and Y-based alloys show a fully amorphous structure. However, die-casting revealed that Sm-based alloys exhibit a higher GFA than Y-based alloys. The as-cast Sm₇₀Fe₂₀Al₁₀, Sm₆₀Fe₂₀Al₁₀Co₁₀ and Sm₆₀Fe₂₀Al₁₀Co₅Cu₅ cylinders (3 mm×50 mm) contain a mixture of amorphous and crystalline phases after copper-mold casting. A new bulk metallic glass was obtained for the Sm₆₀Fe₁₀Al₁₀Co₁₅Cu₅ alloy, which shows ferromagnetic behavior. In contrast, as-cast Y-based alloys are completely crystalline. Based on the data of the activation energy for crystallization of the amorphous phase, E_x, and the crystallization temperature, T_x, together with magnetic measurements, it is concluded that the as-cast Sm₆₀Fe₁₀Al₁₀Co₁₅Cu₅ cylinder displays a tendency for clustering. The improved glass-forming ability of Sm-based alloys is interpreted in terms of classical nucleation theory.     

Formation and thermal stability of new Zr–Cu-based bulk glassy alloys with unusual glass-forming ability

The simultaneous addition of Al and Ag to Zr–Cu binary alloys increased in the stabilization of supercooled liquid, the reduced glass transition temperature and γ value, leading to greatly enhance the glass-forming ability (GFA). The Zr–Cu–Ag–Al glassy alloy samples with diameters above 15 mm were obtained in the wide composition range of 42–50 at% Zr, 32–42 at% Cu, 5–10 at% Ag, and 5–12 at% Al. The best GFA was obtained for Zr₄₈Cu₃₆Ag₈Al₈ alloy, and the glassy samples with diameters up to 25 mm were fabricated by an injection copper mold casting. The Zr₄₈Cu₃₆Ag₈Al₈ glassy alloy exhibited high tensile and compressive fracture strength of over 1800 MPa.     

Influence of oxygen on the crystallization behavior of Zr65Cu27.5Al7.5 and Zr66.7Cu33.3 metallic glasses

The influence of oxygen on the crystallization behavior of Zr_65−xCu_27.5Al_7.5O_x (x=0.14, 0.43 and 0.82) and Zr_66.7−xCu_33.3O_x (x=0.14 and 0.82) metallic glasses has been studied. The supercooled liquid regime (ΔT_x) decreases with increase in oxygen content for the Zr–Cu–Al alloy, while it increases for the Zr–Cu metallic glass. In the case of the Zr–Cu metallic glass, the crystallization product (Zr₂Cu) is not influenced by the oxygen content, while in Zr–Cu–Al alloys the oxygen level has a strong influence on the crystallization sequence. At low oxygen level (x=0.14), the ternary glass crystallizes polymorphously to Zr₂(Cu,Al). At higher oxygen content, the ternary amorphous alloy crystallizes in two stages by primary crystallization into an icosahedral phase and subsequently to the stable Zr₂(Cu,Al) phase. Three-dimensional atom probe results have shown that the composition of the icosahedral and amorphous phases is close to Zr₇₅Cu₁₅Al₅O₅ and Zr₆₂Cu₂₄Al₁₄, respectively.     

EFFECT OF Gd ADDITION ON THE GLASS FORMING ABILITY AND MECHANICAL PROPERTIES IN A Zr–BASED BULK AMORPHOUS ALLOY

适量的Gd掺杂可提高Zr_50.7Cu₂₈Ni₉Al_12.3块体非晶合金的玻璃形成能力, 当Gd元素掺杂量 (原子分数) 为1%时, 即(Zr_50.7Cu₂₈Ni₉Al_12.3)₉₉Gd₁, 柱状非晶合金直径可达16 mm (不掺杂时为14 mm). 稀土Gd掺杂降低了锆基块体非晶合金的断裂强度与塑性 变形能力. 随着Gd含量的增加, 其断裂方式由单一的剪切断裂转变为剪切断裂与破碎断裂的复合形式, 且含Gd元素掺杂的非晶合金断口呈现了脉状纹络与纳米周期性条纹共存的特征.     

A Ni-free Zr-based bulk metallic glass with remarkable plasticity

The effect of Nb and Pd combination on the glass forming ability (GFA) and mechanical properties of Zr₅₃Cu₃₀Nb_xPd_9?xAl₈ (x = 3.5–6.0) bulk metallic glasses (BMGs) were systematically investigated by X-ray diffractometry (XRD), differential scanning calorimetry (DSC), transmission electron microscopy (TEM), and compression test. TEM observation revealed that a nanocrystalline phase embeds in the amorphous matrix of the as-cast Zr₅₃Cu₃₀Nb_4.5Pd_4.5Al₈ alloy. A tiny nano-crystalline phase (with size about 5–20 nm) embedded uniformly in the amorphous matrix of the Zr₅₃Cu₃₀Nb_4.5Pd_4.5Al₈ alloy was observed and identified to be the tetragonal structured NbPd₃ phase based on the analyses of nano beam electron diffraction. According to the results of thermal analyses, the composition of Zr₅₃Cu₃₀Nb₅Pd₄Al₈ and Zr₅₃Cu₃₀Nb_4.5Pd_4.5Al₈ present the optimum GFA as well as thermal stability in the Zr₅₃Cu₃₀Nb_xPd_9?xAl₈ (x = 3.5–6.0) alloy system. In addition, the result of compression test shows that the yield strength significantly increases from 1700 MPa (Zr₅₃Cu₃₀Nb₅Pd₄Al₈) to 1900 MPa (Zr₅₃Cu₃₀Nb_4.5Pd_4.5Al₈). A remarkable compression plastic strain (11.2%) occurs at Zr₅₃Cu₃₀Nb_4.5Pd_4.5Al₈ BMG rod with 2 mm in diameter. This significant increase in plasticity is presumably due to the restriction on shear banding by the nano-size second phase.     

A Cu-based amorphous alloy with a simultaneous improvement in its glass forming ability and plasticity

An amorphous alloy, Cu₄₃Zr₄₃Al₇Be₇, was synthesized. The alloy showed a large supercooled liquid region (115 °C), a significant glass forming ability (Φ12 mm) and considerable strain to fracture (8–9%), which collectively have not been observed in other Cu-based amorphous alloys. The alloy has a unique microstructure characterized by atomic-scale phase separation, which most likely resulted from the large difference in the mixing enthalpy between the binary pairs. This study discusses a possible mechanism underlying the simultaneous enhancement in the GFA and plasticity by considering the atomic packing state and atomic-scale compositional separation resulting from Al and Be.     

Effects of minor Cu and Si additions on glass forming ability and mechanical properties of Co-Fe-Ta-B Bulk metallic glass

Effect of Cu and Si substitutions for Co and B on the glass forming ability (GFA) of Co_(43-x)Cu_xFe₂₀Ta_5.5B_(31.5-x)Si_y (x=0-1.5 and y=5-10) were systematically investigated by X-ray diffraction, optical microscopy, scanning electron microscopy, and differential scanning calorimetry. In order to evaluate the contribution of copper and silicon, appropriate amounts of copper and silicon were individually introduced to the base alloy composition. By using the effects of copper and silicon together, significant enhancement was obtained and the critical casting thickness (CCT) of the base alloy was increased three times from 2 mm to 6 mm. Moreover, mechanical properties of the alloys were examined by compression tests and Vickers hardness measurements. The compression test results revealed that the glassy alloys having enhanced GFA shows high strength of about 3500-4000 MPa. In addition, existence of (Co,Fe)₂B and (Co,Fe)_20.82Ta_2.18B₆ crystalline phases in glassy matrix influences the hardnesses of the alloys compared to monolitic glassy structure having hardness of about 1200 Hv.     

How can a minor element added to a binary amorphous alloy simultaneously improve the plasticity and glass-forming ability?

Minor elements, when added to binary amorphous alloys in small percentages, can often lead to significant improvements in both the plasticity and glass-forming ability (GFA) of the alloys. Considering that plasticity and GFA are two contrasting properties dependent on short-range orders (SROs) of differing degrees, this experimental observation at first seems paradoxical when considered from an SRO viewpoint. In this study, comparative studies on amorphous alloys Cu₅₀Zr₅₀ and Cu_47.5Zr_47.5Al₅ were performed using experiments and simulations to elucidate how these two apparently mutually exclusive properties can be realized at the same time. Using molecular dynamics simulations, we resolved the local structures of Cu₅₀Zr₅₀ and Cu_47.5Zr_47.5Al₅ in terms of icosahedral medium-range orders. In addition, the role of the minor element (Al) on the formation of the icosahedra and their medium-range structures during cooling, as well as their disordering behavior during subsequent plastic relaxation, was clarified.     

Zr–Cu–Ni–Al bulk metallic glasses with superhigh glass-forming ability

Zr–Cu–Ni–Al quaternary amorphous alloy compositions with varying glass-forming ability are developed by an efficient method of proportional mixing of binary eutectics. The critical diameter of the glassy sample is improved from 6 mm for Zr₅₃Cu_18.7Ni₁₂Al_16.3 to 14 mm for Zr_50.7Cu₂₈Ni₉Al_12.3 by straightforwardly adjusting the eutectic unit’s coefficients. The drastic improvement in GFA is attributed to balancing the chemical affinities of the Zr, Cu, Ni and Al components in the melt prior to solidification which makes the precipitation of competing crystalline phases more difficult. As the glass-forming ability increases, the concentration of Cu in the alloys exhibits a same trend. Based on synchrotron radiation high-energy X-ray diffraction analysis and Miracle’s structural model, it is envisioned that the substitution of additional Cu atoms for Zr atoms in the investigated alloys stabilizes the efficient cluster packing structure of the amorphous alloys, leading to the pronounced increase in their glass-forming ability.     

Influence of similar atom substitution on glass formation in (La–Ce)–Al–Co bulk metallic glasses

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 (La_xCe_1−x)₆₅Al₁₀Co₂₅ alloys (0 < x < 1), the fully glassy rods of the (La_0.7Ce_0.3)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 (La_xCe_1−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.     

Formation of crystalline phase in the glass matrix of Zr-Co-Al glass-matrix composites and its effect on their mechanical properties

The microstructural evolution and mechanical properties of Zr-Co-Al alloys, with compositions of (Zr₅₀Co₅₀)_x (Zr₅₆Co₂₆Al₁₈)_1-x (x = 1/6, 2/6, 3/6, 4/6, 5/6, 1) and Zr₅₄Co₃₅Al₁₁, (referred to as Z1, Z2, Z3, Z4, Z5, Z6, and Z4.5), were investigated. Alloys Z1-Z3 consisted of crystalline phases, while alloys Z4 and Z4.5 consisted of crystalline phase particles (~3 vol% and ~35 vol%, respectively) embedded within the glassy matrix. Alloys Z5 and Z6 consisted of a monolithic glass phase. The crystalline phase of alloys Z1-Z4.5 consisted of primary B2-ZrCo dendrite and an interdendritic B2-ZrCo/Zr₆CoAl₂ eutectic phase. The B2-ZrCo dendritic phase exhibited a high work-hardening rate, which originated from the deformation-induced B2-to-B33 martensitic transformation. However, when the brittle interdendritic B2-ZrCo/Zr₆CoAl₂ eutectic phase fraction increased, the work-hardening rate significantly decreased. The ductility of the glass-matrix composites was significantly impaired by the presence of the interdendritic eutectic phase in the crystalline phase. The results indicate that the design of the crystalline particle microstructure is important with regard to enhancing the plasticity of glass-matrix composites.     

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 (d_c) 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 (Zr_0.5Ti_0.02Cu_0.38Al_0.1)₉₈Lu₂. This study is beneficial for the improvement of surface properties and further application of Zr-based BMGs.     

Cast structure and mechanical properties of Zr–Cu–Ni–Al bulk glassy alloys

Homogeneous melting without any nuclei was performed using the cold copper nozzle arc casting furnace and ladle arc-melt type furnace. Casting of a bulk glassy alloy can be achieved by using a copper nozzle arc casting furnace, which eliminates nucleation site (cold spot) for crystallization. Besides, the pouring molten alloy was melted homogeneously by arc heating before casting into the mold, similar to a pseudo float melting state. To produce a bulk glassy alloy sheet, a combination of the ladle arc-melt type furnace and squeeze cast method was used. Using this method, we succeeded in producing Zr₅₀Cu₃₀Ni₁₀Al₁₀ bulk glassy alloys in a rod shape by the former method and in a sheet form by the later method. Tensile strength of the Zr₅₀Cu₃₀Ni₁₀Al₁₀ bulk glassy alloy sheet is about 1900 MPa and the plasticity of the alloy at room temperature is significantly improved by cold rolling.     

Glass forming ability and crystallization of Zr-Cu-Ag-Al-Be bulk metallic glasses

The glass forming ability of Zr₄₆Cu_37.64−xAg_8.36Al₈Be_x (x = 0, 6 and 10 at.%) bulk metallic glasses (BMGs) were significantly improved by Be addition. The critical size of amorphous rods can be over 35 mm diameter. The high GFA achieved is mainly due to the decrease of melting point and liquidus temperature, and suppression of the formation of crystalline phases during solidification from liquid state. The high stabilization with supercooled liquid regime of 115 K was found for the BMG with x = 10 at.%. Two independent exothermic events happen in x = 0 and 6 at.% BMGs, corresponding to the formation of primary crystalline phases Cu₁₀Zr₇ and AgZr, then transforming to final stable crystalline phases Zr₂Cu and AlCu₂Zr. However, in the x = 10 at.% BMG, the precipitation of primary phases and transformation to final stable phases are within the first exothermic event and the AlCu₂Zr phase is totally suppressed.     

Glass formation in La-based La–Al–Ni–Cu–(Co) alloys by Bridgman solidification and their glass forming ability

Six La-based La–Al–Ni–Cu–(Co) alloys were subjected to a systematical study of glass formation by Bridgman unidirectional solidification at growth velocities between 0.1 and 4.82 mm/s at a temperature gradient of 15 K/mm. With increased Cu content the critical growth velocity for glass formation in La₅₅Al₂₅Cu_20−xNi_x (x=0–20) alloys shows a steep minimum at 10 at.% Cu, indicating the largest glass forming ability for the La₅₅Al₂₅Ni₁₀Cu₁₀ alloy. However, replacement of Ni by Co leads to a further decrease in the critical cooling rate for the La₅₅Al₂₅Ni₅Cu₁₀Co₅ alloy. Critical cooling rates for glass formation in the present alloys were also obtained through a study of their melting and solidification behaviours by thermal analytical measurement. The effect of alloying addition and the significance of reduced glass transition temperature for the glass forming ability of these alloys is discussed.     

Formation and properties of Ti-based Ti–Zr–Cu–Fe–Sn–Si bulk metallic glasses with different (Ti + Zr)/Cu ratios for biomedical application

Ti-based Ti–Zr–Cu–Fe–Sn–Si bulk metallic glasses (BMGs) free from highly toxic elements Ni and Be were developed as promising biomaterials. The influence of (Ti + Zr)/Cu ratio on glass-formation, thermal stability, mechanical properties, bio-corrosion resistance, surface wettability and biocompatibility were investigated. In the present Ti-based BMG system, the Ti₄₇Zr_7.5Cu₄₀Fe_2.5Sn₂Si₁ glassy alloy exhibited the highest glass forming ability (GFA) corresponding to the largest supercooled liquid region, and a glassy rod with a critical diameter of 3 mm was prepared by copper-mold casting. The Ti-based BMGs possess high compressive strength of 2014–2185 MPa and microhardness of 606–613 Hv. Young's modulus of the Ti₄₇Zr_7.5Cu₄₀Fe_2.5Sn₂Si₁ glassy alloy was about 100 GPa, which is slightly lower than that of Ti–6Al–4V alloy. The Ti₄₇Zr_7.5Cu₄₀Fe_2.5Sn₂Si₁ glassy alloy with high GFA exhibited high bio-corrosion resistance, and good surface hydrophilia and cytocompatibility. The mechanisms for glass formation as well as the effect of (Ti + Zr)/Cu ratio on bio-corrosion behavior and biocompatibility are discussed.     

Glass formation and magnetic properties of Fe-based metallic glasses fabricated by low-purity industrial materials

Fe-based metallic glasses of (Fe₇₄Nb₆B₂₀)_100-xCr_x (x=1, 3, 5) with high glass forming ability (GFA) and good magnetic properties were prepared using low-purity raw materials. Increasing Cr content does not significantly change glass transition temperature and onset crystallization temperature, while it enhances liquidus temperature. The addition of Cr improves the GFA of the (Fe₇₄Nb₆B₂₀)_100-xCr_x glassy alloys compared to that in Cr-free Fe-Nb-B alloys, in which the supercooled liquid region (ΔT_x), T_rg and γ are found to be 50–54 K, 0.526–0.538, and 0.367–0.371, respectively. The (Fe₇₄Nb₆B₂₀)_100–xCr_x glassy alloys exhibit excellent soft magnetic properties with high saturation magnetization of 139–161 A·m²/kg and low coercivity of 30.24–58.9 A/m. Present Fe-Nb-B-Cr glassy alloys exhibiting high GFA as well as excellent magnetic properties and low manufacturing cost make them suitable for magnetic components for engineering application.