Effects of a small amount of Si or Ge addition on stability and hydrogen-induced internal friction of Ti34Zr11Cu47Ni8 glassy alloys

Effects of a small amount of Si or Ge addition on stability and hydrogen-induced internal friction behavior of Ti₃₄Zr₁₁Cu₄₇Ni₈ glassy alloys have been investigated by X-ray diffraction, thermal analysis and temperature dependence of internal friction. It is found that the addition of 1 at.% Si, 2 at.% Si or 1 at.% Ge is effective to stabilize the glassy state and that Si is more effective than Ge. The peak internal friction of the single glassy phase alloy increases with increasing hydrogen content below about 20 at.% H. It is found that (Ti₃₄Zr₁₁Cu₄₇Ni₈)₉₉Si₁ glassy alloys have lower peak internal friction than the Ti₃₄Zr₁₁Cu₄₇Ni₈ glassy alloys, while (Ti₃₄Zr₁₁Cu₄₇Ni₈)₉₈Si₂ and (Ti₃₄Zr₁₁Cu₄₇Ni₈)₉₉Ge₁ glassy alloys have much higher peak internal friction. It should be noted that a (Ti₃₄Zr₁₁Cu₄₇Ni₈)₉₈Si₂ glassy alloy containing 14.4 at.% H shows high internal friction, Q⁻¹ of about 4 × 10⁻². The peak temperature of the single glassy phase alloys decreases with increasing hydrogen content below about 20 at.%. It should be noted that the addition of an extremely small amount of Si is effective to increase the peak temperature of the single glassy phase alloys. The relationship between the tensile strength and specific damping capacity indicates that the hydrogenated (Ti₃₄Zr₁₁Cu₄₇Ni₈)₉₈Si₂ glassy alloys have almost the same potential for a damping material as crystalline Mn–Cu–Al and Cu–Al–Ni alloys and hydrogenated Zr–Cu–Al glassy alloys.     

Relationship between activation energy for hydrogen permeation and hydrogen permeation properties of amorphous Cu50Zr50 and Cu65Zr35 membranes

We investigate the role of hydrogen solubility and diffusivity on the activation energy for hydrogen permeability and the relationship between the hydrogen permeability and resistance to hydrogen embrittlement in amorphous membranes, Cu₅₀Zr₅₀ and Cu₆₅Zr₃₅. The membrane with the lower activation energy for permeation showed higher hydrogen permeability, but it showed lower durability under hydrogen atmosphere. This relationship between the two properties is discussed on the basis of the nature of the short-range ordered (SRO) structures constituting amorphous membranes under hydrogen ambient.     

Molecular dynamic simulation study of the structural anisotropy in Cu50Zr50 and Cu64.5Zr35.5 metallic glasses induced by static uniaxial loading within the elastic regime

The structural anisotropy in both Cu₅₀Zr₅₀ and Cu_64.5Zr_35.5 metallic glasses induced by various static uniaxial loads within the elastic regime was studied by molecular dynamic simulations. Constant tensile and compressive loads from zero up to 200 MPa below the flow stress were applied in the simulation. The degree of anisotropy was characterized using a second order contact fabric tensor. It is found that the degree of anisotropy within the elastic regime increases with the applied load following an exponential growth function. The most part of the structural anisotropy can be attributed to the Zr–Cu atomic pairs in Cu_64.5Zr_35.5 and Zr–Cu, Cu–Cu atomic pairs in Cu₅₀Zr₅₀. The evolution of the structural anisotropy associated with the Zr–Zr and Cu–Cu pairs exhibits complex behavior, which implies that the deformation mechanism and the dynamics of Cu₅₀Zr₅₀ and Cu_64.5Zr_35.5 metallic glasses under compressive loads may be quite different from those under tensile loads.     

Glass forming ability and stability: Ternary Cu bearing Ti,Zr, Hf alloys

Four Cu bearing alloys of nominal composition Zr₂₅Ti₂₅Cu₅₀, Zr₃₄Ti₁₆Cu₅₀, Zr₂₅Hf₂₅Cu₅₀ and Ti₂₅Hf₂₅Cu₅₀ have been rapidly solidified in order to produce ribbons. All the alloys become amorphous after melt-spinning. In the Zr₃₄Ti₁₆Cu₅₀ alloy localized precipitation of cF24 Cu₅Zr phase can be observed in the amorphous matrix. The alloys show a tendency of phase separation at the initial stages of crystallization. The difference in crystallization behavior of these alloys with Ni bearing ternary alloys can be explained by atomic size, binary heat of mixing and Mendeleev number. It has been observed that both Laves and Anti-Laves phase forming compositions are suitable for glass formation. The structures of the phases, precipitated during rapid solidification and crystallization can be viewed in terms of Bernal deltahedra and Frank–Kasper polyhedra.     

Structure and crystallization kinetics of a Cu50Zr45Ti5 glassy alloy

The crystallization kinetics and structure changes in a melt-spun Cu₅₀Zr₄₅Ti₅ glassy alloy on heating were investigated by X-ray diffractometry, transmission electron microscopy, differential scanning calorimetry and differential isothermal calorimetry. The glassy phase in the Cu₅₀Zr₄₅Ti₅ alloy was crystallized forming Cu₁₀Zr₇ and CuZr₂ phases upon thermal annealing. The activation energy for crystallization obtained by the Arrhenius equation was 435 kJ/mol. The crystallization process took place by nucleation and growth mechanism, and an Avrami exponent of about 3.3 may indicate a three-dimensional interface-controlled growth of nuclei with a decreasing nucleation rate.     

Dependence of GFA and thermal stability of the Cu50Zr50 alloy on temperature-functioned different liquid states

Liquid polyamorphism and transitions between different states have triggered great interest, concerning which the present paper aimed to investigate the correlations of the glass formation ability (GFA) and glassy thermal stability of Cu₅₀Zr₅₀ alloy with its original liquid states. As structurally sensitive, the resistivity (ρ) change pattern of liquid Cu₅₀Zr₅₀ was explored as temperature (T) elevated, hereby two obvious turns of ρ-T slope were observed, and corresponding to the first turn an endothermic peak appeared on DTA curve, which suggest alterations of its liquid structural state. Based on the results, by preparing Cu₅₀Zr₅₀ metallic glasses with different quenching temperature (T_q), experiments were carried out to find out the above mentioned correlations. It is verified by resistivity and DSC methods that there are two crystallization stages for the melt-spun glassy ribbons with T_q below the first turn, while there is only one crystallization stage for cases above the first turn. More significantly, although characteristic parameters of the glassy ribbons change indistinctively with T_q below the first turn, all they change obviously with T_q elevated above the first turn, i.e. T_g, T_x move to higher degree, and T_rg, ΔT_x and γ become larger. The former trend indicates a better thermal stability of glassy Cu₅₀Zr₅₀, and the latter trend signifies an enhanced GFA of the melt. By the copper mould cast method, it is intriguingly proved that GFA of Cu₅₀Zr₅₀ can rise to Ф3, when its melt prepared with temperature above the second turn.     

Effect of Zr Addition on Microstructure and Properties of Cu–Ag–Ti Alloys

Effects of small addition of Zr on the microstructures and properties of as-cast Cu₅₀Ag_46?xZr_xTi₄ alloys were investigated by differential scanning calorimeter (DSC), x-ray diffraction, microscope, and property testings. The results show that the melting point of the Cu₅₀Ag₄₆Ti₄ alloys does not change obviously with the addition of Zr at the melting points of about 779 °C. Adding Zr reduces the volume fraction and size of the board strips of Cu₃Ti phase, promotes the uniform distribution of the new phase Cu₄AgZr, and improves the Vickers hardness and shear strength of the based alloys. Moreover, increasing the Zr content can improve the high-temperature oxidation resistance of alloys.     

Surface analyses and biocompatibility study of 500 °C oxidized Ni50Ti50 and Ni40Ti50Cu10 shape memory alloys

Ni₅₀Ti₅₀ and Ni₄₀Ti₅₀Cu₁₀ shape memory alloys (SMAs) are oxidized at 500 °C. Considering the surface roughness, the thicknesses of oxide layer and Ni-free layer, the surface Ni concentration, the proper oxidation times for oxidized specimens are found to be 60 min for Ni₅₀Ti₅₀ and 30 min for Ni₄₀Ti₅₀Cu₁₀. Experimental results reveal that the oxidation is diffusion-controlled with its oxide layer containing titanium oxide and that the surface Ni concentration is much lower than the nominal composition. When Ni₅₀Ti₅₀ and Ni₄₀Ti₅₀Cu₁₀ SMAs are oxidized at these times, the latter has better corrosion resistance than the former in Hanks' solution at 27 °C. However, the results of cytotoxicity and cell proliferation assays indicate that the biocompatibility of unoxidized Ni₄₀Ti₅₀Cu₁₀ is worse than that of unoxidized Ni₅₀Ti₅₀, but that of oxidized Ni₄₀Ti₅₀Cu₁₀ ranks as good as that of oxidized Ni₅₀Ti₅₀.     

Studying fatigue behavior and Poisson's ratio of bulk-metallic glasses

High-cycle fatigue (HCF) experiments were conducted on zirconium (Zr)-based bulk-metallic glasses (BMGs): Zr₅₀Cu₄₀Al₁₀, Zr₅₀Cu₃₀Al₁₀Ni₁₀, Zr_41.2Ti_13.8Cu_12.5Ni₁₀Be_22.5, and Zr₅₀Cu₃₇Al₁₀Pd₃ (in atomic percent) in air. The fatigue-endurance limit of Zr₅₀Cu₃₇Al₁₀Pd₃ was significantly greater than those of Zr₅₀Cu₄₀Al₁₀, Zr₅₀Cu₃₀Al₁₀Ni₁₀, and Zr_41.2Ti_13.8Cu_12.5Ni₁₀Be_22.5. The resonant ultrasound spectroscopy technique was employed to determine the Poisson's ratios, shear moduli, and bulk moduli of these BMGs. The ratio of the fatigue-endurance limit to the tensile strength increases with increasing Poisson's ratio. A possible relationship between the ratio of the fatigue-endurance limit to the tensile strength and the ratio of the shear modulus to the bulk modulus or Poisson's ratio will be discussed.     

A study of the corrosion behaviour of Zr50Cu(40−X)Al10PdX bulk metallic glasses with scanning Auger microanalysis

The anodic-polarization behaviours of Zr₅₀Cu₄₀Al₁₀ and Zr₅₀Cu₃₃Al₁₀Pd₇ (atomic, at., %) bulk metallic glasses were investigated in aerated and deaerated 0.6 M NaCl. Polarization in both environments yielded similar results. Initial anodic-polarization of both alloys demonstrated that small increases in the applied potential resulted in significant increases in the current density. Continued polarization produced diffusion controlled polarization. Scanning Auger microanalysis was used to analyze the corrosion pits. Pits formed on both BMGs were enriched with Cu and Cl. Palladium enrichment was also observed in pits on Zr₅₀Cu₃₃Al₁₀Pd₇. A corrosion mechanism related to the formation of CuCl and Cu₂O is proposed.     

Annealing effects on the crystallization and shape memory effect of Ti50Ni25Cu25 melt-spun ribbons

As-spun Ti₅₀Ni₂₅Cu₂₅ ribbon is fully amorphous with a lower wavenumber Q_p than the amorphous Ti–Ni alloys owing to its high Cu content. Both crystallization activation energy E_a and onset temperature T_x for Ti₅₀Ni₂₅Cu₂₅ ribbon are lower than those for Ti₅₀Ni₅₀ ribbon, indicating that the former has lower thermal stability. When Ti₅₀Ni₂₅Cu₂₅ ribbon is annealed at 500 °C for 3 min, the initial as-crystallized grains contain a low Cu content and perform a prominent shape memory effect. Through prolonging the annealing time, more grains are crystallized in the ribbon but it becomes more fragile and its recoverable strain decreases. This is due to the increasing Cu content in the crystallized grains. Crystallized Ti₅₀Ni₂₅Cu₂₅ ribbon can exhibit a good shape memory effect only under appropriate annealing conditions.     

Effect of cooling rate on microstructure and glass-forming ability of a (Ti33Zr33Hf33)70(Ni50Cu50)20Al10 alloy

The alloy (Ti₃₃Zr₃₃Hf₃₃)₇₀(Ni₅₀Cu₅₀)₂₀Al₁₀ developed by equiatomic substitution was prepared by using different quenching rates, i.e. rapid quenching by melt-spinning and relatively slow cooling using suction casting. The microstructural comparison between the as-spun ribbons and the as-cast bulk specimens reveals a different length scale of an icosahedral phase that formed upon solidification. The as-spun sample exhibits a mixture of nano-scale icosahedral, Zr₂Cu-type and amorphous phases after complete crystallization at 973 K indicating a high stability of the nano-scale icosahedral phase. Due to its small size (30–50 nm) there is no significant strain in the icosahedral phase. On the other hand, in the as-cast bulk sample Zr₂Cu-type and amorphous phases form in the micro-scale modulated icosahedral phase without any discernible exothermic reaction. The structural modulation of the icosahedral phase indicates the occurrence of strains during the growth. The different local accumulation of strain during the growth of the icosahedral phase induces a phase selection between the Zr₂Cu-type or amorphous phases in this alloy.     

Cu–Zr–Al (Ti) bulk metallic glasses: Cluster selection rules and glass formation

The present paper investigates the bulk metallic glass formation in Cu–Zr–Al and Cu–Zr–Ti ternary systems by using the cluster line criterion. The binary basic clusters are first selected for constructing cluster lines. Three cluster selection rules are proposed: topologically dense packing, chemical short-range order and composition distance to deep eutectics. Three Cu–Zr clusters Cu₈Zr₅, Cu₆Zr₅ and Cu₅Zr₆ are selected according to the three rules. The bulk metallic glass-forming ranges in these two systems are determined. The thermal characteristic parameters of the Cu–Zr–Al BMGs on every composition line increase with increasing Al content and decrease with increasing Ti content in the Cu–Zr–Ti glass-forming range. The optimum bulk amorphous compositions in the Cu–Zr–Al system are Cu_58.1Zr_35.9Al₆ and Cu_39.7Zr_47.1Al_13.2, respectively, located in Cu₈Zr₅–Al and Cu₅Zr₆–Al cluster lines. In the Cu–Zr–Ti system, the Cu₆₄Zr_28.5Ti_7.5 composition with the largest T_g/T_l is located in Cu₉Zr₄–Ti cluster line and the Cu_57.6Zr_32.4Ti₁₀ composition with the largest glass-forming ability is located in Cu₆₄Zr₃₆–Ti line.     

Microstructure and Mechanical Behavior of Microwave Sintered Cu<Subscript>50</Subscript>Ti<Subscript>50</Subscript> Amorphous Alloy Reinforced Al Metal Matrix Composites

In the present work, Al metal matrix composites reinforced with Cu-based (Cu₅₀Ti₅₀) amorphous alloy particles synthesized by ball milling followed by a microwave sintering process were studied. The amorphous powders of Cu₅₀Ti₅₀ produced by ball milling were used to reinforce the aluminum matrix. They were examined by x-ray diffraction (XRD), scanning electron microscopy (SEM), microhardness and compression testing. The analysis of XRD patterns of the samples containing 5 vol.%, 10 vol.% and 15 vol.% Cu₅₀Ti₅₀ indicates the presence of Al and Cu₅₀Ti₅₀ peaks. SEM images of the sintered composites show the uniform distribution of reinforced particles within the matrix. Mechanical properties of the composites were found to increase with an increasing volume fraction of Cu₅₀Ti₅₀ reinforcement particles. The hardness and compressive strength were enhanced to 89 Hv and 449 MPa, respectively, for the Al-15 vol.% Cu₅₀Ti₅₀ composites.     

Oxidation Behavior of Ti50Ni40Cu10 Shape-Memory Alloy in 700–1,000 °C Air

The isothermal-oxidation behavior of Ti₅₀Ni₄₀Cu₁₀ shape memory alloy (SMA) in 700–1,000 °C air was investigated by TGA, XRD, SEM and EPMA. Experimental results indicate that a multi-layered oxide scale formed, consisting of an outermost Cu₂O(Ni,Ti) layer, a layer of the mixture of TiO₂, TiNiO₃ and irregular small pores, a layer of the mixture of Ni(Ti,Cu), TiO₂ and irregular large pores, a Ti(Ni,Cu)₃ layer and an innermost Ti₃₀Ni_43–47Cu_27–23 layer. The apparent activation energy for the oxidation reaction of Ti₅₀Ni₄₀Cu₁₀ SMA is determined to be 180 kJ/mol, and the oxidation rate follows a parabolic law. A schematic oxidation mechanism of Ti₅₀Ni₄₀Cu₁₀ SMA is proposed to explain the observed results.     

Composition dependence of the microstructure and mechanical behavior of Ti–Zr–Cu–Pd–Sn–Nb bulk metallic glass composites

Ti-based bulk metallic glass composite alloys Ti₅₆Zr₆Cu_19.8Pd_8.4Sn_1.8Nb₈, Ti₆₄Zr₄Cu_13.2Pd_5.6Sn_1.2Nb₁₂ and Ti₆₈Cu_13.2Pd_5.6Sn_1.2Nb₁₂ were designed to obtain the microstructure composing of β-Ti dendrites and glassy matrix. The compressive and three-point bending properties were investigated. It was found that the actual microstructure of the Nb-added alloys consisted of primarily precipitated β-Ti dendrites, network-like glassy matrix, and extra island-like Ti₂Cu intermetallic phase with different volume fractions. Under compressive loading, all the Nb-added alloys presented higher yield strength combined with remarkably increased plasticity. Under bending condition, however, the alloys Ti₅₆Zr₆Cu_19.8Pd_8.4Sn_1.8Nb₈ and Ti₆₄Zr₄Cu_13.2Pd_5.6Sn_1.2Nb₁₂ with higher Ti₂Cu volume fractions became completely brittle. The alloy Ti₆₈Cu_13.2Pd_5.6Sn_1.2Nb₁₂ could keep its plastic deformability due to the decreased Ti₂Cu volume fraction. Compressive deforming behavior of the Nb-added alloys was determined by the ductile β-Ti phase and glassy matrix, nevertheless, bending deforming behavior of the alloys was determined by the volume fraction and distribution of the brittle intermetallics.     

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.     

Evaluation of Cu-Zr-Ti-In Bulk Metallic Glasses via Nanoindentation

In this paper, the mechanical properties of two bulk metallic glasses, Cu₆₀Zr₃₄Ti₅In₁ and Cu₅₈Zr₃₄Ti₅In₃, have been evaluated by nanoindentation tests. The hardness and Young’s modulus of as-cast Cu₆₀Zr₃₄Ti₅In₁ bulk metallic glass increase from the center to the edge of the rod, but Cu₅₈Zr₃₄Ti₅In₃ shows an inverse trend. The Young’s modulus of Cu₅₈Zr₃₄Ti₅In₃ is lower than that of Cu₆₀Zr₃₄Ti₅In₁. For both bulk metallic glasses, serrations on the nanoindentation load-displacement curves depend not only on loading rate but also on the maximum load. Alternatively, the onset position of the appearance of serrations on the curves increases with the loading rate. In addition, the hardness of both samples decreases as the size of the indent increases due to indentation size effects.     

Effect of precipitation on the shape memory effect of Ti50Ni25Cu25 melt-spun ribbon

The present research aims to provide accurate understanding of the relation between precipitation (volume fraction, morphology, type) and shape memory effect of Ti₅₀Ni₂₅Cu₂₅ melt-spun ribbon. Rapid thermal annealing was used to control the microstructural development while the shape memory effect of the ribbon was determined under constraint thermal cycling. The results show that the precipitation process takes the following sequence: B11 TiCu → B11 TiCu + Ti₂(Ni, Cu) → Ti₂(Ni, Cu) with increasing annealing temperature or duration. The shape memory effect is found to depend on both the volume fraction and the distribution of the precipitates. The former affects the shape recovery strain through reduction of the transformation volume participating the shape recovery. The latter affects the shape recovery strain through strengthening the matrix thus reducing the martensite strain which is more predominant under low constraint stresses. Precipitation strengthening, on the other hand, reduces the tendency of dislocation generation/movement, thus reducing the irreversible strain and improving shape recovery strain. This understanding provides guidelines on the optimization of the shape memory properties of the Ti₅₀Ni₂₅Cu₂₅ melt-spun ribbon via post-processing annealing.     

Effect of Titanium Additions on the Thermophysical Properties of Glass-Forming Cu<Subscript>50</Subscript>Zr<Subscript>50</Subscript> Alloy

Differential scanning calorimetry, laser flash method, and dilatometry were used to study the thermophysical properties of quenched Cu₅₀Zr_50–xTi_x (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 Cu₅₀Zr_50–xTi_x 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.