The bulk metallic glass formation in Zr-Al-Ni-Ti quaternary system

The optimum metallic glass compositions are located close to the intersecting line of the e/a-constant and atomic size-constant planes in a quaternary composition chart. According to these criteria, a series of Zr-Al-Ni-Ti quaternary alloys have been designed and prepared by suction casting. The electron concentration and average atomic size of two ternary glass forming alloys, Zr₆₀Al₂₀Ni₂₀ and Zr₅₃Al_23.5Ni_23.5, have been used. Pure glass state is reached only within a small composition range of Ti. Ti addition deteriorates the thermal stabilities, but maintains the same glass forming abilities of bulk metallic glasses.     

Tribological Studies of a Zr‐Based Glass‐Forming Alloy with Different States

The tribological characteristics of a glass‐forming alloy, Zr_52.5Cu_17.9Ni_14.6Al_10.0Ti_5.0, in atomic percent (at.%, Vit 105), with different microstructural states have been investigated. Friction and wear studies were conducted using a ball‐on‐flat reciprocating sliding apparatus against an AISI E52100 bearing steel under dry condition. The observed wear resistance in an ascending order is: the deformed, creep‐tested, and as‐cast states. Wear analyses suggested that the wear processes of glass‐forming alloys involved abrasion, adhesion, and oxidation. The differences in hardness, free volume, and brittleness in different states significantly affected the friction and wear behaviors of the glass‐forming alloys.     

Effects of additional elements (M) on the thermal stability and structure of (Zr52.2Cu39.1Al8.7)100?xMx (M?=?Ag, Be, Gd, x?=?8, 7, 2) amorphous alloys

The effects of Ag (8 at.%), Be (7 at.%), and Gd (2 at.%) addition on structure and thermal stability, as well as bulk glass forming ability, in (Zr_52.2Cu_39.1Al_8.7)_100−x M _x (M = Ag, Be, Gd) alloys are investigated by means of X-ray diffraction and differential scanning calorimetry. The alloy containing Ag and Be have a critical diameter of more than 10 mm, with larger supercooled liquid region and atomic packing efficiency than Zr_52.2Cu_39.1Al_8.7 alloy, while the (Zr_52.2Cu_39.1Al_8.7)₉₈Gd₂ alloy only has a critical diameter of up to 5 mm and shows smaller supercooled liquid region and atomic packing density. CuZr is the main competing crystal phase with amorphous phase in the present Zr-Cu-based alloys. Ag and Be atoms in Zr_52.2Cu_39.1Al_8.7 alloy decrease the long range diffusion of Cu atoms and hinder the crystallization process under rapid solidification conditions. As a result, the glass forming ability of (Zr_52.2Cu_39.1Al_8.7)₉₂Ag₈ and (Zr_52.2Cu_39.1Al_8.7)₉₃Be₇ alloys are effectively enhanced.     

Laser-induced self-propagating reaction synthesis of amorphous-based composite Zr-Al-Ni-Cu alloys

Strong exothermic reaction due to large negative enthalpy of mixing can occur among major components of bulk metallic glass forming alloy systems. Based on this idea, we developed a new technique to fabricate amorphous-based composite materials using Laser-induced Self-propagating Reaction Synthesis (LSRS). The LSRS of the Zr₅₅Al₁₀Ni₅Cu₃₀ alloy shows that the products mainly consist of the amorphous, Zr₃Al₂ and Zr₂Cu phases. Hardness and wear resistance of the produced composite alloys are measured and are compared to the single amorphous phase alloy of the same composition.     

Influence of melt temperature on the compressive plasticity of a Zr–Cu–Ni–Al–Nb bulk metallic glass

Zr_63.78Cu_14.72Ni₁₀Al₁₀Nb_1.5 BMGs (bulk metallic glasses) were cast at the melt temperatures ranging from 1,073 to 1,313 K with the same interval of 40 K. The structure, thermal, and mechanical properties of the BMGs were investigated by XRD, DSC, HRTEM, dilatometric measurements, micro-hardness tests, and uniaxial compression. The results indicate that the higher the casting temperature, the fewer the nano-crystallites, the more the free volumes, and the lower the micro-hardness in the BMGs, leading to the larger plastic strains. The plasticity of BMGs deteriorates with the increase of nano-crystallites as decreasing the casting temperature. The free volume, instead of the nano-crystallites, favors the plastic deformation in Zr_63.78Cu_14.72Ni₁₀Al₁₀Nb_1.5 BMGs. The microstructures and mechanical performance of BMGs are closely affected by the casting temperature. The preparing parameters are important to improve the plasticity of the BMGs.     

Mechanical properties and thermal stability of a Cu-based bulk metallic glass microalloyed with silicon

(Cu₄₂Zr₄₂Al₈Ag₈)_{100? x} Si _x (x?=?0?～?1) amorphous alloy rods of 2–6?mm diameter were prepared by Cu-mold drop casting. The thermal properties, microstructure evolution, and mechanical properties were studied by differential scanning calorimetry (DSC), X-ray diffractometry (XRD), transmission electron microscopy (TEM), hardness test, and compression test. The XRD result revealed that all as-quenched (Cu₄₂Zr₄₂Al₈Ag₈)_100?x Si _x alloy rods exhibited a broad diffraction pattern in the amorphous phase. The (Cu₄₂Zr₄₂Al₈Ag₈)_99.5Si_0.5 alloy was found to possess the highest glass forming ability (GFA) as well as the best thermal stability among all tested samples. In addition, both its hardness and yield strength were increased by the microalloyed Si content. The fracture strength and the plastic strain of (Cu₄₂Zr₄₂Al₈Ag₈)_99.5Si_0.5 amorphous alloy can reach 2000?MPa and 3.5 %.     

Cu?Zr?Al?Ti Bulk Metallic Glass with Enhanced Glass‐Forming Ability,Mechanical Properties,Corrosion Resistance and Biocompatibility

The effect of titanium addition on the glass forming ability (GFA), plasticity, corrosion resistance and biocompatibility of Cu? Zr? Al alloy are evaluated by XRD, DSC, compression tests, corrosion, and cytotoxicity tests. The GFA of Cu₄₅Zr₄₈Al₇ amorphous alloy is greatly improved by titanium addition, as evidenced by the increase of critical size from less than 8 mm for Cu₄₅Zr₄₈Al₇ alloy to 10 mm for Cu₄₅Zr_46.5Al₇Ti_1.5 alloy when the samples are prepared by copper mold casting. Cu₄₅Zr_46.5Al₇Ti_1.5 alloy shows enhanced plastic strain up to 10%, good corrosion resistance and biocompatibility in comparison to Cu₄₅Zr₄₈Al₇ alloy.     

Effect of prior compression treatment on the deformation behavior of Zr based bulk metallic glass

In the present work, the plasticity of Zr_64.2Cu_11.2 Ni_14.6Al₁₀ bulk metallic glass was enhanced through prior compression treatment. A considerably large compressive plastic deformation (over 6.5%) was achieved by pressing Zr_64.2Cu_11.2 Ni_14.6Al₁₀ bulk metallic glass laterally in specially designed tool steel die before compression test. Numerical analysis was also carried out to investigate the stress distribution under same mechanical conditions. It was revealed that the lateral pressing induced structural heterogeneity and high stress gradients facilitate large plastic strains through the generation of dense multiple shear band network.     

Effect of ZrO2 and SiO2 on glass forming ability of Zr57Cu20Al10Ni8Ti5 alloy

Zr₅₇Cu₂₀Al₁₀Ni₈Ti₅ has very high glass forming ability (GFA) due to its low crystal growth rate which limits development of crystallites arising from container walls or nuclei. Effect of ZrO₂ and SiO₂ on GFA was studied by investigating the solidification microstructures of alloys containing different amount of the oxides. Amorphous ingots were formed by melting and freezing alloys without addition of the oxides using an arc furnace. Partially amorphous ingots were formed for addition of the oxides up to 0.2 wt %. Amorphous forming conditions of alloys containing greater concentration of the oxides were studied using a drop tube. GFA decreases with increasing concentration of the oxides. However, superheating of melts eliminates some effects of the oxides. Different types of oxides leads to different microstructures due to their different heterogeneous nucleation rates and nucleation temperature.     

Transformation of precipitated phases in Zr50·5Cu34·5−xNi4Al11Agx alloy master ingots with adding Ag

Abstract

The transformation of precipitated phases of Zr_50·5Cu_34·5?xNi₄Al₁₁Ag_x alloy master ingots with Ag substitution of Cu was studied in detail by phase analysis. The precipitated (Zr–Cu) rich phases deteriorate the glass forming ability (GFA) of Zr_50·5Cu_34·5Ni₄Al₁₁. Two new (Zr–Cu) rich phases, A1 with bcc structure and a?=?0·339 nm and A2 with fcc superlattice structure and a?=?1·21 nm, were identified by a transmission electron microscope. When x?=?2, A1 phase disappears, and A2 phase remains and is suppressed gradually with further Ag addition. When x?=?13, one precipitated phase with Ag more than 13 at-% begins to deteriorate GFA. In the view of chemistry, the precipitation of (Zr–Cu) rich phases means that the interaction between Cu and Zr atoms is rather drastic. The addition of Ag weakens the interaction between Cu and Zr. The similar competition mechanism proposed by the authors plays an important role in suppressing precipitated phases and improving GFAs.     

Effect of Nb addition on the subsurface deformation behavior in Cu47Ti34Zr11Ni8 bulk metallic glasses through Vickers indentation

In this paper, 3 mm diameter (Cu₄₇Ti₃₄Zr₁₁Ni₈)_100−xNb_x (x = 0,1,2) glass forming alloys were fabricated by water-cooled copper mould cast. Microstructural characterization reveals that the monolithic Cu₄₇Ti₃₄Zr₁₁Ni₈ bulk metallic glass exhibits homogenous amorphous structure. While the alloys with Nb addition exhibit a composite structure. For alloys with x = 1, micro-scaled crystalline particles were found to distribute in the glassy matrix. For alloys with x = 2, the microstructure is dominated by a high density of dendritic phase embedded in the glassy matrix. Bonded interface technique was adopted to study the deformation behavior of the alloys underneath the Vickers indentation. It reveals that the subsurface shear patterns are significantly affected by the precipitated phases. The different deformation mechanism of the alloys resulted from the minor Nb addition was put forward and discussed.     

Micro and nano indentation studies on Zr60Cu10Al15Ni15 bulk metallic glass

Partially vitrified Zr₆₀Cu₁₀Al₁₅Ni₁₅ bulk metallic glass has been synthesized using water cooled copper mold drop casting technique. Kinetically favorable microstructures having different morphologies are observed throughout the volume of the bulk metallic glass sample. X-ray diffraction studies indicate formation of hard intermetallic compounds such as Zr₃Al₂ and Zr₂Ni in certain regions along with amorphous structures. Microindentation studies carried out in different regions of the sample reveal microstructure dependent deformation behavior. Highest hardness is observed in the fully crystallized regions compared to pure glassy regions in the same sample. Further nanoindentation in the same sample is used to understand dynamic mechanical properties of microstructures in different regions. The pile-up morphologies around the indent and differences in load–displacement curves provide vital information on deformation behavior of sample in different microstructure sensitive regions.     

A comparison of crystallization behaviors of laser spot welded Zr–Cu–Ag–Al and Zr–Cu–Ni–Al bulk metallic glasses

A novel Ni-free Zr–Cu–Ag–Al ((Zr₄₈Cu₃₆Ag₈Al₈)Si_0.75) and a Zr–Cu–Ni–Al ((Zr₅₃Cu₃₀Ni₉Al₈)Si_0.5) bulk metallic glass (BMG), for comparison, were employed for Nd:YAG laser spot welding with three pre-selected energy inputs, including a low (6.2 J), a medium (8.0 J) and a high (9.2 J) energy input. After the welding process, the microstructure evolution, glass-forming ability (GFA) and mechanical properties of the welded samples were determined by a combination of scanning electron microscopy (SEM), transmission electron microscopy (TEM), differential scanning calorimetry (DSC) and the Vicker's microhardness test.     

Devitrification of Zr-Ni-Al-Cu-Ti(Nb,Ta) glassy alloys

The devitrification behavior and phase formation in Zr_65-55Ni₁₀Al_7.5Cu_7.5Ti_5-10(Nb,Ta)_5-10 metallic glass have been studied by X-ray diffraction, transmission electron microscopy and differential scanning calorimetry. It has been found that mutual addition of Ti and Ta/Nb benefits the formation of nanoscale icosahedral phase in the glassy phase on heating and the oxygen content in the alloy makes significant influence on the devitrification behavior of these alloys. At the same time in Nb-bearing alloys and alloys containing 5 at.% Ta icosahedral phase was found to coexist with crystalline one.     

Dependence of GFA and Crystallization Behaviors of Al86Ni9La5 Metallic Glass on Its Original Liquid State

During the heating process the temperature‐induced liquid–liquid structure transition (LLST) of Al₈₆Ni₉La₅ melt from 1320 to 1490 K was identified by both electrical resistivity and differential thermal analysis measurement. The effects of liquid structural change on the crystallization behavior and glass forming ability (GFA) of Al₈₆Ni₉La₅ alloy were investigated. The amorphous samples prepared at different melt temperatures according to the liquid states were obtained. The results showed that the formation of intermetallic compounds during the crystallization process of the samples prepared below and within the LLST temperature range was earlier than that prepared above the LLST temperature range. The sample prepared above the LLST temperature range had the lowest GFA.     

Relationship between glass forming ability and thermal parameters of Zr based bulk metallic glasses

Abstract

The compositions of Zr₄₁Ti₁₄Cu₁₂Ni₁₀Be₂₃ and Zr₅₅Ni₁₀Cu₂₀Al₁₅ bulk metallic glasses (BMGs) were modified by the addition of other elements, such as Nb, Fe, Mg, Y, Ta, and C. The modified alloys exhibit excellent glass forming ability (GFA). The glass transition temperature T _g, crystallisation temperature T _x, and offset melting temperature T _l of the composition modified Zr based alloys were determined by differential temperature analysis (DTA).Results show thatthe T _g, T _x,and T _lare allsensitive to the composition. The undercooled temperature from T _l to T _x, Δ T _l defined by Δ T _l = T _l - T _x, has a stronger correlation with the reduced glass transition temperature T _rg (T _rg = T _g/ T _l) than Δ T _x (Δ T _x = T _x - T _g).     

New features of the low temperature ductile shear failure observed in bulk amorphous alloys

Fractographic studies of ductile shear failure under the uniaxial compression for rod–like samples of the Zr_41.2Ti_13.8Ni₁₀Cu_12.5Be_22.5 and Cu₅₀Zr₃₅Ti₈Hf₅Ni₂ bulk amorphous alloys at temperatures 300 and 77 K are presented. The mechanisms of shear deformation and failure appeared to have characteristics in common with other amorphous alloys prepared in the form of thin ribbons. However, there were a number of new fractographic features observed due to the bulk character of the samples and to the large supercooled liquid region of these alloys.     

Overheating effects on thermal stability and mechanical properties of Cu36Zr48Ag8Al8 bulk metallic glass

A pronounced effect of overheating is observed on the thermal stability and mechanical properties of Cu₃₆Zr₄₈Ag₈Al₈ bulk metallic glass. Higher overheated temperature enhances the thermal stability of bulk amorphous alloys, corresponding to higher specific-heat capacity and the smaller initial defect concentration. And a threshold overheating temperature is found for the fully amorphous structure. Bulk amorphous alloys exhibit good compressive plasticity at small overheat levels, whereas the compressive fracture strength and micro-hardness exhibit a significant increase first and then a slightly decrease. Mechanical properties of BMGs can be tailored in certain extent by controlling the overheated level, which is correlated with free volume and residual stresses.     

Supercooled liquid foaming of a Zr-Al-Cu-Ag bulk metallic glass containing pressurized helium pores

Foaming of a Zr-based metallic glass in the supercooled liquid is successfully performed by introducing pressurized pores and subsequent isochronal annealing. Melting of a Zr₄₈Cu₃₆Al₈Ag₈ powder under 12 MPa pressurized helium atmosphere followed by water quenching introduces spherical helium pores, whose average diameter and volume fraction are estimated respectively to be 30 μm and 7%, into a fully glassy bulk Zr₄₈Cu₃₆Al₈Ag₈ alloy. The isochronal annealing of the porous alloy below the crystallization temperature under atmospheric pressure of argon enables the expansion of pores by viscous flow deformation of the supercooled liquid, resulting in a high porosity structure up to 70% with a uniform cell size and cell distribution.     

Structures and properties of a Zr-based bulk glass alloy after annealing

A bulk glass Zr_52.5Ni_14.6Al₁₀Cu_17.9Ti₅ alloy with 6 mm diameter is prepared by pre-melting sponge zirconium together with other pure metal elements and followed by injecting cast. In the samples, the content of oxygen is chemically analyzed in the level of 706 ppm (atomic concentration), which significantly affects the crystallization and the microstructure. When the bulk glass samples are annealed at the temperature far below the crystallization temperature(T_x), the predominant phases of Zr₂Ni_0.67O_0.33 and Zr₂Ni compounds crystallize and uniformly distribute on glass matrix. These predominant phases will grow and join together to form net-shape phase when the annealed temperature is in the range of T_x to above T_x. The glass matrix phase separated by the net-shape phase into the size of about 25 μm at 703 K to 15 μm at 823 K almost fully transforms into Zr₂Ni and a small amount of Zr₂Cu and Zr₄Al₃. At annealing temperatures far above T_x, Zr₂Cu and Zr₄Al₃ compounds crystallize by phase separation to form nanostructure with nano-scale phases of Zr₂Cu and Zr₄Al₃ compounds distributed on the matrix of Zr₂Ni. The micro-compressive tests by Nanoindenter II reveal that the bulk glass phase has a lower elastic modulus and lower microhardness. Increasing the annealing temperature, the modulus and microhardness for the crystallized microstructure increase. With the phase separation taking place, the modulus and microhardness for the nanostructure are improved slightly. But the different deformational mechanism between micro-scale and bulk specimens is unknown.