Mechanical behavior of Cu-Zr bulk metallic glasses (BMGs): A molecular dynamics approach

In the present work, three-dimensional molecular dynamics simulation is carried out to elucidate the nanoinden- tation behaviors of CuZr Bulk metallic glasses （BMGs）. The substrate indenter system is modeled using hybrid interatomic potentials including both many-body Finnis Sinclair （FS） and two-body Morse potentials. A spherical rigid indenter （diameter= 60 A（1 A = 10 ^-10 m）） is employed to simulate the indentation process. Three samples of BMGs including Cu25Zr75, CusoZr50, and Cu75Zr25 are designed and the metallic glasses are formed by rapid cooling from the melt state at about 2000 K. The radial distribution functions are analyzed to reveal the dynamical evolution of the structure of the atoms with different compositions and different cooling rates. The mechanical behavior can be well understood in terms of load-depth curves and Hardness-depth curves during the nanoindentation process. Our results indicate a positive linear relationship between the hardness and the Cu concentration of the BMG sample. To reveal the importance of cooling rate provided during the processing of BMGs, we investigate the indentation behaviors of CusoZr50 at three different quenching rates. Nanoindentation results and radial distribution function （RDF） curves at room temperature indicate that a sample can be made harder and more stable by slowing down the quenching rate.

Role of yttrium in glass formation of Ti-based bulk metallic glasses

Starting with Zr of two different purities, Ti-based bulk metallic glasses （BMGs） with a nominal composition of Ti40Zr25Cu12Ni3Be20 were prepared. The effect of the addition of yttrium at levels of 0.2 at.%, 0.4 at.%, 0.5 at.%, 0.6 at.%, and 1 at.% on the glass forming ability （GFA） of the alloy has been investigated by means of metallography, X-ray diffraction, and differential scanning calorimetry. Experimental data in-dicates that high impurity content dramatically reduces the glass forming ability. Microalloying with 0.5 at.% Y is effective in suppressing the crystalline phase formation and alleviating the detrimental effect of oxygen in the low-purity alloy. On the contrary, in the alloy contain-ing high-purity element, the effective yttrium addition is less than 0.4 at.%. The results indicate that the beneficial effect of the optimum dopants is mainly due to scavenging the oxygen impurity via the formation of innocuous phase.

Formation and corrosion properties of Fe-based bulk metallic glasses

Bulk metallic glass （BMG） formation was explored in the Fe-B-Si-Nb alloy system though combined use of the atomic cluster line approach and the minor alloying strategy. The basic ternary compositions in the Fe-B-Si system were determined by the intersection points of two cluster lines, namely, Fe-B cluster to Si and Fe-Si cluster to B. 3at% -4at% Nb was added to the quaternary Fe-B-Si-Nb alloy. The casting experiments revealed that good glass-forming ability （GFA） occurred at the （Fe73.4Si8.2B18.4）96Nb4 composition, and 3-mm diameter BMG samples were made. The glass transition temperature （Tg）, crystallization temperature （Tx）, and supercooled liquid region （△Tx=Tx-Tg） of this BMG were measured to be 866, 889, and 23 K, respectively. The BMG shows a high Vickers hardness of about Hv 1164, a Young＇s modulus of 180 GPa, and a good corrosion resistance in the solutions of 1 mol/L HCl and 3wt% NaCl.

Preparation and Mechanical Properties of Misch Metal Based Bulk Metallic Glasses

The formation, thermal stability and mechanical properties of Misch metal （Mm）-based alloy bulk metallic glasses （BMGs） with composition of Mm55Al25Cu10Ni5Co5 were investigated by means of X-ray diffraction, differential scanning calorimetry, differential thermal analysis and compression test. The results indicate that the Mm-based BMGs exhibit a distinct glass transition and a wide supercooled liquid region Δ Tx（ 〉 60 K） before crystallization. The alloy can be fabricated into bulk glassy form of 3 mm in diameter by copper mold casting methods. Compared with the La55Al25Cu10 Ni5Co5 BMG, the Mm55Al25Cu10Ni5Co5 BMG shows higher compression fracture strength and lower cost. A new parameter γ and melting temperature Tl are closely correlated with the glass forming ability （GFA） of Mm-based alloys.

Effect of Mo on properties of the industrial Fe–B-alloy-derived Fe-based bulk metallic glasses

The experimental results concerning the effects of Mo on the glass-forming ability(GFA), thermal stability, and mechanical, anticorrosion, and magnetic properties of an(Fe_(71.2)B_(24)Y_(4.8))_(96)Nb_4 bulk metallic glass(BMG) were presented. An industrial Fe–B alloy was used as the raw material, and a series of Fe-based BMGs were synthesized. In BMGs with the Mo contents of approximately 1at%–2at%, the cast alloy reached a critical diameter of 6 mm. The hardness and fracture strength also reached their maximum values in this alloy system. However, the anticorrosion and magnetic properties of the BMGs were not substantially improved by the addition of Mo. The low cost, good GFA, high hardness, and high fracture strength of the Fe-based BMGs developed in this work suggest that they are potential candidates for commercial applications.

Formation, Structure and Properties of Bulk Metallic Glasses

Bulk metallic glasses with up to 72 mm critical section thickness have been obtained by conventional casting techniques and the properties of these materials, particularly the mechanical and magnetic properties have been studied. These materials have been demonstrated to have novel properties which are fundamentally different from their crystalline counterparts. The recent status of research and development in formation, structure and properties of bulk metallic glasses is reviewed. The techniques to produce such bulk glasses are summarized and the glass forming ability and the critical cooling rate of these materials are discussed. Further consideration of the development and application of this new class of materiaIs will be proposed.

Crystallization Kinetics of Misch Metal Based Bulk Metallic Glasses

The crystallization kinetics of Mm55Al25Cu10Ni5Co5 bulk metallic glass （BMG） was investigated by means of differential scanning calorimetry （DSC） in the mode of continuous heating or isothermal annealing. It was found that the apparent activation energy Eg, Ex and Ep of the BMG calculated by Kissinger＇s method were 189.58, 170.68 and 170.41 kJ·mol^-1, respectively, which was bigger than those of La55Al25Cu10Ni5Co5 BMG indicating that thermal stability of the former was higher than that of the latter. The local activation energy obtained using Ozawa equation decreased as crystallization proceeded except for the initial stage. The Avrami exponents were calculated to be in the range of 3.26 - 5.23 for different crystallization stages and isothermal temperatures. This implied that crystallization of Mm55Al25Cu10Ni5Co2 BMG was governed by diffusion-controlled three-dimensional growth with either reduced or increased nucleation rate, depending on isothermal temperature. Inconsistency of thermal stability with glass-forming ability for Mm（La）-Al-Cu-Ni-Co BMGs was discussed.

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

The formation and thermal stabilities of Cu46.25Zr46.25xAl7.5Erx (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 Cu46.25Zr46.25Al7.5 alloy, and the glassy rod with a diameter of at least 12 mm can be formed. The glass transition temperature (Tg), temperature interval of su- percooled liquid region △Tx (=Tx-Tg), and reduced glass transition temperature Trg (=Tg/Tl) of Cu46.25Zr44.25Al7.5Er2 glassy alloy are 699 K, 62 K and 0.607, respectively.

Bulk metallic glasses formed by alloying the Cu_6Zr_5 cluster

The bulk metallic glass formation in the Cu-Zr-M ternary systems by alloying of a binary basic Cu6Zr5 cluster was inves- tigated, where M stands for Sn, Mo, Ta, Nb, Ag, Al and Ti. The Cu6Zr5 cluster is a capped Archimedean antiprism that characterizes the local structure of the Cu10Zr7 crystalline phase. This cluster composition almost superposes with Cu-Zr eutectic Cu0.56Zr0.44. A se- ries of alloys along the cluster line (Cu6Zr5)1-xMx were examined for their glass forming abilities. Alloy rods with a diameter of 3 mm were prepared by copper mould suction casting method and analyzed by XRD and thermal analysis. The Cu-Zr based bulk metallic glasses were discovered with minor Nb, Sn, Mo, Ta additions (≤2at%) and Al, Ti, Ag (8at%≤concentration≤9at%). The alloying mechanism was discussed in the light of atomic size, cluster-linking structure and electron concentration factors.

A thermodynamic approach to assess glass-forming ability of bulk metallic glasses

According to the Gibbs free energy difference between liquid and crystal,a thermodynamic glass-forming ability(GFA) parameter related to characteristic temperatures,onset crystallization temperature(Tx)and liquidus temperature(Tl),was proposed for evaluating the GFA of bulk metallic glasses(BMGs).The new parameter defined asω=Tl(Tl+Tx)/(Tx(Tl-Tx))has good correlation with the critical section thickness(Zc)of Ca-Mg-Cu BMGs.Being verified by the glasses data,including oxide glasses,which were used to validate the former GFA parameters,ωis one of the most reliable and applicable GFA parameters among Trg(=Tg/Tl), γ(=Tx/(Tl+Tg)),α(=Tx/Tl),δ(=Tx/(Tl-Tg),and so on.Finally,predicting GFA of Cu-Ag-Zr-Ti and Cu-Zr-Ti-Al BMGs usingωwas compared with the experimental results.

Formation and mechanical properties of bulk Cu-Ti-Zr-Ni metallic glasses with high glass forming ability

Bulk amorphous Cu52.5Ti30Zr11.5Ni6 and Cu53.1Ti31.4Zr9.5Ni6 alloys with a high glass forming ability can be quenched into single amorphous rods with a diameter of 5 mm, and exhibit a high fracture strength of 2 212 MPa and 2 184 MPa under compressive condition, respectively. The stress—strain curves show nearly 2% elastic strain limit, yet display no appreciable macroscopic plastic deformation prior to the catastrophic fracture due to highly localized shear bands. The present work shows clearly evidence of molten droplets besides well-developed vein patterns typical of bulk metallic glasses on the fracture surface, suggesting that localized melting induced by adiabatic heating may occur during the final failure event.

Glass forming ability of Fe_(60)Co_xZr_(10) Mo_5 W_2B_(23-x)(x=1,3,5,7,9) bulk metallic glasses

The bulk Fe<sup>60 CoxZr<sup>10 Mo5W2B<sup>23-x （x=1, 3, 5, 7, 9） amorphous rods with diameters of 1.5 mm were successfully prepared by copper mold casting method with the low purity raw materials. The amorphous and crystalline states, and thermal parameters, such as the glass transition temperature （Tg）, the initial crystallization temperature （Tx）, the supercooled liquid region （ΔTx=Tx-Tg）, the reduced glass transition temperature T<sup>rg （Tg/Tm, Tm: the onset temperature of melting of the alloy, and Tg/Tl, Tl: the finished temperature of melting of the alloy） were investigated by X-ray diffractometry （XRD） and differential scanning calorimetry （DSC） analysis. Glass forming ability of Fe<sup>60 CoxZr<sup>10 Mo5W2B<sup>23-x （x=1,3,5,7,9） bulk metallic glasses has been studied. According to the results, the alloy （x=7） with the highest T<sup>rg （Tg/Tl=0.607, Tg/Tl=0.590） value, has the strongest glass forming ability among these alloys because its composition is near eutectic composition. The wide supercooled liquid region over 72 K indicates the high thermal stability for this alloy system. This bulk metallic glass exhibits quite high strength （Hv 1020）. The success of production of the Fe-based bulk metallic glass with industrial materials is of great significance for the future progress of basic research and practical application.

Microstructure and mechanical properties of Zr-Cu-Al bulk metallic glasses

Zr49Cu46Al5 and Zr48.5Cu46.5Al5 bulk metallic glasses(BMGs) with diameter of 5 mm were prepared through water-cooled copper mold casting. The phase structures of the two alloys were identified by X-ray diffractometry(XRD). The thermal stability was examined by differential scanning calorimetry(DSC). Zr49Cu46Al5 alloy shows a glass transition temperature, Tg, of about 689 K, an crystallization temperature, Tx, of about 736 K. The Zr48.5Cu46.5Al5 alloy shows no obvious exothermic peak. The microstructure of the as-cast alloys was analyzed by transmission electron microscopy(TEM). The aggregations of CuZr and CuZr2 nanocrystals with grain size of about 20 nm are observed in Zr49Cu46Al5 nanocrystalline composite, while the Zr48.5Cu46.5Al5 alloy containing many CuZr martensite plates is crystallized seriously. Mechanical properties of bulk Zr49Cu46Al5 nanocrystalline composite and Zr48.5Cu46.5Al5 alloy measured by compression tests at room temperature show that the work hardening ability of Zr48.5Cu46.5Al5 alloy is larger than that of Zr49Cu46Al5 alloy.

Compositional dependence of thermal and elastic properties of Cu-Ti-Zr-Ni bulk metallic glasses

Starting from the quaternary Cu47Ti34Zr11Ni8 alloy, the compositional dependence of thermal and elastic properties of Cu-Ti-Zr-Ni alloys was systematically investigated. Quaternary Cu-Ti-Zr-Ni alloys can be cast directly from the melt into copper molds to form fully amorphous strips or rods with the thickness of 3-6 mm. The evidence of the amorphous nature of the cast rods was provided by X-ray spectra. The measured glass transition temperature （Tg） and crystallization temperature （Tx） were obtained for the alloys using differential scanning calorimetry （DSC） at the heating rate of 20 K/s. In the results, the differences between the glass temperature and the crystallization temperature （△Tx=Tx-Tg） are measured with values ranging up to 33-55 K. The reduced glass transition temperature （Trg）, which is the ratio of the glass temperature to the liquidus temperature （T3, is often used as an indication of the glass-forming ability of metallic alloys. For the present Cu-Ti-Zr-Ni alloys, this ratio is typically in the range of 0.5838-0.5959, characteristic of metallic alloys with good glass-forming ability. The elastic constants for several selected alloys were measured using ultrasonic methods. The values of the elastic shear modulus, bulk modulus, and Poisson＇s ratio were also given.

Effect of minor aluminium addition in Cu47Ti34Zr11Ni8 bulk metallic glasses

Cu47Ti34Zr11Ni8 and (Cu47Ti34Zr11Ni8)_ 99Al bulk metallic glass with size of 1mm×10mm×50mm were prepared by copper mold casting, and the influence of minor aluminium addition upon the alloy thermal stability and mechanical properties was studied. The results indicate that with the aluminium addition, the crystallizing behavior of the melt changes at the same cooling rate, and the crystallizing behavior of the glass changes at the same heating rate. The glass transition temperature(T_g), crystallization temperature(T_ x1), temperature interval of supercooled liquid region ΔT_x (=T_ x1-T_g) and reduced glass transition temperature (T_ rg) are proved to be changed from 672K, 734K, 62K and 0.578 to 681K, 729K, 48K and 0.590, respectively. Because of the addition of aluminium, three point-bending flexural strength and flexural modulus of the bulk glass are increased from 2350MPa and 102GPa to 2970MPa and 108GPa, respectively.

Preparation and thermal stability of Pd_(40.5)Ni_(40.5)Si_xP_(19-x) bulk metallic glasses

With the addition of Si to replace some P,Pd40.5Ni40.5SixP19-x（x=0,2.5,5,9.5,14,and 19 in atomic number fraction） bulk glassy samples with the diameter of about 5 mm were successfully prepared by use of flux treatment and water quenching technology.With the increase of Si content,the glass forming ability of Pd40.5Ni40.5Si-xP19-x increases first for low Si content and then decreases for high Si content （Si≥9.5at%）.The Pd40.50Ni40.5Si5P14 glassy alloy possesses the largest supercooled liquid region△T of 119 K,the largest reduced glass transition temperature of 0.621,and the largestγparameter of 0.460,indicating that this glassy alloy possesses very large glass forming ability and very high thermal stability.

Room temperature plastic deformation behavior of ZrCuNiAl bulk metallic glasses

The Zr62.55Cu17.55Ni9.9Al10 bulk metallic glass （BMG） was prepared by using copper-mold suction-casting. X-ray diffraction and differential scanning calorimetry were utilized to determine its structure and thermal stability. Uniaxial compression and Rockwell indenta- tion tests were adopted to study the plastic deformation behavior at room temperature. The results show that the glass transition temperature and the onset temperature of exothermic reaction of the BMG are 651.5 and 748 K, respectively. During the compression test, the BMGs undergo an engineering strain of about 2.5%, i.e., true strain of 2.8%, and then fracture. The BMGs deform via the formation and propagation of shear bands. Under indentation loading, the BMGs deform through the formation of radiation-like and circular shear bands. The circular shear bands form earlier than the radiation-like ones, The formation mechanism of shear bands in the BMGs was analyzed and discussed.

Thermal stability and glass-forming ability of Y-Ce-Co-Al bulk metallic glasses

The thermal stability and glass-forming ability of Y56-xCexCo20Al24 (x=15, 20, 25, 28, 38, 41, 44) bulk metallic glasses with a diameter of 5 mm were investigated by differential scanning calorimetry and X-ray diffraction. The results show that the thermal stability of the alloys decreases with the addition of Ce. It has the best glass-forming ability when x=25, whose calculated values can reach about 30 mm in diameter. The effect of Ce element could be explained on the view of Miedema’s theory and elec- tronegativity difference of amorphous alloys.

Bulk Metallic Glasses in Sm-Cu-Ni-Al Alloy Systems

A new series of Sm-Cu-Ni-Al bulk metallic glasses were prepared by suction casting. Their glass-forming ability and thermal stability were investigated by X-ray diffraction (XRD) and differential scanning calorimetry (DSC). The results of DSC indicate that the alloy components strongly affect the widths of supercooled liquid region (ΔT_x=T_x-T_g onset). The widths of supercooled liquid region for Sm_ 70-xCu_xNi_ 10Al_ 20 (x=12.5, 15.0, 17.5), Sm_ 65-xCu_ 15Ni_xAl_ 20 (x=8, 10, 12) and Sm_ 75-xCu_ 15Ni_ 10Al_x (x=15, 20, 25) increase first and then decrease with the increase of x atomic fraction. And Sm_ 55Cu_ 15Ni_ 10Al_ 20 alloy was found to be with the largest width and it can be cast into bulk metallic glass with up to 3 mm in diameter. The glass-forming ability of the alloys was explained in terms of Miedema′s theory, electronegativity difference and atomic size parameter of the amorphous alloys.