Gibbs Free Energy and Activation Energy of ZrTiAlNiCuSn Bulk Glass Forming Alloys

The Gibbs free energy differences between the supercooled liquid and the crystalline mixture for the (Zr_(52.5)Ti_5Al_(10)-Ni_(14.6)Cu_(17.9))_((100-x)/100)Sn_x (x=0, 1, 2, 3, 4 and 5) glass forming alloys are estimated by introducing the equationproposed by Thompson, Spaepen and Turnbull. It can be seen that the Gibbs free energy differences decrease firstas the increases of Sn addition smaller than 3, then followed by a decrease due to the successive addition of Snlarger than 3, indicating that the thermal stabilities of these glass forming alloys increase first and then followed by adecrease owing to the excessive addition of Sn. Furthermore, the activation energy of Zr_(52.5)Ti_5Al_(10)Ni_(14.6)Cu_(17.9) and(Zr_(52.5)Ti_5Al_(10)Ni_(14.6)Cu_(17.9))_(0.97)Sn_3 was evaluated by Kissinger equation. It is noted that the Sn addition increases theactivation energies for glass transition and crystallization, implying that the higher thermal stability can be obtainedby appropriate addition of Sn.

Cast bulk glassy alloys:fabrication,alloy development and properties

Metallic glasses represent an interesting group of materials as they possess outstanding physical, chemical and mechanical properties compared to their crystalline counterparts.Currently, with well designed compositions it is possible to cast liquid alloys into the glassy state at low critical cooling rates from 100 K·s-1 to 1 K·s-1 and in large critical sample sizes up to several centimeters, which significantly enhances the promise for possible applications as advanced engineering materials.This paper reviews the development of (ZrCu)-based bulk metallic glasses with large sizes by copper mold casting and their unique properties.Additionally, the ex-situ and in-situ second phases reinforced BMG composites with large plasticity are also presented.

Effect of strain rate and crystalline inclusions on mechanical properties of bulk glassy and partially crystallized Zr_(52.5)Cu_(17.9)Ni_(14.6)Al_(10)Ti_5 alloy

The mechanical properties of the Zr52.5Cu17.9Ni14.6Al10Ti5 alloy were presented, with an emphasis on the strain rate effect and presence of crystalline inclusions on the deformation and fracture mechanisms. X-ray diffraction studies indicated fully amorphous alloy structures with lower oxygen contents and partial crystalline structures at higher oxygen levels;however, completely different compressive deformation behaviour was observed. Uniaxial compression tests of the fully amorphous alloy showed elastic deformation, followed by yielding, distinct plastic deformation and serration flow behaviour. An increase in strain rate from 1×10-4 to 1×10-2 s-1 did not affect the yield strength;however, it decreased the compressive fracture strength and reduced the plastic strain. Scanning electron microscopy (SEM) observations with energy dispersive spectroscopy (EDS) analysis showed that the intermetallic CuZr2 phase was present even in the low oxygen content alloy, leading to lower fracture strength and ductility loss. For the high oxygen level samples, the presence of the dendritic Zr51Cu28Al21 phase was confirmed, leading to fracture strength impairment. The difference between ductile and brittle samples has been reflected on the fracture surfaces. The higher the plastic strain was, the higher the density of shear bands forming during deformation manifested by a serration flow behaviour on stress-strain curves.

Bulk glass formation in ternary Cu-Zr-Ti system

The formation of bulk metallic glasses (BMGs) in ternary Cu-Zr-Ti system was investigated by a copper mold casting method. The nature of the amorphous phase was verified by X-ray diffraction (XRD) and differential scanning calorimetry (DSC). It was demonstrated that the BMGs could be formed in a broad composition range in this system. Cu50Zr42.5Ti7.5, Cu60Zr27.5Ti12.5, Cu60Zr30Ti10 and Cu60Zr32.5Ti7.5 alloys exhibit strong glass-forming ability (GFA), and fully glassy rods of 5 mm in diameter can be obtained. In the center region of the ternary diagram, however, the GFA of the alloys was degraded due to the presence of Laves phase. The degradation of the GFA results from easy nucleation of the Laves phase in the undercooled liquid.

Crystallization behavior of Zr_(52) Cu_(18) Ni_(15) Al_(10) Ti_5 bulk glass with quenched-in crystals

Zr 52 Cu 18 Ni 15 Al 10 Ti 5 bulk glass samples with a diameter of 8 mm prepared by copper mold with water cooling have a mixing structure of amorphous phase and quenched in crystals. By isothermal annealing at different temperatures, the crystallization process of the glass alloy is shown to be a multi staged crystallization reaction as follows: Am+quenched in crystals→Am′+cellular phase+(Zr, Ti) Al→Am′+cellular phase+(Zr, Ti) Al+(Zr, Ti) 2(Cu, Ni). Morphology of the quenched in crystals changes from dot or dendritic phase in the as cast bulk glass to cellular phase at different annealing states. The residual region surrounded by the cellular phase has a mixing structure of nano scale phase and amorphous phase.

Thermal stability and mechanical properties of Gd-Co-Al bulk glass alloys

The glass forming ability of Gd-Co-Al ternary alloy systems with a composition ranging from 50% to 70% (molar fraction) for Gd and from 5% to 40% (molar fraction) for Al were investigated by copper mold casting and Gd60Co25Al15 bulk glass alloy cylinders with the maximum diameter of 5 mm were obtained. The reduced glass transformation temperature (Tg/Tm) and the distance of supercooling region △Tx are 0.616 and 45 K, respectively for this Gd-Co-Al alloy. The compressive fracture strength (σf) and elastic modulus (E) of Gd-Co-Al glassy alloys are 1 170-1 380 MPa and 59-70 GPa, respectively. The Gd-Al-Co bulk glassy alloys with high glass forming ability and good mechanical properties are promising for the future development as a new type function materials.

Casting effect on compressive brittleness of bulk metallic glass

An interesting phenomenon of cooling-rate induced brittleness in Zr52.5Cu17.9Ni14.6Al10Ti5 bulk metallic glass （BMG） was reported. It was found that the as-cast BMG specimens exhibited a brittle-ductile transition when the larger specimens were machined into smaller specimens through removing the cast-softening surface layer by layer. After compression tests, the as-machined small specimens, owing to the absence of the cast-softening surface, displayed highly dense and intersecting shear bands, and extensive plastic deformation. This is in contrast to the catastrophic failure and low deformability in the as-cast large specimens. More free volume was detected in the smaller as-fractured specimens, by differential scanning calorimetry, which may be attributed to the occurrence of strain softening and increased plasticity. Compared with the relatively smooth fracture surface in the smaller specimens, the larger specimens showed more diverse features on the fracture surface due to their graded structures.

Effect of Ti on microstructure,mechanical and corrosion properties of (Zr_(0.55)Al_(0.1)Ni_(0.05)Cu_(0.3))_(100-x)Ti_x bulk metallic glasses

The（Zr_（0.55）Al_（0.1）Ni_（0.05）Cu_（0.3））_（100-x）Ti_x alloys were prepared using an in-situ suck-casting method in a copper mold. The effects of Ti addition on the microstructure, mechanical and corrosion properties of the（Zr_（0.55）Al_（0.1）Ni_（0.05）Cu_（0.3））_（100-x）Ti_x alloys were investigated by X-ray diffraction, scanning electron microscopy, compressive tests and corrosion tests. It has been found that the addition of Ti higher than 4%（mole fraction） causes the formation of many crystalline phases in the alloy. The alloys with 1%-3% Ti display an obvious yield stage on their compressive stress-strain curves. An appropriate addition of Ti can improve the strength and ductility of the alloys. All the alloys have high corrosion resistance in 1 mol/L Na OH solution, and are corroded in 1 mol/L HCl solution. However, the appropriate addition of Ti can significantly improve the corrosion resistance of the alloys in HCl solution.

Enhanced plasticity of Fe-based bulk metallic glass by tailoring microstructure

The room temperature compressive plasticity of Fe75MosP10Cs.3B1.7 bulk metallic glass （BMG） was improved from 0.5% to 1.8% by increasing the sample diameter from 1.5 mm to 2.0 mm. With increasing the sample diameter to 2.0 mm, a heterogeneous microstructure with in-situ formed a-Fe dendrite sparsely distributed in the amorphous matrix can be attained. This heterogeneous mierostructure is conceived to be highly responsible for the enhanced global plasticity in this marginal Fe-based BMG.

Effects of Y addition on structural and mechanical properties of CuZrAl bulk metallic glass

The effects of Y addition on the structural and mechanical properties of CuZrAl bulk metallic glass（BMG） were studied.The results show that the glass forming ability of CuZrAl system is improved by the addition of Y and the fracture strength decreases with Y addition due to the reduction of binding energy induced by Y.The fracture surface is dominated by vein-like patterns in Cu45Zr48Al7 bulk metallic glass,and changes to smooth regions in Cu46Zr42Al7Y5 BMG.TEM observation shows that Cu45Zr48Al7 BMG has a composite microstructure of nanocrystalline phases dispersed in amorphous matrix.However,the Cu46Zr42Al7Y5 BMG shows a fully amorphous structure.

Electrochemical corrosion properties of Zr- and Ti-based bulk metallic glasses

The corrosion behaviors of Ti-based and Zr-based amorphous alloys and their corresponding crystallized alloys were studied by electrochemical methods. It is found that the corrosion potentials of Zr-based amorphous alloy and its corresponding crystalline counterpart are both lower than those of the Ti-based amorphous alloy in the 1 mol/L H2SO4 solution. In the 3.5% NaCl solution,Zr-based crystallized alloy exhibits the lowest corrosion potential among the experimental samples. No passivation is observed in the corrosion process for the Zr-based crystalline alloy. However, Zr- and Ti-based amorphous alloys both exhibit passivation characteristics. EIS measurements indicate the amorphous alloys exhibit better corrosion resistance than the crystallized one in the NaCl solution. Surface analysis shows that both amorphous alloys in the NaCl solution are eroded by pitting corrosion. In the H2SO4 solution, all the alloys display similar behaviors and their surfaces can mostly keep intact except for some cracks on the corroded surface at local region.

Preparation and properties of novel Cu-based bulk metallic glasses Cu_(55-x)Zr_(37)Ti_8In_x

The glassy rods were successfully fabricated in the Cu-Zr-Ti-In alloy system by casting into a copper mold. The value of ATx reaches a maximum of 66 K for the BMG CusoZraTTi8In5 alloy. The reasons for enhancing glass forming ability of Cu-based BMGs with the addition of indium were discussed from atomic size and thermodynamics. Alternatively, the BMG Cu52Zra7Ti8In3 exhibits the highest compressive strength （1981 MPa） and the best plasticity among glassy Cu55-xZra7TisInx （x_〈5）. The total plastic deformation of Cu52Zr37TisIn3 before fracture approaches 1.2%.

Effect of minor Fe addition on glass forming ability and mechanical properties of Zr_(55)Al_(10)Ni_5Cu_(30) bulk metallic glass

A series of rod samples with diameter of 3 mm（Zr0.55Al0.10Ni0.05Cu0.30）100-xFex（x=0,1,2,3,4） were prepared by magnetic suspend melting and copper mold suction casting method.The effects of a small amount of Fe on glass forming ability（GFA） and mechanical properties of Zr55Al10Ni5Cu30 bulk metallic glass（BMG） were investigated.The results show that the addition of an appropriate amount（less than 3%,mole fraction） of Fe enhances GFA,as indicated by the increase in the reduced glass transition temperature Trg（=Tg/Tl） and the parameter γ（=Tx/（Tg＋Tl）） with increasing Fe content,and GFA gets deteriorated by further Fe addition（4%）.The addition of Fe also effectively improves the compressive plasticity and increases the compressive fracture strength in these Zr-based BMGs.Compressive tests on BMG sample with 3 mm in diameter and 6 mm in length reveal work-hardening and a certain plastic strain in the alloy containing 2% Fe.The BMG composite containing 4% Fe also exhibits a high fracture strength along with significant plasticity.

Growth kinetics for intermetallic compound layer between molten In-Sn alloy and CuZr-based bulk metallic glass

The growth kinetics of intermetallic compound layer between molten In-Sn alloy and Cu40Zr44Al8Ag8 bulk metallic glass substrate was examined by solid state isothermal aging at the temperature range between 333 and 393 K.The aged samples were characterized by scanning electron microscopy and energy dispersive spectrometry.It is found that the intermetallic compound layer is composed of Zr,Cu and Sn.The layer growth of the intermetallic compound is mainly controlled by a diffusion mechanism over the temperature range and the value of the time exponent is approximately 0.5.The apparent activation energy for the growth of total intermetallic compound layers is 98.35 kJ /mol calculated by the Arrhenius equation.

Effect of surface roughness on plasticity of Zr_(52.5)Cu_(17.9)Ni_(14.6)Al_(10)Ti_5 bulk metallic glass

Zr52.5Cu17.9Ni14.6Al10Ti5 bulk metallic glass （BMG） rods were abraded to different surface roughnesses using different types of waterproof abrasive papers and sometimes polishing pastes, and the compressive deformation behavior was examined. The results show that the yield strength of the BMG is hardly affected while the compressive plasticity increases from 2.3% to 4.5% with decreasing the surface roughness. Observation of the fractured samples under a scanning electron microscope indicates that the rise in plasticity is accompanied with an increase in shear band density. The results suggest that it is necessary to reduce the surface roughness of BMGs for achieving a large plasticity.

Dry sliding tribological behavior of Zr-based bulk metallic glass

The tribological behavior of a Zr-based bulk metallic glass（BMG） was investigated using pin-on-disk sliding measurements in two different environments,i.e.,air and argon,against an yttria-stabilized zirconia counterface.It was found that the wear of the Zr-based BMG was reduced by more than 45% due to the removal of oxygen from the test environment at two different loads,i.e.,16 N and 23 N.The wear pins were examined using X-ray diffractometry,differential scanning calorimetry,scanning electron microscopy and optical surface profilometry.A number of abrasive particles and grooves presented on the worn surface of the pin tested in air,while a relatively smooth worn surface was observed in the specimens tested in argon.The wear mechanism of the pin worn in air was dominated by abrasive wear compared with an adhesive wear controlled process in the tests performed in argon.

Transition of plasticity and fracture mode of Zr-Al-Ni-Cu bulk metallic glasses with network structures

Effect of network structure on plasticity and fracture mode of Zr？Al？Ni？Cu bulk metallic glasses （BMGs） was investigated. The microstructures of transversal and longitudinal sections were exposed by chemical etching and observed by scanning electron microscopy （SEM）. The mechanical properties were examined by room-temperature uniaxial compression test. The results show that both plasticity and fracture mode are significantly affected by the network structure and the alteration occurs when the size of the network structure reaches up to a critical value. When the cell size （dc） of the network structure is ~3μm, Zr-based BMGs characterize in plasticity that decreases with increasingdc. The fracture mode gradually transforms from single 45° shear fracture to double 45° shear fracture and then cleavage fracture with increasingdc. In addition, the mechanisms of the transition of the plasticity and the fracture mode for these Zr-based BMGs are also discussed.

Effects of aspect ratio and loading rate on room-temperature mechanical properties of Cu-based bulk metallic glasses

Room-temperature mechanical properties of Cu50Zr40Ti10-xNix（0≤x≤4,mole fraction,%） bulk metallic glasses （BMG） with aspect ratios in the range of 1：1-2.5：1 and loading rates in the range of1×10^-5-1×10^-2s^-1were systematically investigated by room-temperatureuniaxialcompression test.In the condition of an aspect ratio of 1：1, the superplasticity can be clearly observed for Cu50Zr40Ti10BMG when the loading rate is1×10^-4s^-1, while for Cu50Zr40Ti10-xNix（x=1-3, mole fraction, %） BMGs when the loading rate is1×10^-2s^-1. The plastic strain （εp）, yielding strength （σy） and fracture strength （σf） of the studied Cu-based BMGs significantly depend on the aspect ratio and the loading rate. In addition, theσyof the studied Cu-based BMGs with an aspect ratio of 1：1 is close to the σfof those with the other aspect ratios when the loading rate is1×10^-2s^-1. The mechanism for the mechanical response to the loading rate and the aspect ratiowas also discussed.

Effect of minor-addition of Fe on structural and mechanical properties of CuZrAl bulk metallic glass

The CuZrAl bulk metallic glass with minor-addition of Fe was prepared by rapid quenching method. The structures were examined by X-ray diffraction （XRD）. The effect of Fe on the glass-forming ability was studied by differential scanning calorimetry （DSC）. The minor-addition of Fe obviously extends the supercooled liquid region ΔTx. The plastic strain of the Cu44Zr48Al7Fe bulk metallic glass is about 1.5%. The microstructures were examined by transmission electron microscopy （TEM）. It is found that when 1%-2% Fe （mole fraction） were introduced into the CuZrAl alloy matrix, nanoscale phase separation occurs in the as-prepared Cu44Zr48Al7Fe bulk metallic glass.

Design of high strength Fe-(P,C)-based bulk metallic glasses with Nb addition

Bulk metallic glass（BMG） rods Fe71Mo5-xNbxP12C10B2（x=1,2,3,4 and 5） with diameter of 1 or 2 mm were synthesized by copper mold casting.The effects of Nb substitution for Mo on the structure,thermal and mechanical properties of Fe71Mo5-xNbxP12C10B2 alloys were studied by X-ray diffraction,differential scanning calorimetry and compressive testing.The results show that the substitution of Nb for Mo leads to a decreased glass forming ability,but with plasticity of 1.0%,the fracture strength of Fe71Mo2Nb3P12C10B2 alloy increases up to 4.0 GPa.The improvement of the fracture strength is discussed in terms of the enhancement of atomic bonding nature and the favorite formation of a network-like structure due to the substitution of Nb for Mo.