High-Temperature Deformation Behavior and Formability of a Zr-Cu-Al-Ni Bulk Metallic Glass

The deformation behavior of a monolithic Zr₅₅Cu₃₀Al₁₀Ni₅ (at. pct) bulk metallic glass (BMG) fabricated by suction casting has been investigated at elevated temperatures in this study. A series of compression tests has been performed in the supercooled liquid temperature region. In the homogeneous flow regime, this alloy exhibited a transition from the Newtonian to non-Newtonian flow depending upon both the strain rate and the temperature. These two flow modes were then described by applying the Newtonian viscous flow theory and the transition state theory, respectively. On the basis of a dynamic materials model (DMM), a processing map could successfully be constructed to estimate the feasible forming conditions for this BMG alloy. Imaginary laboratory-scale extrusion tests were also performed to determine solid-to-solid formability, and the results from both the finite element method (FEM)-based simulation and processing map were then compared and discussed. This article is based on a presentation given in the symposium entitled “Bulk Metallic Glasses IV,” which occurred February 25–March 1, 2007 during the TMS Annual Meeting in Orlando, Florida under the auspices of the TMS/ASM Mechanical Behavior of Materials Committee.     

Dynamic Fracture of a Zr-based Bulk Metallic Glass

In the present study, dynamic fracture experiments are performed on fully amorphous Liquidmetal-1 (LM-1), a Zr-based BMG, to better understand fracture initiation and propagation in notched specimens. Experiments are conducted on notched (110 μm notch radius) four-point bend specimens using an instrumented modified split-Hopkinson pressure bar apparatus. The results of these experiments suggest that the critical dynamic stress intensity factor achieved by the notched LM-1 specimens is ~110 MPa m^1/2, which is similar to the fracture toughness determined from previous quasi-static fracture experiments. This insensitivity of the fracture toughness to crack tip loading rate suggests negligible loading-rate sensitivity on the dynamic fracture initiation toughness in LM-1. In situ high-speed camera images of the notched sample during the dynamic loading process show multiple fracture initiation attempts and subsequent arrests prior to catastrophic fracture initiation. Controlled stress wave loading experiments designed to induce sub-critical levels of damage in the notched specimens show extensive deformation banding extending 150 to 200 μm outward from the notch. The deformation bands, nominally perpendicular to each other, run along the direction of the notch and perpendicular to it. They are consistent with slip-line fields in notched samples of elastic perfectly plastic materials. Subsequent loading of the damaged specimen again shows several attempts at crack initiation followed by blunting; the initial sub-critical damage in the region around the notch is understood to increase the energy required for catastrophic specimen failure and is consistent with an increase in the effective notch radius due to preexisting damage.     

Microstructural Analysis of a Laser-Processed Zr-Based Bulk Metallic Glass

Laser processing is a precision manufacturing technique capable of producing materials with highly nonequilibrium microstructures. Due to the localized heat input and high cooling rate inherent to the process, this technology is attractive for the production of metallic glasses. In the present work, we use a laser deposition process to deposit a Zr-based metallic glass forming powder on both amorphous and crystalline substrates of the same nominal composition. Amorphous melt zones are observed surrounded by distinct crystalline heat-affected zones (HAZs). Detailed examination of the HAZ in the glassy substrates reveals the formation of microscale spherulites, in contrast to the nanocrystalline phases observed following crystallization by isothermal annealing of the glass at the crystallization temperature as well as in the HAZ of the crystalline substrates. The spherulites have a different crystal morphology and structure from the nanocrystalline phases, indicating that the more stable nanocrystalline phases are completely bypassed when the glass is devitrified at the higher heating rate. Reducing the heat input during laser processing results in the near elimination of the crystalline HAZ in the amorphous substrates, suggesting that a critical heating rate range is required to avoid devitrification.     

应变速率对锆基非晶复合材料力学性能的影响

采用铜模吸铸法制备出直径3mm的[Zr0.72+x(Cu0.59Ni0.41)0.28-x]88Al12(x=0.05、0.10)棒状非晶复合材料。考察应变速率对合金压缩力学性能的影响。结果表明,随应变速率的增大,合金的塑性变形区域减小,锯齿流变现象逐渐消失;在相同成分下,随应变速率的增大,弹性模量逐渐升高,塑性应变和抗压强度则逐渐降低,屈服强度和断裂强度也基本呈下降趋势。在x=0.05、应变速率为0.55×10-4s-1时,塑性应变、抗压强度和断裂强度均为最大值,分别为6.77%、1 758MPa和1 629MPa。     

高压等温处理后LaAlCuNi大块非晶的结构弛豫及其压痕下力学行为

采用铜模吸铸法制备出La62.0Al15.7(Cu0.5, Ni0.5)22.3大块非晶合金,并在室温和3.0～5.0 GPa压力条件下对该非晶合金进行了等温高压处理,研究了高压处理对该非晶结构弛豫和力学行为的影响.结果表明,高压处理对非晶合金的玻璃转变温度无明显影响,但使合金发生了明显的结构弛豫,其自由体积和第一晶化温度随压力的增加先增加后减小,最大值出现在4.0 GPa压力之下.纳米压痕和维氏硬度测试表明,其硬度值随压力变化规律与自由体积随压力变化规律一致.     

Production and Mechanical Properties of Roll Bonded Bulk Metallic Glass/Aluminum Laminates

Twin roll casting has been used to produce sheet of Mg₆₀Cu₂₉Gd₁₁ bulk metallic glass (BMG). Sheet can be produced with thicknesses between 1 and 4 mm, the width of sheet produced can be between 25 and 75 mm. The dimensional stability of the produced sheet in a cast run is ±1 mm in the width direction and ±0.05 mm in the thickness direction. As with all magnesium-based BMGs the sheet produced is strong yet brittle at room temperature. The maximum flexural stress of a twin roll cast Mg₆₀Cu₂₉Gd₁₁ BMG strip is 150 MPa with a flexural strain of 0.005. The Charpy impact energy of a Mg₆₀Cu₂₉Gd₁₁ BMG strip is 0.02 J. In order to improve the toughness values of the Mg₆₀Cu₂₉Gd₁₁, BMG strip laminates of BMG and aluminum alloy (UNS A91100) were produced via roll bonding. The introduction of aluminum layers to the sheet structure provides a barrier to shear band movement stopping the sudden catastrophic failure of the sheet. After rolling the BMG was examined via X-ray diffraction (XRD) to confirm that the BMG layer remained amorphous. The flexural stress, flexural strain, and Charpy impact energy properties of BMG-Al laminates are improved when compared to monolithic glass properties. The flexural stress values for laminates compared to the monolithic glass improve by 60 pct from 150 to 250 MPa. The flexural strain values improve by over an order of magnitude from 0.005 to 0.14. The Charpy impact energies increase by 2 orders of magnitude from 0.02 to 2.5 J.     

Influence of Strain Rate on Compressive Deformation Behavior of a Zr-Cu-Ni-Al Bulk Metallic Glass at Room Temperature

The compressive-deformation behavior of the Zr_50.7Cu₂₈Ni₉Al_12.3 bulk metallic glass (BMG) was investigated over a wide strain-rate range at room temperature. The yield strength of the BMG studied is independent of the strain rates applied upon quasi-static loading; however, it decreases remarkably upon dynamic loading. Serrated flows and shear bands appear at low quasi-static strain rates; nevertheless, they vanish as the strain rate increases to 1.0 × 10⁻¹ s⁻¹. Cracks appearing on the side surface of the fractured sample after dynamic compression yield a strain-accommodation deformation mechanism upon dynamic loading. Scanning electron microscopy observations reveal that molten liquids increase on the fractured surfaces with increasing strain rate, indicating that adiabatic heating in the shear bands is enhanced as the strain rate increases.     

A Highly Fatigue-Resistant Zr-Based Bulk Metallic Glass

The strength-normalized fatigue endurance strength of the bulk metallic glass (BMG) Zr_52.5Cu_17.9Ni_14.6Al₁₀Ti₅ (Vitreloy 105) has been reported to be the highest for any BMG; however, to date, there has been no explanation of why this material is so much better than other Zr-based compositions. In this study, the fatigue-crack growth behavior of Zr_52.5Cu_17.9Ni_14.6Al₁₀Ti₅ was compared in ambient air vs dry nitrogen environment. The excellent fatigue life behavior is attributed to a relatively high fatigue threshold (ΔK _TH ≈ 2 MPa√m) and a lack of sensitivity to environmental effects on fatigue-crack growth in ambient air, as compared to other Zr-based BMGs. Fatigue life experiments conducted in ambient air confirmed the excellent fatigue life properties with a 10⁷-cycle endurance strength of ~0.24 of the ultimate tensile strength; however, it was also found that casting porosity, even in limited amounts, could reduce this endurance strength by as much as ~60 pct. Overall, the BMG Zr_52.5Cu_17.9Ni_14.6Al₁₀Ti₅ appears to have excellent strength and fatigue properties and should be considered as a prime candidate material for future applications where good mechanical fatigue resistance is required.     

块状金属玻璃研究进展与应用

综述了块状金属玻璃的研究进展，介绍了块状金属玻璃的应用及几种制备方法，阐明了块状金属玻     

Ti基大块金属玻璃的研究与应用

阐述了Ti基大块金属玻璃(BMG)的成分设计原则及制备方法，并对Ti基非晶合金及其部分晶化复合材料的力学性能及断裂机理进行了评述。结果表明：Ti基大块金属玻璃具有较高的断裂强度、弹性延伸率及一定的塑性延伸率，而经过部分晶化获得的非晶合金基纳米颗粒复合材料，其室温塑性获得很大的改善。在此基础上探讨了该合金目前所存在的问题、研究热点以及其应用前景。     

High-Pressure Equation of the State of a Zirconium-Based Bulk Metallic Glass

The high stress U _s -U _p Hugoniot equation of state (EOS) of a zirconium-based bulk metallic glass (BMG, Zr₅₇Nb₅Cu_15.4Ni_12.6Al₁₀) was determined using plate impact experiments on disk-shaped samples of 10-mm diameter and 2-mm thickness. The National Institute for Materials Science (NIMS) two-stage light-gas gun was used for the high stress measurements (∼26 to 123 GPa), and the Georgia Institute of Technology (GT) single-stage gas gun was used for the lower stress measurements (∼5 to 26 GPa). The NIMS experiments were instrumented with streak photography and used the inclined mirror (IM) method to simultaneously measure shock velocity and free surface velocity. The GT experiments used polyvinylidene fluoride (PVDF) stress gages and velocity interferometry (VISAR) to simultaneously measure the shock velocity, free surface velocity, and stress. Results from the streak camera records and PVDF gages + VISAR traces, as well as impedance matching calculations, were used to generate the U _s -U _p Hugoniot EOS for the BMG over a wide range of stresses. The U _s -U _p data show evidence of a low pressure phase, a transition to a mixed phase region at ∼26 GPa, followed by transition at ∼67 GPa to a high-pressure phase of bulk modulus of 288 GPa. This article is based on a presentation made in the symposium entitled “Dynamic Behavior of Materials,” which occurred during the TMS Annual Meeting and Exhibition, February 25–March 1, 2007 in Orlando, Florida, under the auspices of The Minerals, Metals and Materials Society, TMS Structural Materials Division, and TMS/ASM Mechanical Behavior of Materials Committee.     

连续钨丝增强锆基块体金属玻璃变形过程中剪切带演化

研究体积分数为60%的连续钨丝/Zr41.2Ti13.8Cu12.5Ni10Be22.5块体金属玻璃复合材料准静态压缩变形过程中剪切带的演化过程。发现在弹性变形段不形成剪切带,剪切带是在塑性变形过程中产生并发展的,且剪切带的数量随着变形量的增加而增大,间距随着变形量的增加而减小;当间距减小到一定值时产生剪切裂纹并不断扩展,最终导致断裂破坏。     

Corrosion Behavior of Fe-based Bulk Metallic Glass and In-situ Dendrite-reinforced Metallic Glass Matrix Composites in Acid Solution

The corrosion behavior study was conducted on a novel Fe_(77)Mo_5P_9C_(7.5)B_(1.5)in-situ metallic glass matrix composite(MGMC).This composite sample was developed by introduction of bccα-Fe dendrites as reinforcing phase.The corrosion behavior of this composite was compared to its monolithic counterpart and other Fe-based alloys such as 304 Land 2304Lstainless steels.The corrosion resistance of MGMCs in H_2SO_4 solution shows inferior to that of other Fe-based alloys.Experiments suggest that Fe-BMGs samples possess better corrosion resistance property than that of Fe-MGMCs.The possible underlying reasons can be the inhomogeneity induced by the precipitation ofα-Fe dendrites in the MGMCs.     

Crystallization of a Ti-based Bulk Metallic Glass Induced by Electropulsing Treatment

The effect of electropulsing treatment (EPT)on the microstructure of a Ti-based bulk metallic glass (BMG)has been studied.The maximum current density applied during EPT can exert a crucial role on tuning the microstructure of the BMG.When the maximum current density is no more than 2 720 A/mm2 ,the samples retains amorphous nature,whereas,beyond that,crystalline phases precipitate from the glassy matrix.During EPT,the maximum temperature within the samples EPTed at the maximum current densities larger than 2 720 A/mm2 is higher than the crystallization temperature of the BMG,leading to the crystallization event.     

Kinetics of Glass Transition and Crystallization in Carbon Nanotube Reinforced Mg-Cu-Gd Bulk Metallic Glass

Mg65Cu25Gd10 bulk metallic glass and its carbon nanotube reinforced composite were prepared. Differential scanning calorimeter （DSC） was used to investigate the kinetics of glass transition and crystallization processes. The influence of CNTs addition to the glass matrix on the glass transition and crystallization kinetics was studied. It is shown that the kinetic effect on glass transition and crystallization are preserved for both the monothetic glass and its glass composite. Adding CNTs in to the glass matrix reduces the influence of the heating rate on the crystallization process. In addition, the CNTs increase the energetic barrier for the glass transition. This results in the decrease of GFA. The mechanism of the GFA decrease was also discussed.     

Pd-Cu-Ni-P Bulk Metallic Glass: A Very Low Damping Material

The present work addresses damping experiments performed in a Pd-Cu-Ni-P bulk metallic glass. After an appropriated thermal treatment, this material exhibits a very low damping coefficient, down to 10⁻⁶. This result is discussed considering the different possible origins of the damping phenomena: thermoelasticity, energy dissipation by electrons, phonons, defects, and residual stresses. Thermoelasticity and defects appear to be the most important sources of mechanical damping. This article is based on a presentation given in the symposium entitled “Bulk Metallic Glasses IV,” which occurred February 25−March 1, 2007 during the TMS Annual Meeting in Orlando, Florida under the auspices of the TMS/ASM Mechanical Behavior of Materials Committee.     

Effect of Sn Additions on the Damage Tolerance of a ZrCuNiAl Bulk Metallic Glass

Damage tolerance (toughness and plasticity) properties of a ZrCuNiAl bulk metallic glass (BMG) are tailored through Sn alloying under ambient conditions. The result shows that the measured fracture energy is clearly correlated with the product (R) of Young’s modulus and averaged size of vein patterns on mode I crack surfaces of these BMGs. The implications of the current result on other BMGs are also briefly discussed, which might be useful for the evaluation of damage tolerance of tough BMGs.     

冷却介质对退火态Cu50Zr42Al8块体非晶合金力学性能的影响

考察在过冷液相区内790K+30min保温后炉冷和液氮冷却对Cu50Zr42Al8压缩断裂行为的影响。5mm铸态非晶复合棒的屈服强度、断裂强度和杨氏模量分别为1670MPa,1849MPa和104.4GPa,塑性应变为1.9%。经炉冷和液氮冷却试样的压缩断裂强度和杨氏模量下降,分别为912,678MPa和38,56.5GPa。液氮冷却试样为部分非晶结构,炉冷试样完全晶化。晶化相均为正交晶相Cu10Zr7,四角晶相CuZr2和DO3结构的AlCu2Zr三种脆化相。     

Primary Transformation Kinetics in Zr-Al-Ni-Cu-Pd Bulk Metallic Glass Correlated with Relaxation State

The primary transformation kinetics of nanoicosahedral quasicrystalline (QC) phase formation were investigated in Zr₆₅Al_7.5Ni₁₀Cu_12.5Pd₅ bulk metallic glass (BMG) in various relaxation states. A less relaxed (unrelaxed) BMG exhibited higher activation energy for atomic diffusion in the glassy structure than that of a relaxed one, which represents a change in the nucleation and grain growth kinetics of the primary phase with the relaxation state. Actually, the grain growth rate of a QC particle near the crystallization temperature was approximately 1 × 10^?9 m/s in the less relaxed BMGs, which was less than half of that in the relaxed BMGs. In contrast, the calculated homogeneous nucleation rate significantly increased in the less relaxed samples. It increased with the volume fraction transformed in the early stage. It is concluded that the relaxation state of glassy alloys markedly affects the primary transformation kinetics. The current study also indicates a necessity of development of the relaxation state for structure controlling in industrial applications of BMGs.     

Ni-Nb-Sn Bulk Metallic Glass Matrix Composites Fabricated by Microwave-Induced Sintering Process

Using a gas-atomized Ni_59.35Nb_34.45Sn_6.2 metallic glassy alloy powder blended with Sn powder of various contents, Ni-Nb-Sn bulk metallic glassy matrix composites were fabricated by a microwave (MW)–induced sintering process in a single-mode 2.45 GHz MW applicator in a separated magnetic field. The Ni_59.35Nb_34.45Sn_6.2 glassy alloy powder and its mixed powders containing Sn particles could be heated well in the magnetic field. The addition of Sn particles promoted densification of the sintered Ni_59.35Nb_34.45Sn_6.2 metallic glassy powder. Bulk samples without crystallization of the glassy matrix and with good bonding state among the particles were achieved at a sintering temperature of 833 K.