SYNTHESIS OF PLASTIC Zr–BASED BULK METALLIC GLASS WITH CRYSTAL PHASE BY DIRECTIONAL SOLIDIFICATION

通过Bridgman定向凝固成功制备了成分为Zr_58.5Ti_14.3Nb_5.2Cu_6.1Ni_4.9Be_11.0的内生枝晶增塑的非晶复合材料. 内生枝晶的尺寸和体积分数可以经抽拉速度的改变得以控制, 进而实现了对其力学性能的调节. 研究表明, 枝晶的大小与抽拉速度呈线性关系, 体现出定向凝固在制备非晶复合材料方面可调控析出相的优势.通过对实验参数抽拉速度的优化得出, 当抽拉速度为1.0 mm/s时, 最高压缩强度达到了1930 MPa, 断裂塑性达到11.3%.     

Ti48Zr20Nb12Cu5Be15 非晶复合材料的内耗行为

对Ti₄₈Zr₂₀Nb₁₂Cu₅Be₁₅非晶复合材料的室温力学性能以及随温度变化的动态力学性能进行了研究。结果表明,该非晶复合材料的室温拉伸强度约为1350 MPa,断裂应变约为0.13。随着温度的升高,该非晶复合材料的整体状态由弹性转变为粘弹性。在准点缺陷模型框架下,引入了诸如损耗因子、相关系数等相关物理参数,全面分析了该非晶复合材料动态力学行为,并且模型的理论曲线与实验数据拟合程度较好。因此,准点缺陷模型可以很好地描述不同温度下的Ti₄₈Zr₂₀Nb₁₂Cu₅Be₁₅非晶复合材料的动态力学行为。     

Mechanical properties of Zr56.2Ti13.8Nb5.0Cu6.9Ni5.6Be12.5 ductile phase reinforced bulk metallic glass composite

Ductile phase containing bulk metallic glass composites are prepared via an in situ method by rapid quenching of a homogenous Zr_56.2Ti_13.8Nb_5.0Cu_6.9Ni_5.6Be_12.5 melt. The microstructure of the resulting two phase material is investigated by SEM, X-ray diffraction, and microprobe analysis. The composite material, as well as single phase materials with the corresponding matrix and second phase compositions, are tested in uniaxial tension and compression. Young's Modulus, shear modulus and Poisson ratios are analyzed by ultrasonic sound velocity measurements. The composite material demonstrates strongly improved Charpy impact toughness (by a factor of 2.5 compared to Vitreloy 1) and ductility (average fracture strain up to 8.3% in compression and 5.5% in tension). These remarkable improvements are explained by the effect of the mechanically soft and ductile second phase, which acts stabilizing against shear localization and critical crack propagation.     

Effect of minor Nb addition on mechanical properties of in-situ Cu-based bulk metallic glass composite

In-situ formed (Cu_0.6Zr_0.3Ti_0.1)₉₅Nb₅ bulk metallic glass (BMG) composite with Nb-rich dendrite randomly dispersed in hard glassy matrix was prepared by casting into a water-cooled copper mold. The dendrite has much smaller hardness and elastic modulus than glassy matrix, and the stress concentration at interface provides a channel for the initiating and branching of shear bands upon loading, thus leading to a high compressive fracture strain of 6.08% and fracture strength about 2200 MPa. Comparing with other Cu-based BMG composite, the fracture strength of present (Cu_0.6Zr_0.3Ti_0.1)₉₅Nb₅ composite is not significantly reduced, indicating that the addition of Nb in the current work is an effective and effortless way to fabricate new practical BMG composites with enhanced strength and good plasticity.     

Zr41Ti14Cu12.5Ni10Be22.5非晶棒料摩擦焊接

设计了一种非晶合金摩擦焊装置,以Zr₄₁Ti₁₄Cu_12.5Ni₁₀Be_22.5非晶棒料为研究对象,进行了摩擦焊试验.焊接样品经SEM,XRD,维氏硬度、TEM等检测,结果显示焊接界面无明显未熔合,样品仍然保持非晶态,接头硬度总体增大,接头处出现了纳米晶.采用ANSYS软件对非晶合金摩擦焊的温度场进行仿真.结果表明,在摩擦时间t=0.25s时摩擦界面中心温度超过非晶棒料玻璃转变温度,接触面全部进入过冷液相区,应进行顶锻.仿真结果与摩擦焊试验结果基本吻合,有利于指导焊接试验.     

Improved mechanical behavior of Cu–Ti-based bulk metallic glass by in situ formation of nanoscale precipitates

The mechanical properties of Cu₄₇Ti₃₄Zr₁₁Ni₈, Cu₄₇Ti₃₃Zr₁₁Ni₈Fe₁, and Cu₄₇Ti₃₃Zr₁₁Ni₈Si₁ bulk metallic glasses prepared by copper mold casting are investigated. Room temperature compression tests reveal fracture strengths above 2000 MPa, Young’s moduli around 100 GPa and elastic strains slightly exceeding 2.0%. Only Cu₄₇Ti₃₃Zr₁₁Ni₈Si₁ exhibits distinct plastic strain due to a unique composite microstructure with in situ formed nanoscale precipitates in the glassy matrix.     

Containerless processing of the undercooled metallic melts — overview

Brief overview of current containerless electrostatic levitation processing technique and research progress of the area of bulk metallic glass formation is introduced. Undercooling behavior during solidification of the bulk metallic glass forming Zr_41.2Ti_13.8Cu_12.5Ni_10.0Be_22.5 alloy has been studied using the containerless electrostatic levitation processing technique. The melt is successfully undercooled to the glass transition temperature forming the amorphous phase with the proper thermal treatment. Differential scanning calorimetry (DSC) is used to determine the Gibbs free energy difference between the crystal and the undercooled liquid. The results indicate that the Gibbs free energy difference between the metastable undercooled liquid and the crystalline solid of the Zr_41.2Ti_13.8Cu_12.5Ni_10.0Be_22.5 alloy is relatively small compared to that of conventional metallic glass forming binary alloys even for large undercoolings. The hemispherical total emissivity of undercooled liquid is measured in the whole region of undercooled liquid state. Due to the combining effects of excellent thermal stability of the undercooled liquid in the Zr_41.2Ti_13.8Cu_12.5Ni_10.0Be_22.5 alloy with unique experimental technique of the containerless electrostatic levitation processing, it is possible to construct the complete time-temperature-transformation (TTT) diagram. The measured TTT diagram exhibiting the expected “C” shape can not be satisfactorily explained by the existing models due to the complex crystallization mechanisms.     

Plastic deformation in nanostructured bulk glass composites during nanoindentation

Nanoindentation experiments of a Ti₄₅Zr₁₆Be₂₀Cu₁₀Ni₉ bulk metallic glass and partially vitrified nano-composite metallic glass matrix have been performed under a constant maximum load of 10 mN and constant loading rate of 0.08 mN s^?1 with the aim of comparative study of their micro-plastic deformation behavior. Remarkable difference in deformation behavior was found in load–displacement curves of nanoindentation and pile-up morphologies around the indents. The difference in shear banding behavior has been attributed to the presence of nanosized icosahedral particles in amorphous matrix.     

Synthesis and characterization of particulate reinforced Zr57Nb5Al10Cu15.4Ni12.6 bulk metallic glass composites

The Zr₅₇Nb₅Al₁₀Cu_15.4Ni_12.6 bulk metallic glass forming liquid is reinforced with WC, SiC, W, or Ta particles. Structure, microstructure and thermal stability of the composites are studied by X-ray diffraction, optical microscopy and differential scanning calorimetry. The metallic glass matrix remains amorphous after adding up to 20 vol.% of particles. The reactions at the interfaces between the matrix and the different reinforcing materials are investigated with scanning electron microscopy, transmission electron microscopy and electron microprobe. The mechanical properties of the composites are studied in compression and tension. The influence of the introduced particles on the thermal stability of the matrix as well as on the mechanical properties is discussed.     

Dynamic shear punching of metallic glass matrix composites

Dynamic shear punching is employed to process Zr_36.6Ti_31.4Nb₇Cu_5.9Be_19.1 metallic glass matrix composites. A brittle fracture dominates during punchforming, and no macroscopic cracks or ruffles can be found, indicative of a good surface finish. The softening instability for metallic glasses happens once the yielding is available, avoiding the existence of shear bands and achieving smooth surfaces. No crystallization is accompanied in the heavy deformation zones during dynamic shear punching. The thickness of punched sheets for various BMG systems is highly dependent on the shear strengths. Furthermore, it is deduced that larger glass-transition temperatures of BMGs correspond to the thinner punched sheets, which provides a theoretical guidance to rapidly process metallic glass sheets.     

Beryllium-distribution in metallic glass matrix composite containing beryllium

The morphologies, sizes, compositions and volume fractions of dendritic phases in in situ Ti-based metallic glass matrix composites (MGMCs) containing beryllium (Be) with the nominal composition of Ti₄₇Zr₁₉Cu₅V₁₂Be₁₇ (mole fraction, %) were investigated using XRD, SEM, EBSD, TEM, EDS and three-dimensional reconstruction method. Moreover, visualized at the nanoscale, Be distribution is confirmed to be only present in the matrix using scanning transmission electron microscopy–electron energy loss spectroscopy (STEM–EELS). Based on these findings, it has been obtained that the accurate chemical compositions are Ti_28.3Zr_19.7Cu₈V_6.4Be_37.6 (mole fraction, %) for glass matrix and Ti_62.4Zr_18.4Cu_2.6V_16.6 (mole fraction, %) for the dendritic phases, and the volume fractions are 38.5% and 61.5%, respectively. It is believed that the results are of particular importance for the designing of Be-containing MGMCs.     

A thermoplastic forming map of a Zr-based bulk metallic glass

A thermoplastic forming (TPF) map of a Zr₃₅Ti₃₀Be_26.75Cu_8.25 bulk metallic glass was constructed through systematic hot-embossing experiments, spanning a wide range of strain rates and temperatures in the supercooled liquid region. By comparison with the corresponding deformation map, it is found that Newtonian flow, non-Newtonian flow and inhomogeneous flow regions correspond well to fully filled, partially filled and non-filled regions, respectively, in the hot-embossing TPF map. Furthermore, the spatio-temporally homogeneous flow facilitates the thermoplastic formability of the Zr-based bulk metallic glass, which is rationalized in terms of free volume theory as well as by finite element simulations. Finally, our results are corroborated by potential application tests.     

Binding and dispersion behavior of amorphous powders in diamond particles

This work was to prepare the diamond reinforced Cu₅₄Ni₆Zr₂₂Ti₁₈ bulk metallic glass matrix composites using Spark Plasma Sintering (SPS) process. The effect of mixing methods such as mechanical alloying (MA), and turbula mixing–dry mixing (DM) and wet mixing (WM) on the uniformity of constituent phase was also investigated. Examination of microstructure and evaluation of mechanical properties of the composites were performed depending on the mixing processes. As a result, WM composite showed the highest mechanical properties. The experimental results indicated that the mixing method was essential parameter to determine the quality of MG/diamond composites such as the uniformity of phase and binding behavior.     

Wetting angle and infiltration velocity of Zr base bulk metallic glass composite

The contact angles of Zr₄₇Ti₁₃Cu₁₁Ni₁₀Be₁₆Nb₃ alloy on tungsten substrate were measured by sessile drop technique at the temperature range from 1023 to 1323 K and different processed time. Based on the morphology of the melt drop, the surface tension as function of processing temperature and holding time was obtained. Diffusion band was observed at the fringe of metallic drop, which confirms that the wetting between the melt and tungsten belongs to reactive wetting. The relationship between the flow velocity of melt and processing parameters, such as infiltration pressure, volume fraction of fibers and the filtration length, was calculated comprehensively.     

一种具有优异玻璃形成能力的Zr50Ti5Cu27Ni10Al8大块非晶合金的开发

多组元的Zr基非晶合金成分的复杂性对开发具有优异玻璃形成能力的Zr基非晶合金提出巨大的挑战。另外,大部分Zr基非晶合金含有有毒元素Be或者贵金属。因此,采用一种简单有效的方法开发无毒无贵金属元素的多组元Zr基非晶合金十分必要。本文中采用二元共晶比例法和部分元素替代法快速的开发出了一种新的临界尺寸大于10mm的 Zr50Ti5Cu27Ni10Al8非晶合金。这个非晶合金的热稳定性和硬度也通过原位高温X射线衍射和纳米压痕方法测量得出。     

Effects of infiltration parameters on mechanical and microstructural properties of tungsten wire reinforced Cu47Ti33Zr11Ni6Sn2Si1 metallic glass matrix composites

Cu₄₇Ti₃₃Zr₁₁Ni₆Sn₂Si₁-based bulk metallic glass matrix composites reinforced with tungsten wires were fabricated by infiltration process at different temperatures (850, 900, 950 and 1000 °C) and time (10, 20 and 30 min) in a quartz or a steel tube. The mechanical tests were carried out by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results show that the maximum strength and total strain of the composite are 1778 MPa and 2.8% fabricated in steel tube at 900 °C for 10 min, and 1582 MPa and 3.6% fabricated in quartz tube at 850 °C for 10 min, respectively.     

Mechanical properties of tungsten fiber reinforced ZrAlNiCuSi metallic glass matrix composite

Tungsten fiber reinforced (Zr₅₅Al₁₀Ni₅Cu₃₀)_98.5Si_1.5 metallic glass composites were fabricated and characterized. The mechanical properties of the composite under compression and tension were investigated. Tungsten reinforcement greatly increased compressive strain to failure compared to the unreinforced (Zr₅₅Al₁₀Ni₅Cu₃₀)_98.5Si_1.5 metallic glass. The compressive failure mode changed from a single shear band to multiple shear bands and to localized fiber buckling and tilting as the volume fraction of tungsten fiber increased. The maximum tensile strength and strain to failure of each of the composites were lower than those of unreinforced material due to the lack of substantial shear bands. Tensile toughness changed to some extent due to different interface reactions. The reason for the improved mechanical properties is discussed.     

Characterization of interface between the particles in NiNbZrTiPt metallic glassy matrix composite containing SiC fabricated by spark plasma sintering

We investigated the microstructure, in particular, the interface structure between powder particles in the Ni_52.5Nb₁₀Zr₁₅Ti₁₅Pt_7.5 bulk glassy alloy composites containing 10 vol.%SiC particulates prepared by a spark plasma sintering (SPS) process by means of scanning and transmission electron microscopies. The SiC particulates were dispersed homogeneously in the Ni_52.5Nb₁₀Zr₁₅Ti₁₅Pt_7.5 glassy matrix. No crystallization of the Ni_52.5Nb₁₀Zr₁₅Ti₁₅Pt_7.5 glassy alloy took place during the SPS process. The good bonding states between SiC particulates and glassy matrix, as well as between glassy particles were recognized. No intermediate layer in the bonded interfaces was observed.     

Joining of Ti-based bulk metallic glasses using resistance spot welding technology

Ti₄₀Zr₂₅Ni₃Cu₁₂Be₂₀ bulk metallic glass was used to study the influence of key process parameters on the spot welds microstructures and mechanical properties. Spot weld size and crystallized volume fraction were found to interact in a complex fashion in controlling the joint mechanical response. Assessment of cooling rates indicated that crystallized volume fraction was more liable to reach significant levels in the heat-affected zone than the fusion zone. Conditions for which the welds sustained a glassy environment were also determined. Resistance spot welding was found to be a feasible technique for joining bulk metallic glasses.     

Thermodynamic optimum friction welding of glassy rods

A non-linear heat transfer model, based on Coulomb friction and viscous dissipation heat sources, was developed to study rotational friction welding of Ti₄₀Zr₂₅Ni₃Cu₁₂Be₂₀ glassy rods. The thermodynamic zones of the welding surface were identified, and the optimum welding window for the bulk metallic glass was determined in terms of Reynolds number of rotation and Fourier number. Crystallization at the welding surface can effectively be controlled by selecting suitable combinations of Fourier number and Reynolds number of rotation.