Salient shear bands and second-phase addition interactions of bulk metallic glass matrix composite

This article discusses Charpy impact testing and fracture morphology of the Zr_41.25Ti_13.75Cu_12.5Ni₁₀Be_22.5 bulk metallic glass matrix composite with long tungsten fibers. Energy to failure was measured via the impact test as well as by integrating the compressive stress-strain curves, and compared for various fiber fractions. Failure energy increased with fiber volume fraction by both measures. Observation of fracture surfaces was made by using scanning electron microscopy. The results show that the fracture surface of the unreinforced bulk metallic glass (BMG) exhibits three different regions, i.e., the impact zone, the transition zone, and the ridged zone, which have different morphology. The composites present uneven or jagged morphology on macroscopic scale, while the microstructure exhibits salient shear bands and second-phase addition interactions. Bridge formation between tungsten fibers is interpreted as evidence that the shear band propagation in the matrix is suppressed by the fibers. Furthermore, shear lips were observed for the composites containing over 50 pct, fiber volume fraction, showing a great improvement in toughness.     

W纤维增强高Cu含量W-Cu复合材料的研究

选用0.13mm的W纤维编织成纤维毡,通过控制压制压力制备一系列孔隙度不同的W骨架,用高温熔渗得到Cu-W基复合材料。采用金相观察、物理和力学性能测试等试验手段,研究其显微组织、密度、硬度和电学性能。结果表明:用螺旋状W纤维织得的纤维毡,熔渗可得到较宽范围Cu含量的W纤维增强Cu基复合材料,W纤维均匀地分布在Cu基体内;W-Cu合金的相对密度达到98%以上,硬度超过86HB,电导率最高达到78.4%IACS。     

Properties of bulk metallic glasses

A relatively small number of revolutionary materials have been discovered in the field of physical metallurgy and metal physics in the last several decades, and bulk metallic glasses are among them. Their strength and hardness are considerably higher and their modulus of normal elasticity is considerably lower than that of crystalline alloys, which leads to large stored elastic strain energy. These materials also have very good corrosion resistance. In this article, we present the properties of bulk metallic glasses, in particular, thermal, mechanical, magnetic, and electrical properties, corrosion resistance, as well as the application fields of these alloys.     

Electrochemical behavior of Ca-based bulk metallic glasses

Since 2002, numerous Ca-based bulk metallic glass (BMG) alloys have been discovered. These BMG alloys are of interest because of their low densities and costs; however, few studies have examined the properties of these novel materials. In this study, the thermophysical and electrochemical behavior of three Ca-based BMGs was examined and compared to a crystalline, Mg-based alloy. Cyclic-anodic polarization tests were conducted in a 0.05 M Na₂SO₄ electrolyte, and posttest analyses by scanning electron microscopy were conducted to assess the damage to the exposed surfaces.     

Thermodynamic modeling of Zr-Ti-Cu-Ni-Be bulk metallic glass

In the present thermodynamic model, the optimization of bulk metallic glass forming compositions in Zr-Ti-Cu-Ni-Be system using enthalpy of chemical mixing (ΔH_chem) as thermodynamic, mismatch entropy (ΔS _σ /k_B) as topological and configurational entropy (ΔS_config/R) as statistical parameters were studied. The product of ΔH_chem and ΔS _σ /k_B which is termed as ΔP_HS in the ΔS_config/R range of 0.9 to 1.0 can be strongly correlated to glass forming ability. Using the contributions of ΔP_HS values of all ternary compositions possible in Zr-Ti-Cu-Ni-Be system, the final quinary composition is designed. Composition obtained from present model was found to closely match with compositions reported in literature.     

Crystallization mechanism of CeAlFeCo bulk metallic glasses

Crystallization behaviors of Ce60Al15Fe5+xCo20-x(x=0,5,10) bulk metallic glasses(BMGs) were studied by means of differential scanning calorimeter(DSC) and X-ray diffraction(XRD).The crystallization processes of different samples were simulated by JMA equation.Experimental results demonstrated that incubation and crystallization time increased with decreasing isothermal temperature for the same sample.The crystallization mechanism of CeAlFeCo BMGs was discussed.     

Effects of B addition on glass forming ability and thermal behavior of FePC-based bulk metallic glasses

The FePC-based bulk metallic glasses (BMGs) have been demonstrated to possess high plasticity and good soft magnetic properties.However, the relatively poor glass forming ability (GFA) and thermal stabilities limited their application in industries.The effects of microalloying with B in FePC-based BMGs on the GFA and thermal behaviors were systematically investigated.It was found that a small amount of B addition can dramatically enhance the GFA of FePC-based BMGs, which in turn leads to the critical maximum diameter up to 2 mm for full glass formation even using low cost raw materi-als.The underlying mechanism of the enhancement of GFA from the competing crystalline phase with amorphous phase, the average thermal expansion coefficient and dynamic viscosity were dis-cussed in detail.     

Fatigue and fracture behavior of bulk metallic glass

Tensile, compressive, cyclic tension-tension, and cyclic compression-compression tests at room temperature were systematically applied to a Zr_52.5Cu_17.9Al₁₀Ni_14.6Ti₅ bulk metallic glass for comprehensive understanding of its damage and fracture mechanisms. Under tensile loading, the metallic glass only displays elastic deformation followed by brittle shear fracture. Under compressive loading, after elastic deformation, obvious plasticity (0.5 to 0.8 pct) can be observed before the final shear fracture. The fracture strength under compression is slightly higher than that under tension. The shear fracture under compression and tension does not occur along the maximum shear stress plane. This indicates that the fracture behavior of the metallic glass does not follow the Tresca criterion. The fracture surfaces show remarkably different features, i.e., a uniform vein structure (compressive fracture) and round cores coexisting with the radiating veins (tensile fracture). Under cyclic tension-tension loading, fatigue cracks are first initiated along localized shear bands on the specimen surface, then propagated along a plane basically perpendicular to the stress axis. A surface damage layer exists under cyclic compression-compression loading. However, the final failure also exhibits a pure shear fracture feature as under uniaxial compression. The cyclic compression-compression fatigue life of the metallic glass is about a factor of 10 higher than the cyclic tension-tension fatigue life at the same stress ratio. Based on these results, the damage and fracture mechanisms of the metallic glass induced by uniaxial and cyclic loading are elucidated.     

放电等离子烧结制备铁基大块非晶材料

以惰性气体雾化的非晶铁基粉末为原料,采用放电等离子烧结技术(SPS)制备大块非晶材料.探索了SPS烧结温度对烧结体的物相、相对密度、微观结构和性能的影响.试验表明,采用优化的SPS烧结工艺,用粉末冶金的方法,可以获得致密的大块非晶材料,部分性能与铸态相当.     

钢纤维对摩擦材料性能的影响

树脂基复合材料性能优异,被大量用做汽车制动材料.以酚醛树脂为基体,钢纤维为增强纤维,添加填料,采用热压法制成刹车片,并进行摩擦试验.通过试验研究了酚醛树脂基复合材料中钢纤维不同添加量(质量分数)对复合材料冲击强度、摩擦性能的影响.结果表明:该配方类型中,在100～300℃温度范围内,材料冲击强度先增大后减小,钢纤维质量分数为24%时为转折点;材料的摩擦系数先增大后减小,钢纤维质量分数为26%时为转折点;磨损率随钢纤维添加量的增加而增大,钢纤维最佳添加量为24%～26%.     

Development of bulk metallic glasses based on the Dy-Al binary eutectic composition

A series of dysprosium-based ternary, quadruple, and quintuple bulk metallic glasses （BMGs） based on Dy-Al binary eutectic composition were obtained with the partial substitution of Co, Gd, and Ni elements, for dysprosium. The results showed that the Dy31Gd25Co20Al24 alloy, which had the best glass forming ability （GFA）, could be cast into an amorphous rod with a diameter of 5 ram. The GFA of alloys was evaluated on the basis of the supercooled liquid region width, 7 parameter, the formation enthalpy, and the equivalent electronegativity difference of amorphous alloys. It was found that the eutectic composition was closely correlated with the GFA of the Dy-based BMGs.     

Investigation and simulation of crystallization of bulk zirconium-based metallic glasses

This article is devoted to the investigation and simulation of the crystallization kinetics of zirconium-based bulk metallic glasses under heating with a constant rate, as well as under isothermal holding at an elevated temperature. The investigation into crystallization kinetics with time can provide a deeper under-standing of the crystallization mechanism of bulk metallic glasses and promote the scientifically substantiated selection of thermal treatment modes to form the desired structure and properties of composite materials on their basis.     

Measurements of the bulk velocity during solidification of metallic alloys

The ultrasound Doppler velocimetry (UDV) was applied to measure the bulk flow in a Sn-15 wt pct Pb alloy solidified directionally from a water-cooled copper chill. The flow is driven by a rotating magnetic field (RMF). Our results show that the velocity profiles undergo distinct modifications during solidification indicating the occurrence of more sophisticated flow patterns as known from the isothermal case. Furthermore, the UDV data allow an assessment of the current position of the dendritic solidification front. This research is supported by the Deutsche Forschungsgemeinschaft (DFG) in the form of the SFB 609 “Electromagnetic Flow Control in Metallurgy, Crystal Growth and Electrochemistry.” This support is gratefully acknowledged by the authors.     

Modelling and simulation of twin-roll casting of bulk metallic glasses

As an economic and direct route to continuous thin strip production from the melt, twin roll casting (TRC) has been established as an effective process for aluminium alloys. Its adaptation to casting of bulk amorphous alloy strip necessitates matching of the thermal and mechanical behaviour of the cooling multi-component melt to the requirements (especially cooling rate, and strip exit temperature and thermal gradient) of vitrification. Using a dedicated control volume numerical model of TRC, simulation of the casting of 2 mm thick Vit 1 (Zr_41.2Ti_13.8Cu_12.5Ni₁₀Be_22.5) alloy strip shows that the acceptable casting speeds are in the range 2.5 to 3.5 cm/s. The effects of varying strip thickness and strip-roll heat transfer coefficient (HTC) on this casting window are assessed. The differences between modelling of conventional alloy solidification and metallic glass formation are presented.     

Strength of diamond-containing composite material based on tungsten carbide hard alloy

Translated from Poroshkovaya Metallurgiya, No. 9(333), pp. 64–68, August, 1990.     

活化烧结对金刚石增强型硬质合金复合齿性能的影响

在金刚石增强型硬质合金复合齿基体中球磨添加不同量红磷，比较相应的金刚石增强型硬质合金基体的性能，确定添加(质量分数)0．3％P的复合齿基体性能最好；同时采用化学镀Ni-P合金添加P结合球磨添加0．1％P的方式，其超硬复合齿基体力学性能及复合齿的磨耗比、抗冲击功远远优于单纯球磨添加0．3％P方式超硬复合齿的性能。说明为了实现金刚石增强型硬质合金复合齿的活化烧结方式，磷元素最优的添加方式是化学镀结合球磨的添加方式。     

In-situ microfracture observation of strip-cast Zr-Ti-Cu-Ni-Be bulk metallic glass alloys

In this study, Zr-Ti-Cu-Ni-Be bulk metallic glass (BMG) alloys containing a small amount of crystalline phase particles were fabricated by strip casting, and their improvement of mechanical properties and fracture toughness was explained by direct observation of the microfracture process. The compressive and fracture toughness test results indicated that strength, strain to failure, and fracture toughness of the strip-cast BMG alloy containing coarse crystalline particles were higher than those of the as-cast monolithic BMG alloy or the strip-cast BMG alloy containing fine crystalline particles. From in-situ microfracture observations, the improvement of overall mechanical properties of the strip-cast BMG alloy containing coarse crystalline particles could be interpreted by taking consideration of both the existence of coarse crystalline particles and the role of the particles to block crack propagation and to form multiple shear bands. Such property improvement suggests new applicability of the strip-cast BMG alloys containing coarse crystalline particles, which can work as toughening and strengthening reinforcements, to structures and components requiring excellent mechanical properties.     

Metastability and thermophysical properties of metallic bulk glass forming alloys

The absence of crystallization over a wide time/temperature window can be used to produce bulk metallic glass by relatively slow cooling of the melt. For a number of alloys, including several multicomponent Zr-based alloys, the relevant thermodynamic and thermomechanical properties of the metastable glassy and undercooled liquid states have been measured below and above the glass transition temperature. These measurements include specific heat, viscosity, volume, and elastic properties as a function of temperature. As a result, it becomes obvious that the maximum undercooling for these alloys is given by an isentropic condition before an enthalpic or isochoric instability is reached. Alternatively, these glasses can also be produced by mechanical alloying, thus replacing the thermal disorder by static disorder and resulting in the same thermodynamic glass state. During heating through the undercooled liquid, a nanoscale phase separation occurs for most glasses as a precursor of crystallization. This article is based on a presentation made in the “Structure and Properties of Bulk Amorphous Alloys” Symposium as part of the 1997 Annual Meeting of TMS at Orlando, Florida, February 10–11, 1997, under the auspices of the TMS-EMPMD/SMD Alloy Phases and MDMD Solidification Committees, the ASM-MSD Thermodynamics and Phase Equilibria, and Atomic Transport Committees, and sponsorship by the Lawrence Livermore National Laboratory and the Los Alamos National Laboratory.