ZrCuAlNb大块非晶合金的热稳定性

利用电弧炉+铜模吸铸的方法制备了Zr46.3Cu43.4Al8.3Nb2(at%)块体非晶合金。利用示差扫描量热仪(DSC)研究了合金的热稳定性,利用Kissinger方法计算了其特征温度表观激活能,利用Doyle方法计算了其局域激活能。结果表明,Zr46.3Cu43.4Al8.3Nb2块体非晶合金具有良好的热稳定性。各特征温度的表观激活能分别为:玻璃转变激活能(Eg)为302.7 kJ/mol、晶化起始激活能(Ex)为445.853 kJ/mol、晶化峰值激活能(Ep)为389.20 kJ/mol。局域激活能随着晶化体积分数的增加而显著减小。     

Hydrogen damage and delayed fracture in bulk metallic glass

Initiation, propagation, arresting and breaking of hydrogen blistering and hydrogen-induced delayed fracture (HIDF) under sustained load in a bulk metallic glass of Zr_41.2Ti_13.8Ni₁₀Cu_12.5Be_22.5 have been investigated. Results show that when the current density, i, is smaller than 20 mA/cm² corresponding to total hydrogen concentration of 3310 wppm, there are no hydrogen blistering and microcrack on the surface of the specimen without loading, but HIDF under sustained load can occur, and the threshold stress intensity factor for a single edge notched sample, K_IH, is 0.63 times of the notched toughness, K_Q, which is 62.2 MPa m^1/2. When i is equal to or larger than 20 mA/cm², hydrogen blistering or blistering plus microcrack appears on the surface of specimen without loading, as well as K_IH is 0.26 times of K_Q and independent upon i. The relative losses of the notched toughness induced by both atomic hydrogen and the blistering are all 37%. The critical pressure necessary for a stable blister formation, P_i, is 3.6 GPa, and that for cracking of the blister, P_C, is 3.9 GPa. The blister cracking will arrest after propagating for 20-30 μm, and the arrested crack will propagate again because of entering of hydrogen atoms. At last, the blister with cracking will break and leave local cleavage fracture surface with arrested lines on the sample surface without loading.     

Plasticity and structural instability in a bulk metallic glass deformed in the supercooled liquid region

The deformation behavior of a bulk amorphous Zr–10Al–5Ti–17.9Cu–14.6Ni alloy was characterized in the supercooled liquid region. The alloy was observed to exhibit Newtonian behavior at low strain rates but to become non-Newtonian at high strain rates. Structures of the amorphous material, both before and after deformation, were examined using X-ray diffraction and high-resolution electron microscopy. Experimental results showed the presence of nanocrystallites in the deformed samples, suggesting that the non-Newtonian behavior was associated with the concurrent crystallization of the amorphous structure during deformation; that is, a mixed crystalline-plus-amorphous structure was being tested. A mechanistic model based upon structural evolution has been developed to interpret the observed non-Newtonian behavior.     

Enhanced thermal stability by pre-charged hydrogen of a Zr-based bulk metallic glass

Tb³⁺/Dy³⁺ and Eu³⁺/Sm³⁺ doped rare-earth borate glasses have been synthesized and characterized. Under UV excitation, Dy³⁺, Tb³⁺, Sm³⁺ and Eu³⁺ emit intense yellowish white, green, reddish orange and red lights, respectively. In Tb³⁺/Dy³⁺ co-doped glasses, the enhancement of Tb³⁺ green emission is observed, and the sensitization is related to the efficient energy transfer from Dy³⁺ to Tb³⁺. In Eu³⁺/Sm³⁺ co-doped glasses, the excitation wavelength range of Eu³⁺ emission is broadened owing to the energy transfer from Sm³⁺ to Eu³⁺. This broadening makes the Ar⁺ 488 nm wavelength laser a powerful excitation source for Eu³⁺ fluorescence. The rare-earth doped glasses with various visible emissions are useful for developing new color light sources, fluorescent display devices, UV-sensor and tunable visible lasers.     

Fracture surface morphology of compressed bulk metallic glass-matrix-composites and bulk metallic glass

The fracture morphology of Zr-based bulk metallic glass-matrix-composites (BMGCs) and Cu-based bulk metallic glass (BMG) after compression testing has been studied. The quasi-static compression fracture surface displays a mixture of three different distinct patterns: vein-like, smooth featureless and river-like features. The last one corresponds to the morphology known from tensile tests of BMGs. Moreover, randomly distributed transversal steps on the fracture plane are also present. This is in contrast to previous studies where a characteristic vein-like pattern is considered a unique feature of the fracture of BMGs under quasi-static uniaxial compression. The presence of different fracture features indicates that the development of the fracture plane occurs in a stepwise mode.     

Tribological studies of a Zr-based bulk metallic glass

In the present study, the tribological behavior of a Zr_52.5Cu_17.9Ni_14.6Ti₅Al₁₀ bulk metallic glass (BMG) was investigated using pin-on-disk sliding measurements under an argon atmosphere, rubbing against a type 303 stainless steel counterface. The tested pins and disk were examined using X-ray diffractometry, optical microscopy, profilometry, scanning electron microscopy and transmission electron microscopy. The results showed that the wear of the BMG pins was substantially larger compared with previous tests performed against a zirconia counterface. Strain softening was found in the near-surface region of the glassy pin due to the highly localized shearing. Frictional heating contributed to the occurrence of viscous flow and material transfer on the worn surface of the wear pin and the disk, respectively. Thus, the pin exhibited a severe adhesive-dominated sliding wear.     

Boss formability of a Zr-based bulk metallic glass

Macroscopic solid-to-solid hot formability of a Zr-based bulk metallic glass has been investigated in this study by applying a boss forming process within supercooled liquid region (SLR). The morphology and microstructures after boss forming were first examined by using an optical microscopy (OM), a field emission scanning electron microscope (FE-SEM), X-ray diffraction (XRD), and transmission electron microscope (TEM). The variation of thermal properties before and after boss forming was also analyzed by using a differential scanning calorimeter (DSC). The glass transition temperature, T_g and the crystallization onset temperature, T_{x, onset} were found to decrease with increasing test time and temperature. Macroscopic extrusion formability was found to match well with the results predicted through a processing map based on a dynamic materials model (DMM). The specimens were found to form well under the conditions of high temperature and slow punch jig speed. A FEM simulation study has also been carried out to understand the causes of piping problem. A sound boss without a pipe could be formed by reducing the flow rate difference in the contact and the core sites.     

Preparation, thermal stability, and magnetic properties of Fe---Co---Zr---Mo---W---B bulk metallic glass

A bulk metallic glass (BMG) cylinder of Fe₆₀Co₈Zr₁₀Mo₅W₂B₁₅ with a diameter of 1.5 mm was prepared by copper mould casting of industrial raw materials. The amorphous state and the crystallization behavior were investigated by X-ray diffraction (XRD). The thermal stability parameters, such as glass transition temperature (T_g), crystallization temperature (T_x), supercooled liquid region (ΔT_x) between T_g and T_x, and reduced glass transition temperature T_rg (T_g/T_m) were measured by differential scanning calorimetry (DSC) to be 891, 950, 59 K, and 0.62, respectively. The crystallization process took place through a single stage, and involved crystallization of the phases -Fe, ZrFe₂, Fe₃B, MoB₂, Mo₂FeB₂, and an unknown phase, as determined by X-ray analysis of the sample annealed for 1.5 ks at 1023 K, 50 K above the DSC peak temperature of crystallization. Mössbauer spectroscopy was studied for this alloy. The spectra exhibit a broadened and asymmetric doublet-like structure that indicated paramagnetic behavior and a fully amorphous structure. -Fe was found in the amorphous matrix for a cylinder with a diameter of 2.5 mm. The success of synthesis of the Fe-based bulk metallic glass from industrial materials is important for the future progress in research and practical application of new bulk metallic glasses.     

Crystallization of Mg-based bulk metallic glass

1 Introduction Since INOUE et al[1,2] reported that amorphousalloy with the composition of Mg65Cu25Y10 could beproduced with thickness up to 4 mm by conventionamold casting technique, Mg-based bulk metallic glasses(BMGs) have been proposed as a new kind …     

Shear punch tests for a bulk metallic glass

A shear punch test technique was used for characterization of the mechanical properties of Zr–5Ti–17.9Cu–14.6Ni–10Al bulk metallic glass. The ultimate shear stress values matched very closely with values derived from uniaxial compression tests reported in the literature. This is consistent with a lack of pressure sensitivity in compression reported for this particular metallic glass. Deformation response was strain rate insensitive up to a critical rate, beyond which softening occurred. The latter was attributed to thermal heating effects.     

块体非晶合金的应用与连接

综述了块体非晶合金在国内外的应用现状、前景,以及目前对块体非晶合金连接的研究现状.报导了采用液相焊接方法如爆炸焊、电子束焊、激光焊等和超冷液相焊接方法如摩擦焊成功实现同质、异质块体非晶合金以及块体非晶合金与晶态合金的连接.分析了实现液相焊接块体非晶合金的关键是采用高能量密度的焊接方法以及块体非晶合金具有强的玻璃形成能力;实现超冷液相焊接块体非晶合金的关键在于块体非晶合金处于过冷液态的热稳定性、超塑性和粘滞性.     

Forming of bulk metallic glass microcomponents

The present article considers forward extrusion, closed-die forging and backward extrusion processes for fabrication of individual microcomponents from two bulk metallic glass (BMG) compositions: Mg₆₀Cu₃₀Y₁₀ and Zr₄₄Cu₄₀Ag₈Al₈. Two types of tooling were used in the present work: relatively massive die sets characteristic of cold forming operations for crystalline metals and lightweight die sets adapted to the special characteristics of BMGs. In addition to demonstrating that microcomponents of several geometries can be readily fabricated from BMGs, rheological properties are combined with crystallization kinetics to formulate a generally applicable method that can guide selection of optimal forming parameters. Finally, the use of particulate-based lubricants for BMG forming is shown to result in individual lubricant particles becoming mechanically locked into the BMG surface.     

Tribological behaviors of Zr-based bulk metallic glass versus Zr-based bulk metallic glass under relative heavy loads

As a novel engineering material, bulk metallic glass (BMG) has received much attention. However, the knowledge concerning the tribological behavior of BMG versus BMG under relatively heavy loads is still insufficient. In this study, Zr₄₁Ti₁₄Cu_12.5Ni₁₀Be_22.5 metallic glass pins and discs were prepared by copper-mold suction casting. The dry sliding friction and the wear characteristics of the as-cast Zr-based BMG versus Zr-based BMG were tested under loads of 100, 125 and 150 N, respectively, using a pin-on-disc tribological apparatus at room temperature. The worn surfaces were studied by scanning electron microscopy in order to identify the wear mechanisms. The results showed that both the coefficient of friction and the wear rate increased with both the normal load and the rotational sliding velocity. X-ray diffraction patterns recorded after the tribological experiments indicated that no sliding-induced crystallization occurred. Transmission electron microscopy was also used to confirm the amorphous of the BMGs after sliding tests. In addition, the wear mechanisms changed with the experimental conditions. For a normal load of 100 N, the main mechanisms were abrasive wear, slight grooves and micro-cracks. For higher loads, adhesive wear was predominant, accompanied by abrasive wear and deeper grooves and more micro-cracks. When the rotational sliding velocity was increased, the dominant wear changed from slight grooves to viscous flow and adhesive wear.     

A Dy-based bulk metallic glass with high thermal stability and excellent magnetocaloric properties

A new heavy rare-earth-based Dy₃₆Ho₂₀Al₂₄Co₂₀ bulk metallic glass (BMG) with high thermal stability and excellent magnetocaloric properties has been prepared by a copper mold casting. Compared with the other known rare-earth-based BMGs, this BMG alloy possess higher glass transition temperature and crystallization temperature, larger effective activation energy for glass transition and crystallization. Under a modest magnetic field, this BMG alloy exhibits a comparable or even larger magnetocaloric effect than that the previously reported RE-based BMGs and crystalline compounds. The high thermal stability and the excellent magnetocaloric effect together with other merits of the BMGs make this BMG alloy suitable candidate for use as magnetic refrigerant in a temperature range below 50 K.