Rapid quenching by the Taylor wire technique

The Taylor method for obtaining fine wires has been used to investigate glass formation at high cooling rates. The rates of 10³ to 10⁵ K sec^–1 obtained by this process lie between those associated with splat cooling and bulk quenching methods. The formation of novel oxide and sulphate glasses is used to both illustrate the scope of the Taylor technique and to emphasize its major disadvantage — contamination of the core material by the glass sheath.     

Fatigue and fracture properties of thin metallic foils

Metallic thin foils are essential structural parts in microsystems, which may be subjected to fatigue loading caused by thermal fluctuations and mechanical vibrations influencing their reliability in numerous engineering applications. It is well known that the fatigue properties of bulk material cannot be adopted for small scaled structures. For a better understanding of the `size-effect' in the present investigation fatigue crack growth near threshold in the high cycle fatigue regime and associated fracture processes were studied. Free-standing rolled and electrodeposited Cu-, Mo- and Al foils of thickness from 20 m to 250 m in different conditions have been tested in a special experimental set up operating at R=–1 and a testing frequency of 20 kHz. At a given constant strain value the fatigue crack growth behaviour has been recorded accompanied by intermittent observation of the change of the dislocation structure in the vicinity of the growing crack by use of the electron channeling contrast imaging (ECCI)-technique in a scanning electron microscope (SEM). In a load shedding technique fatigue threshold stress intensity factor values have been derived and compared with data of bulk material. Typical crack growth features were detected depending on thickness and grain sizes of the foils. Various criteria (compliance, extent of plastic zones and plastic strain gradients) were selected for the explanation of this anomalous behaviour. Additionally fractomicrographs of uniaxial strained and fatigued foils have been studied to obtain further insight of the effect of dimensional constraint.     

Fatigue and fracture properties of thin metallic foils

Metallic thin foils are essential structural parts in microsystems,which may be subjected to fatigue loading caused by thermal fluctuations and mechanical vibrations influencing their reliability in numerous engineering applications. It is well known that the fatigue properties of bulk material cannot be adopted for small scaled structures. For a better understanding of the `size-effect' in the present investigation fatigue crack growth near threshold in the high cycle fatigue regime and associated fracture processes were studied. Free- standing rolled and electrodeposited Cu-, Mo- and Al foils of thickness from 20 m to 250 m in different conditions have been tested in a special experimental set up operating at R=–1 and a testing frequency of 20 kHz. At a given constant strain value the fatigue crack growth behaviour has been recorded accompanied by intermittent observation of the change of the dislocation structure in the vicinity of the growing crack by use of the electron channeling contrast imaging (ECCI)-technique in a scanning electron microscope (SEM). In a load shedding technique fatigue threshold stress intensity factor values have been derived and compared with data of bulk material. Typical crack growth features were detected depending on thickness and grain sizes of the foils. Various criteria (compliance, extent of plastic zones and plastic strain gradients) were selected for the explanation of this anomalous behaviour. Additionally fractomicrographs of uniaxial strained and fatigued foils have been studied to obtain further insight of the effect of dimensional constraint.     

Study on continuous casting of bulk metallic glass

Continuous casting method for massive production of steel, aluminum, copper or other crystalline alloy ingot is a very important industrial technology for its low energy consumption and high productivity. In this study, a new continuous casting method was developed for the massive production of bulk metallic glass ingot with centimeter-scale diameter without length limitation. An intermittent withdrawal procedure was practiced for continuous casting of bulk glassy alloy. The new developed continuous casting method can provide a cooling speed as high as that provided by the stationary mold casting method. A Zr-based glassy alloy rod with a diameter of about 10 mm and length of tens of centimeters was prepared by the continuous casting method for the first time.     

非晶合金与羟基磷灰石复合材料的研究

利用渗流铸造法制备了直径为6mm的vit106非晶合金与羟基磷灰石(HA)的复合材料,分别采用扫描电镜(SEM)、X射线衍射(XRD)分析了铸态合金的组织形貌和相组成.实验结果表明,铸态合金由非晶组织和HA组成,二者均匀分布,界面结合良好.力学性能实验表明,复合材料的压缩断裂强度为250MPa,最大塑性变形量达到了65%.与目前钛合舷金/20%(体积分数)HA复合材料相比,强度得到了提高;与块体非晶合金多孔材料相比,在相近的强度指标下,具有更高的塑性.由于HA与非晶合金都具有良好的生物相容性,因此这种复合材料在生物移植材料上具有一定应用前景.     

铸造工艺对锰钢锤头的组织及力学性能的影响

对传统铸造技术进行改进得到激振旋转综合作用铸造机。通过对激振旋转综合作用铸造机铸造出的铸造件试样进行显微组织、力学性能等分析,并探讨了激振旋转综合作用铸造机铸造机理。实验表明,利用激振旋转综合作用铸造机铸造出的铸造件晶粒细小且均匀、冲击韧性较好、硬度高、磨损性能较好,与传统铸造工艺相比,新的铸造技术可以延长铸造件使用寿命。     

烧结NdFeB铸造新工艺-薄片铸锭法

合金铸造技术是制备高性能烧结NdFeB磁体的关键工艺之一 .根据高性能磁体制造的设计要求 ,NdFeB合金铸锭微观组织应该具有柱状晶完整 ,没有α -Fe偏析相 ,富钕相弥散分布的特点 .本文比较了现有几种生产中常用的铸造方法 -平板铸造、柱状铸造、薄板铸造等得到的合金铸锭 ,然后介绍了目前国际上高性能NdFeB磁体制备的铸造新工艺 -薄片铸锭法 ,并通过扫描电镜观察了不同Nd含量薄片铸锭的组织结构 .最后展望了薄片铸锭在我国的应用前景 .     

Shear-accelerated crystallization of glass-forming metallic liquids in high-pressure die casting

As one of the most important forming technologies for industrial bulk metallic glass(BMG) parts with complex shapes, high-pressure die casting(HPDC) can fill a die cavity with a glass-forming metallic liquid in milliseconds. However, to our knowledge, the correlation between flow and crystallization behavior in the HPDC process has never been established. In this study, we report on the solidification behavior of Zr₅₅Cu₃₀Ni₅Al₁₀ glass forming liquid un...     

Estimation of the impurity levels in polyimide foils and the life-time of the foils irradiated by charged projectiles

The life-time of thin polyimide foils (prepared by in-situ polymerisation) in beams of 2.0 MeV helium ions and 1.5 MeV protons has been studied, irradiating foils with beams of different intensities. The impurity levels of the foils measured by PIXE and RBS were found to be in order of ng/cm².     

The curvature of amorphous metallic ribbons interpreted with a homogeneous quenching model

To explain the curvature of metallic ribbons obtained by quenching techniques, a model is developed in terms of isothermal planar layers, and a well defined solidification plane. Both the cooling rate and the thermal gradient are taken to be constant. Assuming that the ribbon can shrink but not bend during solidification, the resulting curvature is calculated, and is found to equal the thermal gradient multiplied by the linear thermal expansion coefficient. The obtained values compare well with the experimental data. The case of a non-constant thermal gradient is also considered, from a qualitative point of view.     

Development of gas electron multiplier foils with a laser etching technique

Fine-pitch gas electron multiplier (GEM) foils have been produced for cosmic X-ray polarimeters using a carbon dioxide laser etching technique. The finest hole pitch of the foil which can be produced repeatedly is and the smallest hole diameter is . The electron amplification factor was measured as a function of applied voltage. The behavior of the factor is almost the same as the -pitch standard foil fabricated by CERN. Our GEMs had no rate-dependent gain instability, which is expected of the GEMs having holes of good cylindrical geometry. The amplification factor of the foil in a mixture of 70% argon and 30% carbon dioxide reaches about 5000 without any micro-discharge at a voltage of 570 V between foil electrodes.     

Production of metallic glass ribbons by the chill-block melt-spinning technique in stabilized laboratory conditions

The results of extensive studies on the production of metallic glass ribbons by a single jet chill-block melt-spinning technique in laboratory conditions are summarized with emphasis on the data of practical importance. A device that stabilizes quenching conditions by surrounding the melt puddle with an atmosphere of He gas is described. The conditions for high stability are defined. The dependence of ribbon width and thickness on the volumetric flow rate, injection angle and substrate velocity are experimentally determined in such stabilized conditions. The cross-sectional geometric uniformity of the ribbons, analysed by Talysurf, is shown to be comparable with those produced by commercial laboratories, and/or within specially constructed chambers.     

Melt-spinning technique for preparation of metallic glasses

Rapid solidification of metallic melts at a rate ≳10⁵ °K/sec has gained considerable interest for casting non-equlibrium crystalline structures in general and metallic glasses in particular. Of the variety of techniques used for rapid solidification, melt-spinning and melt-extraction are widely used. This paper describes the design and development of a melt-spinning technique in our laboratory. Optimization of spinning parameters for smooth and continuous ribbons is discussed. Glassy ribhons of Cu-Zr and Pd-Ge alloys have been made under optimized conditions. A brief account of some of the structural and electronic properties of these glasses is illustrated.     

Pressure generated by the electric explosion of metal foils

We have measured the pressure generated by the electric explosion of various metal (Cu, Al, Fe, Ta, Ti, Pb, W, and brass) foils. The pressure amplitude as a function of the specific energy supplied to the exploding foil is well approximated by a linear dependence.     

Optimization of sol-gel technique for coating of metallic substrates by hydroxyapatite using the Taguchi method

In this study, the Taguchi method of design of experiment (DOE) was used to optimize the hydroxyapatite (HA) coatings on various metallic substrates deposited by sol-gel dip-coating technique. The experimental design consisted of five factors including substrate material (A), surface preparation of substrate (B), dipping/withdrawal speed (C), number of layers (D), and calcination temperature (E) with three levels of each factor. An orthogonal array of L₁₈ type with mixed levels of the control factors was utilized. The image processing of the micrographs of the coatings was conducted to determine the percentage of coated area (PCA). Chemical and phase composition of HA coatings were studied by XRD, FT-IR, SEM, and EDS techniques. The analysis of variance (ANOVA) indicated that the PCA of HA coatings was significantly affected by the calcination temperature. The optimum conditions from signal-to-noise (S/N) ratio analysis were A: pure Ti, B: polishing and etching for 24 h, C: 50 cm min^?1, D: 1, and E: 300 °C. In the confirmation experiment using the optimum conditions, the HA coating with high PCA of 98.5 % was obtained.     

Modelling and simulation of bulk metallic glass production process with suction casting

Abstract

An integrated model, which coupled nucleation and crystalline growth with the heat transfer process, is presented in the present paper. The temperature, temperature gradient, cooling rate and the crystalline fraction of Zr₆₅Al_7·5Cu_17·5Ni₁₀ in suction casting have been calculated with this model. The results show that the metallic glass can be obtained at the bottom and the radial boundary of the rod sample, and that the crystalline phase precipitates in the centre of the sample. The crystalline fraction reaches the highest value of 0·0128 in the centre of the sample. Comparatively lower nucleation rate, as well as the higher viscosity and the cooling rate account for the formation of the bulk metallic glass.