Manufacture of amorphous alloy ribbons

Amorphous alloys are prepared in continuous ribbon form by rapid quenching directly from the melt. In particular, the process of chill block melt-spinning involves the continuous impingement of molten alloy against a rapidly moving substrate surface. Principles of chill block melt-spinning are presented with regard to the formation of continuous, rapidly-quenched amorphous alloy ribbon. The effects of numerous process variables on sample geometry and physical properties are examined through experimental results obtained by the author and by other researchers. Principles of narrow ribbon manufacture are extended to describe means of fabricating wide ribbon. Manufacturing problems unique to extended runs and potential solutions are cited. Effects of process parameters on magnetic and physical properties of as-cast samples are discussed.     

Nitrogen as an alloying element in some metallic glasses

Glassy alloy ribbons containing nitrogen as an alloying element have been produced by chill block melt-spinning master alloys which were specially pre-melted for enhanced nitrogen content. Alloying substantial amounts of Cr, a potent nitride former, has been found to greatly increase the amount of nitrogen in solution. In turn, thermal stability of the Cr-bearing metallic glasses has been found to increase as much as 31 K with only a 0.5 at% nitrogen addition. No analogous changes in glassy alloy embrittlement or Curie temperature have been observed. However, although weak, the response of Curie temperature to annealing in the Cr-bearing metallic glasses was found to be affected by the presence of nitrogen. Thus, nitrogen appears to be a viable alloying element in some metallic glasses and may have a potent effect on some properties.     

Effects of elemental additions and superheat on melt surface tension and metallic glass embrittlement

Additions of antimony, selenium, tellurium and some other alloying elements to iron-nickel base alloys have been investigated with regard to effects on melt surface tension and resultant metallic glass formation and characteristics. Surface tension of the molten alloys has been measured as a function of composition and melt temperature using a variation of the maximum bubble pressure method. The density of molten Fe₄₀Ni₄₀B₂₀ alloy has been measured as a function of temperature. Attempts to chill block melt-spin and alloys of the present investigation into metallic glass ribbons were largely successful. A few compositions were partially crystalline in the as-cast state and even fewer were not castable at all. The amorphous structure of ribbons made was assessed by X-ray diffraction, differential scanning calorimetry, and embrittlement temperatures for one hour anneals. A correlation has been established between changes in melt surface tension and metallic glass embrittlement temperature with the addition of surface active elements.     

Martensitic Transformation and Magnetic-Field-Induced Strain in Magnetic Shape Memory Alloy NiMnGa Melt-Spun Ribbon

A magnetic shape memory alloy with nonstoichiometric Ni50Mn27Ga23 was prepared by using melt-spinning technology. The martensitic transformation and the magnetic-field-induced strain (MFIS) of the polycrystalline melt-spun ribbon were investigated. The experimental results showed that the melt-spun ribbons underwent thermal-elastic martensitic transformation and reverse transformation in cooling and heating process and exhibited typical thermo-elastic shape memory effect. However the start temperature for martensitic transformation decreased from 286 K for as-cast alloy to 254 K for as-quenched ribbon and Curie temperature remains approximately constant. A particular internal stress induced by melt-spinning resulted in the formation of a texture structure in the ribbons, which made the ribbons obtain larger martensitic transformation strain and MFIS. The internal stress was released substantially after annealing, which resulted in a decrease of MFIS of the ribbons.     

Digital photocalorimetric measurements of cooling rates in chill block melt spinning of MmNiCoMnAl5 hydride forming alloy

Abstract

A digital photocalorimetric technique has been developed and applied to obtain in situ temperature measurements from chill block melt spun ribbons of a MmNiCoMnAl5 hydride forming alloy. Compared with conventional colour transmission temperature measurements, this technique offers special advantages in terms of high resolutional and positional accuracy, which under the prevailing experimental conditions are found to be +-29 K and +-0.1 mm respectively. Moreover, it is shown that the cooling rate in the solid state is approximately 2.5 times higher than observed during solidification, indicating that the solid ribbon stays in intimate contact with the wheel surface down to very low metal temperatures before the bond is broken. During this contact period, the cooling regime shifts from near ideal in the melt puddle to near Newtonian towards the end, when heat transfer from the solid ribbon to the wheel becomes the rate controlling step.     

Effect of rapid solidification on giant magnetostriction in ferromagnetic shape memory iron-based alloys

Ferromagnetic shape memory Fe–29.6 at.% Pd alloy ribbons prepared by the rapid solidification, melt-spinning method, showed a giant magnetostriction of 830 microstrain when an external magnetic field of 7 kOe was applied nearly normal to the ribbon surface at room temperature. This ribbon’s magnetostriction was several times as large as conventional polycrystalline bulk’s one before rapid solidification. The magnetostriction in the rolling direction depended strongly on a direction of applied magnetic field. We considered that this phenomenon is caused by a rearrangement of activated martensite twin variants just below the austenite phase transformation temperature. We investigated their basic material properties, i.e. the dependencies of magnetostriction on temperature as well as on magnetic angular orientation to the surface, magnetic properties, crystal structure, surface texture morphology and shape memory effect of Fe–29.6 at.% Pd ribbon samples by comparing with conventional bulk sample. It can be concluded that the remarkable anisotropy of giant magnetostriction of ribbon sample is caused by the unique uniaxial-oriented fine grain structure formed by the melt-spinning method. In addition, we confirmed the possibility of rapidly solidified Fe–Pt ribbon as a new kind of iron-based ferromagnetic shape memory alloys for magnetostrictive material.     

The microstructure and mechanical properties of Bi(Pb)-Sr-Ca-Cu-Ag metallic precursor ribbons produced by the melt-spinning process

Metallic precursor ribbons of Bi-Pb-Sr-Ca-Cu with nominal compositions of 1.4-0.6-2-3-4, respectively, were made by vacuum induction melting followed by melt-spinning. Silver at the level of 12–81 vol% was added to produce precursor-Ag alloy ribbons. These ribbons were subjected to a controlled atmosphere oxidation and annealing to produce superconducting oxide/Ag microcomposites. All of the alloys with up to 73 vol% Ag can be processed into superconducting ribbons with zero resistance atT=104–110 K and a critical current density of 200–600 A cm⁻² at 77 K in zero field. The relationship of the Ag content, melt-spinning processes, microstructure and mechanical properties of the metallic precursor ribbons were studied by microhardness tests, bending tests, scanning electron microscopy and electron probe microanalysis. The maximum bending strain of the metallic precursor ribbons was found to increase from 0.3–1.7% as the silver content increased from 12–81 vol%, while the ribbon hardness was found first to increase with silver content increasing from 12–62 vol%, then to decrease with further increases in silver content. The mechanical properties were also strongly affected by the melt-spinning processes,i.e. by the ejection pressure applied to the melt and wheel surface speed. The best bending strain for the metallic precursors with 52 vol% Ag achieved so far is ∼0.85%, which was obtained by using an ejection pressure of 69 kPa and a wheel speed of 9.5 m s⁻¹. The mechanical properties of the precursor ribbons is critically important for producing superconducting coils and long wires, which were made by first winding the metallic ribbons on MgO spools, followed by suitable oxidation and annealing.     

Effect of rapid solidification on giant magnetostriction in ferromagnetic shape memory iron-based alloys

Ferromagnetic shape memory Fe–29.6 at.% Pd alloy ribbons prepared by the rapid solidification, melt-spinning method, showed a giant magnetostriction of 830 microstrain when an external magnetic field of 7 kOe was applied nearly normal to the ribbon surface at room temperature. This ribbon's magnetostriction was several times as large as conventional polycrystalline bulk's one before rapid solidification. The magnetostriction in the rolling direction depended strongly on a direction of applied magnetic field. We considered that this phenomenon is caused by a rearrangement of activated martensite twin variants just below the austenite phase transformation temperature. We investigated their basic material properties, i.e. the dependencies of magnetostriction on temperature as well as on magnetic angular orientation to the surface, magnetic properties, crystal structure, surface texture morphology and shape memory effect of Fe–29.6 at.% Pd ribbon samples by comparing with conventional bulk sample. It can be concluded that the remarkable anisotropy of giant magnetostriction of ribbon sample is caused by the unique uniaxial-oriented fine grain structure formed by the melt-spinning method. In addition, we confirmed the possibility of rapidly solidified Fe–Pt ribbon as a new kind of iron-based ferromagnetic shape memory alloys for magnetostrictive material.     

Structural inhomogeneities of AlSi alloys rapidly quenched from the melt

Hypo- and hyper-eutectic AlSi alloys were rapidly quenched from the melt using the melt-spinning technique with two spinning velocities. Structural differences between the wheel (chill) and upper sides of the melt-spun ribbons were investigated by optical and scanning electron microscopy and X-ray diffraction methods (texture- and size-strain analyses). The Al-rich phase of the hypo-eutectic alloys was textured. The textures observed from both sides of the ribbons were different; in neither case was it of fibre type. For the larger spinning velocity applied, the structural imperfection of the wheel side was larger than that of the upper side for both the Al-rich and the Si-rich phases.     

Morphological characteristic of the conventional and melt-spun Al-10Ni-5.6Cu (in wt.%) alloy

The Al-10Ni-5.6Cu alloy was prepared by conventional casting and further processed melt-spinning technique. The resulting conventional cast and melt-spun ribbons were characterized using X-ray diffraction, optical microscopy, scanning electron microscopy together with energy dispersive spectroscopy, differential scanning calorimetry and microhardness techniques. The X-ray diffraction analysis indicated that ingot samples were α-Al, intermetallic Al₃Ni and Al₂Cu phases. The optical microscopy and scanning electron microscopy results show that the microstructures of rapidly solidified ribbons are clearly different from their ingot alloy. Al-10Ni-5.6Cu ribbons reveal a very fine cellular structure with intermetallic Al₃Ni particles. Moreover, at high solidification rates the melt-spun ribbons have a polygonal structure dispersed in a supersaturated aluminum matrix. The differential scanning calorimetry measurements revealed that exothermic reaction was between 290 °C and 440 °C which are more pronounced in the ternary Al-10Ni-5.6Cu alloy.     

Corrosion behaviors of amorphous and nanocrystalline Fe-based alloys in NaCl solution

Amorphous Fe(73.5)Si(13.5)B9Nb3Cu1 alloy was prepared by the chill block melt-spinning process and nanocrystalline Fe(73.5)Si(13.5)B9Nb3Cu1 alloy was obtained by annealing. The crystallization behaviors were analysed by DSC, XRD and TEM. The electrochemical corrosion behaviors in different annealed states were performed by linear polarization method and electrochemical impedance spectroscopy in 3.5% NaCl solution. The results show that the crystallization of amorphous alloy occurs in the two steps. Some nanometer crystals appear when annealing in 550 degrees C and 600 degrees C, respectively with grain size 13 nm and 15 nm. The nanocrystalline alloy has a tendency to passivation and lower anodic current density than amorphous alloy. It indicates that nanocrystalline alloy has a higher corrosion resistance. Amorphous Fe(73.5)Si(13.5)B9Nb3Cu1 alloy consisted of only single semi-circle. When the alloy was annealed in 600 degrees C, its EIS consisted of two time constants, i.e., high frequency and low frequency capacitive loops. The charge transfer reaction resistances increases as annealing temperature rises.     

Heterostructured crystallization mechanism and its effect on enlarging the processing window of Fe-based nanocrystalline alloys

The harsh melt-spinning and annealing processes of high saturation magnetization nanocrystalline softmagnetic alloys are the biggest obstacles for their industrialization. Here, we proposed a novel strategy to enlarge the processing window by annealing the partially crystallized precursor ribbons via a heterostructured crystallization process. The heterostructured evolution of Fe_84.75Si₂B₉P_3C0.5Cu_0.75(at.%)alloy ribbons with different spinning rate were studied in detail, to demonstrate the gradient nucleation and grain refinement mechanisms. The nanocrystalline alloys made with industrially acceptable spinning rate of 25-30 m/s and normal annealing process exhibit excellent magnetic properties and fine nanostructure. The small quenched-in crystals/clusters in the free surface of the low spinning rate ribbons will not grow to coarse grains, because of the competitive grain growth and shielding effect of metalloid elements rich interlayer with a high stability. Avoiding the precipitation of quenched-in coarse grains in precursor ribbons is thus a new criterion for the composition and process design, which is more convenient than the former one with respect to the homogenous crystallization mechanism, and enable us to produce high performance nanocrystalline soft-magnetic alloys. This strategy is also suitable for improving the compositional adjustability, impurity tolerance, and enlarging the window of melt temperature,which is an important reference for the future development of composition and process.     

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.     

含硅合金熔体对TiAl基合金表面改性的研究

使用含硅合金熔体对TiAl基合金进行了表面渗硅处理，渗硅处理温度范围是：913－1053K，实施发现，TiAl基合金与Al-Si熔体之间发生了界面反应，界面生成以Si,Ti,Al三元素为主的灰白色基体和条状，小块状黑色相。表面处理后样品经1173K／100h高温氧化后，表层形成了Al2O3,SiO2等致密的氧化膜，并保留有稳定的Si-Ti-Al相，因而改善了表面氧化层结构，大大增强了TiAl基合金的高温抗氧化能力。     

Structure and properties of a Pb-Ca-Sn battery alloy crystallized under nonequilibrium conditions

We have studied the properties of a Pb-Ca-Sn alloy for the positive current collector of lead-acid storage batteries, prepared by an existing industrial process and an experimental technique that involves melt jet quenching from the liquid state (QLS). The QLS process ensures good stability of the properties and structure of the alloy at elevated temperatures. Doping with trace levels of barium is shown to influence the properties of QLS ribbons.     

Microstructure — cooling rate correlations in melt-spun alloys

Photocalorimetric techniques have been used to measure top surface temperatures during melt spinning of Ni-Al and 316L stainless steel ribbons, in order to investigate the effect of cooling rate on the melt-spun alloy microstructures. Cooling conditions during melt-spinning are found to be near-Newtonian, with mean cooling rates, heat transfer coefficients and Nusselt numbers in the range 4×10⁴ to 5×10⁵ K sec^–1, 5×10⁴ to 3× 10⁵ Wm^–2K^–1 and 0.07 to 0.22, respectively, for wheel speeds in the range 4 to 36 m sec^–1. The cooling rate during melt-spinning is directly proportional to the wheel speed and inversely proportional to the square of the ribbon thickness. Melt-spun Ni-Al and 316L stainless steel ribbons exhibit a columnar through-thickness solidification microstructure, with a segregation-free region adjacent to the wheel surface. Solidification takes place by heterogeneous nucleation of the undercooled liquid on the wheel surface, followed by partitionless solidification during recalescence, and finally cellular breakdown and segregated solidification. The columnar grain size decreases and the fractional segregation-free thickness increases with increasing wheel speed and cooling rate, indicating that the nucleation undercooling in the liquid is proportional to the cooling rate.     

Grain-size gradient NiTi ribbons with multiple-step shape transition prepared by melt-spinning

A grain-size gradient NiTi ribbon with multiple-step shape transition was papered by means of melt-spinning.The ribbons contain coarse and fine grains in the free surface side and copper roller surface side,respectively.The grain-size gradient microstructure induces a two-stage phase transformation behavior in the ribbons during heating or cooling.After tensile deformation pre-treatment,the ribbons exhibit a back-and-forth shape change (shape A→ B-A) upon a single heating or cooling process,resulting from the sequential phase transformation through the thickness of the ribbon as dictated by gradient grain size.The activating performance of the ribbons,i.e.shape transition amplitude and speed,can be customized by controlling the pre-deformation strain.This work offers a new opportunity for innovative designs to reach a novel shape memory behavior in NiTi alloys conveniently and efficiently.     

Surface composition of scratched and sputtered Al–Cu ribbons prepared by melt-spinning

In this study, aluminium–copper ribbons of various compositions are prepared by melt-spinning and analysed by Auger electron spectroscopy. Rapidly solidified ribbons usually show a microcrystalline or featureless microstructure, especially in zones located near the surface solidified in direct contact with the rotating wheel. The composition of that surface of the ribbons was analysed by Auger electron spectroscopy. These measurements were performed in both scratched and also ion sputtered zones. After sputtering of the ribbon surface with argon ions, a surface enrichment in copper was observed. However scratching the surface of the ribbons produced a surface composition nearly identical to the bulk. The interest of rapidly solidified alloys in calibration applications is discussed.     

Heat transfer characteristics in centrifuge melt-spinning

Centrifuge melt-spinning (CMS) is a new technique for the production of rapidly solidified metallic ribbons. In CMS, centrifugal forces are used twice: to eject the liquid melt on to the quenching substrate (a copper rim) by rotation of the casting crucible, and to ensure prolonged contact of the solidifying ribbon with the heat extraction sink by making the quenching rim rotate too, in the opposite direction. The heat transport in CMS has a Newtonian nature, as it can be considered as a constant-resistance heat transfer process. Calculated heat transfer coefficients h range between (1.55 to 4.30)×10^–6 W m^–2 sec^–1, a half to one order of magnitude higher than for conventional melt-spinning. Increasing the ejection pressure from 1.8 to 269 kPa causes the apparent heat transfer coefficient to increase by a factor of three. Conversely to conventional melt-spinning, two additional phenomena contribute to the heat transfer characteristics in CMS at high extraction velocities: forced convection and mechanical dragging of the melt. The overall effect is a net improvement of the heat transfer ability in CMS as compared to conventional melt-spinning.     

Effects of rare earth additions on structures and properties of rapidly solidified copper alloys

Abstract

Copper based Cu–RE alloys (where RE represents lanthanum, neodymium, or samarium) with alloying content up to 16 wt-% were prepared by chill block melt spinning into ribbons of thickness between 40 and 100 μm. The melt spun ribbons were heat treated isochronally for 2 h at 300, 400, 500, 600, 700, and 800°C, respectively. The melt spun and heat treated ribbons were tested for microhardness and resistivity and were characterised by optical and transmission electron microscopy (TEM) and X-ray diffractometry (XRD). Microstructures were of the typical zone B type for Cu–1RE and Cu–3RE ribbons and of the zone B/zone A type for Cu–5RE, Cu–8RE, and Cu–12RE ribbons. Only microstructures of the zone A type were found in Cu–15La ribbons. The metastable extended solid solubilities of the rare earth elements were evaluated by measurements of the lattice parameters of the supersaturated solid solutions and significant extension from the equilibrium solid solubility was found for all three alloys. The secondary phase was identified by TEM and XRD as Cu₆RE for all ribbons except Cu–15La ribbons in which metastable Cu₅La and Cu₁₃La phases were also found. Observations using TEM and XRD also showed a reduction in the α-Cu grain size of the as spun ribbons with increasing alloying content, producing nanosized α-Cu grains on the chill side of the ribbons. Heat treatment of the ribbons at 400°C for 2 h produced no significant coarsening of α-Cu grains as the size of these grains was still in the nanometer region. Both α-Cu and Cu₆RE grains coarsened as a result of heat treatment for 2 h at temperatures of 600°C and above for all the alloys.