MATERIALS TRANSACTIONS
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ONLINE ISSN: 1347-5320
PRINT ISSN: 1345-9678

MATERIALS TRANSACTIONS Vol. 43 (2002), No. 2

  • High Purity Metals as Primary Calibration Materials for Elemental Analysis-Their Importance and Their Certification

    pp. 90-97

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    DOI:10.2320/matertrans.43.90

    The Bundesanstalt für Materialforschung und -prüfung, BAM (Federal Institute for Materials Research and Testing) continues to establish a system of primary reference materials to meet the demands of metrological traceability. The materials act as national standards in the field of elemental analysis. For all elements of the periodic table—excepting those that are gases or radioactive—two different kinds of reference materials are being certified. The substances are of very high purity and of defined stoichiometry. Pure elements and metals are used as far as possible. They are certified by determining the trace contents of most elements of the periodic table at very low levels using different trace element analysis methods. Recent application of these methods is described and examples of the certification of some pure metals (copper, iron and lead) are given.
  • Measurement of Oxygen and Nitrogen in High Purity Metals Used as National Standards for Elemental Analysis in Germany by Classical Carrier Gas Hot Extraction (HE) and HE after Activation with Photons

    pp. 98-100

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    DOI:10.2320/matertrans.43.98

    The special importance of the analysis of non-metals in high purity metals, which will serve as national standards for elemental analysis in Germany, is illustrated for oxygen and nitrogen. The typical range of the mass fraction of oxygen and nitrogen in these materials is below 10 \\microgram/g, often close to 1 \\microgram/g. The two methods applied at BAM for these measurements are classical carrier gas hot extraction (HE) and carrier gas hot extraction after activation with photons (PAA-HE). The approach, the methods and their advantages and limitations are discussed. Comparative results from the measurement of oxygen and nitrogen in Cu, Fe, Ga, Pb, Sn and W are presented.
  • Determination of Trace Amounts of Antimony and Boron in High-Purity Iron and Steel by Isotope Dilution/Inductively Coupled Plasma Mass Spectrometry

    pp. 101-104

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    DOI:10.2320/matertrans.43.101

    The highly sensitive and precise determination method for trace amounts of Sb and B in high-purity iron and steel has been established by the isotope dilution/Inductively coupled plasma mass spectrometry. For the determination of Sb, the iron matrix was separated by anion-exchange chromatography using Dowex I-X8 in hydrofluoric acid solution, and the isotope ratio (121Sb/123Sb) of the HNO3/H2O2 eluate was measured by ICP-MS . The isobaric interference of 123Te was corrected by subtracting the intensity of 123Te obtained by the relative intensity of 123Te and 125Te. For the determination of B, after the treatment of sulfuric acid-phosphoric acid fuming for the complete decomposition of boron nitride, B was separated by the anion-exchange chromatography using Amberlite IRA-743 at pH 8. The CyDTA was added to prevent the hydrolysis of iron. The isotope ratio (11B/10B) of the HCl eluate was measured by ICP-MS . By these methods, Sb and B in the range of \\microgram/g to sub-\\microgram/g could be determined with good precision. The limit of detection is 5.8 ng/g for Sb and 16 ng/g for B in steel.
  • Determination of Trace Element Quantities in Ultra High-Purity Iron by Spectrochemical Analysis after Chemical Separation

    pp. 105-110

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    DOI:10.2320/matertrans.43.105

    When trace elements in an ultra high-purity iron were determined, an analytical blank on a chemical analysis interfered with the determination of them. Similarly, the existence of major component in a sample interfered with the determination of trace elements. Therefore, in order to determine trace elements, it was examined that how to remove or decrease an analytical blank and how to separate trace elements from major component of a sample. For example, when C and S in an ultra high-purity iron were determined by combustion/infrared absorption method, an accelerator for combustion of an analytical sample contained C and S as blank. The accelerator consisted of a mixture of tungsten and tin. By heating it in ambient atmosphere, carbon blank was removed to be zero and sulfur blank was decreased to lower level. Consequently, when detection limit was defined as a value corresponding to 3 times of the standard deviation of blank value, it of carbon was infinitesimal and it of sulfur was 0.2 \\microgram g−1. Infinitesimal detection limit of carbon resulted from zero of the blank value of carbon. For that reason, detection limit of carbon was read as 0.01 \\microgram g−1 of carbon that was minimum scale for carbon on the analytical instrument, because the standard deviation of the blank value could not to be calculated. Independently, in order to determine trace Sn, Ag and Au in a high-purity iron, these elements were separated from major component (iron) by co-precipitation. Metallic Pd was used as co-precipitant. Metallic Pd had been rarely used as co-precipitant. The elements were determined by electrothermal atomic absorption spectrometry (ET-AAS). When these elements were detected by ET-AAS, the Pd was available as chemical modifier. By the separation, content 0.002–0.02 \\microgram g−1 of the elements was determined.
  • Chemical Form of Precipitate by Coprecipitation with Palladium for Separation of Trace Elements in High-Purity Metals

    pp. 111-115

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    DOI:10.2320/matertrans.43.111

    The reductive coprecipitation with palladium has been reported for separation and pre-concentration of trace elements in high-purity metals. In order to evaluate the chemical forms of precipitate by this method, precipitates from acidic solution containing Se, Te, Au, Ag and Pd (only or mixture) were produced under the condition of quantitative precipitation and measured by X-ray diffraction and electron diffraction. The precipitates from solutions including single element were confirmed by X-ray diffraction or electron diffraction. In measurement of Te and Pd precipitate, X-ray diffraction peaks of each element were increase as leaving time lengthens. In measurement of Se precipitate, no X-ray diffraction patterns were found independent of leaving time in the acidic solution. But when leaving time was 24 h, electron diffraction spots of Se were found. The precipitates from solutions including mutual elements (mixture of Pd and the other elements (Se, Te, Au and Ag)) were confirmed by X-ray diffraction or electron diffraction. In measurement of Pd–Au or Pd–Ag precipitate, these elements were respectively precipitated as elementary substance. However, in measurement of Pd–Se or Pd–Te precipitate, it was found that palladium selenide (PdxSey) or palladium telluride (PdxTey) was product.
  • Neutron Activation Analysis of Ultrahigh-Purity Ti-Al Alloys in Comparison with Glow-Discharge Mass Spectrometry

    pp. 116-120

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    DOI:10.2320/matertrans.43.116

    Neutron activation analysis (NAA) of ultrahigh-purity Ti–Al alloys has been performed without chemical treatments using normal and graphite-shielded irradiations. The Ti–Al alloys were made of ultrahigh-purity Ti (99.9999 mass% or 99.995 mass%) and Al (99.9998 mass%) by melting in ultrahigh vacuum with a copper-crucible induction-heating furnace. Concentrations and detection limits were evaluated for 35 impurity elements analyzed also by glow-discharge mass spectrometry. Seven impurity elements As, Cu, Ga, Na, Mn, Sb and W were detected by NAA. The sensitivities of NAA for Ga, In, Mn, Sb and Sc were better than those of glow-discharge mass spectrometry. Differences between the two analytical methods were mostly acceptable. The effectiveness of the graphite-shielded irradiation to suppress fast neutron reactions was clearly demonstrated.
  • Preparation of Highly Perfect Aluminum Crystal by Cold-Crucible Induction Melting in Ultra-high Vacuum

    pp. 121-124

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    DOI:10.2320/matertrans.43.121

    To make a highly perfect aluminum crystal, high purity aluminum was melted in ultra-high vacuum of 2×10−7 Pa for 2 h using a cold-crucible induction furnace. The surface of as-melted ingot had a metallic luster, and heavy oxidization on the surface was not recognized. In the ingot, a large cylindrical-single crystal of diameter 60 mm and length 40 mm grew and dislocation density in the crystal was about 107 m−2. The purity of the refined aluminum was estimated to be near 99.9999% from the residual resistance ratio. The impurity elements removed with high purification efficiency had a distribution coefficient of less than unit. A large amount of highly perfect aluminum crystal of ultra-high purity was produced by melting only once under the ultra-high vacuum.
  • Formation of Mono-Layer Honeycomb Structure in High-Purity Iron by Single Pass Hot-rolling

    pp. 125-128

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    DOI:10.2320/matertrans.43.125

    Microstructure change in high-purity irons was investigated at various cooling rates after single pass hot-rolling. Large columnar grains, which are named mono-layer honeycomb grains, developed through the thickness when high-purity iron (C:1.5 mass ppm, N:0.8 mass ppm, S:1.5 mass ppm, Si+Mn+P<1.0 mass ppm) was hot-rolled at 1273 K and cooled in a furnace with the average cooling rate of about 8.5×10−3 K/s. Mono-layer honeycomb grains developed in neither high-purity iron water-quenched after hot-rolling, nor middle-purity (C: 1.5 mass ppm, N: 9 mass ppm, S: 10 mass ppm, Si+Mn+P: 42 mass ppm) and low-purity (C: 20 mass ppm, N: 8 mass ppm, S: 10 mass ppm, Si+Mn+P: 270 mass ppm) irons. The crystal orientation of mono-layer honeycomb grains was determined by electron back scattering pattern method. The crystal orientation of mono-layer honeycomb grains does not have any specific α-texture. Grain growth behavior was investigated by using the cold-rolled and annealed irons. The grains in the high-purity iron grew faster and larger than those in middle-purity and low-purity irons. It is considered that the hot-rolled γ-grains in the high-purity iron recrystallize and coarsen in cooling, and then the γ-grains transform into α-grains. The α-grains grow larger due to the effect of purification. Consequently, mono-layer honeycomb grains are developed in high-purity iron.
  • Influence of Purity and Cooling-Rate on the Microstructure of Hot-Forged Pure Irons

    pp. 129-134

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    DOI:10.2320/matertrans.43.129

    The influence of purity and cooling-rate on the microstructure of hot-forged pure irons was investigated by using two kinds of pure irons. One was K-Iron of 99.981 mass% purity and the other was M-Iron of 99.993 mass% purity. After forging at 1263 K, above the α-γ transformation temperature, the specimens were immediately cooled to room temperature at various cooling-rates: by water-quenching, oil-quenching, air-cooling, ash-cooling, and furnace-cooling. The microstructure of forged iron was strongly affected by the purity and the cooling-rate. It should be emphasized that in M-Iron columnar grains grew in parallel to the forging direction independent of the cooling-rate. On the other hand, equiaxed grains were formed in all specimens of K-Iron forged at 1263 K. On both M-Iron and K-Iron, α-grains became larger with decreasing cooling-rate. The crystal orientation of α-grains on the forged plane of each specimen was measured by electron back-scattering diffraction-pattern method. On the forged plane of M-Iron, {101} of α-grains was predominant in the case of water-quenching and {111} or {221} was predominant in the other cases; on the other hand, the crystal orientation in K-Iron was random at all cooling-rates. Metallurgical factors controlling these characteristic microstructures in M-Iron were discussed in terms of growth of recrystallized of α- and γ-grains, mobility of γ⁄α interface, nucleation site and cooling-rate.
  • Influence of Carbon Additions on the Dynamic Recrystallization of High Purity α-Iron

    pp. 135-140

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    DOI:10.2320/matertrans.43.135

    The influence of carbon content on the dynamic recrystallization mode of α-Iron containing various amounts of carbon, ranging from 5 to 200 ppm, was investigated. Uniaxial compression tests were carried out, followed by metallographic analyses by optical microscopy. All the alloys exhibit discontinuous dynamic recrystallization. Furthermore, the values of the apparent activation energies of deformation, as well as the steady state average grain sizes show that they are very sensitive to carbon additions in the range of high purities, i.e. 0–50 ppm. An interpretation of this effect is proposed on the basis of grain boundary solute segregation.
  • Effect of Tungsten on Mechanical Properties of High-Purity 60 mass%Cr-Fe Alloys

    pp. 141-146

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    DOI:10.2320/matertrans.43.141

    The effect of the tungsten addition on the mechanical properties of high-purity 60 mass%Cr–Fe alloy was investigated. High-purity 60 mass%Cr–Fe-4 mass%W alloy ingots were prepared by melting in a newly designed high-frequency induction furnace equipped with a cold copper crucible. The purity of the ingots were higher than 99.98 mass% after the analysis of 21 elements. The deformability at temperatures of 1273 to 1573 K and the tensile properties between 293 K and 1073 K were measured by Gleeble test and tensile test. It was found that the tensile strength of 60 mass%Cr–Fe-4 mass%W alloy is higher than that of 60 mass%Cr–Fe alloy, and the addition of tungsten is effective in improving tensile properties of a 60 mass%Cr–Fe alloy.
  • Effect of Aging on the Tensile Properties of High-Purity Fe-50Cr Alloys

    pp. 147-154

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    DOI:10.2320/matertrans.43.147

    The effects of strain rate and aging on the tensile property of high-purity Fe–50 mass%Cr and 166 mass ppm carbon-doped Fe–50 mass%Cr alloys were investigated by tensile tests and microstructural observations. The serration occurring by dynamic strain aging on the stress-strain curves disappears at the strain rate below 4.2×10−5 s−1 and above 1.7×10−2 s−1 at 773 K in a high-purity Fe–50 mass%Cr alloy with the grain size of 29 \\micron. The deformation twinning in a high-purity Fe–50 mass%Cr alloy with the grain size of 108 \\micron at 773 K occurs at the same stress of 480 MPa, independent of strain rate. The pre-strained specimen of high-purity Fe–50 mass%Cr alloy shows static strain aging after aging at 573 K . The aging treatment at 773 K causes the precipitation of carbides and thereby the formation of deformation twins in tensile tests. In a carbon-doped high-purity Fe–50 mass%Cr alloy, the heat treatment for precipitating carbides on grain-boundaries restrains the formation of deformation twins at 773 K.
  • Effects of Various Alloying Elements on Tensile Properties of High-Purity Fe-18Cr-(14-16)Ni Alloys at Room Temperature

    pp. 155-162

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    DOI:10.2320/matertrans.43.155

    High-purity Fe–18Cr–14Ni/Si, Mn, P, S, C, N alloys and high-purity Fe–18Cr–16Ni/Mo alloys were prepared by a cold crucible method to investigate the intrinsic effects of alloying elements on the tensile properties of Fe–18Cr–(14–16)Ni alloys at room temperature. The results show that C and N interstitials had the greatest solid-solution strengthening effect, followed by the ferrite-forming substitutional elements Mo and Si, while Mn, P and S, had little or no solid-solution strengthening effect. Grain refinement caused a decrease in elongation and an increase in tensile strength and the magnitude was considerable in Fe–18Cr–16Ni–Mo alloys. The addition of Mo to Fe–18Cr–16Ni alloys caused an increase in both the internal stress σ0 and coefficient k in the Hall-Petch relation (σ0.20+kd−1⁄2; where σ0.2, d, and σ0 and k are 0.2% proof stress, grain diameter, and constants, respectively). The 0.2% proof stress of high-purity Fe–18Cr–16Ni alloys obeyed the equation, 0.2% PS (MPa)=80.9+19.4(Mo)+{0.314+0.048(Mo)}×d−1⁄2, where the parentheses indicate Mo content in at% and d is the average grain size in m.
  • Mechanical Properties of Ultrahigh-Purity Ti-45 mol%Al Alloy

    pp. 163-167

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    DOI:10.2320/matertrans.43.163

    An ultrahigh-purity Ti–45 mol%Al alloy ingot was isothermally hot-pressed along each of the X, Y and Z coordinates at 1473 K . The hot-pressed ingot consisted mainly of very fine recrystallized grains, with an average size of 5 \\micron. The mechanical properties of this fine-grained Ti–Al alloy were examined by tensile test at 293 K, 823 K, and 923 K at strain rate of 1.1×10−4 s−1 in a vacuum of 1.3×10−3 Pa. The ductile-brittle transition temperature (DBTT) was determined by the tensile tests and scanning electron microscope observation of the fracture surfaces of the samples. This ultrahigh-purity Ti–45 mol%Al alloy showed the following excellent high-temperature mechanical properties: (1) The 0.2% proof strength was 486 MPa and elongation at 923 K was 45%. (2) The DBTT was 870 K, which is about 200 K lower than that of conventional binary Ti–Al alloys with similar composition.
  • Effect of Trace Amounts of Carbon and Nitrogen on the High Temperature Oxidation Resistance of High Purity FeCrAl Alloys

    pp. 168-172

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    DOI:10.2320/matertrans.43.168

    The growth rate and adhesion of the protective alumina scales on the heat resistant FeCrAl alloys are known to depend on minor metallurgical additions of the “reactive elements” such as Y, Ti, Zr, etc. The present study of high purity model FeCrAl alloys illustrates that the oxidation behaviour of these materials is strongly affected by trace amounts (up to 300 mass ppm) of carbon and/or nitrogen impurities. During long term high temperature oxidation testing of high purity model alloys it has been found that the carbon and nitrogen can interact with the reactive elements, such as Zr and Ti in the ferritic alloy matrix, resulting in a number of important effects on the scale growth and adherence. These effects can be beneficial as well as detrimental, depending on the exact amount and/or distribution of the mentioned minor alloying elements and C/N-impurities.
  • Self-Diffusion along Dislocations in Ultra High Purity Iron

    pp. 173-177

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    DOI:10.2320/matertrans.43.173

    Self-diffusion along dislocations in ultra high purity iron containing 0.5–1.2 mass ppm carbon, 0.1–1.0 mass ppm nitrogen and 1.8–4.0 mass ppm oxygen has been studied by the radioactive tracer method with the sputter-microsectioning technique. Below 700 K, the self-diffusion coefficient along dislocations has been determined directly from the type C kinetics classified by Harrison, whereas above 800 K it has been obtained by the type B kinetics assuming that the effective radius of dislocation pipe is equal to 5×10−10 m. The temperature dependence of the self-diffusion coefficient along dislocations does not show a linear Arrhenius relation. Below 900 K the Arrhenius plot shows slightly downward curvature. However, above 900 K the self-diffusion coefficient along dislocations increases remarkably with increasing temperature. The value at 900 K is 10−14 m2s−1, while it takes 10−10 m2s−1 at the Curie temperature (1043 K). It seems that the steep increase of the self-diffusion coefficient along dislocations near the Curie temperature is related to the magnetic transformation in ultra high purity iron.
  • Diffusion of Cr and Fe in a High-Purity Fe-50 mass%Cr-8 mass%W Alloy

    pp. 178-181

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    DOI:10.2320/matertrans.43.178

    Volume and grain boundary diffusivities of 51Cr and 59Fe in a high purity Fe–50 mass%Cr–8 mass%W (Fe–50Cr–8W) alloy have been determined in the temperature range between 1023 and 1373 K with the sputter-microsectioning technique. The volume diffusion coefficients of Cr and Fe in the Fe–50Cr–8W alloy are smaller than those in a high-purity Fe–50 mass%Cr (Fe–50Cr) alloy. Linear Arrhenius lines for the volume self-diffusion coefficients of both tracers have been observed in the temperature range examined. The activation energies for the volume diffusion of both components in the Fe–50Cr–8W alloy are somewhat smaller than those in the Fe–50Cr alloy. On the other hand, the grain boundary diffusivities of Cr and Fe in the Fe–50Cr–8W alloy at 1123 K are about two orders of magnitude smaller than those in the Fe–50Cr alloy.
  • Composition Dependence of the Zener Relaxation in High-Purity FeCr Single Crystals

    pp. 182-185

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    DOI:10.2320/matertrans.43.182

    High-purity FeCr single crystals with Cr contents between 34 at% and 60 at% and orientations close to the ⟨111⟩ direction were prepared by containerless inductive zone melting under Ar atmosphere. The internal friction was measured between temperatures of 300 to1200 K using an inverted torsion pendulum in the frequency range between 2 and 80 Hz. A strong damping is observed below the Curie temperature due to domain wall motion. Above the ferromagnetic transition temperature a relaxation maximum occurs at about 950 K . This relaxation can be assigned to the so-called Zener relaxation which is due to the stress-induced reorientation of short-range ordered Fe and Cr atoms, respectively. An analysis yielded an effective activation enthalpy of (3.1±0.3) eV showing no significant dependence on the composition. The relaxation strength shows a maximum value near the equiatomic composition and decreases for lower and higher Cr contents. Furthermore, the influence of the σ phase on the internal friction and the dynamic torsional shear modulus was studied on a single crystal with a Cr content of 48 at%. After annealing for 24 h at 973 K the torsional shear modulus increases with temperature up to over 1000 K, indicating a hardening due to precipitates of the σ phase.
  • Quenching Studies of Lattice Vacancies in High-Purity Aluminium

    pp. 186-198

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    DOI:10.2320/matertrans.43.186

    The experimental techniques for obtaining reliable enthalpies of formation and migration of vacancies in pure metals and the importance of achieving high accuracy are critically discussed, with emphasis on studies based on the quenching-in of ‘thermal’ vacancies. From measurements of the residual electrical resistance introduced into high-purity Al foils (thickness 0.1 mm) by ultrafast quenches (initial quenching rate≈2×106 K s−1) from temperatures T between 800 K and 530 K and the literature data on high-temperature differential dilatometry, the enthalpy, H1VF=(0.65±0.01) eV, and the entropy, S1VF=(0.76±0.04)kB (kB=Boltzmann’s constant), of monovacancy formation as well as the resistivity ρ1V=(1.9±0.1) \\microΩm per unit atomic concentration of vacancies are derived. Combining these results with the Al self-diffusion data deduced from nuclear magnetic resonance leads to the migration enthalpy H1VM=(0.61±0.02) eV and the pre-exponential factor D1V0=6×10−6 m2s−1 of the monovacancy diffusivity D1V=D1V0exp(−H1VMkBT). The divacancy binding enthalpy is found to be H2VB=(0.175±0.025) eV . This is in full agreement with earlier determinations by Doyama and Koehler and by Levy, Lanore and Hillairet, who employed a different technique, but in stark contrast to the recent assertion H2VB≈0 of Carling et al.
  • Effect of Silicon Particles on the EDM Characteristics of Al-Si Alloys

    pp. 199-205

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    DOI:10.2320/matertrans.43.199

    The second phase of the Aluminum-Silicon (Al–Si) alloy embedded in microstructure includes primary silicon particles and hypereutectic silicon particles. Variations in the area fraction of these silicon particles significantly influences Electro Discharge Machining (EDM) characteristics. The area fraction of these silicon particles is proportional to materials removal rate (MRR). Experimental data obtained using Scanning electron microscope (SEM) revealed that discharge craters were formed as a ridge on the EDMed surface. The increased average surface roughness (Ra) resulted in an increased EDM rate. The area fraction of second phase silicon particles, and the ridge density on the rapidly resolidified layer of the EDMed surface tended to increase. However, most silicon particles were found on the peaks on the sub-layer of the EDMed surface, formed by rapidly solidification of molten fluid during discharge melting. Therefore the presence of silicon particles in the rapidly resolidified layer was largely governed by the formation of discharge peaks. The formation of peaks was governed by EDM conditions and silicon content. The electrodes showed stable wear during EDM when the pulse duration exceeded 150 \\microsecond. Wear increased as the area fraction of silicon particles increased.
  • Modeling of Fluid Flow and Heat Transfer in Twin-Roll Casting of Aluminum Alloys

    pp. 206-213

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    DOI:10.2320/matertrans.43.206

    A two-dimensional finite element based mathematical model of coupled turbulent fluid flow, heat transfer, and solidification in horizontal twin-roll thin strip casting was developed. Basic formulations for simulating the coupled thermal and flow fields are described in this paper. A k-ε turbulence model was used to calculate the turbulent viscosity in the melt pool. A variable viscosity model was used to model the mushy region. Inlet velocity, strip/roll heat transfer coefficient, alloy composition, and melt superheat were the main process variables considered. The effect of the above process variables on the sump depth, mean strip exit temperature, roll surface temperature, and temperature gradients inside the roll, was analyzed.
  • Modeling of Thermo-Mechanical Stresses in Twin-Roll Casting of Aluminum Alloys

    pp. 214-221

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    DOI:10.2320/matertrans.43.214

    A two-dimensional steady state thermo-mechanical stress model was developed using the commercial structural analysis package ANSYS, to compute the stresses arising from thermal gradients and mechanical loads applied to strip and roll during a horizontal twin-roll thin strip casting process. The finite element mesh and the nodal temperature values obtained from the fluid flow, heat transfer, and solidification model developed on FIDAP, were transported to ANSYS. Mechanical loads like roll separating force and strip exit tension were also applied on the strip. A visco-plastic constitutive relation has been used to describe the behavior of solidifying aluminum alloy. The effects of inlet velocity of the melt and contact strip/roll heat transfer coefficient on the resultant stress profile in the strip and the rolls were investigated.
  • Phonon Band Structures and Resonant Scattering in Na8Si46 and Cs8Sn46 Clathrates

    pp. 222-226

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    DOI:10.2320/matertrans.43.222

    The low and glasslike thermal conductivity of metal doped semiconductor clathrate compounds makes them potentially high efficiency thermoelectric materials. The cause of this unique and remarkable property has been postulated to be due to resonant scattering of lattice phonons by localized vibrations of the dopants. We present theoretical evidence in support of this hypothesis through the analysis of electronic and vibrational interactions between dopant atoms with the host framework. In particular, the contrasting behavior of two clathrates: the glasslike thermal conductivity in Na8Si46 and the normal behavior in Cs8Sn44 can be rationalized.
  • The Influence of Phosphorus Concentration of Electroless Plated Ni-P Film on Interfacial Structures in the Joints between Sn-Ag Solder and Ni-P Alloy Film

    pp. 227-231

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    DOI:10.2320/matertrans.43.227

    The interface structure between Sn–3Ag solder and electroless plated Ni film and the structure near that interface were examined. Plated electroless Ni films contained 3.7 mass% phosphorus or 8.5 mass% phosphorus. A P-enriched layer is formed at the joining interface between plated electroless Ni film and Sn–3Ag solder, in each sample with 3.7 mass%P and 8.5 mass%P. P-enriched layers of both P concentration samples contained double the P concentration than the original plated Ni films. Also, the P-enriched layer of the Ni–8.5 mass%P sample was much thicker than that of the Ni–3.7 mass%P sample. Both P-enriched layers have been composed of Ni–Sn–P layer and P enriched Ni–P layer. Kirkendall voids were formed between the 1st Ni–Sn–P layer and 2nd Ni–P layer. The number of voids observed in Ni–8.5 mass%P sample was much greater than those in the Ni–3.7 mass%P sample. Intermetallic compounds, mixtures of Ni3Sn2 and Ni3Sn4, were formed by the interfacial reaction. In the case of the Ni–3.7 mass%P sample, Ni–Sn intermetallic compounds continuously crystallized on the P-enriched layer, while in the case of the Ni–8.5 mass%P sample, Ni–Sn intermetallic compound crystallized dispersively in the solder.
  • Quaternary Diffusion in 7000 Aluminum Alloys

    pp. 232-238

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    DOI:10.2320/matertrans.43.232

    Quaternary and ternary interdiffusion experiments of 7000 aluminum alloys have been performed at 725 and 755 K. The concentration profiles indicate that the diffusion distance of Cu is shorter than those of Zn and Mg in the solid solutions. The direct interdiffusion coefficients \\ ildeDZnZnAl, \\ ildeDMgMgAl are positive, and indirect coefficients \\ ildeDZnMgAl, \\ ildeDMgZnAl are negative in the ternary Al–Zn–Mg alloys. The effective interdiffusion coefficients in 7000 aluminum alloys are in the order \\ ildeDZn,Ceff>\\ ildeDMg,Ceff>\\ ildeDCu,Ceff. When the concentration distribution of Zn and Mg are almost constant and the concentration of Cu approaches zero in the Al–Zn–Mg/Al–Zn–Mg–Cu couple, it is obvious that \\ ildeDCu,Ceff=\\ ildeDCuCu4=\\ ildeDCu(Al–Zn–Mg). The ratio values of indirect to direct diffusion coefficients suggest that attractive interactions of Zn–Mg and Cu–Mg exist in the Al–Zn–Mg–Cu alloys.
  • Effect of Au addition on Microstructural and Mechanical Properties of Sn-Cu Eutectic Solder

    pp. 239-245

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    DOI:10.2320/matertrans.43.239

    The effect of Au addition on the microstructural and the tensile properties of Sn–0.7 mass%Cu alloy was examined. Tensile strength and 0.2% proof stress remarkably increase up to 0.3 mass%Au primarily due to solid solution hardening. Beyond 0.3 mass%Au, due to precipitation of large intermetallic compounds, elongation decreases while tensile strength and 0.2% proof stress increase slightly. With Au addition to Sn–Cu binary alloy, the eutectic endothermic peak in DSC, i.e., the melting reaction at 227°C, becomes broader and shifts to the lower temperature range. With Au beyond 2 mass%, the broad peak becomes smaller splitting into two peaks and moving towards lower temperature while a new peak appears at about 212°C. These thermal reactions can be well explained by the formation of β-Sn, Cu6Sn5 and AuSn4 with Au more than 1 mass%. EPMA observation revealed that much amount of Au and Cu dissolve into Cu6Sn5 and AuSn4, respectively.
  • Ageing Processes in Al-Mg-Si Alloys during Continuous Heating

    pp. 246-255

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    DOI:10.2320/matertrans.43.246

    The precipitation behaviours during continuous heating in the Al–Mg2Si alloys with excess Mg and Si contents have been investigated by means of Vickers hardness measurements, differential scanning calorimetry and transmission electron microscopy. The first exothermic reaction occurring at the lowest temperatures is due to the annihilation of quenched-in vacancies by the collapse of vacancy clusters and the migration of vacancies to various sinks such as grain boundaries. The prismatic dislocation loops formed by this collapse are frequently observed. The second reaction detected as broad hardening increases with increasing excess Si content and can be interpreted as the formation of solute atom clusters. The sharp and large exothermic reaction inducing the largest hardening corresponds to the precipitation of β′′ needles. The following exothermic reaction arises from the precipitation of β-Mg2Si particles. The formation of β and Type-B rods can be recognised in the quasi-binary and the excess Si at slightly higher temperatures.
  • Recycling of Rare Earth Magnet Scraps Part III Carbon Removal from Nd Magnet Grinding Sludge under Vacuum Heating

    pp. 256-260

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    DOI:10.2320/matertrans.43.256

    The removal of the carbon from Nd magnet scraps is indispensable for high-quality recycling by the induction melting method as a preliminary process. The Nd magnet scraps can be decarburized to a level of less than 0.03 mass% by using an oxygen source at high temperatures, as reported in Part 1. The decarburized Nd magnet scraps can then be deoxidized by using the Ca reduction to a level that allows commercial melting in an induction furnace, as reported in Part II. However, the undesirable iron oxide (Fe2O3) which causes a disadvantage for Ca reduction is inevitably generated by using an oxygen source at high temperatures. The aim of this work is to investigate an economical decarburization method in which only the carbon sources in Nd magnet scraps are decarburized, without generating iron oxide. The grinding sludge as Nd magnet scraps is effectively decarburized to a level of less than 0.03 mass% without generating any iron oxide by heating at above 1073 K under a pressure of less than 5.32×10−2 Pa. The amount of oxygen in the decarburized powder is about 8 mass%, which is lower in comparison with its value in Part 1. In this report, the decarburization mechanism under reduced pressure using the grinding sludge, and its economic significance prior to the decarburizing method described in Part 1, are discussed.
  • Surface Characterization of Amorphous Zr-Al-(Ni, Cu) Alloys Immersed in Cell-Culture Medium

    pp. 261-266

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    DOI:10.2320/matertrans.43.261

    For the evaluation of zirconium-base amorphous alloys as biomaterials, the surface compositions of amorphous Zr–Al–Ni–Cu and Zr–Al–Cu alloys were characterized using X-ray photoelectron spectroscopy. The alloys were polished, autoclaved, and immersed in Hanks’ solution or Eagle’s minimum essential medium containing fetal bovine serum, MEM+FBS. Aluminum was enriched in the surface oxide film and the substrate just under the film of the alloys polished in water. After autoclaving, aluminum and copper were enriched in the substrate while zirconium was preferentially oxidized and incorporated into the surface oxide film. In Hanks’ solution, copper and nickel decreased in the substrate and surface oxide film, resulting in the enrichment of aluminum in the substrate. In MEM+FBS, zirconium preferentially decreased by the effects of amino acids and proteins while copper was enriched in the substrate. The surface composition of zirconium-base amorphous alloys was much influenced by amino acids and proteins in MEM+FBS.
  • New Glassy Zr-Al-Fe and Zr-Al-Co Alloys with a Large Supercooled Liquid Region

    pp. 267-270

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    DOI:10.2320/matertrans.43.267

    New Zr–Al–Co and Zr–Al–Fe ternary glassy alloys were found to exhibit a large supercooled liquid region above 50 K before crystallization. The largest value of the supercooled liquid region was 64 K for Zr55Al20Co25 and 50 K for Zr70Al15Fe15. The highest value of the reduced glass transition temperature (TgTl) was 0.61 for Zr55Al20Co25 and 0.60 for Zr70Al15Fe15. The use of the Zr55Al20Co25 alloy with the highest TgTl has enabled us to form bulk glassy alloy rods with diameters up to 3 mm by copper mold casting. The Young’s modulus, yield strength, compressive fracture strength, elastic elongation and fracture elongation of the Zr55Al20Co25 glassy rod are 92 GPa, 2050 MPa, 2200 MPa, 2.1% and 0.9%, respectively. The distinct plastic elongation indicates that the Zr-based bulk glassy alloy has rather a good ductile nature. The synthesis of the high-strength bulk glassy alloy in the new ternary system is expected to gain a new application field as a new type of bulk glassy alloy.
  • Kinetics of Phase Separation in Fe-Cr-Mo Ternary Alloys

    pp. 271-276

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    DOI:10.2320/matertrans.43.271

    Numerical simulations were performed using a model based on the Cahn-Hilliard equation in order to investigate asymptotic behavior of a minor element associated with phase decomposition of the major element in Fe–Cr–Mo ternary alloys. Bifurcation of peaks of Mo along peak tops of Cr concentration occurs in an Fe–40 at%Cr–5 at%Mo alloy at 800 K . Bifurcation of peaks of Cr is also shown in an Fe–40 at%Mo–5 at%Cr alloy at 800 K . The amplitude of a peak of Mo in an Fe–40 at%Cr–5 at%Mo alloy at 1025 K increases with time. The asymptotic behavior of Mo or Cr along a trajectory of a peak top of Cr or Mo concentration depends on the sign of the second derivative of the chemical free energy with respect to the concentrations of Cr and Mo. For the case in which both Cr and Mo are within the spinodal region of an Fe–Cr–Mo ternary phase diagram, both Cr and Mo decompose separately and induce separation of the other element. Simulated asymptotic behavior of Mo and Cr in Fe–Cr–Mo ternary alloys is in good agreement with that predicted by the theory proposed by the present authors.
  • Bulk Glass Formation of Ti-Zr-Hf-Cu-M (M=Fe, Co, Ni) Alloys

    pp. 277-280

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    DOI:10.2320/matertrans.43.277

    The glass-forming ability of Ti–Zr–Hf–Cu–M (M=Fe, Co, Ni) alloys was examined by melt-spinning and copper mold casting methods. New Ti20Zr20Hf20Cu20Ni20 bulk glassy rod of 1.5 mm in diameter was formed by copper mold casting. The Tx and Tg of the glassy rod were 711 K and 658 K and TgTm was 0.57. The bulk glassy alloy can be characterized by equal concentration of constituent elements without distinct host component. It is confirmed that more multicomponent glassy systems have a better glass-forming ability as compared with simpler alloy systems. The glassy alloy rod also exhibits good mechanical properties which are similar to those for ordinary glassy alloys. The finding of this alloy system may provide a new synthesis method of bulk glassy alloys.

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