Ni8Ta in nickel-rich Ni−Ta alloys

An ordering reaction has been observed in the nickel-rich binary alloys of the Ni?Ta system that are aged below 570°C following quenching from elevated temperatures. This reaction has been investigated by employing electron diffraction microscopy, X-ray diffraction, and electrical resistivity techniques. The ordered phase has been identified as Ni₈Ta and its structure is identical to that of the Ni₈Nb (Cb) reported earlier. In the stoichiometric Ni₈Ta alloy (Ni-11.1 at. pct Ta) three variants of the Ni₈Ta phase are nucleated apparently “homogeneously” throughout the matrix. The precipitate or domain morphology has been identified as a cuboid elongated in one direction such that the cube faces are parallel to the {100} planes of the matrix. The cuboid morphology of the precipitates tends to disappear as the precipitates coalesce and the particle size approaches 1000Å.     

Combustion synthesis of Ni3Al and Ni3Al-matrix composites

The self-propagating mode of combustion synthesis (SHS) of Ni₃Al starting from compacts of stoichiometrically mixed Ni and Al powders readily forms fully reacted structures with about 3 to 5 pct porosity, if green density of the compacts is greater than about 75 pct of theoretical. SHS-produced Ni₃Al matrix composites with up to 2 wt pct A1₂O₃ whiskers also have relatively low porosity levels. Porosity increases rapidly with lower green densities, higher Al₂O₃, or SiC whisker contents, and the degree of reaction completeness diminishes. The SiC whiskers undergo reaction with the matrix, while Al₂O₃ whiskers are nonreactive. All of these observations correlate well with temperature measurements made during the course of the reaction. The SHS mode can be achieved with agglomerated particle size ratioD _Al/D _Ni ≥ 1, larger than the limit established from studies of the thermal explosion mode of combustion synthesisD _Al/D _Ni ≃ 0.3. This paper is based on a presentation made in the symposium “Reaction Synthesis of Materials” presented during the TMS Annual Meeting, New Orleans, LA, February 17–21, 1991, under the auspices of the TMS Powder Metallurgy Committee.     

Properties of Ni and La Ni Electrode Materials Prepared by MVS

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Ni/海泡石及Ni-Sm/海泡石催化剂的研究

采用海泡石为载体,金属镍为活性组份,稀土为助剂,用不同方法制备了Ｎｉ／Ｓｅｐ 和Ｎｉ－Ｓｍ ／Ｓｅｐ 催化剂,并考察了它们的苯加氢反应性能。结果表明：Ｎｉ／Ｓｅｐ 催化剂的活性明显高于Ｎｉ／Ａｌ２Ｏ３,稀土Ｓｍ 对Ｎｉ／Ｓｅｐ 催化剂有较大的改性作用。ＴＰＲ、ＴＰＤ、ＣＯ吸附结果表明,海泡石和钐能使镍的还原温度降低,氢吸附量增大,活性中心增加,同时使镍原子电子密度增高。     

Properties of Electroless Ni–B and Ni–P/Ni–B Coatings Formed on Stainless Steel

In this study, Ni–P/Ni–B duplex coatings and Ni–B single layer were deposited on 410 stainless steel by the electroless process. The surface morphology and cross section observations were analyzed using scanning electron microscopy and optical microscopy. The results showed that by using the Ni–high P layer under the Ni–B deposit, the hardness value was increased. Also, the surface roughness of Ni–high P/Ni–B duplex coating was lower than the surface roughness of the Ni–B single layer. In addition, by using the Ni–high P layer as an intermediate layer prior to Ni–B coating, the surface morphology could be compressed. The mass loss diagram and the worn surfaces indicated that the Ni–high P/Ni–B duplex coating was the best wear resistant among the other coatings.     

Grain boundary segregation in Ni and binary Ni alloys doped with sulfur

The kinetics and temperature dependence of sulfur segregation in Ni and binary alloys of Ni with Cu, Al, Cr, Mo, W, and Hf, all containing between 70 and 100 atomic ppm sulfur, have been measured using Auger spectroscopy over the temperature range 500 to 1000 °C. No evidence for cosegregation of these alloying elements with sulfur is found. The alloying elements do influence the precipitation of sulfides, however, and this influences the amount of segregation which occurs. Comparison with theoretical models of grain boundary segregation allows the sulfur solubility in the various alloys to be determined.     

Strengthening by ordered precipitates in a Ni−Ni4Mo system

The strength characteristics and microstructures of aged Ni−Mo alloys containing ordered (Ni₄Mo) precipitates were studied as a function of aging time and temperature. It was found that 17 at. pct Mo alloy aged at 750°C produced a uniform dispersion of cuboidal β precipitates which coarsened with time producing a gradual increase in flow stress. The flow stress increment was found to vary in qualitative agreement with both order strengthening and coherency strain models. Both these models give over-estimates of the strengthening increment. A negative dependence of flow stress on temperature is attributed to coherency strain contributions.     

Diffusion of63Ni in the intermetallic B82-alloys in the systems Ni/Sn and Ni/In

The self-diffusion of⁶³Ni has been investigated in single crystals of the ordered intermetallic compounds Ni₆₁Sn₃₉, Ni₆₂Sn₃₈ and Ni₆₄In₃₆. The activation energies for diffusion perpendicular and parallel to the hexagonal c-axis are nearly the same and the values are between 2.14 and 2.34 eV. Moreover the D₀-values are direction dependent and range from 0.5 to 0.8 cm²/s for Ni/Sn and from 65 to 110 cm²/s for Ni/In. The experimental values of D_⊥/D_∥ are between 1.13 and 1.68 for Ni/Sn and between 0.87 and 0.79 for Ni/In, depending on temperature. These values are to be compared with theoretical values for the different diffusion mechanisms. The majority mechanism should be a site change of the tracer atom between the Ni-chains in c-direction and the double tetraeder interstices (DTI) with a further jump to another chain. Moreover two other mechanisms as minority mechanisms are possible. With rising temperature and filling the DTI's the part of minority mechanisms increases.     

First-principles computations of mechanical properties of Ni2Cr and Ni2Mo

Nickel-based alloys are being considered for use as the outer container of the waste package for the disposal of high-level nuclear waste. During fabrication processes and long-term storage, Ni-based alloy outer containers can undergo microstructural changes due to the formation of Ni₂Cr, Ni₂Mo, and Ni₂(Cr, Mo), which are ordered orthorhombic (oI6) phases whose mechanical properties are unknown because of fabrication difficulties. To circumvent the experimental limitation, a first-principles quantum-mechanical code based on the full-potential linearized augmented plane-wave (FLAPW) method was used to compute the elastic constants and the theoretical stress-strain curves of Ni₂Cr and Ni₂Mo. The theoretical mechanical properties were then correlated with charge-density distributions of the stressed oI6 unit cell to identify the critical conditions at the onset of fracture. Using first-principles results as material input, the unstable stacking energy and the Peierls-Nabarro (P-N) barrier energy were computed and used to estimate the tensile ductility and fracture toughness of Ni₂Cr and Ni₂Mo. The influences of the elastic anisotropy and slip vector on dislocation mobility in Ni₂Cr and Ni₂Mo are identified and contrasted to those in MoSi₂ with a tetragonal (tI6) crystal structure. This article is based on a presentation made in the symposium “Computational Aspects of Mechanical Properties of Materials,” which occurred at the 2005 TMS Annual Meeting, February 13–17, 2005, in San Francisco, CA, under the auspices of the MPMD-Computational Materials Science & Engineering (Jt. ASM-MSCTS) Committee.     

Tensile strength of Ni/Cu/(001)Ni triple layer films

Tensile properties of Ni/Cu/(001)Ni triple layer films and single crystal films of (00l)Cu and (00l)Ni were studied. The specimen films having the thickness of 50 to 500 nm were prepared by the epitaxial evaporations on (001)NaCl substrates. The stress-strain curves of tensile tests in the direction of [100] of Ni/Cu/(001)Ni triple layer films were almost linear until fracture and showed extremely small plastic deformation. The yield stresses of these specimens were 600 to 700 MPa independently of the layer thicknesses, which were 2.5 to 5 times higher than those of Ni or Cu single crystal films, and were also higher than the values given by the mixture rule for Ni and Cu single crystal films. The increase of yield stress was evaluated from the repulsive force acting on the mobile dislocations originating from the stress fields of misfit dislocation arrays at the Ni-Cu interface. Formerly Graduate Student, Faculty of Engineering, Osaka University     

Solubility of hydrogen in solid Ni−Co and Ni−Cu alloys

The solubility of hydrogen was measured in solid Ni, Co, and Cu, and in the Ni?Co and Ni?Cu systems. A unique sampling technique was used in which equilibrated specimens were quenched by dropping into mercury. The measurements were made as a function of temperature in the range from 700° to 1225°C and of hydrogen pressure, up to 1 atm. Dissolved hydrogen in all metals and alloys obeyed Sieverts' Law. An attempt was made to correlate the hydrogen solubility with solution models based on the electronic structure of the alloys. A nonlinear correlation was found with the electronic specific heat coefficient which relates to the density of states at the Fermi surface.     

Thermodynamics of the Fcc Fe−Ni−C and Ni−C alloys

The activity of carbon in the fcc solid solution of the Fe?Ni?C system has been measured at 800°, 1000°, and 1200°C by comparison with observed values in the Fe?C binary by equilibration with methane-hydrogen mixtures. Defining the lattice ratioz _C≡n _C/(n _Fe+n _Ni?n _C), the activity coefficient Ψ_C≡a _C/z _C has been determined as a function of temperature and composition. At infinite dilution log Ψ_C goes through a maximum at about 70 pct Ni in agreement with Smith. The partial molar free energy of carbon in the dilute solution referred to graphite is not a linear function of the base alloy composition, but has a large deviation with maximum at about 60 pct Ni. Similar maxima occur in both ΔH _C ^° and ΔS _C ^° . Linear equations are derived for the activity coefficient of carbon in three composition ranges of Fe?Ni?C alloys; a simplified equation applicable to nickel steels is included. The solubility of graphite in nickel has been determined. The marked deviation from linearity is ascribed to the existence of iron atoms in two electronic states, γ₁ and γ₂ which differ in energy and are antiferromagnetic and ferromagnetic, respectively.