Binary Ni-Cr Alloys Research Articles

Solubility of nitrogen in liquid nickel and Ni-Cr alloys under elevated pressure

The present work focuses on the experimental evaluation of the solubility of nitrogen during the melting process in nickel and binary Ni-Cr alloys under elevated nitrogen partial pressure at 1550°C. In order to estimate the attainable nitrogen concentrations, the solubility of nitrogen in dependence of melt temperature and nitrogen partial pressure has been calculated by using Thermo-Calc. Thermo-Calc supported predictions of the achievable nitrogen contents referring to the investigated alloys show good agreement with the experimental data only up to nitrogen partial pressures of 0.1 MPa. The applicability of Sievert's law has been examined for nitrogen partial pressures up to 6 MPa and Ni-Cr alloys with chromium mass contents of 15, 20, 30, 40 and 50 %. A deviation from Sievert's law was observed for the alloys with chromium mass contents higher than 20 % and a nitrogen partial pressure above 0.1 MPa. The effect of chromium and the nitrogen partial pressure on the solubility of nitrogen is described in terms of the Wagner's first and second order interaction parameters.

Mass-spectrometric determination of the thermodynamic mixing behavior of liquid ternary Fe–Ni–Cr alloys

Thermodynamic investigations on liquid ternary Fe–Ni–Cr alloys have been performed by means of the computer-aided Knudsen cell mass spectrometry. Ternary thermodynamically adapted power (TAP) series are used for the algebraic representation of the thermodynamic excess properties. At 1950 K, the molar excess Gibbs energy G E is negative in the predominant part of Gibbs triangle (minimum value: −2980 J/mol at x Ni=0.55, x Cr=0.45), and positive only near the liquid binary Cr–Fe alloys (maximum value: 940 J/mol at x Cr=0.375, x Fe=0.625). The molar heat of mixing H E is exothermic for nearly all Fe–Ni–Cr melts (minimum value: −4770 J/mol at x Fe=0.38, x Ni=0.62). Only the Cr-richest ternary melts near the Ni–Cr binary alloys are slight endothermic (maximum value: 80 J/mol at x Ni=0.125, x Cr=0.87). The molar excess entropy S E is slight negative for ternary Fe–Ni–Cr melts near the two binary boundary systems Fe–Ni and Cr–Fe with a minimum S E value of −1.27 J/mol K at x Cr=0.40 and x Fe=0.60, and slight positive at the side of binary Ni–Cr melts (maximum S E value: 1.35 J/mol K at x Ni=0.50, x Cr=0.50). The Fe-activities of liquid ternary Fe–Ni–Cr alloys as determined, in this work, show slight negative deviations from the ideal behavior in the range of composition below the section of constant mole fraction x Cr/ x Ni=1, and slight positive deviations from Raoult's law above this section line. The Ni-activities of all ternary Fe–Ni–Cr melts show negative deviation from the ideal behavior. The Cr-activities show slight positive deviations from Raoult's law in the range of composition on the left-hand side of the section of constant mole fraction x Ni/ x Fe=1, and slight negative deviations from the ideal behavior on the right-hand side of this section line. The results of this work can be used successfully for phase-diagram calculations.

Bond Strength of Dental Adhesive Resins to Ni-Cr Binary Alloys

Bond Strength of Dental Adhesive Resins to Ni-Cr Binary Alloys

The Stress Corrosion Performance of Diffusion-Bonded Nickel-Base Alloys

Abstract Excellent mechanical strength can be achieved in diffusion-bonded nickel-base alloys when approximately 0.01 mm of nickel is plated on the surfaces before bonding. However, rapid stress corrosion cracking (SCC) takes place in the bond line region when such materials are tested in high-purity water at 360°C. The failures are caused by the low concentration of chromium in the nickel-rich bond line region. Long-time high-temperature anneals to diffuse chromium into the bond line dramatically improve the stress corrosion resistance. Measurements of the local chromium in the bond line and separate tests of Ni-Cr binary alloys show that chromium contents approaching that of the bulk alloy are necessary to eliminate the cracking susceptibility.

A corrosion study of Ni and Ni-Cr alloys in SO 2/H 2O/H 2 atmospheres using gas analysis

The corrosion behaviour of nickel and binary Ni-Cr alloys in helium containing small amounts of SO 2, H 2 and H 2O has been investigated. The main emphasis was placed on the behaviour of Ni-25Cr, at 850°C with the aim of studying the conditions under which a protective chromia layer is formed. To investigate the formation of a chromia layer and its destruction due to sulphidation, the gas/metal kinetics were measured quantitatively by semi-continuous gas chromatographic analysis of the gas components at the inlet and the outlet of the test chamber. The results obtained can be explained by assuming a direct reaction between the metal surface and the gas molecules SO 2, H 2O and H 2 rather than by classical equilibrium considerations involving equilibrium oxygen and sulphur partial pressures.

Microstructure of the Oxide Scale Formed on Ni-Cr Binary Alloys at High Temperature

Microstructure of the Oxide Scale Formed on Ni-Cr Binary Alloys at High Temperature

Electrochemical measurement of oxygen in liquid Ni-based alloys--the effects of Cu and Cr as additive elements.

The oxygen concentration in molten binary Ni-based alloys was estimated by an electrochemical method using solid electrolytes. The electrochemical cell was Pt|Mo+MoO2|ZrO2(MgO)|O(in liquid)|Mo. The activity of oxygen determined from the electromotive force (EMF) of the cell increased when Cu was added to pure Ni. Namely, the oxygen concentration was higher than that for pure Ni only when the amount of Cu was between 1wt% and 30wt%. In binary Ni-Cr alloys, it was deduced that the addition of 15 and 20wt% Cr to pure Ni showed the lower oxygen concentration, although the liquid Ni-based alloys having 5, 7 and 10wt% Cr tended to have higher oxygen concentrations than pure Ni.

Ni-Cr合金のNa<SUB>2</SUB>SO<SUB>4</SUB>-NaCl混合塩による高温腐食

Ni-Cr合金のNa<SUB>2</SUB>SO<SUB>4</SUB>-NaCl混合塩による高温腐食

Oxidation of high-chromium Ni-Cr alloys

The oxidation of binary Ni-Cr alloys containing 44 and 50 wt. % Cr has been studied over a range of oxygen partial pressures at temperatures between 800 and 1100°C. The effects of cold work, surface preparation, and distribution of the Cr-rich second phase have been studied. The oxidation behavior is complex and cannot be described by a single model. The oxide grows by short-circuit diffusion as well as bulk transport through Cr 2 O 3 scales. The scale-growth mechanism includes extensive metal-oxide separation requiring Cr vapor transport to the scale, compressive stresses within the oxide which result in scale bulging and cracking, and the formation of a second oxide layer which results in voids being incorporated into the scale. Any factor which reduces the oxide grain size, such as cold work, finer distribution of the Cr-rich α phase or reduced oxygen pressure, results in an increased oxidation rate of binary alloys because of an increased number of grain-boundary short-circuit diffusion paths.

The tribological behaviour of nickel and nickel-chromium alloys at temperatures from 20° to 800 °C

Measurements are presented of friction and wear during sliding of specimens of Ni-Cr alloys containing 0% to 40% Cr on like specimens in air at 20°, 400° and 800 °C. The worn specimens have been examined by optical and scanning electron microscopy, electron probe microanalysis and electron diffraction and microhardness measurements have been made. Under the sliding conditions used, all the alloys show a transition temperature above which a low coefficient of friction and usually relatively low wear are observed after a time and below which these parameters remain relatively high throughout. Above the transition temperatures, the frictiontime loci show sharp reproducible changes from relatively high to low coefficients of friction. Such changes can be associated with the formation of a thermally softened oxide layer (termed a glaze) on the bearing areas during sliding. Once the glaze is formed, very little further wear occurs for the high chromium-content alloys, although further damage does take place with the weaker low chromium-content alloys, especially at temperatures just above the transition temperature. These tribological properties of the glaze are associated with its low shear strength and the strength of the underlying alloy substrate. During sliding at temperatures below the transition temperatures, metal-to-metal contact takes place, although oxide is formed on the bearing area of the low chromium-content alloys even at 20 °C. The friction and wear behaviour is largely determined by the strength and work-hardenability of the alloy. Correlations between the tribological behaviour of these binary Ni-Cr alloys and commercial Nimonic alloys indicate that the trace elements in the latter play only a relatively minor role in determining this behaviour. It is concluded that high strengths and relatively rapid transient oxidation rates of the alloys, and appropriate physical properties of the resulting oxide films, are important qualities of the alloys under the conditions used.

種々の高Cr·Ni基耐熱合金の1100°CにおけるV<SUB>2</SUB>O<SUB>5</SUB>-Na<SUB>2</SUB>SO<SUB>4</SUB>合成灰による腐食について

High Cr, Ni-base alloys seem to have excellent resistivity to ash-corrosion because of their high Cr contents. Their corrosion resistivities were investigated experimentally by means of a contact test with 80 mol% V2O5-20 mol% Na2SO4 mixed salt for 30 hr at 1100°C. Maximum penetrations of the corrosion were also confirmed by metallographic observation of specimens after the contact test. Effects of alloying elements on the ash-corrosion resistivity of the alloys were qualitatively estimated from the weight loss in regard to (a) the effect of Cr on Ni-Cr binary alloys containing 20 to 80 wt% Cr. (b) effects of Al, B, Co, Mn, Mo, Nb, Ta, Ti, V, W and Zr on 40 Cr-Ni alloy, and (c) effects of Al, B, C, Co, Cr, Mo, Ta and Ti on C-Alloy (36 Cr, 1 Al, 1 Ti, 4 Mo, 5 Ta bal. Ni).The results are sammarized as follows:(1) The corrosion loss of Ni-Cr binary alloy is rapidly decreased for the composition of more than 40% Cr.(2) Additions of Al, B, Zr and Ti improve the ash-corrosion resistivity of 40 Cr-Ni alloy. Amoung various alloying elements the effects of B and Zr are outstanding. Additions of Nb and V are deleterious. Intergranular corrosion with S was observed in 40 Cr-Ni, 40 Cr 10 Co-Ni and 40 Cr 5 Mn-Ni alloy.(3) Similar effects were obtained for C-alloy. The corrosion loss of C-0.1 B alloy, which is a typical high Cr, Ni-base alloy, was 1/3.5 of that of U-500 and 1/5 of that of S-816.It is important to consider the alloy composition with regard to ash-corrosion resistivity even in high Cr, Ni-base alloy.

Ni-Cr合金の耐熱強度について

This investigation was conducted to evaluate the high-temperature strength of Ni-Cr binary alloys ranging from 20%Cr to 40%Cr in homogenized state after casting or rolling of about 30% at 750°C, by measuring the high-temperature hardness, testing the bending-cre p behavior, etc. It was found that rolled specimens are hard r in high-temperature-hardness and strong r in b n-ding-cr p-tests than sp cim ns without rolling. The deflection in bending-creep-tests at 700°C of 35%Cr-Ni alloy was found to be minimum in specimens homogenized without rolling, and that of 25%Cr-Ni alloy was minimum in roll d and homog nized specimens. With heating of specimens ranging from 30%Cr to 40%Cr at 700°C for 100 hrs, troostic decomposition was found to take place at the grain boundaries and spread into the grains. This was conspicuous in rolled 40%Cr alloy. One of the causes for weakness in bending-creep-strength of the rolled 40%Cr alloy will be due to the finer grains and the more decomposition. 20%Cr-Ni alloys were found to show Widmanstätten structure and subgrains after 100 hr-heat at 700°C. This phenomenon might have more or less relation with the so-called anomaly of the γ solid solution at low temperature.