Ni Cr Mo Alloy Research Articles

A general model for the repassivation potential as a function of multiple aqueous solution species

A general model for predicting the localized corrosion repassivation potential of alloys in multicomponent electrolyte solutions is described. The model assumes that the status of localized corrosion is determined by competitive processes at the metal–salt film–solution interfaces leading to either metal salt or oxide formation. The model successfully predicts the observed effects of aggressive species, such as chloride and bromide, inhibiting species, such as nitrate, and non-aggressive species, such as acetate, for a number of Fe–Ni–Cr–Mo alloys. Furthermore, the model accurately predicts the effect of nitrate in a three-component system of chloride + nitrate + acetate, based only on parameters regressed for the constituent binary systems.

Fractal study of Ni–Cr–Mo alloy for dental applications: effect of beryllium

Different Ni-based alloys with various compositions were prepared by varying the amounts of beryllium. Effect of the amount of beryllium added to the alloy on its corrosion in an electrolyte solution of artificial saliva was investigated. Fractal dimension was used as a quantitative factor for surface analysis of the alloys before and after storage in the artificial salvia. The fractal dimensions of the electrode surfaces were determined by means of the most reliable method in this context viz. time dependency of the diffusion-limited current for a system involving “diffusion towards electrode surface”. The results showed that increase of the beryllium amount in the alloy composition significantly increases the alloy corrosion. It is accompanied by increase of the fractal dimension and roughness of the electrode surface, whereas a smooth and shiny surface is required for dentures. From the methodology point of view, the approach utilized for fractal analysis of the alloy surfaces (Au-masking of metallic surfaces) is a novel and efficient method for study of denture surfaces. Generally, this approach is of interest for corrosion studies of different metals and alloys, particularly where changes in surface structure have a significant importance.

Microsegregation in open and closed multicomponent systems

A simplified model for microsegregation in multicomponent systems has been developed for solidification, remelting, and dissolution of solid that may occur due to thermal and solutal changes. Compared to existing models, calculations are simplified by considering only the solid/liquid interface and the liquid portion of the domain at any given time, eliminating the solid composition integral from the mixture equation. Predictions may be made using a predefined cooling curve and composition history, or the model may be run in a fully coupled mode with a macro-scale model. Simulation results are presented for three Ni–Cr–Mo alloys under different solidification conditions, including open systems. The results demonstrate the multiple phase formation and tracking capabilities of the model in addition to highlighting the differences in the enthalpy- and temperature-controlled formulations.

Influence of Plastic Deformation on Creep Behaviour of NiMoCr Alloy

Creep behaviour of nickel-base solid solution strengthened NiMoCr alloy after different applied hot and cold rolling conditions was investigated. The results of creep tests showed that the creep characteristics including strain rate, fracture strain, and lifetime were greatly dependent on the plastic deformation conditions carried out prior to the creep. Failure process including crack nucleation and crack propagation was strongly dependent on grain size. Fine recrystallized structures have provided much less resistance to creep deformation compared to coarse grain size. A comprehensive study of creep deformation as a function of plastic deformation conditions of NiMoCr alloy is also presented.

Corrosion behavior of NiCrMo Alloy 625 in high temperature, hydrogenated water

The corrosion behavior of NiCrMo Alloy 625 (UNS N06625) has been characterized in a 10,000 h test conducted in hydrogenated water at 260 °C. The corrosion kinetics were observed to be parabolic, the parabolic rate constant being determined by chemical descaling to be 0.074 mg dm −2 h −1/2. Characterizations of the corrosion oxide layer via grazing incidence X-ray diffraction and X-ray photoelectron spectroscopy in combination with argon ion milling and target factor analysis, revealed the presence of two spinel oxide phases and significant amounts of recrystallized nickel. Based on the distribution of three oxidized alloying constituents (Ni, Cr, Fe) with respect to depth and oxidation state, it was concluded that: (a) corrosion occurs in a non-selective manner, but significant amounts of nickel(II) ions are released to the water, and (b) the spinel oxides exist as a chromite-rich inner layer (Ni 0.7Fe 0.3)(Cr 0.8Fe 0.2) 2O 4 underneath a coarser, ferrite-rich outer layer (Ni 0.9Fe 0.1)(Cr 0.1Fe 0.9) 2O 4. The trivalent cation distribution in each of these phases appears to represent a solvus in the immiscible NiCr 2O 4–NiFe 2O 4 binary.

Controlled Rolling of Hastelloy-N

This paper provides information of the uniform grain structure after application of hot and cold rolling conditions and recrystallization processes followed by various annealing times in NiMoCr alloy. The different structure would result in high temperature mechanical properties such as yield strength, tensile strength, ductility, fatigue, and creep strength. The microstructural changes as results from all tested programs were investigated by optical microscope. The obtained results showed that the uniformity of recrystallized structure relates strongly to amount of deformation during hot and cold rolling and period of annealing time. It was also found that the uniformity of recrystallized structure increased with higher deformation and longer annealing times. The formability was tested and the base deformation resistances (BDR) were also calculated.

Experimental procedure for crevice corrosion studies of Ni–Cr–Mo alloys in natural seawater

An experimental procedure intended for crevice corrosion studies on Ni–Cr–Mo alloys is demonstrated. In this procedure a potentiostatic control of crevice corrosion specimens is applied to an immersible crevice cell design that uses a fluoroelastomer gasket crevice former. The procedure is demonstrated for a crevice susceptibility study on Alloy 625 in elevated temperature natural seawater, where crevice corrosion initiation and propagation are shown to be influenced by the electrochemical potential. Potentiostatic current monitoring establishes the crevice initiation time and rate of propagation, while post-mortem inspections confirm the extent of crevice damage.

Optimization of mechanical properties of a Ni–Mo–Cr alloy by structural modifications induced by changes in heat treatment

The influence of modifications of heat treatment applied to a commercial Ni–25 wt.%Mo–8 wt.%Cr age-hardenable alloy (HAYNES® 242™) on microstructure and mechanical properties were investigated. The standard heat treatment (aging at 650°C for 72 h), producing coherent long-range ordered domains with the Ni 2(Mo, Cr) stoichiometry, was modified by short duration thermal exposures at temperatures at between 760 and 980°C (preceding the alloy's aging). The intermediate heat treatment (IHT) affected the size of the long-range order domains and produced precipitations of a μ phase on the grain boundaries. The size of the ordered domains depended on the temperature of the IHT. The largest domains occurred after the IHT at 760°C. With the increase in the IHT temperature, the domain size decreased. The yield strength of the alloy increased with increasing domain size. The amount of grain boundary particles, and not the size of the ordered domains, controlled the ductility of the material subjected to the IHT: The more grain boundary precipitates there were, the lower tensile ductility. Optimization of the tensile properties (strength and ductility) of the examined alloy occurred when the conventional aging was preceded by the IHT at 760°C.

Fabrication of YBa 2Cu 3O 7− x superconducting film with CeO 2/BaTiO double buffer layer

Good quality superconducting YBa 2Cu 3O 7− x (YBCO) thin films have been fabricated on Hastelloy (Ni–Cr–Mo alloys) metallic substrates with CeO 2 and BaTiO 3 buffer layers in situ by pulsed laser deposition in a multi-target processing chamber. YBCO film with CeO 2 single buffer layer shows a T c of 71.64 K and a grain size less than 0.1 μm. When BaTiO 3 is used as a single buffer layer, the grain size of YBCO is observed to be 200 times larger than YBCO/CeO 2 and the transition temperature of the film is enhanced by approximately 84 K. The CeO 2/BaTiO 3 double buffer layer has been adopted to enhance the superconducting properties, which results in an enhancement of the critical temperature and the critical current density by approximately 85 K and 8.4×10 4 A/cm 2 at 77 K, respectively, mainly due to the enlargement of the grain size of YBCO film.

Effect of CeO 2, BaTiO 3 and CeO 2/BaTiO 3 double buffer layers on the superconducting properties of Y 1Ba 2Cu 3O 7−x grown on metallic substrates by pulsed laser deposition

We have fabricated good quality superconducting YBa 2Cu 3O 7− x (YBCO) thin films on Hastelloy (Ni–Cr–Mo alloys) metallic substrates with CeO 2 and BaTiO 3 buffer layers in situ by pulsed laser deposition in a multi-target processing chamber. YBCO films with CeO 2 single buffer layer show T c of 71.64 K and the grain size less than 0.1 μm. When BaTiO 3 is used as a single buffer layer, the grain size of YBCO is observed to be larger than that of YBCO/CeO 2 by 200 times and the transition temperature of the film is enhanced to be about 84 K. CeO 2/BaTiO 3 double buffer layer has been adopted to enhance the superconducting properties, which results in the enhancement of the critical temperature and the critical current density to be about 85 K and 8.4 × 10 4 A/cm 2 at 77 K, respectively mainly due to the enlargement of the grain size of YBCO film.

Epitaxial growth of YBCO on Hastelloy with YSZ buffer layer by laser ablation

Good quality superconducting YBa 2Cu 3O 7− δ (YBCO) thin films were grown on Hastelloy (Ni–Cr–Mo alloys) with yttria-stabilized zirconia (YSZ) buffer layers by in situ pulsed laser deposition in a multi-target processing chamber. Generally, Hastelloy exhibits excellent resistance to corrosion, fatigue, thermal shock, impact, and erosion. However, it is difficult to make films on flexible metallic substrates due to interdiffusion problems between metallic substrates and superconducting overlayers. To overcome this difficulty, it is necessary to use YSZ buffer layer since it will not only limit the interdiffusion process but also minimize the surface microcrack formation due to smaller mismatch between the film and the substrate. In order to enhance the crystallinity of YBCO films on metallic substrates, YSZ buffer layers were grown at various temperatures different from the deposition temperature of YBCO films. On YSZ buffer layer grown at higher temperature than that for depositing YBCO film, the YBCO thin film was found to be textured with c-axis orientation by X-ray diffraction and had a zero-resistance critical temperature of about 83 K.

Spray diffusion: new method for surface modification combined with thermal spray and heat treatment

This paper describes post-heat treatment reaction diffusion between thermal sprayed aluminium and several kinds of substrate. The alloy layer formedby the spray diffusion process depends strongly on the composition of the substrate. It was found that appropriate surface properties can be obtained by selecting substrates of suitable composition and/or byselecting appropriate interlayers between the substrate and aluminium top coating. First, formation of alloy phases between an aluminium spray coating and a pure iron or plain carbon steel substrate by spray diffusion was examined in order to obtain fundamental information. Second, an 18Cr–8Ni austenitic stainless steelsubstrate was selected for testing. Finally, interdiffusion of multiple layered coatings with Ni–Cr–Mo alloys and aluminium on to stainless steel substrates was investigated.

The “C” family of Ni‐Cr‐Mo alloys' partnership with the chemical process industry: The last 70 years

AbstractThe “C” family of alloys, the original being Hastelloy® alloy C (1930's) was an innovative optimization of NiCr alloys having good resistance to oxidizing corrosive media and NiMo alloys with superior resistance to reducing corrosive media. This combination resulted in the most versatile corrosion resistant alloy in the “NiCrMo” alloy family, with exceptional corrosion resistance in a wide variety of severe corrosive environments typically encountered in CPI and other industries. The alloy also exhibited excellent resistance to pitting and crevice corrosion attack in low pH, high chloride oxidizing environments and had virtual immunity to chloride stress corrosion cracking. These properties allowed this alloy to serve the industrial needs for many years, although it had some limitations. The decades of the 1960's (alloy C‐276), 1970's (alloy C‐4), 1980's (alloy C‐22 and 622) and 1990's (alloy 59, alloy 686 and alloy C‐2000) saw newer alloy developments with improvements in corrosion resistance, which not only overcame the limitations of alloy C, but further expanded the horizons of applications as the needs of the CPI became more critical, severe and demanding.Today the originally alloy “C” of the 1930's is practically obsolete except for some usage in form of castings. This paper presents a chronology of the various corrosion resistant alloy developments during this century, with special emphasis on the last 70 years evolution in the “C” family of NiCrMo alloys and their applications.

Corrosion-resistant NiCrMo alloys in hot concentrated sulphuric acid with active carbon

Abstract Dewpoint corrosion by sulphuric acid has often been observed in the heat exchangers of coal-burning plants. If ashes contain active carbon, corrosion becomes particularly serious. Various nickel-base alloys with high corrosion resistance in such environments have been designed. The corrosion behaviour of these alloys was examined in hot concentrated sulphuric acid with and without active carbon. The corrosion resistance of ternary NiCiMo alloys in the acids without active carbon increases with increasing alloy molybdenum content. When active carbon is added to the acids, the corrosion rate increases significantly. This is due to acceleration of transpassive dissolution of molybdenum as a result of enhancement of cathodic activity with the addition of active carbon. The corrosion resistance in the acids with active carbon is enhanced by an increase in alloy chromium content, which improves the passivity in the acids.

Studies on the influence of BE content on the corrosion behavior and mechanical properties of Ni-25Cr-10Mo alloys

The influence of Be content on the corrosion behavior and strength of dental alloys was examined using experimental Ni-25Cr-10Mo-xBe alloys with graduated Be contents of 0, 0.6, 1.1, 1.6 and 2.1 wt.%. It became evident that the corrosion resistance is reduced even by a 0.6 wt.% Be content. Strength increases by 51 % with increasing Be content, while ductility is reduced by 84 %. The results revealed that, from the standpoint of corrosion resistance, Be-free NiCrMo alloys should be preferred in clinical use.

Marginal accuracy of complete crowns made from alternative casting alloys

The marginal accuracy of complete cast crowns made from five alternative casting alloys was measured and compared with that of crowns made from the traditional type III high-gold alloy. The alternative alloys studied were low-gold-palladium, high palladium, silver-palladium, nickel-chrome-molybdenum, and copper-aluminum. The findings indicated that Ag-Pd alloy crowns exhibited the best marginal accuracy among the alternative alloys tested. However, their marginal discrepancy value was still slightly higher than that of crowns made of type III high-gold alloy. Conversely, Ni-Cr-Mo alloy crowns exhibited the poorest marginal accuracy.

4906437 Corrosion resistant hot and cold forming parts of NICRMO alloy and method of making same : Ulrich Heubner, Michael Kohler, Manfred Rockel, Ernst Wallis, Werdohl, Federal Republic of Germany assigned to VDM Nickel-Technologie Aktiengesellschaft

4906437 Corrosion resistant hot and cold forming parts of NICRMO alloy and method of making same : Ulrich Heubner, Michael Kohler, Manfred Rockel, Ernst Wallis, Werdohl, Federal Republic of Germany assigned to VDM Nickel-Technologie Aktiengesellschaft

Passivation of NiCrMo alloys in chloride solution a new kinetics model

In studying the current I a decay versus time under anodic polarization during the passive film growth the experiment data are found to obey the relation: I a = A t −b exp(Ct). The C coefficient accounts for the observed deviations, characterized by downward or upward bendings observed on the logI a=f(logt) plots. The potential dependencies of the A and C kinetics parameters allows a better understanding of the nickel base alloys behaviour in chloride solutions, in which the pit initiation competes with the passivation process for potentials higher than a critical value E c, lower than the pitting potential. A new kinetics model of the film growth is then proposed, leading to the final expression of the metal cations concentration including the electrical migration transposed in the finite oxide medium. This model pointed out the high effect of the electrostatic field on the current responses of the studied systems.

Determination of the corrosion rates of six dental NiCrMo alloys in an artificial saliva by chemical analysis of the medium using ICP-AES

So that the influence of salivary components upon the corrosion rate of six dental NiCrMo alloys could be established, their mass loss was determined in a medium consisting of a modified Fusayama's artificial saliva to which 300 mg KSCN/L had been added (pH 5.0). Nickel was the main element released; its loss vs. immersion time curves on a log-log plot resembled straight lines. The total nickel losses after one week ranged from 0.4 to 12.5 μg/cm 2. From the nickel loss, corrosion currents were calculated. The corrosion currents at 24 hours of immersion were up to 67% larger than the currents in a previous study of these alloys, where the medium consisted of a 20 mM KCl-5 mM phosphate buffer solution (pH 7). The alloys with the least molybdenum content showed the largest corrosion current increase.

Electrochemical Behavior and Its Relation to Composition and Sensitization of NiCrMo Alloys in ASTM G-28 Solution

Abstract Nickel-chromium-molybdenum alloys are usually tested in a ferric sulfate-sulfuric acid solution according to ASTM G-28 to ensure that intergranular attack caused by sensitization of grain ...