Ni Cr Mo Alloy Research Articles

On the irradiation tolerance of nano-grained Ni–Mo–Cr alloy: 1 MeV He+ irradiation experiment

The irradiation damage behavior was studied in the nano-grained Ni–Mo–Cr alloy (nano-grained GH3535), which was irradiated by He ion to various dose. The evolution of defects and hardness changes are characterized by transmission electron microscopy and nanoindentation to explore the irradiation tolerance of the nano-grained GH3535 and the coarse-grained GH3535 (annealed GH3535), where the later was chosen as reference material to make comparison with nano-grained GH3535. The results show that though both the average size and number density of He bubbles increase with an increase in the irradiation dose, the smaller volume fraction is found in the nano-grained GH3535 compared with the coarse-grained GH3535 under the same irradiation condition. This indicates that the nano-grained GH3535 possess better irradiation swelling resistance than the coarse-grained GH3535. However, the increase in the hardness of the nano-grained GH3535 is more significant than in the coarse-grained GH3535 under the same irradiation dose. This suggests stronger irradiation-induced hardening of the nano-grained alloy comparing to coarse-grained alloy, due to the impeding effect caused by grain boundaries decorated with He bubbles. This study provides insight into the design of irradiation-tolerant nickel-based alloys for nuclear industry applications.

Portevin-Le Chatelier effect, twinning-detwinning and disordering in an aged Ni–Cr–Mo alloy during large plastic deformation

Abstract Portevin-Le Chatelier (PLC) effects, twinning-detwinning and disordering phenomena in long-range ordered (LRO) phase strengthened Ni–Cr–Mo alloys during hot compression are reported and investigated. The results reveal that the PLC effects with type-C serrations occur in the solution-treated and aged alloys, and that the Pt2Mo-type LRO phase can increase the serration amplitude at the early stage of deformation. Only after the early stage of deformation, the twinning of aged alloy can be activated. However, the deformation twin and the Pt2Mo-type LRO phase are not stable during the severe deformation. The potential disordering process of the LRO phase is provided as the slipping of the dislocation on the two valid {111} slip systems. The occurrence of the steps on the twin boundaries of the remanent deformation twins reveals that the detwinning mechanism is likely the dislocation-twin boundary interaction.

A study on the bacterial adhesion of Streptococcus mutans in various dental ceramics: In vitro study

AbstractStreptococcus mutans(S. mutans) has been identified as a major etiologic agent of human dental caries and forms a significant proportion of oral streptococci in carious lesions. This study investigates the correlation of surface properties (effect of contact angle [CA] and free surface energy) on three restorative materials (zirconia, nickel–chromium–molybdenum alloy and composites) used in dental prosthetics with bacterial adhesion toS. mutans. Ten samples of each material (zirconia, nickel–chromium–molybdenum alloy and composites) of 8 mm diameter and 2.5 mm thickness were used. Aqueous CA measurements, free surface energy and bacterial adhesion to the sample surfaces were performed. Bacterial adhesion is determined by planting samples in the blood agar cultures and using an electron microscope (scanning electron microscopy [SEM]). The highest values of bacterial adhesion are found in composites, followed by the metal alloy, while the lowest values are observed in zirconia. Measurements show that zirconia has 17 bacteria; Ni–Cr–Mo alloy has 65, while the composite has 80 bacteria. The composites showed the highest degree of bacterial adhesion, compared to the other investigated materials, which correlates with the free surface energy of the samples (24.31 mJ/m2for zirconia, 31.78 mJ/m2for Ni–Cr–Mo alloy and 48.82 mJ/m2for the composite).

The Effect of Microstructure and Welding-Induced Plasticity on the Strength of Ni–Mo–Cr Alloy Welds

The mechanical performance of a Ni–Mo–Cr (GH3535) alloy weldment, produced using a matching filler metal, was assessed and compared to the surrounding parent metal. Ambient-temperature mechanical characterisation included hardness testing, small punch testing and uniaxial tensile testing, while a crystal plasticity finite element model was used to assess the impact of crystallographic texture on the mechanical properties. Despite the similar chemical composition, the weld metal exhibited superior strength and ductility to that of the parent metal. The higher strength was primarily attributed to the high dislocation density in the weld metal imbued by the welding-induced thermo-mechanical loading. In contrast, the ductility difference was attributed to M6C carbide stringers in the parent metal that initiated fracture at lower strains than for the weld metal, with the latter containing much finer, well-dispersed M6C carbides.

Twinning during deformation in a Pt2Mo ordered phase strengthened Ni–Cr–Mo alloy

Twinning during deformation in a Pt2Mo ordered phase strengthened Ni–Cr–Mo alloy

Corrosion Characteristics of Typical Ni–Cr Alloys and Ni–Cr–Mo Alloys in Supercritical Water: A Review

The corrosion of supercritical water system materials under high-temperature and high-pressure conditions exists widely, which may result in the serious damage of the supercritical water reactor. T...

Corrosion Behavior of a Ni–Cr–Mo Alloy Coating Fabricated by Laser Cladding in a Simulated Sulfuric Acid Dew Point Corrosion Environment

For this study, aimed at proposing a potential direction to prevent sulfuric acid dew point corrosion, a Ni–Cr–Mo alloy Hastelloy C22 coating was fabricated by coaxial laser cladding technology. The phase composition, microstructure, and corrosion behavior in a simulated sulfuric acid dew point corrosion environment were investigated and compared with a Hastelloy C22 alloy, a titanium alloy TC4, and 09CrCuSb steel (ND). The results showed that the phase composition of the C22 coating is essentially similar to that of the C22 alloy, consisting of a γ-Ni solid solution and Ni6Mo6C1.06. The finer microstructure of the C22 coating mainly contains eutectic and dentrite, presenting a typical solidification feature of laser cladding. The corrosion resistance of the C22 coating is very close to that of the C22 alloy, and outclasses that of TC4 and ND. The corrosion behavior of the C22 coating is intergranular corrosion resulting from the segregation of molybdenum, chromium containing corrosion products, and smaller anode micro-batteries.

Laves Phase Formation and Segregation of Nb in Ni–Cr–Mo Superalloy over 316L by Hot Wire (HW) TIG Cladding Process

The Ni-based alloys are widely used in power plant components such as boiler and piping systems that require good creep strength and resistance to corrosion. The present study focuses on metallurgical and mechanical properties of Ni–Cr–Mo (ERNiCrMo-3) alloy cladded over 316L plate by hot wire TIG process. This alloy is prone to microfissuring and also reduced corrosion resistance due to microstructural changes caused by weld solidification. The microstructure and phasic characterization were identified using scanning electron microscopy and X-ray diffraction techniques. From the microstructural observation, it was observed that Nb present in Ni–Cr–Mo alloy tends to segregate during solidification of weld thereby promoting the Nb-rich Laves phase formation. The growth of dendrites enhanced the segregation of Nb. The coarse dendritic microstructure was due to the effect of high heat input that decreases solidification rate near the interface zone. Dimples and quasi-cleavage fracture morphology was observed on the fractured samples of the tensile test. The resistance to corrosion was evaluated using potentiodynamic polarization method using 3.5 wt% NaCl solution. The results confirmed that Ni–Cr–Mo alloy acts as an efficient clad for 316L substrate from corrosion attack.

Impact of dislocations and dislocation substructures on molten salt corrosion of alloys under plasticity-imparting conditions

Molten-salt-based energy-generation and energy-storage systems are expected to function under plasticity-imparting in-service operating conditions. It is thus of utmost importance to understand the effect of these operating conditions on the corrosion performance of molten-salt-facing structural alloys. Here, we investigate the impact of high-temperature creep on the molten salt corrosion of a NiMoCr alloy in FLiNaK molten salt. We show that high-temperature creep leads to an increased susceptibility of the alloy to molten salt corrosion via the development of a dislocation substructure, which promotes mass diffusion of alloying elements towards the salt–alloy interface (exposed surface). In addition, the corrosion-affected near-surface layer undergoes recrystallization leading to a significant increase in the amount of grain boundaries, which further promotes ongoing diffusion processes. This then causes increased molten salt corrosion attack resulting in an accelerated mass loss during the alloy’s exposure to the molten salt. The present results thus unambiguously highlight the importance of the state of the microstructure as well as the evolution of the microstructure under in-service operating conditions on the alloy’s molten salt corrosion performance.

Influence of interatomic interactions on the mechanical properties of face-centered cubic multicomponent Co–Ni–Cr–Mo alloys

The composition of a multicomponent solid solution has a significant influence on its mechanical and microstructural properties. Herein, the microstructures, phase stabilities, mechanical properties, and interatomic interactions of multicomponent Co–(5–55)Ni–19Cr–9Mo (mass%) alloys with varying Ni contents were comprehensively investigated. First-principles calculations were performed to predict the mechanical properties, electron distributions, atomic bonding states, and density of states of the alloy system. The local charge distribution revealed that the alloying elements exhibit stronger bonds with Co atoms than with Ni atoms, and the Ni–Ni bond is the weakest; accordingly, an increase in the Ni content generally diminishes the interatomic interactions in the studied alloy system. Meanwhile, significant augmentations in the strength and elastic modulus were observed at 45 mass% Ni. This was attributed to the additional interactions that are prevalent in 45 and 55 mass% Ni alloys that stem from the second-nearest Ni atoms with vacant 3d states and involve Co, Cr, and Mo atoms. Strengthening analyses indicated that the shear moduli predetermined the changes of yield strength with respect to the Ni contents. The stacking fault energies (SFEs) were calculated ab initio at 0 K and thermodynamically at 1500 K. A similar trend in the SFE variations was obtained under special consideration of the concentration dependence of the Co–Ni interaction, which indicated the significant influence of interatomic interactions even at elevated temperatures.

Molten salt corrosion (FLiNaK) of a Ni–Mo–Cr alloy and its welds for application in energy-generation and energy-storage systems

The molten salt corrosion performance of a Ni–Mo–Cr (GH3535) alloy weldment, produced using matching filler metal, was assessed. Corrosion testing was performed in FLiNaK molten salt at 750 °C for 500 h. Present results reveal that, despite a similar chemical composition, the weld metal has somewhat superior corrosion resistance to the parent metal. The difference is primarily attributed to the significantly lower density of high-angle grain boundaries (HAGBs) in the weld metal. Results further suggest that large M6C carbides present in the parent metal may contribute to corrosion attack of the alloy matrix via galvanic corrosion.

Dissimilar Cladding of Ni–Cr–Mo Superalloy over 316L Austenitic Stainless Steel: Morphologies and Mechanical Properties

The solid solution strengthened Inconel 625, a Ni-based alloy is known for its excellent strength and good corrosion resistance at extreme environments used in thermal plants, boiler tubes, petrochemical industry and power plant. The presence of Cr content (~ 20 wt%) along with Mo-rich, Nb and Fe makes Ni–Cr–Mo–Nb austenitic alloy called as Inconel 625 to achieve excellent corrosion resistance property. Using cold metal arc transfer (CMT) cladding, the metallurgical, mechanical and corrosion properties of Inconel 625 on 316L is evaluated. The process parameters selected includes welding current, torch angle and travel speed with a constant voltage. From the results of microstructural and EDS inferences, the formation of cellular dendritic structure with secondary phases like Laves phase, complex nitrides along with the interdendritic segregation of Mo and Nb as well as microsegregation of Cr, Ni and Fe. In case of Ni–Cr–Mo alloy, Ni and Cr contribute to resistance to corrosion in NaCl environments. The formation of Cr2O3 and the passivation action of the clad zone is due to the presence of Cr. The solid solution effect in Ni–Cr matrix is contributed by the presence of Nb and Mo. Apart from that the strengthening action happens due to the precipitation of Ni3 (Al, Ti, Nb) commonly known as γ′, γ″ and MC carbides confirmed through XRD. Uni-axial tensile tests and Vickers-micro hardness indentation tests were performed on Inconel 625 cladded over 316L. Based on the fractographic results fatigue striations, tear rigdes with river markings, dimples with fibrous structure and cleavages are observed. Unlike other studies, unique type of cuboidal precipitates are seen, which is due to the presence of Ti, which form carbonitrides containing Ti, which are further characterised as NbC. The potentiodynamic polarisation tests is performed on 3.5% NaCl solution. The results suggest that Ni–Cr–Mo alloy protects the substrate from corrosion.

Effect of addition of recast materials on characteristics of Ni-Cr-Mo alloys

Abstract The purpose of this study was to assess the effect on selected mechanical properties, of adding recast materials to the NiCrMo alloy of newly produced castings. Three groups of dental alloy NiCrMo (trade named Remanium CS+) were prepared by mixing 50% new alloy to alloy remnants from previous castings. The specimens in the first casting group used 100% new alloy and served as control (C1). The second group consisted of equal amounts of new alloy and alloy remnants cast only once (C2). The third group contained 50% of new alloy and alloy cast twice (C3). Microstructural analysis was performed and the chemical composition, hardness and the metal-ceramic bond strength were assessed. In addition, EDS analysis (mapping) was undertaken. Hardness and bond strength results were also statistically analysed. In spite of the fact that recasting brought about small changes in hardness and chemical composition (C, Cr and Mo), these effects were found to not affect their functional properties in the oral cavity. Still, significant differences between new alloy and the recasted groups (p < 0.05) were demonstrated in the course of statistical analysis of Vickers hardness test (for α = 0.05). All analysed research groups have a similar average adhesion at 48.51÷49.24 MPa (p > 0.05). The recasting procedure described in the paper can be done safely in dentistry. If previously casted material is used, it should be mixed with new material. The use of the material prepared in this way can lower the costs of NiCrMo castings.

Early-stage NiCrMo oxidation revealed by cryo-transmission electron microscopy

Hydroxide formation at the surface of corroded alloys is critical for understanding early-stage oxidation of many corrosion-resistant alloys. Many hydroxides are unstable in an ambient environment and are electron-beam sensitive, limiting the use of conventionally-prepared specimens for transmission electron microscopy characterization of these alloy-water interfaces. In order to avoid sample dehydration, NiCrMo alloys corroded in a Cl−-containing electrolyte solution were cryo-immobilized by plunge freezing. A cryo-focused ion beam microscope was used to thin the sample to electron transparency, while preserving the alloy-water interface, and the sample was then cryo-transferred to a transmission electron microscope for imaging and diffraction. The presence of rocksalt Ni1-xCr2x/3O and β-Ni1-xCr2x/3(OH)2 phases and their orientational relationship to the underlying alloy were observed with electron diffraction, confirming the preservation of the surface structure through the fully-cryogenic sample preparation and analysis.

Nonequilibrium Solute Capture in Passivating Oxide Films.

We report experimental results on the composition and crystallography of oxides formed on NiCrMo alloys during both high-temperature oxidation and aqueous corrosion experiments. Detailed characterization using transmission electron microscopy and diffraction, aberration-corrected chemical analysis, and atom probe tomography shows unexpected combinations of composition and crystallography, far outside thermodynamic solubility limits. The results are explained using a theory for nonequilibrium solute capture that combines thermodynamic, kinetic, and density functional theory analyses. In this predictive nonequilibrium framework, the composition and crystallography are controlled by the rapidly moving interface. The theoretical framework explains the unusual combinations of composition and crystallography, which we predict will be common for many other systems in oxidation and corrosion, and other solid-state processes involving nonequilibrium moving interfaces.

Repassivation Behavior of Individual Grain Facets on Dilute Ni–Cr and Ni–Cr–Mo Alloys in Acidified Chloride Solution

The effects of crystal orientation and prior etching on the polarization and repassivation behavior of Ni–Cr and Ni–Cr–Mo alloys have been investigated in acidic chloride environment using dc potentiostatic and ac single-frequency electrochemical impedance spectroscopy. Tests were conducted within the passive region at potentials where local oxide breakdown was possible. Surface morphologies of grains across a wide range of orientations were measured before and after passivation using atomic force microscopy. Oxide growth was monitored on isolated low- and high-index crystallographic planes as a function of repassivation time, enabling the independent measurement of the oxidation and total anodic current densities. Grains exhibited the tendency to either passivate with significant or minimal oxidation or instead resist active passivation and repassivation. The oxidation performance was a function of the crystallographic orientation of the exposed grain surface. The oxides grown on various-orientated surfa...

In Situ Observations of Early Stage Oxidation of Ni-Cr and Ni-Cr-Mo Alloys

Results of in situ transmission electron microscopy experiments on the early stage oxidation of Ni-Cr and Ni-Cr-Mo alloys are reported. An epitaxial rock-salt oxide with compositions outside the conventional solubility limits initiated at the surface of both alloys, progressing by a layer-by-layer mode. Kirkendall voids were found in Ni-Cr alloys near the metal/oxide interface, but were not seen in the Ni-Cr-Mo. The voids initiated in the oxide then diffused to the metal/oxide interface, driven by the misfit stresses in the oxide. A sequential oxide initiation was observed in NiCr alloys: rock-salt → spinel → corundum; however, for NiCrMo alloys, the metastable Ni2-xCrxO3 (corundum structure) phase formed shortly after the growth of the rock-salt phase. Chemical analysis shows that solute atoms were captured in the initial oxide before diffusing and transforming to more thermodynamically stable phases. The results indicate that Mo doping inhibits the formation of Kirkendall voids via an increase in the nucleation rate of corundum, which was verified by density functional theory calculations.

X‐Ray Diffraction Technique for Residual Stress Measurement in NiCrMo Alloy Weld Metal

In the present work, residual stresses in nickel‐based (Ni 625) superalloy weld metal of a 9%Ni steel‐welded joint were measured by X‐ray diffraction (XRD). This technique presents some difficulties in performing measurements in coarse and preferentially oriented weld metal microstructures. It is proposed a preliminary surface treatment by rotating steel wire brushing to perform the stress analysis through XRD technique possible for this kind of material. Stress measurements with proposed XRD technique showed that the stress state in Ni 625 weld metal on the outside surface of the welded joint is characterised by tensile stresses in the transverse and longitudinal directions, while compressive transverse and tensile longitudinal residual stresses are developed in the root pass region.

Effect of Recasted Material Addition on the Quality of Metal‐Ceramic Bond: A Macro‐, Micro‐, and Nanostudy

Using the recasted alloys in dental prosthetics could affect the quality of the metal‐ceramic bond. However, scientists, alloys producers, and prosthetists are still of different opinions. The purpose of this study was to estimate the influence of recasting of the NiCrMo alloy on the metal‐ceramic bond quality. The research was carried out on macro‐, micro‐ and nanoscales using the three‐point bending test procedure and hardness tests as well as atomic force microscopy and SEM analyses. The SEM analyses showed good integrity of the metal‐ceramic bond. The τb index of all test samples was greater than 45 MPa. The highest values were recorded for the samples made of 50% and 100% of a brand new material. SEM analysis made after the bending test confirmed good metal‐ceramic bond and exhibited adhesive‐cohesive fracture. The largest hardness of metal plates was found for the samples containing 50% of the recycled material. Atomic force microscopy studies showed that the alloy containing 50% of the recycled material was characterized by the highest values of surface roughness parameters.

Electrochemical and corrosion behavior of two chromium dental alloys in artificial bioenvironments

The purpose of this study is to compare the corrosion and tarnish behavior of NiCrMo and CoCrMo cast dental alloys in artificial bio environments. The cobalt chromium alloys are known and used in dentistry for many years, but its difficult machinability because of the strength and hardness, is an argument for scientists to study alternative materials with comparable biocompatibility. On the other hand, for dentistry devices beside corrosion behavior is important the aesthetic so, the used alloys have to preserve their shining and do not stain. The corrosion resistance has been evaluated using the Atomic mass spectroscopy method for ion release determination, the anodic polarization curves and the open circuit potential – time monitoring for corrosion behavior evaluation and optical microscopy for the structure analysis. The tarnish tendency of alloys was estimated using the method of cyclic immersion with frequency of 10 seconds for each minute during 72 hours in Na 2 S containing solution. The most important conclusion is that the alloys are comparable from corrosion and tarnish point of view, but we recommend to use the nickel base alloy only for orthodontic devices implanted for short periods of time, because of higher quantity of released ions.