High Ni Alloys Research Articles

Corrosion Behavior of Candidate Structural Materials for Molten Salt Reactors in Flowing NaCl-MgCl2

Abstracts. A high-temperature molten salt natural convection loop was designed and manufactured for chloride-based salts. NaCl-MgCl2 salt was prepared and injected into the loop. Corrosion coupons composed of SS304, SS316L, and high-Ni alloys were also prepared as candidate structural materials for molten chloride salt reactors. After a corrosion experiment was conducted for 500 h, the salt was drained from the loop to the drain tank; inductively coupled plasma optical emission spectroscopy was used to investigate metal dissolution from the materials into the salt. The corroded materials were analyzed using scanning electron microscopy and energy-dispersive X-ray spectroscopy to calculate the corrosion rate. Materials exposed to NaCl-MgCl2 molten salt showed varying levels of corrosion resistance. The high-Ni alloy demonstrated the highest resistance, followed by SS316L and SS304. Furthermore, corrosion products were observed to migrate along the molten salt through natural convection, eventually depositing onto the surface of the high-Ni alloy in the cold leg of the loop.

Long-term creep behaviours and structural stabilities of austenitic heat-resistant stainless steels

ABSTRACT For heat resistant alloys, long-term structural stability at high temperatures is a critical issue for alloy design and applications. In this paper, the long-term creep behaviours and structural stabilities of six heat resistant high Ni alloys and austenitic stainless steels have been studied. The longest creep rupture life is up to 359 283 hours. High Ni and Cr alloys show a good combination of high creep and oxidation resistances. Precipitation of nano MX particles with a very low growth rate improves long-term creep resistance at high temperatures. Long-term stable multiple nanoprecipitates of MX, Cu-rich, Laves and M23C6 phases can greatly contribute to the creep strength. Low Ni austenitic stainless steels show comparatively low oxidation and creep resistances. It was first found that at 800°C, Cr2N could form in the low Ni steel with a long-term crept by the absorption of nitrogen from the air into the matrix.

A study on WC-Ni cemented carbides: Constitution, alloy compositions and properties, including corrosion behaviour

The manuscript presents a systematic study on three groups of Ni-based cemented carbides (WC-20 wt% Ni, WC-20 wt% Ni15Cr and WC-20 wt% Ni11Cr6Mo) based on thermodynamic calculations and experimental studies. Samples were prepared with different gross carbon contents (carbon activities) with the aim to provide a comprehensive overview on: constitution and phase formation, solubility of elements in the binder phase, binder and composite hardness, as well as their corrosion behaviour. A WC-20 wt% Co8Cr was used as standard binder system for comparison.The results show that the amount of alloying elements that can be dissolved in the binder phase is significantly higher in the Ni binder as compared to the Co binder (e.g., the solubility of W in WC-Ni is about double of that observed in conventional WC-Co). The degree of alloying is primarily affected by the carbon content. The lower the gross carbon content within the processing window, the higher is the degree of binder alloying. In WC-Ni, up to 12 at% W is observed in solution in low carbon alloys, as compared to 4 at% W in high carbon grades. Additions of Cr are limited to 9–11 at% Cr, depending on the gross carbon content. When exceeding this value, Cr3C2 is formed in high carbon Ni alloys. The solubility of Mo in WC-NiCrMo cemented carbides is limited to about 2 at%, at higher additions a carbide is formed, most likely (W,Mo)C.The high hardness values observed in NiCr and NiCrMo alloys when compared to plain Ni alloys can be attributed to the effect of Cr and Mo as WC grain growth inhibitors, and not to a significant enhancement of the intrinsic binder hardness. In contrast, our standard Co grade demonstrated a significantly higher binder and composite hardness than all of the nickel variants studied.Finally, high-alloyed materials (low carbon NiCr- and NiCrMo alloys) did present a superior corrosion resistance compared to the CoCr grade even in the most severe corrosion environments. Higher degree of alloying (i.e., higher amounts of Cr, W, and Mo present in solid solution in the binder) is indicative of superior corrosion behaviour due to the nature of the protective layers formed under corrosive environments.

Hot Chlorination Corrosion of Metallic Nickel by Chlorine Catalyzed by Sodium Chloride.

Reducing chlorine corrosion to metals at high temperatures is a big problem for many industrial processes. Some high Ni alloys such as Hastelloy C-276 (Ni > 50 wt %) have been widely used for this purpose. Chlorine and chlorides often coexisted in many industrial processes at high temperatures, such as some industrial incinerators and metallurgical furnaces. Thus, a comprehensive experimental investigation regarding the effect of NaCl on the chlorination corrosion of metallic nickel powder by chlorine at a high temperature was performed. It was more convenient to investigate the intrinsic chlorination mechanisms and kinetics of metallic Ni if Ni powder was used instead of a Ni plate. It was found that there existed a critical chlorination temperature of 450 °C for relative safe use of Ni-based alloy in the presence NaCl. The Ni chlorination in the presence of NaCl was increased with increasing temperature and reached a maximum of 97% at 700 °C, which was about 21% higher than that in the absence of NaCl. An anhydrous NiCl2 was initially formed at about 700 °C during the chlorination process and then immediately reacted with NaCl to form a novel eutectic complex with a flaky shape, a melting point of 585 °C, and a simplified molecular formula of NiNa0.33Cl2.33 based on X-ray diffraction (XRD), differential thermal analysis (DTA), scanning electronic microscopy (SEM), and chemical analysis with inductively coupled plasma atomic emission spectroscopy (ICP-AES). As a result, only the complex of NiNa0.33Cl2.33 and NaCl was left in the chlorinated product. At 700 °C, the chlorinated product evaporated only in the form of complex NiNa0.33Cl2.33 instead of individual NiCl2 or NaCl. The chlorination mechanisms of metallic Ni at a high temperature, for example, 700 °C, in the presence of NaCl were as follows. Step 1: Formation of initial chlorinated solid product NiCl2 (mp 1001 °C) at a high temperature; step 2: The NiCl2 reacted with solid additive NaCl (mp 801 °C) to form a final liquid product NiNa0.33Cl2.33 (mp 585 °C); step 3: External Cl2(g) was dissolved in the liquid product layer; step 4: The chlorine dissolved in the liquid product of NiNa0.33Cl2.33 reacted with the unreacted Ni core. The external Cl2(g) passed through the liquid product NiNa0.33Cl2.33 layer faster than the solid product NiCl2 layer formed in the absence of NaCl. This resulted in 21% more chlorination corrosion of metallic Ni powder with NaCl addition than that without NaCl addition.

Metallurgical Characterization of the Interfaces in Steel Plates Clad with Austenitic Steel or High Ni Alloys by Hot Rolling

An integrated experimental-theoretical approach to the metallurgical characterization of the interfaces in steel plates clad by hot rolling is proposed. Three different couplings of materials have been studied: ASTM A 515 Gr.60 low carbon steel clad with austenitic stainless steel AISI 304L; extra low carbon steel ASTM A283 clad with high Ni content Alloy 59; and, low carbon steel AISI 1010 clad with Cu-Ni Monel 400. Experimental investigations, which are addressed to analyse the microstructural changes near the interfaces and identify the present phases, have been carried out through scanning electron microscopy (SEM) observations, microanalytical measurements by energy dispersive spectroscopy (EDS), and Vickers microhardness tests. In all of the cases examined, the zones that are affected by detrimental microstructural changes results in being considerably less thick than the overall cladding layer. Simulations that are based on theoretical diffusion modelling have been integrated to the experimental characterization by introducing a cladding parameter that acts on the diffusion bonding efficiency, in order to evaluate the effects of process temperature and time variations on diffusion bonding efficiency and stability. In particular, this analytical investigation has shown how the shorter is the duration of the diffusion transient and the higher the temperature, the lower results the sensitivity of the diffusion processes to temperature fluctuations.

Corrosion of Additively Manufactured CoCrFeMnNi High Entropy Alloy in Molten NaNO3-KNO3

Exposure testing was performed on CoCrFeMnNi equiatomic high entropy alloy (HEA) produced via directed energy deposition additive manufacturing in NaNO3-KNO3 (60–40 wt%) molten salt at 500 °C for 50 h to evaluate the corrosion performance and oxide film chemistry of the HEA. Potentiodynamic electrochemical corrosion testing, scanning electron microscopy, focused ion beam milling coupled with energy dispersive spectroscopy, Raman spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and inductively coupled plasma optical emission spectroscopy were used to analyze the corrosion behavior and chemistry of the HEA/nitrate molten salt system. The CoCrFeMnNi HEA exhibited a higher passive current density during potentiodynamic polarization testing than steel alloys SS316L and 4130 and the high-Ni alloy 800 H in identical conditions. The oxide film was primarily composed of a (Mn,Co,Ni)Fe2O4 spinel with a vertical plate-like morphology at the surface. Cr and Ni were found to be totally depleted at the outer surface of the oxide and dissolved in high concentrations in the molten salt. While Cr was expected to dissolve into the molten salt, the high concentration of dissolved Ni has not been observed with traditional alloys, suggesting that Ni is less stable in the spinel when Mn and Co are present.

Effect of Composition and Applied Stress on the Transformation Behavior in NiXTi80−XZr20 Shape Memory Alloys

This study demonstrates the effect of Ni content and applied stress on the microstructure and shape memory properties of a range of NiXTi80−XZr20 (X = 50–51 at.%) shape memory alloys, which were produced via arc melting. Uniaxial constant force thermal cycling, differential scanning calorimetry, microhardness, and microscopy were used to evaluate the alloys in the homogenized, solutionized, and aged (500–550 °C) conditions. Transformation temperatures decrease linearly with increasing Ni content for the solutionized and aged samples, while the data demonstrate a rebound in transformation temperatures in the high-Ni alloys in the homogenized condition. In general, hardness increases with Ni content as a result of solution strengthening in the case of the solutionized condition, and precipitation strengthening in the aged conditions. During uniaxial constant force thermal cycling, the austenite finish temperature (AF) increased with increasing stress at a higher rate in the near-stoichiometric compositions than in the high-Ni compositions. Transformation strains also increased with stress, with the stress rate and the magnitude of the peak transformation strain heavily dependent on Ni content. Residual strain decreased with Ni content due to the strengthening effects of the solid solution and H-phase precipitates.

Deformation Twinning Behavior in High Ni-Austenitic Materials

Deformation twinning behaviors have been studied in high Ni alloys, Alloy 28 or Sanicro 28 and Alloy 625 at RT and at cryogenic temperature. The microstructures were evaluated using SEM-EBSD. Some constitutive approach has also been used in the discussion on the deformation twinning in high Ni-alloys. The results show that deformation twinning can occur in high Ni alloys depending on the chemical composition, strain range and stress conditions. TWIP can occur in the Ni based superalloy Alloy 625 at cryogenic temperature, which increases both strength and ductility. This is the first report of this phenomena for this alloy. Deformation twinning in high Ni alloys occurs heterogeneously in the material, depending on crystallographic parameters such as grain orientation and Schmid factor. Formation of deformation twins can lead to high texture in the material, which will contribute to the increase of strength. The mechanisms for the formation of deformation twins in high Ni alloys have been discussed.

The role of dislocation channeling in IASCC initiation of neutron irradiated stainless steel

This study intended to understand how dislocation channeling affects IASCC initiation using a novel four-point bend test. Stainless steels used in this study (irradiated in the BOR-60 reactor) included a commercial purity 304L alloy irradiated to 5.5, 10.2, and 47.5 dpa, and two high purity alloys, Fe18Cr12Ni and Fe18Cr25Ni, irradiated to ∼10 dpa. IASCC was enhanced by MnS inclusions, which dissolve in the NWC environment and form oxide caps, creating a crevice condition with a high propensity for crack initiation. Stress concentration at the grain boundary intersecting these sites induced crack initiation, resulting from discontinuous dislocation channels (DC). Stress to initiate IASCC decreased with dose due to earlier DC initiation. The HP Fe18Cr12Ni alloy had low IASCC susceptibility and the high Ni alloy did not crack. The difference was attributed to the propensity for DCs to transmit across grain boundaries, which controls stress accumulation at DC – grain boundary intersections.

Effect of Cr and Ni on Stress Corrosion Cracking Susceptibility in Ni-Cr-Fe Alloys Under Simulated Pressurized Water Reactor Primary Conditions

The primary water stress corrosion cracking (PWSCC) susceptibility of Ni-based alloys, such as Alloy 600 (UNS N06600), has been much higher than that of Fe-based alloys, such as Type 316 stainless steel (UNS S31600). This phenomenon is generally recognized; however, the effects of Fe, Ni, and Cr are not fully understood. In this study, the effect of Cr and Ni in Ni-Cr-Fe alloys on PWSCC susceptibility was investigated using alloys with a wide range of Ni content. The role of these elements is discussed from the standpoint of grain boundary oxidation. According to the stress corrosion cracking (SCC) test results, high-Ni alloys with low Cr contents had high SCC susceptibility, and the SCC susceptibility in high Ni-content alloys was improved by increasing Cr content. On the other hand, low Ni-content alloys had low SCC susceptibility, irrespective of Cr content. These features agree with the field experience in pressurized water reactor plants. In comparison with the results of SCC tests and immersion test...

Magnetic Properties of Electroformed Ni and Ni-Fe for Micromagnetic MEMS Applications

This paper reports a new technique which is based on electroforming process for high permeability Ni and Ni-Fe alloy. The magnetic properties of Ni and Ni-Fe alloy are investigated as a function of plating current density via scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), and vibrating sample magnetometer (VSM). Concentration-dependent kinetics is used to formulate the deposition rate and also the same is verified by using finite element analysis tool COMSOL Multiphysics. Several experiments are performed to derive the relation between electroplating parameters and magnetic properties. The process conditions are optimized to develop high permeability (∼16000) Ni-Fe alloy (85.71–14.29 %). The higher current density shows a monotonically increasing behavior of relative permeability (μ r ). In addition, the B-H curves indicate that the saturation magnetization (B s a t ) increases and coercivity decreases with increasing plating current density. Our experimental data confirms that the higher current density increase the softness of Ni. The observed properties of Ni and Ni-Fe based on experimental results can be used to study the magnetic behavior of micromagnetic sensors and large force actuators.

Electric Arc Spray Coatings Increase Reliability of Power Generation Systems

Abstract Thermal spray coatings are widely used to keep power plants running at full capacity. An example is the application of HVOF-sprayed CrC-NiCr to protect generating and superheater banks from sulfuric and vanadium gases. Other examples include the use of arc spraying to deposit high Cr content Ni alloy to extend the life of coal-fired boiler tubes and to apply amorphous work hardening coatings to surfaces in the flu gas path that are susceptible to high-temperature corrosion and wear.

Predicting the depletion of chromium in two high temperature Ni alloys

The oxidation resistance of the high temperature Ni-Cr alloys alloy 601 and alloy 602 CA was studied. Based on microanalysis data from cyclic oxidation experiments performed in a burner test rig, the total loss of chromium in the alloy was determined. A numerical analysis using the general diffusion equation was performed to model the mass transport for the observed chromium loss. Chromium depletion profiles were calculated with an effective diffusion coefficient derived from the data of the shortest exposure time. Good agreement was found between the measured and the computed chromium concentration at the alloy-oxide interface for longer exposure.

Fatigue behavior of a thin gage Ni alloy after exposure to elevated temperature

Thin gage Ni-base superalloy materials are being targeted for hypersonic applications up to 1100°C. To achieve an optimized system design, standard mechanical behavior data on these materials are needed under a range of loading conditions such as tensile, creep and fatigue at representative temperatures. In order to meet this need, a unique test system developed in-house for determining materials properties of very thin materials was used to determine the fatigue response of a high temperature Ni alloy, both with and without prior exposure to elevated temperatures. This paper examines the effects of elevated temperature exposure on the ductility and fatigue resistance of Haynes 230 with a thickness of 0.127mm.

Determination of nickel in finished product alloys by instrumental neutron activation analysis and spectrophotometry

Nickel contents in different finished product alloys were determined using a k0-based internal monostandard instrumental neutron activation analysis (IM-INAA) method. Five stainless steels (SS) and three high nickel alloys were analyzed by IM-INAA. BCS CRMs 225/1 (low alloy steel) and 466 (austenitic SS) and NIST SRM 247 (high Ni alloy) were analyzed to evaluate the accuracy of the method. The results of CRMs and SS were found to be in good agreement with certified or specified values. The Ni contents in the high nickel alloys were also determined by relative method of NAA for verification. Nickel contents in BCS CRM 466 and SS 316M were determined by UV–Visible spectrophotometry and the values were found to be in good agreement with IM-INAA results.

Stacking fault energies of Mn, Co and Nb alloyed austenitic stainless steels

The alloying effects of Mn, Co and Nb on the stacking fault energy (SFE) of austenitic stainless steels, Fe–Cr–Ni with various Ni contents, are investigated via quantum–mechanical first-principles calculations. In the composition range ( c Cr = 20%, 8 ⩽ c Ni ⩽ 20%, 0 ⩽ c Mn, c Co, c Nb ⩽ 8%, balance Fe) studied here, it is found that Mn always decreases the SFE at 0 K but increases it at room temperature in high-Ni ( c Ni ≳ 16%) alloys. The SFE always decreases with increasing Co content. Niobium increases the SFE significantly in low-Ni alloys; however, this effect is strongly diminished in high-Ni alloys. The SFE-enhancing effect of Ni usually observed in Fe–Cr–Ni alloys is inverted to an SFE-decreasing effect by Nb for c Nb ≳ 3%. The revealed nonlinear composition dependencies are explained in terms of the peculiar magnetic contributions to the total SFE.

高Ni合金の環境助長割れ感受性条件の検討 （２）高温水環境での応力下酸化挙動と割れ感受性評価

高Ni合金の環境助長割れ感受性条件の検討 （２）高温水環境での応力下酸化挙動と割れ感受性評価

Effects of alloying elements on radiation hardening based on loop formation of electron-irradiated light water reactor pressure vessel model steels

Electron irradiations using a high voltage electron microscope were conducted on several reactor pressure vessel model alloys in order to investigate the effects of alloying elements on the formation and development of defect clusters. In addition, the effects of alloying elements on yield stress change after irradiation were considered, comparing the mean size and number density of dislocation loops with the irradiation-induced hardening. High Cu alloys formed Cu and Mn–Ni–Si rich clusters, and these are important in determining the yield stress increase. High Ni alloys formed a high density of small dislocation loops and probably Mn–Ni–Si rich cluster, which have the effect of increasing the yield stress. High P enhanced radiation-induced segregation on grain boundary, helping prevent dislocation movement.

Development of Textured Coated Superconductor Substrate Tapes by Severe Plastic Deformation Processing

An attempt has been made to fabricate highly cube textured ({001}<100>) polycrystalline nickel substrate tapes for coated superconductor applications using severe plastic deformation route. For this purpose high purity Ni (~99.97%) plates with widely different average grain size (28 µm or fine grained starting material and 650 µm or coarse grained starting material, respectively) are severely deformed by Accumulative Roll Bonding (ARB) up to an equivalent strain level of (εeq = 6.4) and annealed at various temperatures between 300° to 800°C for one hour. Upon annealing at different temperatures, the fine grained starting material developed a much stronger cube texture than the coarse grained starting material. By suitable annealing treatment near 100% cube textured tape could be obtained in the SPD processed fine grained nickel tapes having a predominantly low angle boundary network. The observed difference in the strength of cube texture in the two materials could be explained based on the oriented nucleation mechanism of formation of cube texture. The present results indicate that SPD processing route such as ARB is very effective in fabricating high purity Ni or Ni alloys intended for coated superconductor substrate applications.

Influence of elevated Fe, Ni and Cr levels on tensile properties of SSM-HPDC Al-Si-Mg alloy F357

The microstructures and tensile properties of semi-solid metal high pressure die cast (SSM-HPDC) F357 alloys with low and high levels of Fe, Ni and Cr were compared in different temper conditions. ThermoCalc software was used to predict the different intermetallics that can be expected in the alloys, and scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS) was used to investigate the actual intermetallics that formed. The influence of these intermetallics on tensile properties was quantified. The results show that lower strength is obtained in the alloy with high Fe, Ni and Cr levels. This is attributed mainly to the formation of more ?-Al 8FeMg 3Si 6 phase, which removes strengthening Mg atoms from solid solution. Also, the ductility of the high Fe, Ni and Cr levels alloy is decreased significantly due to microcracking of the higher volume fraction ?-Al 8FeMg 3Si 6 and Al 9FeNi phases. The combination of lower strength and ductility results in a decrease of the quality index of this alloy compared with the alloy with low levels of Fe, Ni and Cr.