Aluminium deposited nickel based superalloy for reactor vessels of a fission microstructure

Abstract

The present invention relates to a process of making a corrosion resistant, aluminium-deposited nickel-based superalloy super alloy for fission microstructures. The alloy comprises a nickel-based substrate (10) containing nickel, chromium, molybdenum, and titanium, with an aluminium layer (20) deposited on the substrate using vacuum plasma deposition. The substrate contains 80-88% nickel, 4-7% chromium, 6-9% molybdenum, and 1-3% titanium by weight. The aluminium layer have a thickness between 50-200µm, and acts as a barrier against fluoride salt attacks, reducing degradation rates and ensuring better structural integrity of the fission microstructure. The aluminium-deposited nickel-based superalloy can be used in various components of fission microstructures, including fuel cladding, heat exchangers, and reactor vessels, to improve the efficiency, longevity, and safety in nuclear environments.

Description

ALUMINIUM DEPOSITED NICKEL BASED SUPERALLOY FOR REACTOR VESSELS OF A FISSION MICROSTRUCTUREFIELD OF INVENTION

[0001] The present invention relates to a corrosion-resistant superalloy. Particularly, the present invention relates to an aluminum-depo sited nickel-based superalloy capable of withstanding high temperatures and corrosive environments that can be used in nuclear fission microstructures.BACKGROUND OF THE INVENTION

[0002] A superalloy is a high performance alloy with the ability to operate at a high fraction of its melting point. Main features of a superalloy include mechanical strength, thermal creep deformation resistance, surface stability, and corrosion and oxidation resistance which make them useful in a variety of applications such as aircraft, gas turbines, rocket engines, nuclear power plants, chemical, and petroleum plants. Three major class of superalloys are iron, cobalt or nickel based alloys. Among these, nickel based alloys are the most widely used for high temperature applications due to their great mechanical strength and excellent surface stability.

[0003] Nickel based alloys can be either solid solution or precipitation strengthened with a basic composition including 10-20% chromium, up to 8% aluminium, up to 8% titanium, 5- 10% cobalt as well as small amounts of carbon, zirconium and boron and the rest nickel. Some common nickel-based superalloys include Alloy C-276 (Hastelloy® C-276), Alloy 718 (Inconel® 718), Alloy 20 and Alloy X (Hastelloy® X, Inconel® HX).

[0004] Solid solution strengthened alloys, such as Hastelloy offers high-temperature strength but do not possess resistance to metal dusting and hot corrosion from molten fluoride salts. They are used in applications requiring only modest strength since exposing Hastelloy to high-stress work processes like welding or machining may cause stress-cracking and potential component failure. Inconel's high strength and excellent corrosion resistance properties make it an ideal material for use in extreme environments. However, its high hardness makes it prone to cracking, wrinkling, or tearing during manufacturing processes.

[0005] Current materials used in fission microstructures, such as titanium and Hastelloy alloys, face significant challenges in environments with molten fluoride salts at high temperatures. These conditions often lead to severe degradation, compromising the structural integrity and safety of the materials.

[0006] A patent application CN102079652B discloses a high thermal shock resisting Cr2O3-A12O3-ZrO2 brick and a method of production. The brick comprises of chromium- aluminium-zirconium or fused zirconia corundum particles in percentage by weight: 60-85%,aluminium dihydrogen phosphate used as binders.

[0007] Another patent application, WO2017062332A1 titled “Ceramic coating for corrosion resistance of nuclear fuel cladding” discloses coating used for radioactive fuel or a structural component in radioactive fuel reactors, that include a ternary monolithic coating or multiple layers of one or more layers of TiAlN TiZrN, TiCrN, TiNbN and / or CrN, ZrN, NbN, TiN, TaN, HfN. TiHfN, TaHfN, TaNbN, or mixed combinations and / or CrN, ZrN, NbN, TiN, TaN, Si3N4, and / or HfN. In addition, one or more layers can be comprised of a nitride, oxide, or carbide or mixed combination from Ti, Al, Zr, Cr, Si, Nb, Hf, or mixed combination However, the metal alloy coatings used in the above disclosed prior arts are not corrosion resistant and are incapable of withstanding the high temperature and oxidation process in fission nuclear reactors.

[0008] In order to overcome the challenges associated with the above state of art, there is a need to develop a nickel-based super alloy that is corrosion resistant and can withstand high temperature and metal dusting in a fission microstructure.OBJECTIVES OF THE INVENTION

[0009] The primary objective of the present invention is to provide an aluminum-depo sited nickel-based superalloy with resistance to corrosion, metal dusting and high temperature.

[0010] Another objective of the present invention is to provide a superalloy that enhances the structural integrity and reduces the risk of material failure in fission microstructure.

[0011] Yet another objective of the present invention is to provide an aluminum-deposited nickel-based superalloy that is resistant to oxidation, thereby extending the lifespan of a fission microstructure.

[0012] Another objective of the present invention is to provide nickel based superalloy with superior resistance to extreme temperature encountered in nuclear environments.

[0013] Yet another objective of the present invention is to provide a nickel based superalloy that is resistant to corrosive fluoride ions in a nuclear environments.

[0014] Other objectives and advantages of the present invention will become apparent from the following description taken in connection with the accompanying drawings, wherein, by way of illustration and example, the aspects of the present invention are disclosed.BRIEF DESCRIPTION OF DRAWINGS

[0015] The present invention will be better understood after reading the following detailed description of the presently preferred aspects thereof with reference to the appended drawings, in which the features, other aspects and advantages of certain exemplary embodiments of the invention will be more apparent from the accompanying drawing in which:

[0016] Figure 1 illustrates the cross-sectional structure of the aluminium-depo sited nickel- based superalloy.

[0017] Figure. 2 illustrates the High-Temperature Fatigue Testing of the aluminium- deposited nickel-based superalloy at various temperatures; Figure. 2(a) evaluates the performance of the aluminide crystal layer at 1093 °C and Figure. 2(b) evaluates the performance of the aluminide crystal layer at 900°C.

[0018] Figure. 3 illustrates the effect of cycle frequency and exposure duration on furnace oxidation resistance of aluminium-deposited nickel-based superalloy at 2000 °F (1093 °C) and 2100° F (1140°C).

[0019] Figure. 4 illustrates the line diagram of the experimental set up.

[0020] Figure. 5 illustrates the microstructure the aluminium-deposited nickel-based superalloy under different magnifications: (a) 500x; (b) lOOOx.

[0021] Figure. 6 illustrates the Cross-sectional view of the aluminium-deposited nickel- based superalloy with an aluminide crystal layer thicknesses of 40 pm.

[0022] Figure. 7 illustrates Energy Dispersive Spectroscopy (EDS) maps showing the distribution of specific elements, showing aluminum concentration gradually decreasing from the outer aluminide crystal layer to the diffusion zone.

[0023] Figure. 8 illustrates the XRD (X-Ray Powder Diffraction) phase analysis of coatings considering deposition time and corresponding layer growth, 8(a): 4 hours and 8(b): 12 hours.

[0024] Figure. 9 illustrates S-N curves for the aluminium-deposited nickel-based superalloy with different aluminide crystal layer thicknesses; hysteresis loops for aluminide crystal layer thicknesses of 20 pm (a, b) and 40 pm (c, d) subjected to fatigue testing at stress amplitudes of 400 MPa and 500 MPa, respectively.

[0025] Figure. 10 illustrates the Fracture surfaces of the aluminium-deposited nickel-based superalloy after fatigue testing at stress amplitude equal to 400 Mpa; showing the following views: (a) detailed and (b) general sub-surface structure; (c) fractured view of the middle part of the specimen.

[0026] Figure. 11 illustrates Fracture surfaces of the aluminium-deposited nickel-based superalloy after fatigue testing at stress amplitude equal to 500 MPa; showing the followingviews: (a) detailed and (b) general sub-surface structure; (c) fractured view of the middle part of the specimen.

[0027] Figure. 12 illustrates the comparison of Commercial Ni-base Alloy 600 (a) and Aluminium deposited nickel based superalloy (b) after 5,700-h exposure to the same metal dusting environment at 593°C.SUMMARY OF THE INVENTION

[0028] The present invention relates to a process of making a superalloy which is an aluminium-deposited nickel-based superalloy, designed to withstand the harsh conditions present in fission microstructures. The corrosion-resistant alloy includes a nickel-based substrate (10) comprising nickel, chromium, molybdenum, and titanium, and an aluminum layer (20) deposited on the nickel-based substrate by vacuum plasma deposition. The nickel- based substrate (10) comprises 80-88% nickel, 4-7% chromium, 6-9% molybdenum, and 1- 3% titanium by weight. The aluminum layer (20) has a thickness between 50-200 micrometers (pm) and acts as a barrier against fluoride salt attacks. The alloy further comprises a diffusion zone (30) between the nickel-based substrate and the aluminum layer, with the diffusion zone (30) and aluminum layer (20) together having a thickness between 125-140pm.

[0029] According to another aspect of the present invention, a method of manufacturing the aluminium-deposited nickel-based superalloy is provided. The method includes preparing a nickel-based substrate (10) comprising nickel, chromium, molybdenum, and titanium, and depositing an aluminium layer (20) on the nickel-based substrate using vacuum plasma deposition. Preparing the substrate (10) involves melting and mixing raw materials, degassing and homogenizing the melted materials, solidifying and hot working the materials, and subjecting them to heat treatments. Depositing the aluminium layer (20) over the nickel based substrate (10) includes placing the substrate in a vacuum chamber, introducing an aluminium- containing gas, energizing the gas into a plasma state, and controlling the process to achieve an aluminium layer thickness between 50 and 200pm. This process results in a super alloy with superior resistance to metal dusting, hot corrosion and high temperature oxidation, making it ideal for fission microstructures.DETAILED DESCRIPTION OF THE INVENTION

[0030] The following description describes various features and functions of the disclosed system and method with reference to the accompanying figure. In the figure, similar symbols identify similar components, unless context dictates otherwise. The illustrative aspects described herein are not meant to be limiting. It may be readily understood that certain aspects of the disclosed system and method can be arranged and combined in a wide variety of different configurations, all of which are contemplated herein.

[0031] Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the embodiments described herein can be made without departing from the scope of the invention. In addition, descriptions of well-known functions and constructions are omitted for clarity and conciseness.

[0032] Features that are described and / or illustrated with respect to one embodiment may be used in the same way or in a similar way in one or more other embodiments and / or in combination with or instead of the features of the other embodiments.

[0033] The terms and words used in the following description and claims are not limited to the bibliographical meanings but are merely used to enable a clear and consistent understanding of the invention. Accordingly, it should be apparent to those skilled in the art that the following description of exemplary embodiments of the present invention are provided for illustration purpose only and not for the purpose of limiting the invention.

[0034] It is to be understood that the singular forms “a”, “an”, and “the” include plural referents unless the context clearly dictates otherwise.

[0035] It should be emphasized that the term “comprises / comprising” when used in this specification is taken to specify the presence of stated features, integers, steps, or components but does not preclude the presence or addition of one or more other features, integers, steps, components, or groups thereof. The equations used in the specification are only for computation purpose.

[0036] The terms ‘aluminium layer’ and ‘aluminide crystal layer’ has been used interchangeably in the disclosure and these two terms mean one and the same.

[0037] Accordingly, the present invention relates to a corrosion-resistant superalloy. Particularly, the present invention relates to an aluminum-deposited nickel-based superalloy capable of withstanding high temperatures and corrosive environments that can be used in nuclear fission microstructures.

[0038] In an embodiment, the present invention relates to an aluminium-deposited nickel based superalloy. The superalloy comprises nickel (Ni) as the primary substrate (10), with chromium (Cr), molybdenum (Mo) and titanium (Ti), followed by coating with a protective aluminium layer (20). Nickel serves as the primary constituent, providing high-temperature strength and a base for corrosion resistance. Chromium is incorporated to enhance oxidation resistance and contribute to overall corrosion protection. Molybdenum is added to improve resistance in reducing environments and certain types of corrosion. Titanium is included to enhance creep resistance and potentially strengthen the protective aluminum layer. The aluminum layer (20) deposited on the nickel -based substrate (10) acts as a barrier against aggressive environments. This layer reduces degradation rates and ensures better structural integrity in the presence of corrosive agents such as fluoride salts. In an exemplary embodiment, the aluminium-deposited nickel based superalloy comprises of 80-88% nickel, 4-8% chromium, 6-12% molybdenum, and 1- 3% titanium by weight and an aluminum layer with a thickness between 50-200 micrometers (pm). The superalloy may also include elements such as iron (Fe), silicon (Si), manganese (Mn), vanadium (V), carbon (C), copper (Cu), tungsten (W), and niobium (Nb). The exact percentages of these minor elements may vary depending on the specific application requirements.

[0039] In an embodiment, the manufacturing process for the aluminium-deposited nickel based superalloy involves the two phases:Phase 1: Preparation of the nickel-based substrate (10); andPhase 2: Deposition of the aluminum layer (20) over the nickel based substrate (10).

[0040] In an embodiment, the phase 1 of the manufacturing process for the preparation of nickel based substrate (10) comprises the following steps:1. Preparing a Ni-Cr-Mo-Ti alloy(10): the raw materials used for the preparation of the nickel based superalloy comprises: preparing a Ni-Cr-Mo-Ti alloy (10) by combining raw materials comprising:• 80-88 % by weight of nickel (Ni) as the primary constituent;• 4-8 % by weight of chromium (Cr);• 6-12 % by weight of molybdenum (Mo);• 1-3 % by weight of titanium (Ti); and• optional elements including iron (Fe), silicon (Si), manganese (Mn), vanadium (V), carbon (C), copper (Cu), tungsten (W), and niobium (Nb) in tailored concentrations;2. melting and mixing the raw materials in a controlled atmosphere using vacuum induction melting (VIM), electroslag remelting (ESR), or a combination thereof, at a temperature range of 1600°C to 1750°C for 2 to 5 hours, in a high vacuum of 103to 106torr or in the presence of inert gases such as Ar or He;3. degassing the molten alloy at a temperature range of 1550°C to 1650°C and pressure less than 103torr for 30-60 minutes to remove trapped gases such as hydrogen, oxygen, and nitrogen;4. homogenizing the molten nickel-based superalloy using electromagnetic stirring (EMS) and isothermal holding at a temperature range of 1600°C to 1700°C for 1-3 hours;5. solidifying and shaping the homogenized alloy by directional solidification or conventional mold casting at a cooling rate of 0.5 to 5°C / s;6. hot working the solidified alloy by processes such as rolling at temperatures between 900-1250°C, pressure of 50-200 MPa, and a reduction ratio of -50% per pass;7. heat treating the worked alloy through controlled heating and cooling cycles in a vacuum furnace, comprising multi-step thermal treatment at 1100°C to 1200°C for 2-4 hours, followed by aging at 750°C to 950°C for 8-24 hours, and cooling by air or oil quenching; and8. performing quality control checks on the final nickel-based superalloy (Ni-Cr-Mo-Ti alloy) to ensure desired specifications for the nickel-based substrate (10) production.

[0041] In an embodiment, phase 2 of the manufacturing process involves deposition of the aluminium layer (20) over the nickel based substrate (10) employing Chemical Vapor Deposition (CVD) process. This involves the following steps:1. cleaning and preparing the nickel based substrate (10) obtained from phase 1 for deposition of the aluminium layer over the substrate (10);2. placing the cleaned nickel based substrate (10) in a vacuum chamber and applying vacuum under reduced pressure for carrying out a controlled reaction;3. introducing an aluminium containing gas into the chamber, followed by energizing the gas into plasma state by electrical discharge;4. providing an aluminium source into the chamber, which is breakdown by the plasma, releasing free aluminium atoms to be deposited on the nickel based super alloy (10) substrate;5. binding the free aluminium atoms on the surface of the prepared nickel based superalloy substrate (10) by maintaining the temperature at 900-1100°C, and pressure at IO-3- IO-5torr for 2-6 hours, forming a thin film of aluminium (20) on the surface of the substrate (10); and6. removing the aluminium deposited nickel based superalloy from the vacuum chamber and performing the quality analysis to ensure the film thickness, uniformity and desired properties.

[0042] Figure 1 illustrates cross-sectional views of aluminium-depo sited nickel based superalloy. Each micrograph reveals a layered structure consisting of three primary regions: a substrate layer (10) at the bottom, a diffusion zone (30) in the middle, and an excess aluminum layer (20) at the top. The thickness of the deposited layers ranges between 125-140 micrometers across all three test pieces, demonstrating consistency in the deposition process.

[0043] In an exemplary embodiment, the melting and mixing of the metal for preparing the nickel based substrate utilizes a vacuum induction melting for precise composition control.

[0044] In another exemplary embodiment, the melting and mixing of the metal for preparing the nickel based substrate utilizes electron beam melting for precise composition control.

[0045] In an exemplary embodiment, the hot working process may include forging or extrusion in addition to or instead of rolling. The heat treatment cycles may be adjusted in number, duration, or temperature to achieve different microstructural characteristics.

[0046] In an exemplary embodiment, the solidified nickel based superalloy obtained in phase 1 is cast into specific shapes, such as, but not limited to, ingots or slabs, depending on downstream processing requirements.

[0047] In another embodiment, the base substrate material used is cobalt-based or ironbased superalloy instead of the nickel-based alloy. These alternative substrates may offer different combinations of properties that may be advantageous for certain applications.

[0048] In an exemplary embodiment, the precursor used in the deposition of the aluminium layer (20) over the nickel based substrate (10) in the Chemical Vapor Deposition (CVD) process is aluminum trichloride (AICE).

[0049] In an exemplary embodiment, the Chemical Vapor Deposition (CVD) process for aluminide crystal layer deposition on the aluminum-deposited nickel-based superalloy may be performed under the following conditions:1. the precursor used as the aluminium source may be A1CE vapour;2. the aluminium deposition temperature may be maintained at approximately 1040°C;3. the pressure in the deposition chamber may be set to 150 mbar; and4. the aluminium deposition time varied based on the desired layer thickness, such as a deposition time of approximately 4 hours created a 20pm thick layer, and a deposition time of about 12 hours created a 40pm thick layer.

[0050] In an alternate embodiment, the aluminium deposition process used may be selected from physical vapour deposition techniques such as sputtering or electron beam evaporation. The thickness of the deposited aluminium layer (20) may be adjusted between 50 and 200 micrometres depending on the specific application requirements.

[0051] In an alternate embodiment, the deposition atmosphere may comprise hydrogen.

[0052] In another exemplary embodiment, the aluminium deposition over the nickel based substrate (10) may be carried out using an Ion-Bond setup, such as an Ion Bond Bernex BPX Pro 325 S, (manufactured by IHI Ion bond AG, Olten, Switzerland) using the following conditions: i. the precursor used as the aluminium source may be A1CE vapour; ii. the aluminium deposition temperature may be maintained at 1040°C; iii. the pressure in the deposition chamber may be set to 150 mbar; iv. the aluminium deposition time was 4 hours for 20pm layer and 12 hours for 40pm layer; and v. the deposition process was carried out in an atmosphere of hydrogen.

[0053] In some embodiments, additional alloying elements may be incorporated into the superalloy composition. Elements such as tantalum, rhenium, or hafnium may be added in small quantities to further enhance high-temperature strength or oxidation resistance.

[0054] In an embodiment, the aluminium layer involves a two-layer structure consisting of an outer layer (20) (P-NiAl) of 20pm and an inner diffusion zone (y’ + P) (30) of 40pm.

[0055] The superalloy may be applied in various forms depending on the application. In some implementations, the alloy may be used as a coating on existing components rather than as a bulk material. This may allow for the enhancement of surface properties of less expensive base materials.

[0056] In an embodiment, the manufacturing process may be scaled to produce components of various sizes. In some cases, large-scale components for conventional nuclear reactors may be produced, while in other implementations, the process may be optimized for small, intricate parts used in micro reactors.

[0057] In some embodiments, the fatigue resistance of the superalloy is improved by postprocessing treatments like shot peening or laser shock peening to induce compressive stresses in the surface layer.

[0058] In an embodiment, aluminium film (20) deposited on the nickel substrate (10) is characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD) analysis, and Energy-dispersive X-ray spectroscopy (EDS) analysis to ensure the production of high- quality aluminide crystal layers on Aluminium deposited nickel based superalloy.

[0059] In an alternate embodiment, the aluminium deposited nickel-based super alloy is subjected to adhesion testing and high temperature fatigue testing to check the quality and consistency of the aluminium layer (20) during oxidation and high temperature stresses.

[0060] The aluminium deposited nickel-based super alloy provided by this invention, exhibit superior resistance to extreme temperatures and also provides resistance to corrosive agents commonly present in nuclear environments, such as molten fluoride salts making it suitable for application in fission microstructure. The aluminum layer (20) deposited on the nickel-based substrate (10) provides exceptional protection against oxidation, further extending the durability of components made from this material. This corrosion resistance helps prevent degradation of critical reactor components, potentially enhancing safety and reducing maintenance requirements.

[0061] In some embodiments, the aluminium-deposited nickel-based superalloy may be used in environments such as chemical processing plants, gas turbines, or aerospace components.

[0062] Experimental Data:

[0063] The following illustrates experimental data and should not be constructed to limit the scope of present invention.

[0064] Quality Control Methods: Several experiments were performed to ensure the quality of the aluminium deposited nickel-based super alloy.

[0065] 1. Chemical Composition Analysis

[0066] X-ray Fluorescence (XRF) Spectroscopy and Optical Emission Spectroscopy (OES):These tests were performed to verify the precise proportions of alloying elements in the aluminium deposited nickel-based super alloy. The ranges of various elements in the nickel based superalloy is as shown in Table.1Table. 1

[0067] 2. Mechanical Properties Testing

[0068] To validate strength, ductility, toughness, and high-temperature performance of the aluminium deposited nickel based superalloy, Tensile Testing (at room temperature andelevated temperatures), Hardness Testing (ASTM El 8), Impact Testing (ASTM E23) and Creep testing (ASTM El 39) were performed. As shown in Figure. 2(a) and 2(b), the impact of aluminide crystal layer on the high-temperature fatigue performance of Aluminium deposited nickel based superalloy, 20 pm and 40 pm thick aluminide crystal layer were applied via chemical vapor deposition (CVD) at 1040°C and 150 mbar pressure, under a hydrogen atmosphere, for 4 hours and 12 hours, respectively. Fatigue tests were conducted at 900°C to assess the influence of the proprietary aluminide crystal growth (with uniform micron thickness) on the superalloy's performance. Post-test fractographic analysis was performed to determine the failure mechanisms. The results showed no significant difference in fatigue life at the same stress amplitude between the two coating thicknesses. As shown in Figure.3, the coating remained well-adhered after specimen fracture, demonstrating its effectiveness in preventing high-temperature oxidation.

[0069] 3. Microstructural Examination

[0070] Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDS): To characterize microstructure, grain size, and phase distribution of the aluminium deposited nickel based superalloy, Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDS) were performed.As shown in the EDS maps of Figure. 6, the aluminum concentration gradually decreasing from the outer aluminide crystal layer to the inner diffusion zone (IDZ). This gradient maintains the protective oxide layer and facilitates coating adherence. Nickel concentration increases towards the IDZ. This region often consists of mixed phases like y-Ni and P-NiAl, forming a transition zone that enhances mechanical bonding. Element distribution is governed by diffusion mechanisms, thermal processing, and the interaction between the aluminide crystal layer and the substrate. Aluminum diffuses inward, forming a gradient essential for oxidation resistance. This diffusion results in a transition from high aluminum content in the outer layer to lower content in the IDZ. The aluminum concentration gradient is crucial for maintaining the protective oxide layer and ensuring strong coating adherence. In the outer aluminide crystal layer, a dense and continuous aluminum oxide (A12O3) layer forms at high temperatures. This oxide layer acts as a barrier, preventing further oxidation. As aluminum content decreases toward the interdiffusion zone, the phase composition transitions, providing a buffer between the brittle outer P-NiAl layer and the more ductile superalloy substrate. This gradient prevents cracks and delamination. The interdiffusion zone, with its mix of y’ (Ni3Al) and P (NiAl) phases, ensures the coating remains firmly anchored, enhancing durability and oxidation resistance. Nickel and substrate elements (Cr, Co, W, Ta, Ti) diffuse outward, forming the interdiffusion zone, which stabilizes the micro structure and enhances adhesion. The interaction between diffusing elements forms intermetallic phases, such as y’-Ni3Al, MxC carbides, and other complex phases in the IDZ, providing structural stability and mechanical strength.The X-Ray Powder Diffraction (XRD) graph shown in Figure. 8 of the aluminide crystal layer on Aluminium deposited nickel based superalloy prominently features peaks indicative of the P-NiAl phase, crucial for oxidation resistance and mechanical stability at high temperatures.This phase typically exhibits distinctive peaks at 29 angles around 20.7° (110), 29.4° (200), 43.6° (211), and 63.0° (220), corresponding to its B2 cubic crystal structure. The 110 peak is usually the most intense, reflecting the high concentration and well-ordered nature of the P- NiAl phase. These sharp peaks indicate a predominantly crystalline structure. The presence of well-defined P-NiAl peaks confirms the effective formation of the aluminide crystal layer, critical for maintaining the structural integrity and oxidation resistance of the underlying Aluminium deposited nickel based superalloy substrate.

[0071] 4. Surface Quality Inspection (Pre-Coating)

[0072] Optical Profilometry and Atomic Force Microscopy (AFM): This test was performed to assess surface roughness and to identify any surface defects on the nickel substrate (10) before the deposition of the aluminide crystal layer deposition, ensuring the surface is suitable for coating. The results obtained were:Surface Roughness (Ra): < 0.3 pmDefect Count (scratches, pits, etc.): < 0.5 per cm2

[0073] 5. Aluminide Crystal Layer Quality Control (Post-Deposition)

[0074] The thickness, adhesion strength and micro structure of the aluminium coating of the nickel based superalloy were checked. Thickness Measurement: was performed by Cross- sectional SEM. Target thicknesses are 20pm ± 2pm and 40pm ± 4pm.

[0075] Microstructural Examination: The superalloy's complex microstructure consists of a gamma (y) matrix strengthened by a substantial volume fraction of gamma prime (y’) precipitates, along with various carbides and solid- solution strengthening elements like aluminum, titanium, and tantalum. These microstructural features give Aluminium deposited nickel based superalloy the necessary strength and stability for high -temperature applications. SEM and EDS to verify the structure and composition of the aluminide crystal layer. The outer layer should be predominantly P-NiAl, and the diffusion zone should show a controlled mixture of y’ + P phases. No cracking or delamination of the coating is observed.

[0076] Aluminium deposited nickel based superalloy was characterized by a coarse micro structure with equiaxed grains (Figure 2). It is primarily composed of a gamma-phase, face-centered cubic (FCC) structure, which acts as a matrix for strengthening phases and provides ductility and toughness. It is typically solid-solution-strengthened by elements like Co, Cr, Mo, W, and Nb. Within the matrix are gamma prime precipitates, such as Ni3(Al,Ti), with an ordered L122 structure, where Ni atoms occupy face-centered positions and Al or Ti atoms are at the corners of the unit cell. The y’ phase is primarily responsible for Aluminium deposited nickel based superalloy's high -temperature strength, impeding dislocation motion and increasing creep resistance. Figure 5 illustrates the microstructure of Aluminium deposited nickel based superalloy under different magnifications: (a) 500x; (b) lOOOx.) and Figure. 6shows the Cross-sectional view of Aluminium deposited nickel based superalloy with different aluminide crystal layer thicknesses at 40 pm.

[0077] Depending on deposition time, aluminide crystal layers of 20 pm and 40 pm thickness were obtained after 4 h and 12 h, respectively. As shown in Figure. 8, both exhibited a two-layer structure: an outer layer (P-NiAl) rich in aluminum, providing excellent oxidation resistance, and an inner diffusion zone (y’ + P) with a mixture of y’ (Ni3 Al) and P-NiAl phases, offering a transition zone strongly adhering to the substrate. The outer layer, mainly P-NiAl, provides a continuous aluminum oxide film and is responsible for oxidation resistance. In the interlayer zone, aluminum diffuses into the base alloy, creating a gradient that ensures strong adhesion and minimizes thermal expansion mismatches. The CVD process leads to interdiffusion between the aluminide crystal layer and the substrate, creating a metallurgical bond that enhances mechanical stability.Deposition time significantly influences the composition and structure of aluminide crystal layers on Aluminium deposited nickel based superalloy, particularly the outer P-NiAl layer and the inner diffusion zone (y’ + P). During aluminizing, extended deposition allows more aluminum to diffuse into the substrate, promoting a thicker P-NiAl outer layer, crucial for oxidation resistance. Simultaneously, prolonged deposition enhances aluminum inward diffusion and nickel outward diffusion, leading to a more pronounced and thicker diffusion zone where y’ (Ni3 Al) and P (NiAl) phases coexist. This aluminum-rich diffusion zone (y’ + P structure) accommodates thermal stresses and enhances the aluminide crystal layer’s mechanical stability. However, excessively long deposition can result in overly thick aluminide crystal layers, potentially introducing brittleness or unwanted phase transformations.

[0078] 6. High-Temperature Performance Testing:

[0079] This test was conducted to evaluate the performance of the coated aluminium deposited nickel based superalloy at elevated temperatures and confirm whether it meets the application requirements.

[0080] High-temperature fatigue testing was performed at 900 °C using an MTS 810 testing machine equipped with a high-temperature MTS extensometer. Fatigue tests were force- controlled under a zero-mean- value, constant stress amplitude with a frequency of 20 Hz in the stress amplitude range from 400 MPa to 520 MPa. Figure. 4 illustrates the line diagram of the experimental set up. Temperature stability was monitored and controlled using a bicolor infrared pyrometer. Cyclic loading was initiated after 0.5 h once the testing temperature was reached. During this time, the testing machine was operated with force control to maintain a force near 0 kN in order to reduce the thermal expansion effects on the material’s behavior during testing. The microstructural characterization and chemical composition analysis were undertaken on grounded and mechanically polished cross-sections of coated specimens using a scanning electron microscope with an Energy-Dispersive Spectroscopy (EDS) attachment. The aluminide crystal layer’s phase composition was analyzed by the grazing incidence X-ray diffraction (GI XRD) technique using Co Kai radiation.High-Temperature Fatigue Testing: The S-N curves for Aluminium deposited nickel based superalloy with different aluminide crystal layer thicknesses are presented. No significant effect of aluminide crystal layer thickness was observed, as the material exhibited a similar service life at the same stress amplitude. A slightly enhanced service life of the 40 pm aluminide crystal layer was observed at 450 MPa and 400 MPa, but the differences were small. To compare the fatigue performance of aluminide crystal layer-coated Aluminium deposited nickel based superalloy, hysteresis loops for different thicknesses and stress amplitudes were compared as shown in Figures 9 (a), (b), (c), (d)). The first cycle, midlife performance, and last cycle were analyzed for each condition. The material’s behavior was reflected in the ratcheting effect, characterized by progressive, incremental inelastic deformation, shifting the stressstrain hysteresis loop along the strain axis. The width of the hysteresis loop for Aluminium deposited nickel based superalloy with the 20 pm aluminide crystal layer slightly increased in subsequent cycles (Figure 6a), suggesting cyclic plasticity. This behavior was not observed for Aluminium deposited nickel based superalloy with the 40 pm aluminide crystal layer at 400 MPa (Figure 6c). For this thickness, the hysteresis loop width remained almost constant, possibly due to the thicker layer's higher stiffness. High-temperature fatigue testing at 500 MPa did not show significant differences, except for higher strain accumulation in Aluminium deposited nickel based superalloy with the 20 pm aluminide crystal layer, reflected by the hysteresis loop shift.

[0081] 7. Coating Adhesion Testing

[0082] Pull-Off Adhesion Test (ASTM D4541) and Scratch Testing: Evaluates the bond strength of the aluminum layer to the alloy substrate. Acceptable Ranges:Pull-Off Strength: >25 MPaCritical Load (Lc) in Scratch Testing: >20 NFractographic Observations: Observations of the fracture surfaces of tested specimens after the high-temperature fatigue test showed no effect of aluminide crystal layer thickness on fracture mode (Figures 10 and 11). The aluminide crystal layer remained well adhered after specimen fracture (Figures 10(a) and 11(a), confirming its effectiveness in protecting the material against high-temperature oxidation. Thus, fracture mechanisms were mainly associated with the performance of Aluminium deposited nickel based superalloy, which exhibits a complex array of features reflecting the alloy’s response to cyclic thermal and mechanical stresses. The fracture surfaces revealed a combination of oxidation-assisted damage (Figures 10(a) and 11(a), intergranular cracking (Figures 10(b) and 11(b), fatigue striations (Figures 10(c) and 8), and areas of both ductile and brittle fracture (Figures 10(c) and 8). Fatigue striations are prominent, characterized by regularly spaced, parallel lines perpendicular to the crack propagation direction, indicating progressive fatigue crack growth. Intergranular cracking is a significant feature, particularly in Aluminium deposited nickel based superalloy at high temperatures, where cracks propagate along grain boundaries due to oxidation-induced embrittlement and brittle phases. This intergranular failure is often exacerbated by the oxidation of grain boundary carbides, leading to weakened interfaces andfacilitating crack growth. Transgranular cracking can also be observed, characterized by crack propagation through the grains, typically associated with regions of high stress concentration or where the y’ precipitates have coarsened or transformed into less stable phases, reducing their strengthening capability. Ductile dimple features may be present, especially in areas of final overload, where the material undergoes localized plastic deformation before ultimate failure. These dimples indicate microvoid coalescence, where voids nucleate, grow, and merge under tensile loading, evidencing the alloy’s ability to deform plastically. Regions of brittle fracture display cleavage facets or the failure of gamma prime (y’) and gamma (y) matrix interfaces, particularly if topologically close-packed (TCP) phases form, which can embrittle the alloy. Oxidation products like alumina (A12O3) scales are often concentrated around crackinitiation sites or along crack paths, indicating the role of high-temperature oxidation in accelerating fatigue crack growth. Oxidation of nickel-based alloys results in a protective external chromia layer, with alumina beneath the surface, occurring both intergranularly and intragranularly. Beneath this layer is a weaker region due to a depletion of y’ particles and grain-boundary carbides. These internal oxides within the subsurface are unfavorable and can impair mechanical properties. Internal oxides at grain boundaries may be prone to cracking, leading to localized stress concentrations that facilitate early failure. 20 pm 40 pm (a) microvoids oxidation products cleavage facets intergranular cracks Microvoids secondary cracks clevage facets voids striations microvoids (b) (c)

[0083] 8. Corrosion Resistance Testing

[0084] Salt Spray Testing (ASTM Bl 17) and Electrochemical Impedance Spectroscopy (EIS): These tests were performed to measure the aluminium coated nickel based superalloy’s resistance to oxidation and corrosion.Acceptable Ranges:Corrosion Rate: <0.1 mm / yearPitting Potential (Epit): >600 mV (vs. Ag / AgCl)

[0085] 9. Metal Dusting Resistance of aluminium deposited nickel based superalloy

[0086] Exposure to Metal Dusting Environment: aluminium deposited nickel based superalloy underwent a rigorous 5,700-hour exposure to a metal dusting environment at 593°C. This study compared Aluminium deposited nickel based superalloy's performance to a commercial Ni-base alloy (Alloy 600) in harsh conditions, such as those found in reformer and petrochemical processes. An alloy tube from a syngas plant that has been severely damaged by metal dusting. Figure.12 shows the photograph of commercial Ni-base Alloy 600 (a) and Aluminium deposited nickel based superalloy (b) after 5,700-h exposure to the same metal dusting environment at 593°C.The study revealed that the key to preventing metal dusting is the interaction between carbon and the oxide scales formed on the metal. While commercial alloys like Alloy 600 formed chromium oxide (Cr2O3) scales, Aluminium deposited nickel based superalloy, with its unique composition of nickel, molybdenum, and aluminum includingsome part of titanium that, formed protective aluminum oxide (A12O3) and titanium oxide (TiO2) scales instead. These oxides were found to provide a more robust barrier against metal dusting, preventing degradation even after prolonged exposure.

[0087] Oxide Scale Formation:

[0088] Aluminium deposited nickel based superalloy's unique alloying elements, including aluminum and titanium, are highly resistant to oxidation and carburization. The aluminum oxide (A12O3) layer is forms a dense, continuous protective film that shields the alloy from carbon penetration.

[0089] Raman Spectroscopy and Surface Analysis:

[0090] Raman spectroscopy confirmed that Aluminium deposited nickel based superalloy maintained a continuous, stable A12O3 scale after 5,700 hours of exposure. This stable oxide layer showed minimal signs of degradation or pitting, in stark contrast to Alloy 600, which exhibited significant pitting and breakdown of the chromium oxide (Cr2O3) scale. The titanium oxide (TiO2) scale on Aluminium deposited nickel based superalloy further contributed to the alloy's exceptional resistance to high-temperature corrosion.

[0091] Extended Performance and Applications:

[0092] The performance of Aluminium deposited nickel based superalloy was vastly superior, maintaining a smooth surface with little to no pitting, while Alloy 600 showed extensive damage. This extended performance ensures Aluminium deposited nickel based superalloy viability for use in industries such as hydrogen production, gas-to-liquid processes, and chemical environments, where metal dusting is a significant challenge. Aluminium deposited nickel based superalloy's ability to resist metal dusting extends its service life, reducing maintenance and replacement costs.

[0093] By using Aluminium deposited nickel based superalloy in metal dusting-prone environments, the reformer processes can recover heat at temperatures of up to 800°C. This has the potential to save up to 4.6 million J / m3of hydrogen. This efficiency translates into an energy savings equivalent to 107 million standard m3 / day of hydrogen production, which equates to approximately 475 billion Btu / day. Moreover, this performance could result in an estimated annual savings of $220-290 million in the hydrogen industry alone, highlighting the significant cost advantages of implementing Aluminium deposited nickel based superalloy over conventional alloys.

[0094] The advantages of the present invention are discussed herein:• The present invention provides a superalloy with resistance to metal dusting and hot corrosion in high temperature.• The present invention provides enhanced structural integrity and hence reduces the risk of material failure in fission microstructure.• The present invention provides better protection against oxidation that extends component lifespan.• The present invention provides an effective material for advanced fission micro energy system. • The present invention provides superior resistance to extreme temperature encountered in nuclear environments.• The present invention provides resistance to corrosive agents in nuclear environments.• The present invention provides a cost effective and energy saving superalloy that can be used in dust prone environments for a prolonged period.

[0095] While this invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the scope of the appended claims.

Claims

CLAIMS:

1. An aluminium deposited nickel based superalloy for reactor vessels of a fission microstructure, comprising: a nickel-based substrate (10) comprising 80-88% nickel, 4-7% chromium, 6-9% molybdenum, and 1-3% titanium by weight; and an aluminum layer (20) deposited on the nickel-based substrate by vacuum plasma deposition, wherein the aluminum layer has a thickness between 50 and 200 micrometers.

2. The aluminium deposited nickel based superalloy as claimed in claim 1, comprising a diffusion zone (30) between the nickel-based substrate and the aluminum layer.

3. The aluminium deposited nickel based superalloy of claim 2, wherein the diffusion zone and the aluminum layer together have a thickness between 125 and 140 micrometers.

4. The aluminium deposited nickel based superalloy 1, wherein the nickel-based substrate comprises one or more elements selected from the group consisting of iron, silicon, manganese, vanadium, carbon, copper, tungsten, and niobium.

5. A method of manufacturing the aluminium deposited nickel based superalloy for fission microstructures, comprising: i. preparing a nickel -based substrate (10) comprising nickel, chromium, molybdenum, and titanium; involving: a. melting and mixing raw materials comprising nickel, chromium, molybdenum, and titanium; b. degassing the melted raw materials; and c. homogenizing the melted raw materials using electromagnetic stirring to form the nickel based substrate (10); and ii. depositing an aluminum layer (20) on the nickel-based substrate (10) using vacuum plasma deposition; involving: a. placing the nickel-based substrate (10) in a vacuum chamber; b. introducing an aluminum-containing gas into the chamber; c. energizing the aluminum-containing gas into a plasma state; and d. controlling the deposition process to achieve an aluminum layer thickness between 50 and 200 micrometers over the nickel based substrate (10) to obtain the aluminium deposited nickel based superalloy.

6. The method as claimed in claim 5, wherein melting and mixing the raw materials for preparing the nickel-based substrate (10) is performed using vacuum induction melting at a temperature between 1600°C and 1750°C for 2 to 5 hours.

7. The method as claimed in claim 5, wherein degassing is performed at a temperature between 1550°C and 1650°C and a pressure less than 103torr for 30 to 60 minutes.

8. The method as claimed in claim 5, wherein homogenizing is performed at a temperature between 1600°C and 1700°C for 1 to 3 hours.

9. The method as claimed in claim 5 comprising solidifying and hot working the homogenized nickel-based substrate (10) at temperatures between 900°C and 1250°C.

10. The method as claimed in claim 5, wherein the aluminum-containing gas is aluminum trichloride (AICU).

11. The method as claimed in claim 5, wherein depositing the aluminum layer is performed at a temperature in the range of 900- 1100°C, a pressure in the range of IO-3- IO-5torr for 2-6 hours, in a hydrogen atmosphere.

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