Metal surface modifications for wear and corrosion resistant applications

Abstract

A method of making a surface-modified article, the method comprising: applying a surface-modifying material to a metallic substrate; forming a metallurgical bond at an interface between the surface-modifying material and the metallic substrate; wherein the surface-modifying material comprises metallic material, ceramic material, or mixtures, combinations, or alloys thereof; and wherein the metallic substrate comprises iron, nickel, cobalt, aluminium, copper, chromium, titanium, tungsten, tantalum, molybdenum, zinc, gold, silver, ruthenium, rhodium, zirconium, or alloys thereof.

Description

METAL SURFACE MODIFICATIONS FOR WEAR AND CORROSION RESISTANT APPLICATIONSField

[0001] The present invention generally relates to metal surface modifications for wear and corrosion resistant applications.Background

[0002] Surface modifications of metals that enhance wear and corrosion resistance have applications in any industry where metal articles, parts, and components are exposed to abrasive and corrosive environments. Industries whose operating environments make such metal surface modifications valuable options include oil refining, wastewater and water treatment, paper manufacturing, power generation, petrochemicals, pharmaceutical, equipment manufacturing, construction, mineral processing, mining, aerospace, automotive, energy, nuclear, transportation, and medical. For example, high pressure acid leaching (HPAL) used in gold, zinc and nickel processing industries requires autoclaves and severe-service metal-seated ball valves, such as acid injection valves, that combine wear and corrosion resistance.

[0003] Finding optimal metal surface modifications for wear and corrosion resistant applications is challenging due to the complex interplay of performance requirements and cost considerations, including the choice of surface modification technique, the choice of substrate, and the choice of surface modification material. Some substrates, such as titanium, copper, and aluminium, are poor candidates for surface modifications that combine wear and corrosion resistance. Some substrates that tolerate surface modifications to combine wear and corrosion resistance include stainless steel, chromium-based alloys, and nickel-based alloys. Some surface modification techniques, such as nitriding, improve wear resistance but adversely affect corrosion resistance. Some surface modification materials, such as tantalum, increase corrosion resistance but are expensive and do not enhance wear resistance.

[0004] Furthermore, existing surface modification techniques such as nitriding, anodizing, thermal spraying, and chemical vapor deposition suffer from limitations including shallowpenetration depth, poor adhesion under thermal cycling, incompatibility with complex geometries, or inability to simultaneously provide both high hardness and chemical stability. In addition, surface modification techniques using noble or refractory metals such as tantalum are expensive or difficult to apply uniformly.

[0005] In view of this background, there is an unmet need for improved metal surface modifications that combine wear and corrosion resistance.Summary

[0006] According to the present invention, there is provided a method of making a surface- modified article, the method comprising: applying a surface-modifying material to a metallic substrate; forming a metallurgical bond at an interface between the surface-modifying material and the metallic substrate; wherein the surface-modifying material comprises metallic material, ceramic material, or mixtures, combinations, or alloys thereof; and wherein the metallic substrate comprises iron, nickel, cobalt, aluminium, copper, chromium, titanium, tungsten, tantalum, molybdenum, zinc, gold, silver, ruthenium, rhodium, zirconium, or alloys thereof.

[0007] The applying the surface-modifying material to the metallic substrate and the forming the metallurgical bond at the interface between the surface-modifying material and the metallic substrate may be performed concurrently or sequentially.

[0008] The surface-modifying material may be applied to the metallic substrate by substrate-to-substrate contact, vapour deposition, ion beam deposition, dry powder layering, chemical deposition, gel deposition, electrodeposition, cold spraying, thermal spraying, laser deposition, or combinations thereof.

[0009] The metallurgical bond may be formed by cladding, diffusion bonding, overcasting, welding, electron beam welding, soldering, brazing, laser, or combinations thereof.

[0010] The metallic material may comprise iron, nickel, cobalt, aluminium, copper, chromium, titanium, tungsten, tantalum, molybdenum, zinc, gold, silver, ruthenium, rhodium, zirconium, or mixtures, combinations, or alloys thereof.

[0011] The metallic material may be provided as a solid thin substrate, or in granulated, particulate, or powder form.

[0012] The ceramic material may comprise metallic oxides, metallic nitrides, metallic carbides, metallic borides, carbon, silicon, or mixtures, combinations, or alloys thereof.

[0013] The ceramic material may be provided in granulated, particulate, or powder form.

[0014] The metallurgical bond may be formed in an ambient or modified atmosphere.

[0015] The modified atmosphere may be an inert atmosphere, a shrouded atmosphere, a vacuum atmosphere, or a reduced pressure atmosphere.

[0016] The modified atmosphere may comprise argon, helium, nitrogen, carbon dioxide, oxygen, acetylene, hydrogen, or combinations thereof.

[0017] The present invention also provides a surface-modified article made by the method described above.Brief Description of Drawings

[0018] Embodiments of the invention will now be described by way of example only with reference to the accompanying drawings, in which:Figure 1 is a flowchart of an example method of making a surface-modified article according to embodiments of the present invention;Figure 2 is table of chemical compositions of NiCrMo surface-modified super duplex stainless steel (SDSS) samples and variations in their hardness and corrosion properties compared to unmodified SDSS;Figure 3 is a table of chemical compositions of TaTi-TiC composite alloy samples and variations in their hardness and corrosion properties compared to unmodified Ti;Figure 4 is a graph of hardness versus distance from external surface though overlay thickness for surface-modified Ti test plates showing increased hardness of TaC weld overlay surface modifications;Figure 5 is a graph of hardness versus distance from external surface though overlay thickness for surface-modified Ta test plates showing increased hardness of TaC weld overlay surface modifications;Figure 6 is a microstructure image of a cross section of an example TaC weld overlay surface modification on a Ta test plate mounted on a Ti mount plate;Figures 7 and 8 are images of two sample TaC surface modifications on Ta substrates before and after immersion for corrosion testing;Figure 9 is a table of mass loss and corrosion rate data for the two TaC-on-Ta samples;Figure 10 is a graph showing hardness versus depth profiles for the two TaC-on- Ta samples;Figure 11 is a micrograph a of cross section with hardness gradients for an example of a hardened Ta overlay metallurgically bonded to a Ti substrate;Figure 12 is a micrograph of a cross section with hardness gradients for another example of a Ta overlay metallurgically bonded to a Ti substrate;Figure 13 is a micrograph of a cross section with hardness gradients for a further example of a hardened TaC overlay metallurgically bonded to a Ti substrate; andFigure 14 is a micrograph of a cross section with hardness gradients for an additional example of a hardened TaC overlay metallurgically bonded to a Ti substrate.Description of Embodiments

[0019] Referring to Figure 1 , an example method 100 of making a surface-modified article according to embodiments of the present invention may generally start at step 110 by applying a surface-modifying material to a metallic substrate. In some examples, the surface-modifying material may be applied to or deposited on the metallic substrate by substrate-to-substrate contact, vapour deposition, ion beam deposition, dry powder layering, chemical deposition, gel deposition, electrodeposition, cold spraying, thermal spraying, laser deposition, or combinations thereof. In some examples, the surfacemodifying material may be applied or deposited with a thickness of 50 microns to 5 millimetres.

[0020] In some examples, the surface-modifying material may comprise metallic material, ceramic material, or mixtures, combinations, or alloys thereof. The metallic material may, for example, comprise iron, nickel, cobalt, aluminium, copper, chromium, titanium, tungsten, tantalum, molybdenum, zinc, gold, silver, ruthenium, rhodium, zirconium, or mixtures, combinations, or alloys thereof. In some examples, the metallic material may be provided as a solid thin substrate, or in granulated, particulate, or powder form.

[0021] In some examples, the ceramic material comprising the surface-modifying material may comprise metallic oxides, metallic nitrides, metallic carbides, metallic borides, carbon, silicon, or mixtures, combinations, or alloys thereof. The ceramic material may, for example, be provided in granulated, particulate, or powder form.

[0022] In some examples, the metallic substrate may comprise iron, nickel, cobalt, aluminium, copper, chromium, titanium, tungsten, tantalum, molybdenum, zinc, gold, silver, ruthenium, rhodium, zirconium, or alloys thereof.

[0023] At step 120, a metallurgical bond may be formed at an interface between the surface-modifying material and the metallic substrate. As used herein, the term “metallurgical bond” refers to a physical and chemical joining between two metallic materials at their interface, wherein the bond is formed through mechanisms such as melting, diffusion, or solid-state transformation, resulting in atomic-level continuity across the interface. Such a bond may include interdiffusion zones, alloyed regions, or intermetallic phases, and is generally stronger and more durable than non-metallurgical (e.g., adhesive or mechanical) bonds. In some examples, the metallurgical bond may be formed by cladding, diffusion bonding, overcasting, welding, electron beam welding, soldering, brazing, laser, or combinations thereof.

[0024] In some examples, the step 110 of applying the surface-modifying material to the metallic substrate and the step 120 of forming the metallurgical bond at the interface between the surface-modifying material and the metallic substrate may be performed concurrently or simultaneously. In other examples, the steps 110 and 120 may be performed sequentially.

[0025] For example, the surface-modifying material may be deposited onto the metallic substrate surface in the form of a powder, and localized heating may be simultaneouslyapplied to the deposited surface-modifying material and the adjacent region of the metallic substrate. The deposition may, for example, be carried out using a technique such as laser cladding. The localized heating may be sufficient to cause melting, partial melting, or diffusion at the interface between the surface-modifying material and the metallic substrate, thereby enabling the formation of a metallurgical bond. The heat source may include a laser, electron beam, electric arc, or induction heating system, and is directed to the region of active deposition. The heated region may be allowed to cool to ambient or controlled temperatures, solidifying the surface-modifying material in a manner that produces a metallurgically bonded interface. The interface may exhibit a diffusion zone, alloy formation, or recrystallized grain structure indicative of atomic-level bonding. The metallurgical bond formed by the method 100 may be characterized by the absence of discrete interfacial boundaries and the presence of atomic interdiffusion, intermetallic phase formation, or alloyed transition zones between the substrate and the coating. The resulting surface-modified structure may demonstrate enhanced adhesion, mechanical strength, and thermal stability compared to coatings that rely solely on mechanical or adhesive bonding mechanisms.

[0026] In one example, the surface-modifying material in alloy powder form may be deposited onto the metallic substrate using laser cladding. The high local temperature generated by the laser causes partial melting of both the alloy powder and the surface of the metallic substrate, resulting in interdiffusion of atoms at the interface. Upon solidification, a metallurgical bond is formed, which exhibits no discernible interface under scanning electron microscopy.

[0027] In another example, titanium powder may be applied to a titanium alloy substrate using physical vapor deposition followed by a diffusion heat treatment. The heat treatment may promote atomic diffusion across the interface, eliminating voids and creating a metallurgical bond without melting either material.

[0028] In a further example, the surface-modifying material in alloy form may be arc sprayed onto a surface of the metallic substrate. To convert the mechanically adhered coating into a metallurgically bonded layer, the coated surface is subjected to induction heating, causing the alloy to partially melt and react with the steel, forming a diffusion layer that resists peeling and corrosion.

[0029] In some examples, the metallurgical bond between the surface-modifying material and the metallic substrate may be formed in an ambient or modified atmosphere. The modified atmosphere may, for example, comprise an inert atmosphere, a shrouded atmosphere, a vacuum atmosphere, or a reduced pressure atmosphere. The modified atmosphere may further or alternatively comprise argon, helium, nitrogen, carbon dioxide, oxygen, acetylene, hydrogen, or combinations thereof. In some examples, the gases used in the modified atmosphere may be selectively and individually varied to control their incorporation and resulting influences on the metallurgical bonding, phase formation, and microstructural evolution at the interface between the surface-modifying material and the metallic substrate.

[0030] In some examples, an inert or shrouded atmosphere may be used with GTAW (Gas Tungsten Arc Welding) as a protective gas environment created around the weld area to shield the molten weld pool, tungsten electrode, and heat-affected zone from reactive gases in the air such as oxygen, nitrogen, and water vapor. The inert atmosphere may use inert shielding gases, such as argon, that do not chemically react with the molten metal or electrode. The shrouded atmosphere may be an extension or enhancement of the inert atmosphere involving physical coverage of the weld zone by a gas shroud (e.g., a wide gas lens, trailing shield, or welding enclosure).

[0031] In some examples of the method 100, the steps of applying the surface-modifying material to the metallic substrate 110 and forming the metallurgical bond at the interface between the surface-modifying material and the metallic substrate 120 may be performed sequentially or simultaneously. For example, in one example, the surface-modifying material may be automatically fed in powder form while the surface of the metallic substrate and the surface-modifying material are both locally melted simultaneously using a high-energy-density laser beam to allow continuous and simultaneous uniform covering and localised heating, and the weld pool may be simultaneously protected by a constant flow of shielding gas.

[0032] In another example, the surface-modifying material may be in the form of a dry powder that is applied in a controlled manner to form one or more discrete or continuous layers over the metallic substrate. Following deposition, the layered powder may be subjected to a thermal treatment, such as in-situ localized heating, to metallurgically bond the surface-modifying material to the surface of the metallic substrate.

[0033] In some examples, the surface-modifying material may be deposited with a controlled composition gradient or particle size distribution to produce a layered or functionally graded structure upon localized heating. In one example, Ta and / or TaC powder may be measured by volume and mixed by shaking. The mixture may be deposited into a powder hopper and applied onto the metallic substrate using APS thermal spray. The thermal spray coating may then be metallurgically bonded / fused / partially melted to the substrate using GTAW. The resulting fusion between the surface-modifying material and the metallic substrate, and the metallurgical bond at their interface, avoid or minimize delamination of the surface-modifying material.

[0034] In other examples, Ta and / or TaC powder may be measured by weight and mixed by shaking. The mixture may be deposited into a powder hopper and deposited and fused onto the substrate using a laser. In some examples, the initial deposited layers may have a different composition to the ensuing layers to achieve fusion and metallurgical bonding with the metallic substrate. Subsequent layers of different material type may impart similar or different combinations of erosion- and corrosion-resistance. In these examples, there may be a controlled composition gradient or particle size distribution to produce a layered or functionally graded structure upon localized heating. In other examples, the method 100 may also permit tailoring of surface-, wear- and corrosion-resistance properties by controlling composition of one or both of surface-modifying materials and shielding gases, single or multilayers, deposition thickness, and localized thermal profiles, yielding a surface modification comprising a gradient structure or functionally graded material (FGM) that reduces delamination and increases corrosion resistance, an outcome not suggested in conventional cladding or coating methods. In some examples, the functionally graded structure may comprise a gradual change in composition, microstructure, or material properties from the metallic substrate to the surface modification.

[0035] The resulting surface modification of the metallic substrate may comprise overlay, cladding, hard-facing, coating, metallic interface, or combinations thereof. Embodiments of the above method may provide a surface-modified article. The surface-modified article may, for example, comprise a metal component or a metal article used in an abrasive and corrosive environment, such as a metal component of a severe-service metal-seated ball valve used in a HPAL process. For example, the metal component may comprise ball valve trim.

[0036] Examples of the present invention advantageously provide a designed and engineered transition of wear- and corrosion-resistant properties rather than accepting natural or weaker interfaces or coatings that are prone to delamination and cracking in use from different coating and substrate thermal expansion rates. Examples of the invention also provide economy of manufacture by reducing amounts of expensive materials needed and reducing cost by reducing the number of process steps necessary to produce surface-modified articles.

[0037] The following Examples are intended to illustrate the invention. They are not intended to limit the scope of the invention.ExamplesNiCrMo cladding on stainless steel substrate

[0038] Surface-modified samples of SDSS 2507 were clad with NiCrMo powder with Ni and Cr in a range of weight concentrations using Plasma Transferred Arc (PT A) cladding and Laser Engineered Net Shaping (LENS) cladding.

[0039] Vickers microhardness testing was performed on cross-sectioned surface modified samples using a 500g load and dwell time of 15s. A Parr 4748 large capacity acid digestion vessel was used for immersion corrosion test in sulphuric acid at high temperature for 7 days.

[0040] Figure 2 shows chemical compositions of the NiCrMo surface-modified SDSS samples and variations in their hardness and corrosion properties compared to unmodified SDSS.TaTi-TiC composite alloys

[0041] TaTi-TiC composite alloys were cast and prepared as test plates for evaluation as suitable example surface-modifying materials to enhance hardness and corrosion resistance of Ti substrates. Hardness and corrosion were evaluated relative to Ti using the same tests as the preceding example.

[0042] Figure 3 is a table of chemical compositions of TaTi-TiC composite alloy samples and variations in their hardness and corrosion properties compared to Ti.TaC weld overlay on Ti substrate

[0043] A mixture of T aC powder was applied to uniformly cover Ti test plates using thermal spraying to produce TaC coatings having a thickness of 150-200pm. The TaC coatings were then overwelded in a N / Ar gas mixture to produce TaC weld overlays on the Ti test plates. Hardness and corrosion were evaluated relative to Ti using the same tests as the preceding examples.

[0044] Figure 4 is a graph of hardness versus distance from external surface though overlay thickness for the Ti test plates showing increased hardness of the weld overlay surface modifications relative to the bulk portion of the underlying Ti substrate.TaC weld overlay on Ta substrate

[0045] The above TaC weld overlay example was repeated on Ta test plates mounted on Ti mount plates using the same parameters. The thicknesses of the Ta test plates and Ti mount plates were 4.4 mm and 25 mm, respectively. Hardness and corrosion were evaluated using the same tests as the preceding examples.

[0046] Figure 5 is a graph of hardness versus distance from external surface though overlay thickness for the Ta test plates showing increased hardness of the weld overlay surface modifications relative to the bulk portion of the underlying Ta substrate.

[0047] Figure 6 is a microstructure image of a cross section of a TaC weld overlay on one of the Ta test plates on the Ti mount plate which shows that the TaC surface-modified Ta test plate became metallurgically fused to the Ti mount plate to form a trimetallic Ta-Ti composite metal structure.Thin Ta substrate on Ti substrate

[0048] As can be seen from Figure 6, a metallurgical bond was formed at the intermetallic interface between the thin Ta substrate of the Ta test plate and the thicker Ti substrate of the Ti mount plate. This metallurgical bond extends beyond the region of the TaC weld overlay. From this it can be inferred that the thin Ta substrate was metallurgically bonded or fused to the thicker Ti substrate to form a bimetallic Ta-Ti composite structure.TaC overlays on Ta substrates

[0049] Samples of TaC overlays were prepared using varying ratios of Ta and C, both applied to a Ta substrate. Sample TAC-2A consisted of a mixture containing 60% Ta and 40% C, while sample TAC-5A was composed of an equal 50:50 ratio of Ta to C.

[0050] Hardness profiling and exposure tests were conducted in 98 wt% sulfuric acid (H2SO4) at 200 °C for one week (168 hours). For corrosion resistance evaluation, the overlays were separated from their substrates via wire cutting.

[0051] Samples TAC-2A and TAC-5A exhibited strong corrosion resistance, with minimal mass loss and low corrosion rates. Figure 7 are images of sample TAC-2A before and after immersion. Corrosion was limited to a superficial level. Figure 8 are images of sample TAC-5A before and after immersion. Again, corrosion was limited to a superficial level.

[0052] The mass loss for each sample was determined, and the corrosion rates were calculated accordingly. The results are summarized in Figure 9.

[0053] Figure 10 is a graph showing hardness versus depth profiles for samples TAC-2A and TAC-5A compared to other overlays.Ta fused to Ti substrate with argon

[0054] This sample was produced by depositing Ta powder onto a Ti substrate using a 100% argon gas environment. The sample consisted of four layers, each with a thickness of 0.82 mm.

[0055] Figure 11 are micrographs of cross sections and hardness results showing the hardened Ta overlay metallurgically bonded to the Ti substrate.Ta fused to Ti substrate with argon and nitrogen

[0056] This sample was produced by depositing Ta powder onto a Ti substrate using a four-layer build-up process. Each layer L1 , L2, L3, L4 was applied with a thickness of 1.4 mm. Two distinct gas environments were employed: 100% argon was used during the deposition of layers L1 and L2, while a 60% argon 140% nitrogen mixture was introduced for layers L3 and L4.

[0057] Figure 12 is a micrograph of a cross section with hardness gradients showing the Ta overlay metallurgically bonded to the Ti substrate.TaC powder fused to Ti substrate with argon

[0058] This sample was fabricated by depositing a TaC powder blend onto a Ti substrate. The overlay consisted of four layers L1 , L2, L3, L4, each with a thickness of 2.65 mm. The deposition was carried out under a 100% argon shielding atmosphere.

[0059] Figure 13 is a micrograph of a cross section with hardness gradients showing the hardened TaC overlay metallurgically bonded to the Ti substrate.TaC fused to Ti substrate with argon and nitrogen

[0060] This sample was created by depositing a TaC powder blend onto a Ti substrate through a four-layer deposition process. Each layer L1 , L2, L3, L4 was applied with a thickness of 3.5 mm. The deposition process involved varying shielding gas compositions between layers. Specifically, 100% argon was used during the deposition of layers L1 and L2, while a 60% argon and 40% nitrogen mixture was employed for layers L3 and L4.

[0061] Figure 14 is a micrograph of a cross section with hardness gradients showing the hardened TaC overlay metallurgically bonded to the Ti substrate.

[0062] The invention is not limited to the examples that have just been given. In other words, those skilled in the art will appreciate that the examples may be reproduced without difficulty, and with similar success, by substituting any of the generically or specifically described surface-modifying materials, substrates, and method steps mentioned anywhere in this specification for those actually used in the preceding examples.

[0063] Embodiments of the present invention provide metal surface modifications that are both generally and specifically useful for providing metal composite structures for use in wear and corrosion resistant applications in a wide variety of fields and industries.

[0064] Unless the context requires otherwise, the word "comprising" means "including but not limited to," and the word "comprises" has a corresponding meaning.

[0065] Any reference to prior art is not an admission that the prior art is common general knowledge.

[0066] The scope of the invention supported by the above examples is defined by the claims that follow.

Claims

Claims1. A method of making a surface-modified article, the method comprising: applying a surface-modifying material to a metallic substrate; forming a metallurgical bond at an interface between the surface-modifying material and the metallic substrate; wherein the surface-modifying material comprises metallic material, ceramic material, or mixtures, combinations, or alloys thereof; and wherein the metallic substrate comprises iron, nickel, cobalt, aluminium, copper, chromium, titanium, tungsten, tantalum, molybdenum, zinc, gold, silver, ruthenium, rhodium, zirconium, or alloys thereof.

2. The method of claim 1, wherein the applying the surface-modifying material to the metallic substrate and the forming the metallurgical bond at the interface between the surface-modifying material and the metallic substrate are performed concurrently or sequentially.

3. The method of claim 1, wherein the surface-modifying material is applied to the metallic substrate by substrate-to-substrate contact, vapour deposition, ion beam deposition, dry powder layering, chemical deposition, gel deposition, electrodeposition, cold spraying, thermal spraying, laser deposition, or combinations thereof.

4. The method of claim 1, wherein the metallurgical bond is formed by cladding, diffusion bonding, overcasting, welding, electron beam welding, soldering, brazing, laser, or combinations thereof.

5. The method of claim 1 , wherein the metallic material comprises iron, nickel, cobalt, aluminium, copper, chromium, titanium, tungsten, tantalum, molybdenum, zinc, gold, silver, ruthenium, rhodium, zirconium, or mixtures, combinations, or alloys thereof.

6. The method of claim 5, wherein the metallic material is provided as a solid thin substrate, or in granulated, particulate, or powder form.

7. The method of claim 1, wherein the ceramic material comprises metallic oxides, metallic nitrides, metallic carbides, metallic borides, carbon, silicon, or mixtures, combinations, or alloys thereof.

8. The method of claim 7, wherein the ceramic material is provided in granulated, particulate, or powder form.

9. The method of claim 1, wherein the metallurgical bond is formed in an ambient or modified atmosphere.

10. The method of claim 9, wherein the modified atmosphere may be an inert atmosphere, a shrouded atmosphere, a vacuum atmosphere, or a reduced pressure atmosphere.

11. The method of claim 9, wherein the modified atmosphere comprises argon, helium, nitrogen, carbon dioxide, oxygen, acetylene, hydrogen, or combinations thereof.

12. A surface-modified article made by the method of claim 1.

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