A method for preparing a surface hardened layer of a nickel alloy

Abstract

This application discloses a method for preparing a surface-hardened layer on a nickel alloy. The method includes using a nickel alloy as a substrate, firstly cleaning and drying the substrate sequentially, followed by ultrasonic rolling; then covering the ultrasonically rolled substrate with a boronizing agent, heating and boronizing at 600-800℃ and holding at that temperature for 3-6 hours; next, under inert gas conditions with a purity greater than 99.5%, subjecting the boronized substrate to solution treatment at 1040-1140℃ and aging heat treatment at 700-850℃; finally, grinding the heat-treated substrate to obtain the target nickel alloy substrate containing the surface-hardened layer. The synergistic combination of ultrasonic rolling and boronizing processes refines the surface microstructure of the nickel alloy, improves the bonding strength between the boronized layer and the substrate, and prevents the formation of microcracks; while ensuring the performance of the surface-hardened layer, it does not damage the original corrosion resistance of the substrate, significantly improving the service life of the nickel alloy under high temperature, high pressure, and strong erosion wear conditions, demonstrating strong process stability and practicality.

Description

Technical Field

[0001] This application relates to the field of metal plating technology, and in particular to a method for preparing a surface hardening layer of a nickel alloy. Background Technology

[0002] Nickel alloys are widely used in high-end industrial fields such as aerospace, petrochemicals, and nuclear power equipment to manufacture key load-bearing components, such as turbine blades, valve cores, and high-temperature fasteners, due to their excellent high-temperature strength, corrosion resistance, and oxidation resistance. However, the hardness of nickel alloy substrates is typically only 215~387HV, and their surface wear resistance is poor. They are prone to early failure under harsh service environments such as high-speed friction and high-temperature erosion, which severely limits their application range in high-load wear-resistant scenarios.

[0003] To improve the surface properties of nickel alloys, various surface hardening technologies have been developed, including carburizing, nitriding, shot peening, and coating deposition. Among these, boronizing is an effective means of enhancing the wear resistance of nickel alloys because it can form a high-hardness boride layer on the metal surface. However, the boronizing process for nickel alloys still faces many technical bottlenecks: the boronized layer obtained by traditional solid boronizing methods has low density and many pore defects, resulting in insufficient bonding strength between the boronized layer and the substrate, making it prone to peeling; some boronizing processes use halides such as ammonium chloride as catalysts, which release toxic gases during heating, causing environmental pollution and equipment corrosion; at the same time, the SiC filler in the boronizing agent easily reacts with the substrate to form a porous nickel-silicon-boron layer, which requires additional machining for removal, increasing the process cost.

[0004] Regarding process synergy, in existing technologies, boronizing and the heat treatment strengthening process of nickel alloys are usually independent. Nickel alloys, especially heat-treated nickel alloys, require solution treatment and heat aging to obtain excellent mechanical properties. However, the traditional boronizing temperature does not match the heat treatment temperature, resulting in multiple heating and cooling cycles during production, leading to long process cycles and high energy consumption. Furthermore, the hardened layer formed by simple boronizing is prone to microstructural degradation and residual compressive stress relaxation under high-temperature service environments, resulting in a decrease in strengthening effect and making it difficult to meet long-term high-temperature wear resistance requirements.

[0005] While surface mechanical strengthening techniques such as ultrasonic rolling can improve the fatigue resistance of materials by introducing residual compressive stress and refining the surface microstructure, their hardened layer depth is limited and their high-temperature stability is insufficient when used alone. How to organically combine surface mechanical strengthening with chemical infiltration technology and achieve synergistic optimization with subsequent heat treatment processes has become a key issue in improving the overall performance of the hardened layer on nickel alloy surfaces.

[0006] Therefore, the poor quality of the diffusion layer, environmental pollution, complicated procedures, and insufficient high-temperature stability in the existing nickel alloy boronizing process are problems that urgently need to be solved. Summary of the Invention

[0007] This application provides a method for preparing a surface hardened layer on a nickel alloy, which solves the problems of poor layer quality, environmental pollution, cumbersome procedures, and insufficient high-temperature stability in the existing boronizing process of nickel alloys. It achieves refined surface microstructure of nickel alloys, improves the bonding strength between the boronized layer and the substrate, and avoids the generation of microcracks. At the same time, the solution treatment and aging heat treatment parameters are adapted to the characteristics of nickel alloys, ensuring the performance of the surface hardened layer without damaging the original corrosion resistance of the substrate. This significantly improves the service life of nickel alloys under high temperature, high pressure, and strong erosion and wear conditions, as well as the process stability and practicality.

[0008] In a first aspect, embodiments of this application provide a method for preparing a surface hardened layer on a nickel alloy, comprising:

[0009] The substrate is a nickel alloy;

[0010] The substrate is cleaned and dried.

[0011] The treated substrate is subjected to ultrasonic rolling.

[0012] After ultrasonic rolling treatment, the substrate is covered with a boronizing agent and then subjected to a heated boronizing treatment.

[0013] The substrate after heating and boronizing was subjected to solution treatment and aging heat treatment under inert gas conditions.

[0014] The substrate after solution treatment and aging heat treatment is subjected to grinding to obtain the target substrate.

[0015] The heating and boronizing temperature is 600~800℃, and the holding time is 3~6h;

[0016] The solution treatment temperature is 1040~1140℃, and the aging heat treatment temperature is 700~850℃;

[0017] The purity of the inert gas is greater than 99.5%.

[0018] In conjunction with the first aspect, in one possible implementation, the size of the substrate after cleaning, drying and ultrasonic rolling is 0.03~0.05 mm larger than the size of the target substrate, and the surface roughness of the substrate is not greater than Ra3.2.

[0019] In conjunction with the first aspect, in one possible implementation, the parameters of the ultrasonic rolling process include a current of 0.5~1.0A, a frequency of 20~30KHz, an amplitude of 10~30μm, a loading force of 250~450N, and a feed speed of 0.05~0.15mm / r.

[0020] In conjunction with the first aspect, in one possible implementation, the boronizing agent comprises 5% to 10%... 8%~12% 78%~87% SiC.

[0021] In conjunction with the first aspect, in one possible implementation, after the heating and boronizing process is completed, the temperature is cooled to below 200°C for air cooling.

[0022] In conjunction with the first aspect, in one possible implementation, the nickel alloy is Hastelloy, Inconel, Monel, or a nickel-based superalloy, and the inert gas is argon or nitrogen.

[0023] In conjunction with the first aspect, in one possible implementation, the grinding process is performed using diamond grinding paste.

[0024] Secondly, embodiments of this application relate to a nickel alloy material containing a surface hardening layer, wherein the nickel alloy material is prepared using the aforementioned preparation method.

[0025] In conjunction with the second aspect, in one possible implementation, the nickel alloy material may be at least one structural component selected from a sphere and a valve core, wherein the sphere has a roundness of less than 0.03 mm and the effective thickness of the surface hardening layer is 70~100 μm.

[0026] In conjunction with the second aspect, in one possible implementation, the hardness of the surface hardening layer is greater than 900. .

[0027] This application embodiment uses a nickel alloy as the substrate. First, the substrate is sequentially cleaned, dried, and ultrasonically rolled. Then, the treated substrate is covered with a boronizing agent and heated at 600-800℃ for 3-6 hours. Next, under inert gas conditions with a purity greater than 99.5%, the boronized substrate undergoes solution treatment at 1040-1140℃ and aging heat treatment at 700-850℃. Finally, the heat-treated substrate is ground to obtain the target nickel alloy substrate with a surface-hardened layer. The synergistic combination of ultrasonic rolling and boronizing processes refines the surface microstructure of the nickel alloy, improves the bonding strength between the boronized layer and the substrate, and prevents the formation of microcracks. Simultaneously, the solution and aging heat treatment parameters are adapted to the characteristics of the nickel alloy, ensuring the performance of the surface-hardened layer without damaging the original corrosion resistance of the substrate. This significantly improves the service life of the nickel alloy under high temperature, high pressure, and strong erosion wear conditions, demonstrating strong process stability and practicality. Attached Figure Description

[0028] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the description of the embodiments of this application or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1 This is a photograph showing the thickness of a boron-hardened layer, provided as an embodiment of this application. Detailed Implementation

[0030] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0031] The following description of some technologies involved in the embodiments of this application is provided to aid understanding and should be considered merely exemplary. Therefore, those skilled in the art should recognize that various changes and modifications can be made to the embodiments described herein without departing from the scope and spirit of this application. Similarly, for clarity and brevity, some descriptions of well-known functions and structures are omitted in the following description.

[0032] The technical solution of the present invention will be described in detail below with reference to specific embodiments. The boronizing agent components used in this embodiment ( , All materials (SiC) are of industrial grade purity (≥99%). The ultrasonic rolling equipment is a CNC ultrasonic rolling machine tool. The heating boronizing equipment is a box-type resistance furnace. The solid solution and aging treatment equipment is a pit-type heat treatment furnace with inert gas protection. The hardness test is performed using a Vickers hardness tester (load 0.1kg). The thickness of the infiltrated layer is observed by a metallographic microscope. All test methods are industry standard methods. Unless otherwise stated, "%" in the examples refers to mass percentage.

[0033] Example 1

[0034] This embodiment uses a DN100 Hastelloy (HC276) ball valve ball as the treatment object, and prepares a hardened layer on its surface. The specific steps are as follows:

[0035] Step 1: The Hastelloy HC276 ball valve ball is machined using a CNC lathe. The outer diameter of the ball is controlled to be 0.03 mm larger than the final design size, and the surface roughness after machining is Ra1.6. The ball is placed in an acetone solution and cleaned for 15 minutes using an ultrasonic cleaner at a frequency of 40 kHz to remove surface oil and chips. Then it is placed in an 80℃ forced-air drying oven to dry for 30 minutes to obtain a clean substrate.

[0036] Step 2: Fix the dried sphere onto an ultrasonic rolling mill for processing. Set the rolling parameters as follows: current 0.7A, frequency 25KHz, amplitude 20μm, loading force 350N, and feed speed 0.1mm / r. Perform full circumferential rolling treatment on the surface of the sphere to form a surface refinement layer with a thickness of about 50μm.

[0037] Step 3: Prepare the boronizing agent, with a composition of 8%. 10% The remainder is SiC. The boronizing agent is placed into the corundum barrel, and the ultrasonically rolled spheres are placed in it, ensuring that the boronizing agent completely covers the spheres (coverage thickness ≥10mm). After sealing the corundum barrel, it is sent into a box-type resistance furnace, and the heating temperature is set to 750℃, with a holding time of 4h. After the holding time is completed, the temperature is cooled to below 200℃ with the furnace. The furnace door is opened, the corundum barrel is taken out, and it is air-cooled to room temperature.

[0038] Step 4: Remove the boron-diffused spheres, blow off any residual boronizing agent from the surface using a high-pressure airflow, then ultrasonically clean with anhydrous ethanol for 10 minutes, dry, and place in a pit-type heat treatment furnace with argon protection (argon purity 99.8%, gas flow rate 1L / min); first heat to 1120℃ for solution treatment, hold for 2 hours, then rapidly cool to room temperature; then reheat to 800℃ for aging treatment, hold for 4 hours, and cool to room temperature with the furnace. Figure 1 This is a photograph showing the thickness of a boron-hardened layer, provided as an embodiment of this application.

[0039] Step 5: Using W1.5 diamond grinding paste, perform grinding on the aged spheres on a precision grinding machine, controlling the grinding pressure at 0.2MPa and the rotation speed at 30r / min, until the sphere size meets the final design requirements (roundness ≤0.03mm).

[0040] The Hastelloy HC276 ball valve ball obtained in this embodiment has a hardened layer thickness of 80 μm and a surface hardness of 970. The substrate hardness is 215HV, the hardened layer is tightly bonded to the substrate, and no cracks or peeling were observed after thermal cycling tests.

[0041] Example 2

[0042] This embodiment uses the Inconel 718 control valve core with a maximum outer diameter of 250mm as the processing object, and the specific steps are as follows:

[0043] Step 1: Prepare the Inconel 718 control valve core by milling and grinding composite machining. The key outer diameter of the control valve core is 0.05 mm larger than the final design size, and the surface roughness is Ra3.2. Clean the core with acetone ultrasonically for 20 min and dry it at 100℃ for 20 min to remove surface impurities.

[0044] Step 2: Set the ultrasonic rolling parameters: current 1.0A, frequency 30KHz, amplitude 30μm, loading force 450N, feed speed 0.15mm / r, and roll the outer circle of the valve core and the sealing surface to form a surface refinement layer with a thickness of about 60μm.

[0045] Step 3: Prepare boronizing agent (10%) 12% The rest are SiC. The valve core is embedded in boronizing agent and sealed in a corundum barrel and sent into a box-type resistance furnace. The heating temperature is set to 800℃, the holding time is 6h, and the furnace is cooled to 180℃ and then air-cooled.

[0046] Step 4: After cleaning the boronizing agent from the valve core surface, clean and dry it with ethanol, and place it in a nitrogen-protected heat treatment furnace (nitrogen purity 99.6%, flow rate 1.5L / min); first, perform a solution treatment at 1040℃ for 1.5h, then water-cool to room temperature; then perform an aging treatment at 850℃ for 3h, and cool it with the furnace.

[0047] Step 5: Use W0.5 diamond grinding paste for precision grinding to ensure that the outer diameter tolerance of the valve core is ≤0.005mm and the flatness of the sealing surface is ≤0.002mm.

[0048] The Inconel 718 control valve core prepared in this embodiment has a hardened layer thickness of 100 μm and a surface hardness of 1200. The substrate hardness is 387HV, the hardened layer showed no rust in the salt spray corrosion test, and the friction coefficient was reduced to 0.15.

[0049] Example 3

[0050] This embodiment uses a DN50 Monel alloy (Monel400) shut-off valve core as the processing object, and the specific steps are as follows:

[0051] Step 1: Machining the Monel400 shut-off valve core with a dimensional allowance of 0.04 mm and a surface roughness of Ra2.0; ultrasonic cleaning with acetone for 18 min and drying at 90℃ for 25 min.

[0052] Step 2: Set the rolling parameters: current 0.5A, frequency 20KHz, amplitude 15μm, loading force 250N, feed speed 0.08mm / r, and roll the valve core sealing surface and valve stem mating surface.

[0053] Step 3: Prepare boronizing agent (5%) 8% (The rest are SiC), after sealing, it is kept at 600℃ for 3 hours, and then cooled to 200℃ by air cooling with the furnace.

[0054] Step 4: Since Monel400 does not require aging strengthening, it is only subjected to solution treatment at 1140℃ for 2.5h under argon protection (purity 99.5%), and then cooled to room temperature with water.

[0055] Step 5: Grind to the designed size using W1.0 diamond grinding paste, ensuring that the valve stem clearance is ≤0.01mm.

[0056] The Monel alloy valve core prepared in this embodiment has a surface hardening layer thickness of 70 μm and a surface hardness of 920. The substrate hardness is 240HV, and the corrosion rate after immersion in 20% sulfuric acid solution for 24 hours is ≤0.05mm / a.

[0057] Comparative Example 1 (without ultrasonic rolling treatment)

[0058] The difference between this comparative example and Example 1 is that the "ultrasonic rolling treatment" step is omitted, while the other process parameters are completely the same.

[0059] The results showed that the hardened layer thickness was only 45 μm and the surface hardness was 820. Furthermore, the presence of micropores within the infiltrated layer, along with localized spalling after thermal cycling tests, indicates that ultrasonic rolling treatment is crucial for improving the thickness, density, and bonding strength of the infiltrated layer.

[0060] Comparative Example 2 (Boronizing temperature out of range)

[0061] The difference between this comparative example and Example 2 is that the heating boronizing temperature is set to 900℃ (exceeding the range of 600~800℃ of this application), while the other process parameters are the same.

[0062] The results showed that oxidation and burning occurred on the surface of the valve core, and an embrittled layer (approximately 15 μm thick) was formed at the interface between the hardened layer and the substrate. The embrittled layer cracked during the hardness test and could not meet the usage requirements, indicating that exceeding the boronizing temperature range would damage the performance of the substrate.

[0063] Comparative Example 3 (Boronizing agent composition is inconsistent)

[0064] The difference between this comparative example and Example 3 is that the boronizing agent used is "15%". 5% The rest are (Deviates from the boronizing agent composition of this application), the rest of the process is the same.

[0065] The results showed that the hardened layer thickness was only 30 μm, and the surface hardness was 750. Furthermore, the boronizing agent reacts with the substrate to form Al-Ni compounds, causing deformation of the valve core sealing surface, which cannot be corrected by grinding. This indicates that the composition of the boronizing agent needs to be strictly controlled.

[0066] Table 1 is a summary table of the performance of this application.

[0067] Table 1 Performance Summary Table

[0068]

[0069] As can be seen from the above embodiments and comparative examples, the present invention, through the synergistic process of "ultrasonic rolling-boroning-solution / aging-grinding", can prepare nickel alloys with a thickness of 70~100μm and a hardness >900 on different types of nickel alloy surfaces. The high-quality hardened layer is tightly bonded to the substrate and has excellent corrosion and wear resistance, which can meet the requirements of use under high temperature, high pressure and strong corrosion conditions; however, if the process parameters of this invention are deviated from or key steps are omitted, the expected strengthening effect cannot be achieved.

[0070] The above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit this application. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of this application.

Claims

1. A method for producing a hardened layer of a nickel alloy surface, characterized by, The application relates to a preparation method of a nickel alloy material. The method comprises the following steps: a substrate is prepared, wherein the substrate is a nickel alloy; the substrate is cleaned and dried; the treated substrate is subjected to ultrasonic rolling treatment; the substrate after the ultrasonic rolling treatment is covered with a boronizing agent and then subjected to heating boronizing treatment; the substrate after the heating boronizing treatment is subjected to solid solution and aging heat treatment in an inert gas; the substrate after the solid solution and aging heat treatment is subjected to finishing processing to obtain a target substrate; the heating boronizing temperature is 600-800 DEG C, and the holding time is 3-6 h; the solid solution temperature is 1040-1140 DEG C, and the aging heat treatment temperature is 700-850 DEG C; the purity of the inert gas is greater than 99.5%; the size of the substrate after the cleaning, drying and ultrasonic rolling treatment is 0.03-0.05 mm larger than that of the target substrate, and the surface roughness of the substrate is not greater than Ra3.2; The components of the boronizing agent include 5%~10% , 8%~12% , 78%~87% SiC.

2. The method of claim 1, wherein the nickel alloy surface hardening layer is formed by a process comprising: the ultrasonic rolling treatment parameters include: current 0.5-1.0 A, frequency 20-30 KHz, amplitude 10-30 mu m, loading force 250-450 N and feeding speed 0.05-0.15 mm / r; 3. The method of claim 1, wherein the nickel alloy surface hardening layer is formed by a process comprising: after the heating boronizing treatment reaches the holding time, the substrate is cooled to below 200 DEG C for air cooling treatment.

4. The method of claim 1, wherein the nickel alloy surface hardening layer is formed by a process comprising: The nickel alloy is a hastelloy alloy, an inconel alloy, a monel alloy or a nickel-based high-temperature alloy, and the inert gas is argon or nitrogen.

5. A nickel alloy material comprising a surface hardening layer, characterized in that, The finishing processing is carried out by using diamond grinding paste.

6. The nickel alloy material containing a hard-facing layer of claim 5, wherein, The nickel alloy material is prepared by using the preparation method in any one of claims 1-4. The nickel alloy material can be at least one structural member of a ball and a valve core, the roundness of the ball is less than 0.03 mm, and the effective thickness of the surface hardening layer is 70-100 mu m.

7. The case hardening layer-containing nickel alloy material according to claim 5, characterized by, The surface hardened layer has a hardness greater than 900 .

Images