760 DEG C low-temperature boriding process for Inconel 718 nickel-based high-temperature alloy

Abstract

The invention discloses a 760 DEG C low-temperature boriding process for Inconel 718 nickel-based high-temperature alloy, and belongs to the technical field of wear-resistant material preparation. A high-hardness and high-wear-resistance boride infiltrated layer with the thickness of about 15 microns is successfully prepared on the surface of the solid-solution-state Inconel 718 nickel-based high-temperature alloy under the low-temperature condition of 760 DEG C by adjusting a boriding agent (preferably B4C, 10% of KFB < 4 > and 5% of amorphous B powder) by utilizing a solid powder embedding boriding technology. Compared with a traditional Inconel 718 alloy high-temperature boriding process, the boriding method has the advantages that the alloy heat treatment aging process and the boriding process can be unified, and the secondary heat treatment procedure after high-temperature boriding is avoided; and the wear resistance of the Inconel 718 alloy is remarkably improved. The infiltrated layer preparation process is simple, the cost is low, and the boride infiltrated layer which is good in quality and firm in combination can be obtained.

Description

Technical Field

[0001] The invention relates to a method for preparing a high-wear-resistant boride layer on the surface of an Inconel 718 nickel-based high-temperature alloy at a low temperature of 760° C., and belongs to the technical field of wear-resistant material preparation. Background Art

[0002] Inconel 718 alloy is a common nickel-based high-temperature alloy with good high-temperature strength, fatigue resistance, oxidation resistance, and thermal corrosion resistance. In particular, it still has good mechanical property stability at temperatures below 650°C. Therefore, it can be used as a common base material for aviation sliding bearings. During the operation of the sliding bearing, the outer ring and the inner ball have a strong interaction, which in turn causes surface wear and affects the performance and service life of the bearing. However, the surface hardness of Inconel 718 alloy is insufficient and its wear resistance is poor. In particular, the lubricant fails in high-temperature service environments, resulting in strong dry friction between the friction pairs, which limits its direct application as a material for high-temperature transmission components. Therefore, surface strengthening is necessary to meet the use requirements of sliding bearings.

[0003] At present, the surface modification technologies for nickel-based high-temperature alloys mainly include thermal spraying, laser cladding, and surface chemical heat treatment. Among them, surface chemical heat treatment boronization has the advantages of easy operation, simple equipment, and good strengthening effect. It has been successfully applied to the surface strengthening of high-temperature load-bearing components of the tail nozzle of a certain type of engine in the United States. Therefore, the boronization method is used to strengthen the surface of Inconel 718. Boronization refers to the process of placing a metal workpiece in a boron-containing medium, heating it under specific boronizing conditions and keeping it warm for a certain period of time, generating active boron atoms through chemical reactions, causing them to diffuse and penetrate into the surface of the workpiece to form a hard layer mainly composed of metal borides. According to the physical state of the infiltrating element medium, chemical heat treatment boronization can be divided into three categories: solid phase method, gas phase method, and liquid phase method. Among them, solid phase boronization has become the most widely used boronization method in industry due to its advantages such as simple equipment, low cost, and stable quality of the boronized layer.

[0004] The boronizing temperature, boronizing time, and boronizing composition of the solid-state boronizing method all affect the thickness and structure of the boronized layer. The boronizing temperature is the key to determining the boronizing effect, and Inconel 718 alloy requires solid solution and aging heat treatment to obtain the appropriate internal structure. According to literature reports, the effective boronizing temperature of Inconel 718 is generally higher than 900°C, which will destroy the precipitated phase structure obtained by the aging treatment of the alloy and have an adverse effect on the mechanical properties. Therefore, how to unify the boronizing process of Inconel 718 with the aging heat treatment process has become the key to the application of solid phase boronizing technology in nickel-based high-temperature alloys. Summary of the Invention

[0005] The purpose of the present invention is to achieve the effective growth of a boride layer on the surface of Inconel 718 alloy for aviation sliding bearings by regulating the components of the boriding agent, and to achieve a higher thickness of the boride layer on the alloy surface at a lower boriding temperature, so as to improve its surface hardness and wear resistance; and then use a variety of material characterization techniques to systematically explore the catalytic mechanism of the new catalyst, the structure and wear resistance of the low-temperature borided layer.

[0006] The method of the present invention utilizes solid-phase powder embedding boronizing technology. On the basis of the original boronizing agent, amorphous B powder is used to replace Al2O3, and the weight percentage of the catalyzer KBF4 is appropriately increased. A boronized layer with a thickness of about 15 μm is successfully produced on a solid solution Inconel 718 substrate. Characterization analysis, microhardness testing, and friction and wear testing have shown that the boronized layer has high hardness and good wear resistance.

[0007] This boronizing method is simple to operate, the workpiece surface is easy to clean after boronizing, the cost of the penetrant is low, and the requirements for the workpiece shape are small. It can effectively improve the thickness and quality of the boronized layer of Inconel 718 at low temperature boronizing, and has commercial promotion value.

[0008] The matrix used is solid solution Inconel 718 nickel-based high-temperature alloy.

[0009] The mass percentage of the self-prepared boronizing agent components is: balance B4C+5%-10% KFB4+5%-10% amorphous B powder, preferably balance B4C+10% KBF4+5% amorphous B powder.

[0010] In order to achieve the above technical objectives, the technical solutions of the present invention are as follows:

[0011] 1) Sandpaper the wire-cut rolled Inconel 718 substrate to 1000#, then use alcohol ultrasonic cleaning and dry it for later use;

[0012] 2) Weigh the boronizing agent in accordance with the set mass ratio, pour the mixture into a container, and place it in a ball mill for ball milling to mix it evenly; place the mixed boronizing agent in a high-temperature drying oven and dry it at 150°C for 2 hours. After drying, take it out for use;

[0013] 3) burying the cleaned sample in step 1) in the dried boronizing agent in a sealed container, placing the sealed container in a tube furnace, and introducing argon as a protective gas;

[0014] 4) Heat to 760°C at a heating rate of 10°C / min, hold for 10 hours, then cool to 650°C at a cooling rate of 10°C / min, hold for 8 hours. After this double aging treatment, the boron element in the boronizing agent fully diffuses into the substrate surface to form a boronized layer. Then, cool to room temperature and remove the sample.

[0015] 5) Use 2000# sandpaper to lightly polish the surface of the sample to remove the residual boronizing agent; then ultrasonically rinse the sample with alcohol, dry it, and seal it for storage.

[0016] The beneficial effects of the present invention are:

[0017] The chemical heat treatment low-temperature solid phase boriding technology was successfully used to prepare a high-thickness, high-quality boride layer on the surface of the solid solution Inconel718 nickel-based high-temperature alloy. By adjusting the components of the boriding agent, the purpose of lowering the boriding temperature was achieved, and the hardness and wear resistance of the nickel-based high-temperature alloy material were improved.

[0018] By solid phase boriding Inconel 718 alloy in a self-prepared new boriding agent, a boride layer with a thickness of about 15μm can be obtained.

[0019] The average surface hardness of the boronized layer measured under a force of 100g can reach 2903.9HV, proving that the boronized layer has high hardness. The friction and wear performance tests show that the friction coefficient of the boronized samples under the two grinding pairs of Si3N4 and 440C is less than 0.60, and the wear rate is less than 2.5×10 -5 mm 3 / N·m, demonstrating good wear resistance under high wear conditions and simulated actual working conditions. The preparation method of the present invention is simple and effective, and has great potential in improving the wear resistance of high-temperature alloys. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Microstructure SEM images of the boride diffusion layers prepared in Examples 1 to 3 and statistical graphs of the diffusion layer thickness; (a) corresponds to the boride diffusion layer obtained in Example 1, (b) corresponds to the boride diffusion layer obtained in Example 2, (c) corresponds to the boride diffusion layer obtained in Example 3, and (d) statistical graph of the diffusion layer thickness.

[0021] Figure 2 This is the XRD pattern of the boride-diffused layer prepared in Example 3;

[0022] Figure 3 Surface hardness diagram of the sample before and after heat treatment of the boronizing agent powder used in Example 3;

[0023] Figure 4 Friction coefficient curves and wear rate histograms of the samples before and after heat treatment of the boronizing agent powder used in Example 3, when grinding with Si3N4 balls and 440C balls under a load of 10N; (a)-(b) correspond to the friction coefficient curves and wear rate histograms using Si3N4 balls, respectively; (c)-(d) correspond to the friction coefficient curves and wear rate histograms using 440C balls, respectively.

[0024] Figure 5These are the SEM images and EDS results of the local surface morphology of the sample after the boride-diffused layer and the substrate in Example 3 were milled with 440C balls and Si3N4 balls under a load of 10N for 30 minutes; (a) The SEM images and EDS results of the local surface morphology of the sample after milling with Si3N4 balls; (b) The SEM images and EDS results of the local surface morphology of the sample after milling with 440C balls.

[0025] Figure 6 The SEM images and EDS results of the local surface morphology of the 440C ball and the Si3N4 ball after the boride-diffused layer and the substrate in Example 3 were ground with a 440C ball and a Si3N4 ball under a load of 10N for 30 minutes; (a) the SEM image and EDS results of the local surface morphology of the corresponding Si3N4 ball; (b) the SEM image and EDS results of the local surface morphology of the corresponding 440C ball. DETAILED DESCRIPTION

[0026] The present invention will be further described below with reference to the examples, but the present invention is not limited to the following examples.

[0027] Example 1: In this example, Inconel 718 substrate is selected.

[0028] First, the Inconel 718 substrate was pretreated. The treatment process included polishing the Inconel 718 substrate with 180-1000# sandpaper until the surface wire cutting marks were completely removed. The surface was cleaned with deionized water and placed in a beaker containing alcohol. After ultrasonic cleaning for 10 minutes, it was dried and wrapped with dust-free paper and sealed in a sample bag for use.

[0029] The self-prepared boronizing agent was weighed in the weight ratio of 90% B4C, 6% KBF4 and 4% Al2O3, poured into a ball mill jar after mixing, and placed in a ball mill for 2 hours to mix evenly, and then sealed and stored in a sample bag for later use.

[0030] Put the mixed boronizing agent into a high-temperature drying oven and dry it at 150℃ for 2 hours. After drying, take it out for use.

[0031] The ceramic crucible was cleaned with deionized water and anhydrous ethanol in turn and dried for use; the dried boronizing agent was evenly spread on the bottom of the crucible, with a height of about half the height of the crucible. The Inconel 718 alloy sample that had been ultrasonically cleaned and dried was taken out and placed on top of the boronizing agent; after placing the sample, the boronizing agent was evenly spread over the entire crucible in preparation for boronizing.

[0032] The crucible was placed in the center of a tube furnace. The furnace was programmed to heat to 760°C at a heating rate of 10°C / min, hold for 10 hours, and then cool to 650°C at a cooling rate of 10°C / min, hold for 8 hours. Argon was used throughout the entire process. A double aging heat treatment system allowed the boron element in the boronizing agent to diffuse into the substrate surface, forming a boronized layer. The sample was then removed from the furnace after cooling to room temperature.

[0033] After boronizing treatment, the sample was removed from the boronizing agent, taking care not to scratch the sample surface when removing the sample; the sample surface was lightly polished with 2000# sandpaper to remove the residual boronizing agent on the sample surface; the sample was rinsed with deionized water and ultrasonically cleaned in anhydrous ethanol for 10 minutes to thoroughly remove the residual boronizing agent and other impurities on the sample surface. After drying, it was wrapped with dust-free paper and placed in a sample bag.

[0034] The specific steps of Example 2-3 are the same as those of Example 1, except that different boronizing agents are used. The specific ratio (weight ratio) of the boronizing agents is shown in Table 1.

[0035] Table 1 Specific ingredient ratios (weight ratios) and manufacturing process parameter settings of Examples 1-3.

[0036]

[0037] Scanning electron microscopy (SEM) was used to characterize the thickness and structure of the boronized layer from the surface to the inside of the sample. The SEM morphology of the cross section is shown in Figure 2. Figure 1 shown.

[0038] SEM results Figure 1 (a) shows that the thickness of the boride layer obtained in Example 1 is about 5.7 μm. Figure 1 (b) shows that the thickness of the borided layer obtained in Example 2 is about 10.6 μm, which is 86% thicker than that in Example 1. Figure 1 Figure (c) shows that the boride layer thickness obtained in Example 3 is approximately 14.95 μm, a 41% increase compared to the boride layer thickness in Example 2. This result indicates that the boride agent ratio used in Example 3 is superior to the other two, and that the thickness of the boride layer increases after a proper increase in the KBF4 content.

[0039] The X-ray energy dispersive spectrum (EDS) was used to analyze the element types and atomic ratios in the micro-area of the boronized coating from the surface to the inside. The micro-area analysis results are as follows: Figure 1 shown.

[0040] EDS results show that the boron atomic concentration of the boride layers of Examples 1-3 gradually decreases with increasing distance from the surface, and the boron concentration of the borided layer of Example 3 is higher than that of Examples 1 and 2. The increase in KBF4 content promotes the generation of active boron atoms, thereby increasing the thickness of the borided layer and the boron concentration in the boride layer under low temperature conditions.

[0041] The phase analysis of the boride layer obtained in Example 3 was performed by X-ray diffractometer (XRD). The XRD pattern is as follows: Figure 2 The XRD results show that the boronized layer phases of Example 3 are mainly Ni2B, CrB, Cr2B and Fe3Ni 20 B6, where CrB is the stable phase of chromium boride under high boron concentration conditions, Cr2B is the stable phase of chromium boride under medium boron concentration conditions, Ni2B is the stable phase of nickel boride under high boron concentration conditions, and Fe3Ni 20 B6 is a ternary stable phase of nickel-iron-boron, but due to the doping of iron, it will transition to a stable state. In general, the phase structure formed by the boride layer of Example 3 is relatively stable.

[0042] KBF4 is a commonly used catalyst in boronizing technology. It begins to decompose at 530°C, producing KF and BF3. BF3 reacts with B4C to produce [B] and BF2. Boron atoms and BF3, along with other gaseous substances, are adsorbed on the workpiece surface and produce an interfacial reaction. During the reaction, active boron atoms may further react with the substrate to produce BF3. Boron atoms that enter the sample surface diffuse into the workpiece. The amorphous boron powder in the boronizing agent also releases active boron atoms upon heating, providing reactants for the boronizing process. The specific reaction equation is as follows:

[0043] KBF4=BF3↑+KF (1)

[0044] 2BF3+B4C=3BF2↑+3[B]+C (2)

[0045] 3BF2=[B]+2BF3↑ (3)

[0046] B(amorphous)→[B] (4)

[0047] y[B]+xMe→Me x B y (5)

[0048]

[0049] Wherein, Me is the metal atom in Inconel 718, and [B] is the active boron atom.

[0050] The surface hardness values of the sample and the substrate of Example 3 were tested using a Vickers hardness tester under 100g and 500g force conditions, as shown in FIG. Figure 3 The substrate hardness is approximately 278 HV, and the surface hardness of the sample is significantly increased after boronization. The boride layer improves the wear resistance of the material by increasing the hardness of the substrate surface. Therefore, it is speculated that the sample in Example 3 has excellent wear resistance.

[0051] In order to verify the wear resistance of the boronized layer obtained under the conditions of Example 3, a friction and wear tester was used to conduct friction and wear tests on the sample surface under different load conditions at room temperature and the same air humidity environment. The friction and wear tester was preheated for 30 minutes, the program was set to reciprocating friction, the friction distance was 5mm, the loading load was 10N, the test time was 30 minutes, the running speed was 33.3mm / s, and the friction pair was Si3N4 ball and 440C ball. Among them, Si3N4 ball is an ideal material for testing wear resistance, and 440C ball simulates the friction and wear of Inconel 718 alloy under actual working conditions. The results of friction coefficient and wear rate are shown in the figure below. Figure 4 shown.

[0052] The friction coefficient of the boride-treated sample obtained in Example 3, when subjected to wear against two friction pairs, initially increased, then decreased, and ultimately stabilized. When the friction pair was Si3N4 balls, the average friction coefficient of the substrate was 0.80, while the friction coefficient of the boride-treated sample was 0.52. When the friction pair was 440C balls, the average friction coefficient of the substrate was 0.82, while the friction coefficient of the boride-treated sample was 0.60. Compared to the friction coefficient of the substrate, the average friction coefficient of the boride-treated sample under both friction pairing conditions was significantly lower, demonstrating the stable wear resistance of the boride-treated layer.

[0053] The wear amount and wear rate of the boronized layer in Example 3 under different friction pair conditions were calculated using white light interferometry. When the friction pair was Si3N4 balls, the substrate wear rate was 2.5×10 -4 mm 3 / N·m, and the wear rate of the sample after boronizing is 5.1×10 -6 mm 3 / N·m, which is 204 times lower than that of the substrate. When the friction pair is 440C ball, the substrate wear rate is 1.47×10 -3 mm 3 / N·m, and the wear rate of the sample after boronizing is 2.4×10 -5 mm 3 / N·m, which is 165 times lower than that of the substrate. The data show that the wear rate of the boronized layer is significantly reduced under both wear pairing conditions, indicating its excellent wear resistance.

[0054] Scanning electron microscopy (SEM) was used to characterize the morphology of the surface wear scars of the substrate and the sample of Example 3 under two grinding pair conditions and the surface morphology of the grinding pair to analyze the friction and wear mechanism of the boronized layer. Figure 5 The surface wear scar morphologies of the substrate and the sample of Example 3 under two grinding pair conditions are shown in Figure 2. Figure 6 The surface morphologies of the two grinding pairs are the substrate and the sample of Example 3. Under the Si3N4 ball grinding conditions, the substrate wear surface is uneven and full of debris, which is related to the high friction coefficient and wear rate of the substrate alloy, exacerbating the adhesive wear. According to the EDS energy spectrum test, it can be seen that the wear scar area contains more oxygen elements. This is because the friction heat caused by sliding under local contact stress causes the local temperature between the contact surfaces to rise, so that the wear surface is continuously oxidized, so its wear mechanism also includes oxidative wear. In comparison, the wear scar of the sample after boronization is narrower, the surface is smoother, and there are only a small amount of oxide particles on the surface. Analysis shows that its wear mechanism is mainly oxidative wear and slight abrasive wear. The presence of boron atoms on the wear scar surface indicates that the boride layer is not completely worn under this condition, showing good wear resistance.

[0055] Under 440C ball grinding conditions, the substrate wear surface exhibits deep and shallow furrows and localized flaking. Combined with the surface morphology of the 440C ball, the surface is quite rough. This is because the high toughness of the ball during friction facilitates plastic flow and adhesive transfer, resulting in severe adhesive wear with the Inconel 718 alloy surface. The wear scar of the boronized sample is generally smoother, with localized shallow furrows and smaller flaking, indicating abrasive wear as the primary wear mechanism. EDS analysis reveals that the wear scar contains boron and oxygen, leading to oxidative wear. The presence of boron atoms on the relatively smooth wear scar surface suggests that the boride layer enhances the wear resistance of the material under these conditions. Overall, boronization alters the wear mechanism of the sample. During the boronization process, boron reacts with alloy surface elements to form borides with a much higher hardness than the substrate, significantly increasing the surface hardness. This suppresses adhesive wear and allows the small amount of flaked hard phase to undergo relatively mild abrasive wear, thereby reducing the friction coefficient and wear rate.

Claims

1. A 760°C low-temperature boronizing method for Inconel 718 nickel-based high-temperature alloy, characterized in that: The following steps are involved: 1) Sandpaper the wire-cut rolled Inconel 718 substrate to 1000#, then use alcohol ultrasonic cleaning and dry it for later use; 2) Weigh the boronizing agent in accordance with the set mass ratio, pour the mixture into a container, and place it in a ball mill for ball milling to mix it evenly; place the mixed boronizing agent in a high-temperature drying oven and dry it at 150°C for 2 hours. After drying, take it out for use; 3) burying the cleaned sample in step 1) in the dried boronizing agent in a sealed container, placing the sealed container in a tube furnace, and introducing argon as a protective gas; 4) Heat to 760°C at a heating rate of 10°C / min, hold for 10 hours, then cool to 650°C at a cooling rate of 10°C / min, hold for 8 hours. After this double aging treatment, the boron element in the boronizing agent fully diffuses into the substrate surface to form a boronized layer. Then, cool to room temperature and remove the sample. 5) Use 2000# sandpaper to lightly polish the surface of the sample to remove the residual boronizing agent; then ultrasonically rinse the sample with alcohol, dry it, and seal it for storage.

2. A 760°C low-temperature boronizing method for Inconel 718 nickel-based high-temperature alloy according to claim 1, characterized in that: The matrix used is solid solution Inconel 718 nickel-based high-temperature alloy.

3. A 760°C low-temperature boronizing method for Inconel 718 nickel-based high-temperature alloy according to claim 1, characterized in that: The mass percentage of the boronizing agent components includes: balance B4C+5%-10% KFB4+5%-10% amorphous B powder.

4. A 760°C low-temperature boronizing method for Inconel 718 nickel-based high-temperature alloy according to claim 3, characterized in that: The mass percentage of the boronizing agent components includes: balance B4C+10% KBF4+5% amorphous B powder.

5. Inconel 718 nickel-based high-temperature alloy prepared according to the method according to any one of claims 1 to 4.

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