Bearing material and preparation method thereof

Abstract

The invention belongs to the field of metallurgy, and particularly relates to a bearing material and a preparation method thereof. The method comprises the following steps: 1) burdening, weighing multi-element iron-cobalt alloy powder and nickel-based multi-element alloy powder, and uniformly mixing to prepare mixed powder; 2) performing granulation and compression molding on the mixed powder to obtain a green body; 3, gradient heat treatment is conducted on the green body to obtain the bearing material.The special alloy bearing material of a gradient component structure can be constructed, and on the basis that it is guaranteed that the bearing material has good mechanical performance, the surface performance of the bearing material is greatly optimized, and especially the fluorine resistance of the bearing material is greatly improved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of metallurgy, and particularly relates to a bearing material and a preparation method thereof. BACKGROUND

[0002] Bearing is a vital component in mechanical equipment, and its performance and service life depend largely on the material used.

[0003] Common bearings include metal bearings and non-metal bearings. Metal bearings mainly include high-carbon steel bearings, chromium steel bearings, stainless steel bearings, alloy steel bearings, bronze bearings, etc., each of which has advantages and disadvantages in performance and cost. For example, AISI52100 high-carbon steel bearings and chromium steel bearings have good mechanical properties but poor weather resistance and corrosion resistance, while stainless steel bearings have poor mechanical properties, high cost, but strong weather resistance and corrosion resistance. Non-metal bearings mainly include ceramic bearings, carbon / graphite bearings and polymer bearings, each of which also has its own advantages and disadvantages.

[0004] However, with the current industrial demand, the demand and requirements for fluorine-resistant special bearings are increasingly high. Fluorine-resistant bearings are obviously a special type of special bearings, which have excellent chemical corrosion resistance, especially excellent fluorine resistance. They are commonly used in special chemical equipment and special fields such as aerospace.

[0005] However, the commonly used bearing materials do not have fluorine corrosion resistance. The bearing materials currently used for fluorine-resistant bearings mainly include polytetrafluoroethylene (PTFE), and less used tetrafluoroethylene-hexafluoropropylene copolymer (FEP) and soluble polytetrafluoroethylene (PFA). However, due to the poor mechanical properties of the latter two, PTFE is usually used. However, as a polymer bearing material, PTFE has significant disadvantages in mechanical properties compared to other inorganic non-metallic materials and metal bearings. Silicon nitride ceramic bearings also have some fluorine corrosion resistance and relatively good mechanical properties, but they are expensive, brittle, and can only withstand low-concentration fluorine corrosion. Therefore, it is necessary to develop a special fluorine-resistant bearing material.

[0006] As the metal bearing with the greatest research and development prospects and development potential, there is currently no high-quality bearing that can resist fluorine corrosion. SUMMARY

[0007] To solve the problems that most existing bearing materials are not resistant to fluorine corrosion, and only a few fluorine-resistant bearing materials have the defect of insufficient mechanical properties, which greatly limits their application fields and application ranges, the present application provides a bearing material and a preparation method thereof.

[0008] The main objective of this invention is to: 1. Construct a composite high-entropy metal bearing material.

[0009] Second, ensure that the bearing material has good fluorine resistance.

[0010] Third, ensure that the bearing materials have excellent mechanical properties.

[0011] To achieve the above objectives, the present invention adopts the following technical solution.

[0012] A method for preparing a bearing material, the method comprising: 1) weighing and mixing multi-element iron-cobalt alloy powder and nickel-based multi-element alloy powder to form a mixed powder.

[0013] 2) The mixed powder is granulated and pressed into shape to obtain a green body.

[0014] 3) Gradient heat treatment is performed on the green blank to obtain bearing material.

[0015] Preferably, the multi-element iron-cobalt alloy powder and the nickel-based multi-element alloy powder mentioned in step 1) are both ternary alloy powders and / or quaternary alloy powders.

[0016] Preferably, the multi-element iron-cobalt alloy powder in step 1) is FeCrCoMoW alloy powder; the nickel-based multi-element alloy powder in step 1) is NiCrTi alloy powder; the atomic percentages of each component in the FeCrCoMoW alloy powder are as follows: Cr 23-26 at%, Co 19-22 at%, Mo 8-10 at%, W 4-6 at%, with the balance being Fe; the atomic percentages of each component in the NiCrTi alloy powder are as follows: Cr 28-32 at%, Ti 9-11 at%, with the balance being Ni.

[0017] Preferably, the multi-element iron-cobalt alloy powder and nickel-based multi-element alloy powder in step 1) are mixed evenly in a mass ratio of 7:(2.8~3.2).

[0018] Preferably, the granulation process in step 2) involves placing the mixed powder in an organic solution containing a binder, mixing and stirring, then filtering, drying and crushing, and passing it through a 100-mesh sieve to obtain a composite powder with a mesh size ≥ 100 mesh; the pressing process in step 2) uses a pressing pressure of 60-120 MPa.

[0019] Preferably, the gradient heat treatment in step 3) includes the following steps: high-frequency induction heat treatment at a surface peak temperature of 1280–1320 °C in a protective atmosphere for 9–12 min, followed by cooling to 880–920 °C and holding at a reducing atmosphere for 25–35 min under hot isostatic pressing, then cooling to 730–780 °C in a nitrogen-containing atmosphere for 2 h, and finally heating to 1120–1180 °C in an oxygen-containing atmosphere for 45–75 min.

[0020] Preferably, the frequency used in the high-frequency induction heat treatment is 200–300 kHz.

[0021] Preferably, the protective atmosphere is an inert gas atmosphere; the reducing atmosphere is a mixture of inert gas and hydrogen, wherein the hydrogen content is 4-6% VOL; and the nitrogen-containing atmosphere is a mixture of inert gas and nitrogen, wherein the nitrogen content is 12-18% VOL.

[0022] Preferably, the hot isostatic pressure control pressure is 45–55 MPa.

[0023] A bearing material having good resistance to fluorine corrosion and good mechanical properties.

[0024] Technical principle explanation: The core of the technical solution of this invention lies in the selection and use of raw materials and the heat treatment process.

[0025] Regarding the selection and use of raw materials, this invention uses dual alloy powders as raw materials, namely multi-element iron-cobalt alloy powder and nickel-based multi-element alloy powder. It can be seen that the technical solution of this invention is first based on the three core elements of iron, cobalt and nickel.

[0026] Iron and cobalt are very common high-entropy alloy skeleton elements. They can form stable face-centered cubic (FCC) solid solution structures with elements such as chromium and nickel, providing excellent plasticity and toughness. They are the basis of bearing mechanical properties and important basic elements for the preparation of high-entropy alloys. Nickel is also one of the common elements in high-entropy alloys. It can stabilize the FCC structure and plays a major role in fluorine resistance strengthening in this invention. It can form fluoride passivation layers in fluorine corrosion environments, thereby giving the bearing material fluorine resistance potential.

[0027] Furthermore, if only the above three alloying elements are used, the mechanical properties and fluorine resistance of the actual product are relatively limited. Therefore, through theoretical design and actual experiments, this invention has finally determined the optimal FeCrCoMoW alloy powder and NiCrTi alloy powder, as well as the relative amounts of the two alloy powders. In addition to the three main elements of iron, chromium, and nickel, this invention first introduces a large amount of cobalt. Cobalt can first stabilize the matrix, improve the heat resistance of the matrix, and improve the creep resistance of the bearing material through solid solution strengthening. It can also reduce the activity of the main element iron in this invention and inhibit its oxidation. On this basis, Ti element is further introduced. Ti element can work with cobalt to further reduce the sensitivity of the bearing material to intergranular corrosion, while achieving grain refinement to improve the mechanical properties of the material, and inducing the directional fluorination / oxidation of Ni and other main fluorine-resistant elements to form a surface protective layer.

[0028] It is evident that the introduction of Co and Ti mainly serves to stabilize the matrix and enhance mechanical properties. At the same time, the synergistic effect of the two achieves fluorination / oxidation induction, thereby indirectly improving the fluorine resistance of the material.

[0029] Building upon this foundation, the present invention further introduces two crucial alloying elements: Mo and W. Both Mo and W are effective fluorine-resistant elements. Tungsten, due to its inherent stability, possesses a certain degree of corrosion resistance. However, molybdenum is even more important. Molybdenum significantly optimizes the pitting corrosion resistance of bearing materials. It can form molybdate ions in localized corrosion zones to transform, strengthen, or repair the passivation layer, stabilizing the passivation protective layer on the bearing material surface and forming a dynamic self-healing capability of the passivation film protective layer, further enhancing the fluorine resistance of the bearing material.

[0030] However, besides the three main elements (iron, cobalt, and nickel), the introduction of other elements requires effective control. For example, insufficient chromium will lead to discontinuous passivation film formed during the final heat treatment process, failing to coordinate the dynamic self-repairing effect of molybdenum and nickel. Excessive chromium, on the other hand, will cause brittle phase precipitation, resulting in a significant decrease in the mechanical properties of the bearing. Molybdenum and titanium, besides their role in coordinating with nickel and chromium to form a dynamic self-repairing passivation layer and their oxidation-induced effect, both have a positive effect on the intergranular corrosion and pitting corrosion sensitivity of bearing materials. Insufficient amounts will lead to insufficient resistance to intergranular corrosion and pitting corrosion. Similarly, excessive amounts of either can easily produce too many coarse grains, leading to the formation of brittle phases and a decrease in the mechanical properties of the bearing material. As for tungsten, in addition to its inertness and resistance to fluorine and inhibition of fluoride ion diffusion, it can also effectively improve the high-temperature resistance of bearings. Insufficient tungsten will cause a decrease in the corresponding bearing performance, but excessive amounts can easily induce micropores due to segregation, resulting in a significant decrease in the overall corrosion resistance of the bearing material.

[0031] After determining the optimal atomic ratio of elements through multiple rounds of experiments, the specific raw materials used still need to be selected. In early experiments, researchers mainly used elemental metals as raw materials for sample preparation. However, it was found that the samples were quite brittle and required longer sintering times. This was mainly because the thermal expansion coefficients of different elemental metals differed greatly during sintering, easily leading to sintering micropores and cracks. This was primarily because the mixed elemental metals were prone to forming brittle intermetallic compounds or amorphous phases due to local compositional fluctuations during heat treatment sintering. For example, Cr-Fe easily forms a σ-brittle phase. Furthermore, the differences in the mixing enthalpy between Ti and Fe / Ni could lead to localized segregation. Therefore, it was necessary to significantly extend the heat treatment time to achieve long-range bulk diffusion of elements and ultimately reduce the aforementioned effects. This invention first alloys elemental powders to create two different alloy powders. This results in two alloy powders with extremely low CTE differences, virtually eliminating sintering micropores or cracks during heat treatment and sintering. Furthermore, by controlling the initial atomic-level mixing of certain elements, the long-range bulk diffusion of elements during the bearing green blank heat treatment process can be transformed into short-range diffusion, thereby significantly reducing sintering time and suppressing undesirable segregation and brittle phase formation. For the bearing material of this invention, micropores and cracks must be absolutely avoided; therefore, strict control of raw material selection is necessary to reduce the CTE difference and increase the sintering density percentage.

[0032] Besides controlling the types and amounts of alloying elements and raw materials, the most crucial part of this invention lies in the gradient heat treatment process.

[0033] The main objective of the gradient heat treatment in this invention is to form a three-layer compositional gradient structure consisting of a surface layer, a transition layer, and a core. During the high-frequency induction heat treatment stage, short-duration ultra-high temperature treatment is employed, leveraging the skin effect of high-frequency induction heat treatment to form a Ni-based saturated solid solution on the surface and promote the phase transformation of the multi-element iron-cobalt alloy powder. The Zener pinning effect generated by the Mo / W ratio in the multi-element iron-cobalt alloy powder inhibits grain coarsening, and the surface-core temperature difference driven by the skin effect promotes element diffusion, achieving the desired elemental distribution. However, this process requires avoiding excessively high peak temperatures to prevent the loss of some important alloying elements, such as titanium.

[0034] Subsequently, after high-frequency induction heat treatment to form a compositional gradient and initially generate a core-shell structure, a medium-temperature isothermal heat treatment in a reducing atmosphere is used to form an intermediate transition layer. During this medium-temperature isothermal heat treatment, a concentration gradient zone is mainly formed by Fe and Cr. A small amount of hydrogen is introduced during this process to avoid hindering the interdiffusion process due to possible oxides in the raw materials and oxidation during granulation and pressing, and to eliminate any possible oxide passivation layer formed on the surface. This reduces the difference in thermal expansion coefficients between the core and shell, improves the thermal stability of the bearing material, and avoids interfacial delamination under high-temperature conditions. Next, a low-temperature isothermal heat treatment in a nitrogen-containing atmosphere is performed to form a partial tungsten nitride passivation film and achieve surface hardening. Finally, a high-temperature heat treatment in an oxygen-containing atmosphere (air can be used in practice to reduce costs) is performed to completely form the surface passivation film and achieve complete high-entropy alloying.

[0035] Therefore, the most important heat treatment process for this invention is the first stage of high-frequency induction heat treatment, because this process controls the distribution trend of alloying elements by forming an internal and external temperature difference field, and ultimately achieves the key step of composition gradient. Although theoretically, the high surface temperature difference in high-frequency induction heat treatment should drive alloying elements (such as nickel) to diffuse inward, due to the special selection of raw materials and composition of this invention, the multi-component nickel-based alloy will rapidly densify during high-temperature induction heat treatment, forming a physical barrier that inhibits the diffusion of nickel atoms. At the same time, the Ti and Ni on the surface will form the γ'-Ni3Ti phase more quickly under high temperature, and its coherent strain field will hinder the further diffusion of nickel atoms. However, the nickel in the core cannot effectively form the above effects. Therefore, although the diffusion rate of nickel in the core is less than that of nickel on the surface, the nickel on the surface is quickly fixed while the nickel in the core diffuses outward under thermal drive, exhibiting a reverse concentration gradient diffusion trend. This leads to an increase in the nickel concentration on the surface. Iron also exhibits a temperature-driven diffusion effect, but since the iron on the surface is not effectively fixed, and a nickel-rich layer is formed as the nickel concentration on the surface increases, the chemical formula of iron in the nickel-rich layer will increase, thus driving the iron atoms to diffuse inward more strongly, also exhibiting a reverse concentration gradient diffusion trend. Thus, the initial formation of the composition gradient is achieved through the combination of temperature difference and multiple driving forces, and this gradient is continuously strengthened in subsequent heat treatment processes.

[0036] The beneficial effects of this invention are: this invention can construct special alloy bearing materials with gradient composition structure, and while ensuring that the bearing materials have good mechanical properties, it can significantly optimize the surface properties of the bearing materials, especially the fluorine resistance of the bearing materials. Detailed Implementation

[0037] The present invention will be further described clearly and in detail below with reference to specific embodiments. Those skilled in the art will be able to implement the present invention based on these descriptions. Furthermore, the embodiments of the present invention described below are generally only some, not all, of the embodiments of the present invention. Therefore, all other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort should fall within the scope of protection of the present invention.

[0038] Unless otherwise specified, all raw materials used in the embodiments of the present invention are commercially available or obtainable by those skilled in the art; unless otherwise specified, all methods used in the embodiments of the present invention are methods mastered by those skilled in the art.

[0039] Unless otherwise specified, the alloy powder used in the embodiments of the present invention is selected from alloy powder with a purity >99.5 wt% and a mesh size of 80.

[0040] Example 1: A method for preparing a bearing material, the method comprising: 1) weighing Fe according to a mass ratio of 7:3 40 Cr 25 Co 20 Mo 10 W5 alloy powder and Ni 60 Cr 30 Ti 10 The alloy powder is mixed evenly to form a mixed powder.

[0041] 2) Weigh 2.5 wt% of stearic acid from the mixed powder and dissolve it in 1.2 times its weight of anhydrous ethanol to prepare a granulation aid. Add the mixed powder to the granulation aid for mixing and granulation. Then filter, dry and crush, and pass through a 100-mesh sieve to obtain a composite powder with a mesh size ≥100. Place the composite powder in a mold and press it with a pressure of 90 MPa to obtain a bearing blank (outer shaft diameter 50 mm, inner shaft diameter 30 mm, thickness 10 mm).

[0042] 3) Gradient heat treatment of green blanks: 3-1) High-frequency induction heat treatment at 220 kHz in an argon atmosphere, controlling the surface peak temperature to be 1300±5 ℃, and holding for 10 min to obtain the initial fired sample.

[0043] 3-2) After cooling to 900 ℃, apply 50 MPa isostatic pressure to the initial calcined sample in an atmosphere of 95% VOL argon + 5 VOL% hydrogen and keep it at that temperature for 30 min.

[0044] 3-3) Cool to 750 °C by introducing 85% VOL argon gas + 15 VOL% nitrogen gas and then keep warm for 2 hours.

[0045] 3-4) Introduce air and heat to 1150 ℃ and hold for 60 min, then air cool to room temperature to complete the gradient heat treatment.

[0046] The bearing material is obtained after gradient heat treatment.

[0047] After sectioning the bearing, sampled surfaces (0–5 μm depth), the transition layer (1.5–2.0 mm depth), and the core (4.5–5.0 mm depth) for compositional characterization. The surface layer showed nitrogen and oxygen atomic percentages exceeding 50 at%, indicating a highly effective passivation protective layer. Furthermore, characterization results revealed a significant nickel enrichment trend on the surface. In this example, after surface sampling and characterization, based solely on alloying elements, the average nickel atomic percentage reached 32.6 at%, while the average iron atomic percentage was only about 14.7 at. Chromium and cobalt atomic percentages were approximately 21.5 at% and 16.2 at%, respectively, while molybdenum, tungsten, and titanium atomic percentages were approximately 7.7 at%, 3.6 at%, and 3.7 at%, respectively. This characterization result indicates a significant nickel enrichment trend on the surface. Besides nickel, the main enriched elements are molybdenum, tungsten, and titanium, all with atomic percentages higher than the theoretical average. This higher-than-the-theoretical-average atomic percentage indicates the formation of enriched regions on the surface relative to the overall bearing material, with titanium and nickel showing the most pronounced enrichment trends. This may be related to the formation of the γ'-Ni3Ti phase, or the fixation of titanium by nitrogen and oxygen during heat treatment, while nickel's surface enrichment and fixation are achieved under the influence of multiple factors. In the transition layer, the atomic percentages of nickel, molybdenum, and titanium begin to show a relatively significant decreasing trend, with nickel's atomic percentage decreasing most significantly to 20.6 at%, while the atomic percentages of chromium and cobalt remain relatively stable, with changes ≤0.5 at% compared to the surface layer. Iron's atomic percentage, however, begins to rise significantly to approximately 25.8 at%. The characterization results for the core show that the atomic percentage of nickel drops sharply to approximately 16.9 at%, while the atomic percentage of iron rises to approximately 30.2 at%.

[0048] The above characterization results clearly demonstrate that the bearing material of the present invention has a distinct compositional gradient distribution.

[0049] Based on this, the mechanical properties and corrosion resistance of the bearing material prepared in this example were characterized.

[0050] The corrosion resistance was characterized using 10 wt% hydrochloric acid, 10 wt% hydrofluoric acid, and 40 wt% nitric acid, respectively, at different temperatures. The test standard was based on ASTM G31-21(2025) Laboratory Immersion Corrosion Test for Metals.

[0051] The specific mechanical properties and corrosion resistance characteristics are shown in Table 1 below.

[0052] Table 1: Characterization results of mechanical properties and corrosion resistance of the sample from Example 1:

[0053] The characterization results in Table 1 clearly show that the bearing material prepared in this example possesses excellent mechanical properties, meeting the mechanical performance requirements for bearings in most situations. Regarding corrosion resistance, the bearing material of this invention exhibits extremely superior corrosion resistance. Especially against hydrochloric acid and hydrofluoric acid, two penetrating corrosive acids, the annual corrosion rate is controlled below 1.5 mm, surpassing even some currently leading corrosion-resistant Hastelloy alloys in these performance characteristics.

[0054] Example 2: A method for preparing a bearing material, the method comprising: 1) weighing Fe according to a mass ratio of 7:3.2 40 Cr 25 Co 20 Mo 10 W5 alloy powder and Ni 60 Cr 30 Ti 10 The alloy powder is mixed evenly to form a mixed powder.

[0055] 2) Weigh 2.5 wt% of stearic acid from the mixed powder and dissolve it in 1.2 times its weight of anhydrous ethanol to prepare a granulation aid. Add the mixed powder to the granulation aid for mixing and granulation. Then filter, dry and crush, and pass through a 100-mesh sieve to obtain a composite powder with a mesh size ≥100. Place the composite powder in a mold and press it with a pressure of 90 MPa to obtain a bearing blank (outer shaft diameter 50 mm, inner shaft diameter 30 mm, thickness 10 mm).

[0056] 3) Gradient heat treatment of green blanks: 3-1) High-frequency induction heat treatment at 220 kHz in an argon atmosphere, controlling the surface peak temperature to be 1300±5 ℃, and holding for 10 min to obtain the initial fired sample.

[0057] 3-2) After cooling to 900 ℃, apply 50 MPa isostatic pressure to the initial calcined sample in an atmosphere of 95% VOL argon + 5 VOL% hydrogen and keep it at that temperature for 30 min.

[0058] 3-3) Cool to 750 °C by introducing 85% VOL argon gas + 15 VOL% nitrogen gas and then keep warm for 2 hours.

[0059] 3-4) Introduce air and heat to 1150 ℃ and hold for 60 min, then air cool to room temperature to complete the gradient heat treatment.

[0060] The bearing material is obtained after gradient heat treatment.

[0061] The mechanical properties and corrosion resistance of the sample prepared in this example were characterized in the same way as in Example 1. The characterization results are shown in Table 2 below.

[0062] Table 2: Characterization results of mechanical properties and corrosion resistance of the samples from Example 2:

[0063] Example 3: A method for preparing a bearing material, the method comprising: 1) weighing Fe according to a mass ratio of 7:3 40 Cr 25 Co 20 Mo 10 W5 alloy powder and Ni 62 Cr 29 Ti9 alloy powder is mixed evenly to form a mixed powder.

[0064] 2) Weigh 2.5 wt% of stearic acid from the mixed powder and dissolve it in 1.2 times its weight of anhydrous ethanol to prepare a granulation aid. Add the mixed powder to the granulation aid for mixing and granulation. Then filter, dry and crush, and pass through a 100-mesh sieve to obtain a composite powder with a mesh size ≥100. Place the composite powder in a mold and press it with a pressure of 90 MPa to obtain a bearing blank (outer shaft diameter 50 mm, inner shaft diameter 30 mm, thickness 10 mm).

[0065] 3) Gradient heat treatment of green blanks: 3-1) High-frequency induction heat treatment at 220 kHz in an argon atmosphere, controlling the surface peak temperature to be 1300±5 ℃, and holding for 10 min to obtain the initial fired sample.

[0066] 3-2) After cooling to 900 ℃, apply 50 MPa isostatic pressure to the initial calcined sample in an atmosphere of 95% VOL argon + 5 VOL% hydrogen and keep it at that temperature for 30 min.

[0067] 3-3) Cool to 750 °C by introducing 85% VOL argon gas + 15 VOL% nitrogen gas and then keep warm for 2 hours.

[0068] 3-4) Introduce air and heat to 1150 ℃ and hold for 60 min, then air cool to room temperature to complete the gradient heat treatment.

[0069] The bearing material is obtained after gradient heat treatment.

[0070] The mechanical properties and corrosion resistance of the sample prepared in this example were characterized in the same way as in Example 1. The characterization results are shown in Table 3 below.

[0071] Table 3: Characterization results of mechanical properties and corrosion resistance of the sample in Example 3:

[0072] As can be clearly seen from the characterization results of the samples in Examples 1-3 shown in Tables 1-3 above, the bearing material of the present invention has good basic mechanical properties and excellent corrosion resistance. Its performance in resistance to hydrofluoric acid corrosion is particularly outstanding.

[0073] Comparative Example 1: A method for preparing a bearing material, the method comprising: 1) weighing an equivalent amount of elemental metal powder according to the proportion of Example 1, wherein the purity of the elemental metal powder used is >99.5 wt% and the mesh size is ≥80 mesh, and mixing them evenly to form a mixed powder.

[0074] 2) Weigh 2.5 wt% of stearic acid from the mixed powder and dissolve it in 1.2 times its weight of anhydrous ethanol to prepare a granulation aid. Add the mixed powder to the granulation aid for mixing and granulation. Then filter, dry and crush, and pass through a 100-mesh sieve to obtain a composite powder with a mesh size ≥100. Place the composite powder in a mold and press it with a pressure of 90 MPa to obtain a bearing blank (outer shaft diameter 50 mm, inner shaft diameter 30 mm, thickness 10 mm).

[0075] 3) Gradient heat treatment of green blanks: 3-1) High-frequency induction heat treatment at 220 kHz in an argon atmosphere, controlling the surface peak temperature to be 1300±5 ℃, and holding for 10 min to obtain the initial fired sample.

[0076] 3-2) After cooling to 900 ℃, apply 50 MPa isostatic pressure to the initial calcined sample in an atmosphere of 95% VOL argon + 5 VOL% hydrogen and keep it at that temperature for 30 min.

[0077] 3-3) Cool to 750 °C by introducing 85% VOL argon gas + 15 VOL% nitrogen gas and then keep warm for 2 hours.

[0078] 3-4) Introduce air and heat to 1150 ℃ and hold for 60 min, then air cool to room temperature to complete the gradient heat treatment.

[0079] The bearing material is obtained after gradient heat treatment.

[0080] The mechanical properties and corrosion resistance of the sample prepared in this example were characterized in the same way as in Example 1. The characterization results are shown in Table 4 below.

[0081] Table 4: Characterization results of mechanical properties and corrosion resistance of Comparative Example 1 sample:

[0082] As can be clearly seen from the characterization results in Table 4 above, the sample prepared in this example exhibits a very significant performance degradation compared to Example 1. The decline in corrosion resistance is particularly pronounced. Further characterization calculations were performed on the sintering density percentage of the samples from Example 1 and this example. Sintering density percentage = (sample density / theoretical density) × 100%, with the sample density selected after the heat treatment in step 3-2). The calculation results show that the sintering density percentage of Example 1 is 98.3%, while that of this example is only 94.2%, indicating the presence of numerous structural defects such as micropores or cracks. One of the main reasons for this phenomenon is the mismatch in the CTE coefficient of the raw materials, leading to the spontaneous formation of micropores or cracks during sintering. The presence of these defects significantly reduces the difficulty of penetration corrosion by harmful ions such as chloride and fluoride ions, resulting in a drastic decrease in corrosion resistance. Simultaneously, the presence of micropores or cracks, as well as the brittle phases generated due to segregation, significantly increases the brittleness of the material, and the elongation also decreases substantially.

[0083] Comparative Example 2: A method for preparing a bearing material, the method comprising: 1) weighing Fe according to a mass ratio of 7:3 40 Cr 25 Co 20 Mo 10 W5 alloy powder and Ni 60 Cr 30 Ti 10 The alloy powder is mixed evenly to form a mixed powder.

[0084] 2) Weigh 2.5 wt% of stearic acid from the mixed powder and dissolve it in 1.2 times its weight of anhydrous ethanol to prepare a granulation aid. Add the mixed powder to the granulation aid for mixing and granulation. Then filter, dry and crush, and pass through a 100-mesh sieve to obtain a composite powder with a mesh size ≥100. Place the composite powder in a mold and press it with a pressure of 90 MPa to obtain a bearing blank (outer shaft diameter 50 mm, inner shaft diameter 30 mm, thickness 10 mm).

[0085] 3) Gradient heat treatment of green blanks: 3-1) In a sintering furnace, argon atmosphere is introduced and constant temperature heat treatment is carried out at 1300 for 10 min to obtain the initial sintered sample.

[0086] 3-2) After cooling to 900 ℃, apply 50 MPa isostatic pressure to the initial calcined sample in an atmosphere of 95% VOL argon + 5 VOL% hydrogen and keep it at that temperature for 30 min.

[0087] 3-3) Cool to 750 °C by introducing 85% VOL argon gas + 15 VOL% nitrogen gas and then keep warm for 2 hours.

[0088] 3-4) Introduce air and heat to 1150 ℃ and hold for 60 min, then air cool to room temperature to complete the gradient heat treatment.

[0089] The bearing material is obtained after gradient heat treatment.

[0090] The mechanical properties and corrosion resistance of the sample prepared in this example were characterized in the same way as in Example 1. The characterization results are shown in Table 5 below.

[0091] Table 5: Characterization results of mechanical properties and corrosion resistance of Comparative Example 2 sample:

[0092] From the characterization results in Table 5 above, it is clear that compared with the sample of Example 1, the mechanical properties of this sample, except for surface hardness, show a certain degree of optimization and improvement in other aspects, including strength and elongation. This indicates that the composition system of the bearing material of this invention has the basis for forming a high-quality multi-element high-entropy alloy, and due to the unique raw material selection strategy of this invention, using two alloy powders with similar CTE as raw materials significantly reduces the difficulty of alloy preparation. However, in terms of corrosion resistance, it shows results far inferior to the sample of Example 1. This is mainly because the heat treatment process 3-1) in this example cannot form an effective compositional gradient distribution structure through the temperature field of temperature difference, thus resulting in the inability to effectively form a corrosion-resistant passivation protective layer on the surface of this example. Although it still shows some performance in nitric acid corrosion resistance, this is mostly due to the properties of the material itself. However, it performs very poorly against hydrochloric acid and hydrofluoric acid, two penetrating corrosive acids, indicating that it cannot effectively block the penetration of corrosive ions, namely chloride ions and fluoride ions, especially the penetration blocking effect of fluoride ions.

[0093] It is evident that, for the technical solution of this invention, the first step of the gradient heat treatment process, high-frequency induction heat treatment, is very important. It is precisely because of its ability to achieve extremely high heating rates and generate temperature difference fields that it can achieve the fixation of surface nickel and the reverse concentration diffusion of nickel. However, conventional heat treatment methods cannot effectively complete this process.

Claims

1. A method for preparing a bearing material, characterized in that, The method includes: 1) weighing and mixing multi-element iron-cobalt alloy powder and nickel-based multi-element alloy powder to form a mixed powder; 2) granulating and pressing the mixed powder to obtain a green blank; 3) subjecting the green blank to gradient heat treatment to obtain bearing material.

2. The method for preparing a bearing material according to claim 1, characterized in that, Step 1) The multi-element iron-cobalt alloy powder and the nickel-based multi-element alloy powder are both ternary alloy powders and / or quaternary alloy powders.

3. A method for preparing a bearing material according to claim 1 or 2, characterized in that, Step 1) The multi-element iron-cobalt alloy powder is FeCrCoMoW alloy powder; Step 1) The nickel-based multi-element alloy powder is NiCrTi alloy powder; The atomic percentages of each component in the FeCrCoMoW alloy powder are as follows: Cr 23~26 at%, Co 19~22 at%, Mo 8~10 at%, W 4~6 at%, with the balance being Fe; The atomic percentages of each component in the NiCrTi alloy powder are as follows: Cr 28~32 at%, Ti 9~11 at%, with the balance being Ni.

4. The method for preparing a bearing material according to claim 3, characterized in that, Step 1) The multi-element iron-cobalt alloy powder and nickel-based multi-element alloy powder are mixed evenly at a mass ratio of 7: (2.8~3.2).

5. The method for preparing a bearing material according to claim 1, characterized in that, Step 2) The granulation process involves placing the mixed powder in an organic solution containing a binder, mixing and stirring, then filtering, drying and crushing, and passing it through a 100-mesh sieve to obtain a composite powder with a mesh size ≥ 100 mesh; Step 2) The pressing and molding process uses a pressing pressure of 60-120 MPa.

6. The method for preparing a bearing material according to claim 1, characterized in that, Step 3) The gradient heat treatment includes the following steps: high-frequency induction heat treatment at a surface peak temperature of 1280-1320 °C in a protective atmosphere for 9-12 min, followed by cooling to 880-920 °C and holding at a reducing atmosphere for 25-35 min under hot isostatic pressing, then cooling to 730-780 °C in a nitrogen-containing atmosphere for 2 h, and finally heating to 1120-1180 °C in an oxygen-containing atmosphere for 45-75 min.

7. The method for preparing a bearing material according to claim 6, characterized in that, The frequency used in the high-frequency induction heat treatment is 200–300 kHz.

8. The method for preparing a bearing material according to claim 6, characterized in that, The protective atmosphere is an inert gas atmosphere; the reducing atmosphere is a mixture of inert gas and hydrogen, wherein the hydrogen content is 4-6% VOL; the nitrogen-containing atmosphere is a mixture of inert gas and nitrogen, wherein the nitrogen content is 12-18% VOL.

9. A method for preparing a bearing material according to claim 6, characterized in that, The hot isostatic pressure control pressure is 45–55 MPa.

10. A bearing material prepared by the method of any one of claims 1 to 9.

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