A high-temperature self-lubricating material based on a NiCoCr medium-entropy alloy and a preparation method thereof

Abstract

The application discloses a high-temperature self-lubricating material based on a NiCoCr medium-entropy alloy and a preparation method thereof, and belongs to the field of high-temperature alloys.The chemical composition of the high-temperature self-lubricating material based on the NiCoCr medium-entropy alloy is as follows: 30-33% of Ni, 30-33% of Co, 28-30% of Cr, 1.8-3.6% of Al+Ti, 4-6.5% of Nb+W+Ta, 0-0.2% of RE, 0.05-0.2% of C, and the rest is inevitable impurities.The preparation process is vacuum induction smelting combined with protective atmosphere electroslag remelting.The high-temperature self-lubricating material has the advantages of high strength, good toughness, low friction coefficient, good wear resistance, oxidation resistance, easy processing and low cost, and solves the problem that high-temperature alloys cannot have both self-lubricating performance and high strength and toughness at room temperature to 650 DEG C.

Description

Technical Field

[0001] This invention belongs to the field of high-temperature alloys, specifically relating to a high-temperature self-lubricating material based on NiCoCr medium-entropy alloy and its preparation method. Background Technology

[0002] With the rapid development of my country's defense industry in fields such as aviation, aerospace, and nuclear power, increasingly harsh service environments (high temperature, corrosion, high load, nuclear radiation, etc.) are accelerating the premature failure of key components, leading to a decrease in the reliability of the entire equipment system. This is especially true for transmission components operating in high-temperature environments, such as high-temperature bearings, bushings, and sealing rings in power systems like aero-engines, gas turbines, and internal combustion engines. The synergistic coupling of high-temperature corrosion and frictional wear has become the main mode of material damage, affecting the reliability and lifespan of the entire system. Therefore, there is an urgent need to develop a high-temperature resistant, corrosion-resistant, long-life solid self-lubricating material.

[0003] Currently, almost all high-temperature solid self-lubricating materials use heat-resistant metals (Fe, Ni, Cu, etc.) as the matrix of composite materials. They obtain self-lubricating composite materials by adding solid lubricating phases, such as fluorides (CaF, BaF), nitrides (BN), sulfides (WS2, MoS2), graphite, etc., and then sintering them. For example, Chinese patent CN200710307295.7 discloses an iron-based alloy self-lubricating composite material, which exhibits good self-lubricating properties in the 500-700℃ range by adding 0.4-4% molybdenum disulfide, 1.5-7% tungsten disulfide, and 0.4-6% metal fluoride; CN201610592419.X discloses a low-friction nickel-based high-temperature self-lubricating composite material and its preparation method, which achieves self-lubricating properties at 500℃ by adding 1-5% graphite, 5-20% tungsten disulfide, and 5-20% precious metal silver; CN201710695048.2 discloses a copper-based high-temperature self-lubricating composite material, which achieves low friction coefficient and low wear at higher temperatures by adding 10-20% graphite, 7-15% lead, and other solid softening phases.

[0004] The aforementioned composite materials all exhibit good self-lubricating properties at high temperatures. However, excessive addition of solid lubricating phases leads to severe damage to the material's plasticity and toughness. Furthermore, the impact of solid lubricating phases on the material's high-temperature oxidation resistance is neglected; in particular, the addition of large amounts of graphite results in low service temperature and poor oxidation resistance. In addition, these composite materials are often sintered using powder metallurgy, resulting in high production costs, poor material processing performance, and limited application scenarios, hindering large-scale production.

[0005] Therefore, designing and developing a high-temperature self-lubricating material that can be prepared through traditional smelting processes and has excellent mechanical properties and high-temperature wear resistance has good application prospects and economic value. Summary of the Invention

[0006] The purpose of this invention is to provide a high-temperature self-lubricating material based on NiCoCr medium-entropy alloy and its preparation method, so as to solve the problem that high-temperature alloys cannot simultaneously possess self-lubricating properties and high strength and toughness from room temperature to 650°C.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A high-temperature self-lubricating material based on NiCoCr medium-entropy alloy has the following chemical composition by mass percentage: Ni 30-33%, Co 30-33%, Cr 28-30%, Al+Ti 1.8-3.6%, Nb+W+Ta 4-6.5%, RE 0-0.2%, C 0.05-0.2%, with the remainder being unavoidable impurities.

[0008] Furthermore, in the high-temperature self-lubricating material of the present invention, the molar ratio of any two of the Ni, Co and Cr elements ranges from 0.9 to 1.1.

[0009] Furthermore, in the high-temperature self-lubricating material of the present invention, the molar ratio of Ti to Al, a constituent element of the ordered γ' reinforcing phase, ranges from 1.4 to 1.6.

[0010] Furthermore, in the high-temperature self-lubricating material of the present invention, Nb, Ta, and W are γ'' reinforcing phases and solid solution reinforcing elements; the mass percentage content of Nb is not less than 4%, and the total addition amount of W and Ta does not exceed 1.5%.

[0011] Furthermore, in the high-temperature self-lubricating material of the present invention, the RE includes one or more rare earth elements such as La, Ce, and Hf.

[0012] The principle for selecting and determining the content range of each component in the high-temperature self-lubricating material of this invention is as follows: (1) The alloy with similar molar amounts of Ni, Co and Cr is designed as the matrix to give the alloy the characteristics of a medium-entropy alloy, ensuring good fracture strength, fracture strain capacity and fracture toughness; on the other hand, Co promotes the formation of cobalt oxide with good lubrication performance under high temperature service environment, Cr promotes the formation of chromium trioxide film, improves the alloy's oxidation resistance and corrosion resistance, and Ni, as the austenite with FCC stable structure, provides good metallurgical stability and thermal stability for the alloy; the contents of the three elements are controlled at Ni 30-33%, Co 30-33% and Cr 28-30% respectively.

[0013] (2) The addition of Ti and Al elements with a molar ratio of 1.4 to 1.6 and a total content of 1.8 to 3.6% can effectively increase the volume fraction of the ordered γ' strengthening phase and improve the alloy strength. On the other hand, Al can promote the formation of an alumina protective film and improve the oxidation resistance. Ti, as an easily oxidized element, can accelerate the formation of surface oxidation products and promote the formation of wear-resistant glaze.

[0014] (3) The design incorporates a significant amount of Nb and small amounts of W and Ta elements. Besides solid solution strengthening and improving the high-temperature strength of the alloy, Nb can also form thermally stable γ''-Ni3Nb and a small amount of δ phase, improving the alloy's high-temperature creep strength and wear resistance. Experiments show that the Nb content should not exceed 5%, otherwise excessive δ phase will be generated, damaging the alloy's high-temperature toughness. Excessive W and Ta, refractory elements, will lead to microstructure segregation. Therefore, the Nb content should be controlled at 4-5%, and the W and Ta content should not exceed 1.5%.

[0015] (4) The design incorporates 0-0.3% of one or more rare earth elements with large atomic radii, including La, Ce, and Hf. Our experiments show that active elements can improve the morphology, size, and distribution of inclusions, forming active element inclusions and reducing damage to high-temperature performance. On the other hand, at high temperatures, active elements promote selective oxidation of metal elements, accelerate the formation of dense oxide films, and also improve the bonding force between the oxide film and the substrate, thereby improving oxidation resistance. Especially in the early stage of oxide formation, they can promote the formation of cobalt oxide lubricating phase on the surface. Their content is generally no more than 0.3%, as too much will agglomerate at grain boundaries and damage the plasticity of the alloy.

[0016] (5) The addition of 0.05-0.2% C element can form many fine and dispersed carbides in situ with W and Ti during heat treatment, which can play a dispersion strengthening role, refine the grains, and improve the strength; on the other hand, the fine carbides formed in situ can effectively improve the wear resistance of the alloy. Our experiments found that if the C addition is too low, the effect is not obvious, while if it is too high, the plasticity and toughness of the alloy will decrease significantly, with a maximum decrease of no more than 0.2%.

[0017] The high-temperature self-lubricating material based on NiCoCr medium-entropy alloy described in this invention has a tensile strength ≥1200MPa, a yield strength ≥950MPa, an elongation ≥15%, a coefficient of friction ≤0.35, and a wear amount ≤2.2mm at room temperature. 3 N -1 m -1 At 650℃, the tensile strength is ≥900MPa, the yield strength is ≥750MPa, the elongation is ≥20%, the coefficient of friction is ≤0.32, and the wear is ≤3.9mm. 3 N -1 m -1The high-temperature self-lubricating material provided by this invention exhibits excellent mechanical properties, good high-temperature wear resistance, and a low coefficient of friction at both room temperature and 650°C.

[0018] This invention also provides a method for preparing the above-mentioned high-temperature self-lubricating material based on NiCoCr medium-entropy alloy, which includes the following steps: S1. The above alloy raw materials are smelted and then cast into a vacuum electrode; S2. Anneal the vacuum electrode obtained in S1. S3. The vacuum electrode obtained in S2 is subjected to electroslag remelting under a protective atmosphere to obtain an electroslag ingot. S4. Perform surface grinding and head and tail cutting on the electroslag ingot obtained in S3. S5. The electroslag ingot obtained in S4 is subjected to high-temperature diffusion treatment before forging, and then forged into shape.

[0019] In step S1, a vacuum electrode is prepared by vacuum induction melting. The refining time is 15 min to 45 min, the refining vacuum degree is ≤0.5 Pa, the oxygen content in the molten steel is ≤10 ppm, the nitrogen content is ≤10 ppm, and the tapping temperature of the molten steel is 1360℃ to 1400℃.

[0020] In step S2, the vacuum electrode annealing temperature is 750℃~850℃, the holding time is 8h~12h, and the electrode surface is polished until it is bright and free of obvious oxide scale.

[0021] In step S3, the electroslag material is prepared with 50-55% calcium fluoride, 20-25% calcium oxide, 15-20% aluminum oxide, and 5-10% titanium dioxide, and 2%-10% of the corresponding rare earth oxides are added according to the rare earth composition of the electrode. The melting rate of the electroslag remelting stage is 3.5 kg / min to 7.5 kg / min.

[0022] In step S4, the cutting height at the head and tail is 20mm to 50mm to ensure that the electrode head and tail are clean.

[0023] In step S5, the heating temperature of the high-temperature diffusion treatment is 1150℃~1200℃, and after holding at that temperature for 48h~72h, it is lowered to 1120℃~1160℃ before being taken out of the furnace for forging. The deformation amount of each forging is 15%~35%, the total forging ratio is ≥6, and the diameter of the forging bar is 80mm~250mm.

[0024] The beneficial effects of adopting the above technical solution are as follows: This invention has comprehensively optimized the composition of self-lubricating composite materials, breaking away from the traditional strengthening approach of adding a large amount of ceramic self-lubricating phase. Through the multi-scale synergistic strengthening effect of micron-scale δ phase, submicron-scale γ' phase, nano-scale γ'' phase and rare earth elements, and by utilizing the high-temperature oxidation mechanism, the strengthening effect of alloying elements is fully utilized, effectively compensating for the shortcomings of poor plasticity and toughness and poor oxidation resistance of self-lubricating materials.

[0025] Compared with existing product technologies, this invention employs a two-stage preparation process combining vacuum induction melting and electroslag remelting. This effectively controls the content of gases such as O, N, and H, improving alloy purity and significantly enhancing the material's ductility, toughness, and high-temperature wear resistance. The entire preparation process is relatively simple, low-cost, and suitable for large-scale mass production. Attached Figure Description

[0026] Figure 1 The wear morphology of the sample prepared in Example 5 at 650°C. Detailed Implementation

[0027] The present invention will be further described below with reference to specific embodiments: Example 1

[0028] The preparation method of the high-temperature self-lubricating material in this embodiment includes the following steps: S1. The raw materials are proportioned according to the element mass percentages shown in Table 1. The raw materials are melted into molten steel using a vacuum induction furnace. The refining time is 45 min and the refining vacuum degree is 0.5 Pa. At this time, the oxygen content and nitrogen content in the molten steel are 10 ppm and the tapping temperature of the molten steel is 1400℃.

[0029] S2. To avoid cracking of the vacuum electrode, the electrode is placed in a heating furnace with a furnace temperature of ≤300℃ for annealing treatment. The annealing temperature is 750℃, and the holding time is 8 hours. After the furnace is cooled to 300℃, the electrode is taken out and air-cooled. The surface of the vacuum electrode is then polished until it is bright and free of obvious oxide scale. It is then welded to the dummy electrode to prepare for electroslag treatment.

[0030] S3. The ingot is remelted in a protective atmosphere electroslag remelting furnace. The electroslag material is proportioned according to the mass percentage of oxide slag material shown in Table 2. The steady-state electroslag melting rate is 7.5 kg / min.

[0031] S4. In order to further improve the purity of the alloy, the cutting height of the head and tail of the electroslag ingot is 20mm to ensure that the head and tail of the electroslag ingot are clean.

[0032] S5. The electroslag ingot is heated to 1200℃ in the furnace and held for 48 hours. Then it is cooled to 1160℃ and held for 2 hours before being taken out of the furnace for forging. The deformation amount under each pressing is 35%, the reheating time for each forging is 1.5 hours, the total forging ratio is 8, and finally a forged bar with an average cross-sectional diameter of 80mm is obtained. Example 2

[0033] The preparation method of the high-temperature self-lubricating material in this embodiment includes the following steps: S1. The raw materials are proportioned according to the element mass percentages shown in Table 1. The raw materials are melted into molten steel using a vacuum induction furnace. The refining time is 30 min and the refining vacuum degree is 0.1 Pa. At this time, the oxygen content in the molten steel is 4 ppm and the nitrogen content is 7 ppm. The tapping temperature of the molten steel is 1360℃.

[0034] S2. In order to avoid cracking of the vacuum electrode, the electrode is placed in a heating furnace with a furnace temperature ≤300℃ for annealing treatment. The annealing temperature is 850℃ and the holding time is 12h. After the furnace is cooled to 300℃, the electrode is taken out of the furnace and air-cooled. The surface of the vacuum electrode is polished until it is bright and there is no obvious oxide scale. It is then welded to the dummy electrode to prepare for electroslag. S3. The ingot is remelted in a protective atmosphere electroslag remelting furnace. The electroslag material is proportioned according to the mass percentage of oxide slag material shown in Table 2. The steady-state electroslag melting rate is 3.5 kg / min.

[0035] S4. In order to further improve the purity of the alloy, the cutting height of the head and tail of the electroslag ingot is 50mm to ensure that the head and tail of the electroslag ingot are clean.

[0036] S5. The electroslag ingot is heated to 1150℃ in the furnace and held for 72 hours. Then it is cooled to 1120℃ and held for 2 hours before being taken out of the furnace for forging. The deformation amount under each pressing is 15%, the reheating time for each forging is 1.5 hours, the total forging ratio is 6, and finally a forged bar with an average cross-sectional diameter of 250mm is obtained. Example 3

[0037] The preparation method of the high-temperature self-lubricating material in this embodiment includes the following steps: S1. The raw materials are proportioned according to the element mass percentages shown in Table 1. The raw materials are melted into molten steel using a vacuum induction furnace. The refining time is 30 min and the refining vacuum degree is 0.3 Pa. At this time, the oxygen content in the molten steel is 6 ppm and the nitrogen content is 9 ppm. The tapping temperature of the molten steel is 1380℃.

[0038] S2. In order to avoid cracking of the vacuum electrode, the electrode is placed in a heating furnace with a furnace temperature ≤300℃ for annealing treatment. The annealing temperature is 800℃ and the holding time is 10h. After the furnace is cooled to 300℃, the electrode is taken out of the furnace and air-cooled. The surface of the vacuum electrode is polished until it is bright and there is no obvious oxide scale. It is then welded to the dummy electrode to prepare for electroslag. S3. The ingot is remelted in a protective atmosphere electroslag remelting furnace. The electroslag material is proportioned according to the mass percentage of oxide slag material shown in Table 2. The steady-state electroslag melting rate is 4.5 kg / min.

[0039] S4. In order to further improve the purity of the alloy, the cutting height of the electroslag ingot head and tail is 30mm to ensure the cleanliness of the electrode head and tail.

[0040] S5. The electroslag ingot is heated to 1180℃ in the furnace and held for 60 hours. Then it is cooled to 1140℃ and held for 2 hours before being taken out of the furnace for forging. The deformation amount under each pressing is 20%, the reheating time for each forging is 1.5 hours, the total forging ratio is 8, and finally a forged bar with an average cross-sectional diameter of 100mm is obtained. Example 4

[0041] The preparation method of the high-temperature self-lubricating material in this embodiment includes the following steps: S1. The raw materials are proportioned according to the element mass percentages shown in Table 1. The raw materials are melted into molten steel using a vacuum induction furnace. The refining time is 25 min and the refining vacuum degree is 0.2 Pa. At this time, the oxygen content in the molten steel is 5 ppm and the nitrogen content is 7 ppm. The tapping temperature of the molten steel is 1370℃.

[0042] S2. In order to avoid cracking of the vacuum electrode, the electrode is placed in a heating furnace with a furnace temperature ≤300℃ for annealing treatment. The annealing temperature is 775℃ and the holding time is 9h. After the furnace is cooled to 300℃, the electrode is taken out of the furnace and air-cooled. The surface of the vacuum electrode is polished until it is bright and there is no obvious oxide scale. It is then welded to the dummy electrode to prepare for electroslag. S3. The ingot is remelted in a protective atmosphere electroslag remelting furnace. The electroslag material is proportioned according to the mass percentage of oxide slag material shown in Table 2. The steady-state electroslag melting rate is 5.5 kg / min.

[0043] S4. In order to further improve the purity of the alloy, the cutting height of the electroslag ingot head and tail is 25mm to ensure the cleanliness of the electrode head and tail.

[0044] S5. The electroslag ingot is heated to 1150℃ in the furnace and held for 60 hours. Then it is cooled to 1120℃ and held for 2 hours before being taken out of the furnace for forging. The deformation amount under each pressing is 25%, the reheating time for each forging is 1.5 hours, the total forging ratio is 6, and finally a forged bar with an average cross-sectional diameter of 150mm is obtained. Example 5

[0045] The preparation method of the high-temperature self-lubricating material in this embodiment includes the following steps: S1. The raw materials are proportioned according to the element mass percentages shown in Table 1. The raw materials are melted into molten steel using a vacuum induction furnace. The refining time is 35 min and the refining vacuum degree is 0.5 Pa. At this time, the oxygen content in the molten steel is 8 ppm and the nitrogen content is 10 ppm. The tapping temperature of the molten steel is 1390℃.

[0046] S2. In order to avoid cracking of the vacuum electrode, the electrode is placed in a heating furnace with a furnace temperature ≤300℃ for annealing treatment. The annealing temperature is 825℃ and the holding time is 110h. After the furnace is cooled to 300℃, the electrode is taken out of the furnace and air-cooled. The surface of the vacuum electrode is polished until it is bright and there is no obvious oxide scale. It is then welded to the dummy electrode to prepare for electroslag remelting. S3. The ingot is remelted in a protective atmosphere electroslag remelting furnace. The electroslag material is proportioned according to the mass percentage of oxide slag material shown in Table 2. The steady-state electroslag melting rate is 6.5 kg / min.

[0047] S4. In order to further improve the purity of the alloy, the cutting height of the electroslag ingot head and tail is 40mm to ensure the cleanliness of the electrode head and tail.

[0048] S5. The electroslag ingot is heated to 1160℃ in the furnace and held for 66 hours. Then it is cooled to 1130℃ and held for 2 hours before being taken out of the furnace for forging. The deformation amount under each pressing is 18%, and the time for returning to the furnace after each firing is 1.5 hours. Finally, a forged bar with an average cross-sectional diameter of 125mm is obtained. Example 6

[0049] The preparation method of the high-temperature self-lubricating material in this embodiment includes the following steps: S1. The raw materials are proportioned according to the element mass percentages shown in Table 1. The raw materials are melted into molten steel using a vacuum induction furnace. The refining time is 40 min and the refining vacuum degree is 0.4 Pa. At this time, the oxygen content in the molten steel is 7 ppm and the nitrogen content is 8 ppm. The tapping temperature of the molten steel is 1380℃.

[0050] S2. In order to avoid cracking of the vacuum electrode, the electrode is placed in a heating furnace with a furnace temperature ≤300℃ for annealing treatment. The annealing temperature is 800℃ and the holding time is 8h. After the furnace is cooled to 300℃, the electrode is taken out of the furnace and air-cooled. The surface of the vacuum electrode is polished until it is bright and there is no obvious oxide scale. It is then welded to the dummy electrode to prepare for electroslag. S3. The ingot is remelted in a protective atmosphere electroslag remelting furnace. The electroslag material is proportioned according to the mass percentage of oxide slag material shown in Table 2. The steady-state electroslag melting rate is 5 kg / min.

[0051] S4. In order to further improve the purity of the alloy, the cutting height of the electroslag ingot head and tail is 35mm to ensure the cleanliness of the electrode head and tail.

[0052] S5. The electroslag ingot is heated to 1190℃ in the furnace and held for 54 hours. Then it is cooled to 1120℃ and held for 2 hours before being taken out of the furnace for forging. The deformation amount under each pressing is 24%, and the reheating time for each firing is 1.5 hours. Finally, a forged bar with an average cross-sectional diameter of 220mm is obtained. Comparative Example 1

[0053] The preparation method of this comparative high-temperature self-lubricating material includes the following steps: S1. The raw materials are proportioned according to the element mass percentages shown in Table 1. The raw materials are melted into molten steel using a vacuum induction furnace. The refining time is 35 min and the refining vacuum degree is 0.5 Pa. At this time, the oxygen content in the molten steel is 8 ppm and the nitrogen content is 10 ppm. The tapping temperature of the molten steel is 1390℃.

[0054] S2. In order to avoid cracking of the vacuum electrode, the electrode is placed in a heating furnace with a furnace temperature ≤300℃ for annealing treatment. The annealing temperature is 825℃ and the holding time is 110h. After the furnace is cooled to 300℃, the electrode is taken out of the furnace and air-cooled. The surface of the vacuum electrode is polished until it is bright and there is no obvious oxide scale. It is then welded to the dummy electrode to prepare for electroslag remelting. S3. The ingot is remelted in a protective atmosphere electroslag remelting furnace. The electroslag material is proportioned according to the mass percentage of oxide slag material shown in Table 2. The steady-state electroslag melting rate is 6.5 kg / min.

[0055] S4. In order to further improve the purity of the alloy, the cutting height of the electroslag ingot head and tail is 40mm to ensure the cleanliness of the electrode head and tail.

[0056] S5. The electroslag ingot is heated to 1140℃ in the furnace and held for 30 hours. Then it is cooled to 1130℃ and held for 2 hours before being taken out of the furnace for forging. The deformation amount under each pressing is 18%, and the time for returning to the furnace after each firing is 1.5 hours. Finally, a forged bar with an average cross-sectional diameter of 125mm is obtained. Comparative Example 2

[0057] The preparation method of the high-temperature self-lubricating material in this embodiment includes the following steps: S1. The raw materials are proportioned according to the element mass percentages shown in Table 1. The raw materials are melted into molten steel using a vacuum induction furnace. The refining time is 35 min and the refining vacuum degree is 0.5 Pa. At this time, the oxygen content in the molten steel is 8 ppm and the nitrogen content is 10 ppm. The tapping temperature of the molten steel is 1390℃.

[0058] S2. In order to avoid cracking of the vacuum electrode, the electrode is placed in a heating furnace with a furnace temperature ≤300℃ for annealing treatment. The annealing temperature is 825℃ and the holding time is 110h. After the furnace is cooled to 300℃, the electrode is taken out of the furnace and air-cooled. The surface of the vacuum electrode is polished until it is bright and there is no obvious oxide scale. It is then welded to the dummy electrode to prepare for electroslag remelting. S3. The ingot is remelted in a protective atmosphere electroslag remelting furnace. The electroslag material is proportioned according to the mass percentage of oxide slag material shown in Table 2. The steady-state electroslag melting rate is 6.5 kg / min.

[0059] S4. In order to further improve the purity of the alloy, the cutting height of the electroslag ingot head and tail is 40mm to ensure the cleanliness of the electrode head and tail.

[0060] S5. The electroslag ingot is heated to 1160℃ in the furnace and held for 66 hours. Then it is cooled to 1130℃ and held for 2 hours before being taken out of the furnace for forging. The deformation amount under each pressing is 18%, and the time for returning to the furnace after each firing is 1.5 hours. Finally, a forged bar with an average cross-sectional diameter of 125mm is obtained.

[0061] Table 1. Chemical composition (%) of high-temperature self-lubricating materials in each embodiment

[0062] Table 2. Proportion of electroslag material in each embodiment (%)

[0063] Table 3. Room temperature and high temperature tensile properties of the self-lubricating materials in the examples.

[0064] Table 4. Tribological and Wear Properties of Self-Lubricating Materials in Examples

[0065] As shown in Tables 2 and 3, the high-temperature self-lubricating material provided by the present invention has excellent mechanical properties, good high-temperature wear resistance, and a low coefficient of friction at both room temperature and 650°C.

[0066] As shown in Table 1, Comparative Example 1 has the same chemical composition as Example 5, but differs in that the electroslag ingot was subjected to high-temperature homogenization treatment at 1140℃ for 30 hours. Due to insufficient homogenization time, easily segregating elements such as Nb and W did not dissolve sufficiently, leading to the precipitation of large carbide particles, ultimately resulting in a decrease in both the strength and plasticity of the alloy. The self-lubricating material obtained in Comparative Example 1 has a room temperature tensile strength of 1120 MPa, a yield strength of 780 MPa, and an elongation of 12%, while its tensile strength at 650℃ is 850 MPa, its yield strength is 720 MPa, and its elongation is only 10%. In contrast, the fully homogenized material in Example 5 has a tensile strength of 1300 MPa, a yield strength of 980 MPa, and an elongation of 19%, while its tensile strength at 650℃ is 1000 MPa, its yield strength is 760 MPa, and its elongation is as high as 28%. Meanwhile, due to the uneven distribution of elements within the alloy, the self-lubricating material prepared in Comparative Example 1 exhibits significant wear during both room temperature and high temperature friction, reaching as high as 3.5 × 10⁻⁶. -5 mm 3 N -1 m -1 and 6.1×10 -5 mm 3 N -1 m -1 In contrast, the self-lubricating material in Example 5 exhibits a wear rate of only 2.1 × 10⁻⁶ at both room temperature and high temperature. -5 mm 3 N -1 m -1 and 3.5×10 - 5 mm 3 N -1 m -1 .

[0067] As shown in Table 1, compared with Example 5, Comparative Example 2 has the same alloying elements, but no rare earth elements La and Ce were added, and other production processes were the same. As shown in Table 3, Comparative Example 2, due to the absence of rare earth elements, did not utilize the rare earth strengthening effect, and the resulting self-lubricating material had a room temperature tensile strength of 1185 MPa, a yield strength of 905 MPa, and an elongation of 20%, while its tensile strength at 650°C was 880 MPa, a yield strength of 740 MPa, and an elongation of only 26%. In contrast, Example 5, which added rare earth elements, had a tensile strength of 1300 MPa, a yield strength of 980 MPa, an elongation of 19%, a tensile strength at 650°C of 1000 MPa, a yield strength of 760 MPa, and an elongation as high as 28%. Meanwhile, because the alloy in Comparative Example 2 lacks rare earth elements, especially during high-temperature friction and wear, it cannot promote the formation of anti-wear and protective oxide films such as cobalt oxide and chromium oxide, thus failing to achieve self-lubrication. This results in significant wear during high-temperature friction, with a high wear rate as high as 7.2 × 10⁻⁶. -5 mm 3 N -1 m -1 In contrast, the high-temperature wear of Example 5 was only 3.2 × 10⁻⁶. -5 mm 3 N -1 m -1 .

[0068] The wear morphology of the sample prepared in Example 5 at 650°C is shown in the figure. Figure 1 .Depend on Figure 1 It can be seen that a continuous and dense glaze layer is formed on the sample surface, which has a good protective effect on the substrate and good wear resistance.

[0069] The above embodiments are only used to illustrate and not limit the technical solutions of the present invention. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the present invention without departing from the spirit and scope of the present invention. Any modifications or partial substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A high-temperature self-lubricating material based on NiCoCr medium-entropy alloy and its preparation method, characterized in that, The chemical composition is as follows: Ni 30-33%, Co 30-33%, Cr 28-30%, Al+Ti 1.8-3.6%, Nb+Ta+W 4-6.5%, RE 0-0.2%, C 0.05-0.2%, with the remainder being unavoidable impurities.

2. The chemical composition of a high-temperature self-lubricating material based on a NiCoCr medium-entropy alloy according to claim 1, characterized in that, The molar ratio of any two of the Ni, Co and Cr elements is in the range of 0.9 to 1.

1.

3. The chemical composition of a high-temperature self-lubricating material based on a NiCoCr medium-entropy alloy according to claim 1, characterized in that, The molar ratio of Ti to Al is 1.4 to 1.

6.

4. The chemical composition of a high-temperature self-lubricating material based on a NiCoCr medium-entropy alloy according to claim 1, characterized in that, The mass percentage of Nb is ≥4%, and the total addition amount of Ta and W is ≤1.5%.

5. The chemical composition of a high-temperature self-lubricating material based on a NiCoCr medium-entropy alloy according to claim 1, characterized in that, The RE element includes one or more rare earth metal elements such as La, Ce, and Hf, and the total amount of rare earth elements added is ≤0.2%.

6. A method for preparing a high-temperature self-lubricating material based on a NiCoCr medium-entropy alloy according to any one of claims 1-5, characterized in that, Includes the following steps: S1. The above alloy raw materials are smelted and then cast into a vacuum electrode; S2. Anneal the vacuum electrode obtained in S1. S3. The vacuum electrode obtained in S2 is subjected to electroslag remelting under a protective atmosphere to obtain an electroslag ingot. S4. Perform surface grinding and head and tail cutting on the electroslag ingot obtained in S3. S5. The electroslag ingot obtained in S4 is subjected to high-temperature diffusion treatment before forging, and then forged into shape.

7. The method for preparing a high-temperature self-lubricating material based on a NiCoCr medium-entropy alloy according to claim 6, characterized in that, In step S1, a vacuum electrode is prepared by vacuum induction melting. The refining time is 15 min to 45 min, the refining vacuum degree is ≤0.5 Pa, the oxygen content in the molten steel is ≤10 ppm, the nitrogen content is ≤10 ppm, and the tapping temperature of the molten steel is 1360℃ to 1400℃.

8. The method for preparing a high-temperature self-lubricating material based on a NiCoCr medium-entropy alloy according to claim 6, characterized in that, In step S2, the annealing temperature is 750℃~850℃, and the holding time is 8h~12h.

9. The method for preparing a high-temperature self-lubricating material based on a NiCoCr medium-entropy alloy according to claim 6, characterized in that, In step S3, the electroslag material is prepared with 50-55% CaF2, 20-25% CaO, 15-20% Al2O3, and 5-10% TiO2, and 2%-10% of the corresponding rare earth oxides are added according to the rare earth composition of the electrode. The melting rate of the electroslag remelting stage is 3.5 kg / min to 7.5 kg / min.

10. The method for preparing a high-temperature self-lubricating material based on a NiCoCr medium-entropy alloy according to claim 6, characterized in that, In step S5, the heating temperature of the high-temperature diffusion treatment is 1150℃~1200℃, and after holding at this temperature for 48h~72h, it is lowered to 1120℃~1160℃ before being taken out of the furnace for forging. The deformation amount under each pressing is 15%~35%, the total forging ratio is ≥6, and the diameter of the forging bar is 80mm~250mm.

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