A self-lubricating CoCrNi-based composite material and a preparation method thereof

Abstract

The application discloses a kind of self-lubricating CoCrNi-based composite material and preparation method thereof, it is related to wear-resistant material technical field;And the method includes: the mass ratio of CoCrNi spherical powder and Al2O3 ceramic powder is always 98:2, selected lubricating phase is nickel-coated molybdenum disulfide, to avoid MoS2 decomposition or reaction with matrix in sintering process, the mass fraction of nickel-coated molybdenum disulfide powder is x wt.% (x=10-20), and the required raw material powder is weighed according to the proportion;Using planetary high-energy ball mill, powder is uniformly mixed, ball-to-material ratio is 3:1, mixing time is 4h, and the rotation speed of ball mill is 180rpm;Using SPS discharge plasma sintering forming technology, self-lubricating block material is prepared.Sintering temperature is 1100 DEG C, pressure is 30MPa, holding time is 5min, and the heating rate and cooling rate are both 100 DEG C / min.The application obtains the solid self-lubricating sample with uniform composition and organization, excellent friction-reducing and wear-resistant performance at low temperature by adjusting the process parameters of SPS.

Description

Technical Field

[0001] This invention relates to the field of wear-resistant materials technology, specifically to a self-lubricating CoCrNi-based composite material and its preparation method. Background Technology

[0002] With the development of polar exploration, energy storage and transportation, and railway transportation in high-altitude and cold regions, the demand for materials in cryogenic environments is becoming increasingly widespread. Cryogenic environments place higher demands on the mechanical and tribological properties of service materials. Traditional materials undergo a ductile-brittle transition at low temperatures, significantly impacting the safe and stable operation and service life of mechanical components, thus limiting their cryogenic applications to some extent. High-entropy / medium-entropy alloys are alloys composed of multiple main elements in equal or near-equal atomic ratios. They possess high mixing entropy, making it easier to form a single solid solution rather than intermetallic compounds during solidification. Typical effects of high-entropy / medium-entropy alloys include the high-entropy effect, lattice distortion effect, cocktail effect, and hysteretic diffusion effect, resulting in excellent mechanical and physicochemical properties such as high strength, high hardness, high fracture toughness, high wear resistance, and high corrosion resistance. CoCrNi is a typical medium-entropy alloy with a cubic structure, exhibiting high strength and fracture toughness at room temperature, making it one of the toughest metallic materials reported to date. CoCrNi exhibits an excellent combination of high strength, ductility and fracture toughness at low temperatures, with excellent low-temperature damage tolerance. It is a highly promising low-temperature alloy material and is expected to play an important role in harsh low-temperature environments such as aerospace and polar regions.

[0003] Lubrication effectively reduces friction and wear on mechanical components during service. However, in low-temperature environments, traditional lubricating oils and greases fail rapidly due to their lack of fluidity. Solid lubrication is the most ideal lubrication method in low-temperature environments. Current research on solid lubrication mainly focuses on solid coating lubrication, which has limited load-bearing capacity and service life, making it difficult to meet the mechanical and tribological performance requirements under extreme conditions. Solid self-lubricating agents, on the other hand, possess both excellent mechanical and lubrication properties, making them suitable for use in extreme conditions such as chemical, aerospace applications, low-temperature, or radiation environments. Summary of the Invention

[0004] To address the problems of MoS2 decomposition, insufficient hardness and lubrication properties during sintering, and unstable material properties that affect the tribological performance and reliability of equipment in low-temperature environments and hinder automatic classification of mixtures, this invention aims to provide a self-lubricating CoCrNi-based composite material and its preparation method.

[0005] To solve the above technical problems, the present invention adopts the following technical solution: a self-lubricating CoCrNi-based composite material, comprising a composite material, wherein the composite material comprises alloy components in the following mass percentages: x wt.% Ni / MoS2, 0.98·y wt.% CoCrNi and 0.02·y wt.% Al2O3, wherein x = 10-20 and y = 100-x, wherein the composite material uses hard second phase Al2O3 as the reinforcing phase and MoS2 as the lubricating phase.

[0006] A method for preparing a self-lubricating CoCrNi-based composite material includes the following steps:

[0007] S1. Raw material preparation: Weigh the required raw material powder according to the proportion of the self-lubricating CoCrNi-based composite material as described in claim 1;

[0008] S2. Composite material powder mixing: Place the weighed raw material powder and grinding balls into the ball mill jar, and start the ball mill to mix the composite material powder evenly.

[0009] S3. Sample sintering: The uniformly mixed composite material is subjected to SPS discharge plasma sintering to obtain the self-lubricating CoCrNi-based composite material product.

[0010] The specific steps of the composite material powder mixing process in S2 are as follows: Weigh 165g of stainless steel beads according to a ball-to-material ratio of 3:1, place the weighed raw material powder and stainless steel beads into a ball mill jar, and use a planetary high-energy ball mill to mix the composite material powder evenly for 4 hours at a rotation speed of 180 rpm; the mass of the ball mill jar placed diagonally during mixing in S2 should be more than 100g; the planetary high-energy ball mill in S2 should rotate clockwise and counterclockwise for 20 minutes each, with an interval of 10 minutes;

[0011] The sintering process of the sample in S3 is as follows: the uniformly mixed composite material powder is placed in a graphite mold, a layer of carbon felt is wrapped around the outside of the mold for heat preservation, a pressure of 30 MPa is applied under an argon atmosphere to pre-compress the powder to densify it, then the temperature is raised to 1100℃ at a rate of 100℃ / min and held for 5 min, then water-cooled to 500℃ at a rate of 100℃ / min, and finally cooled to room temperature with the furnace to obtain the target sample; the operation of purging the cavity and then introducing argon gas in S3 needs to be repeated three times; the composite material powder is pre-compressed at room temperature in S3.

[0012] The weighing of raw material powders in S1 is carried out in a glove box, and CoCrNi spherical powder, nano-sized Al2O3 ceramic powder, and nickel-coated molybdenum disulfide powder are used respectively; the nano-sized Al2O3 ceramic powder is dried in an electric heating drying oven before weighing for 2 hours.

[0013] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0014] 1. The lubricating phase material used in this invention is nickel-coated molybdenum disulfide, which effectively hinders the decomposition of MoS2 during sintering. This invention also introduces a hard reinforcing phase Al2O3 and a solid lubricating phase MoS2. Through process control, a CoCrNi-based self-lubricating composite material with uniform structure and composition was successfully prepared, which has good low-temperature tribological properties.

[0015] 2. This invention employs SPS (Spark Plasma Sintering) technology, which features low holding temperature, short holding time, and rapid cooling, resulting in samples with uniform structure and composition and high density. This preparation method can improve production efficiency and reduce energy consumption. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 SEM morphology images of x wt.% Ni / MoS2 (x = 0 and 20) samples, where a1 is 250 × 0 wt.% Ni / MoS2, a2 ​​is 500 × 0 wt.% Ni / MoS2, b1 is 250 × 20 wt.% Ni / MoS2, and b2 is 500 × 20 wt.% Ni / MoS2.

[0018] Figure 2 Real-time friction coefficient plot at room temperature for x wt.% Ni / MoS2 samples (x = 0, 10, 15 and 20).

[0019] Figure 3 Wear rate plots at room temperature for x wt.% Ni / MoS2 samples (x = 0, 10, 15 and 20).

[0020] Figure 4 The friction coefficients of x wt.% Ni / MoS2 (x = 0 and 20) samples at low temperatures of 0℃, -40℃, -80℃ and -120℃ are plotted.

[0021] Figure 5 Wear rate plots for x wt.% Ni / MoS2 (x = 0 and 20) samples at low temperatures of 0°C, -40°C, -80°C, and -120°C. Detailed Implementation

[0022] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] like Figure 1-5 As shown, the present invention provides a self-lubricating CoCrNi-based composite material, comprising a composite material comprising the following alloy components by mass percentage: x wt.% Ni / MoS2, 0.98·y wt.% CoCrNi and 0.02·y wt.% Al2O3, wherein x = 10-20 and y = 100-x, wherein the composite material uses a hard second phase Al2O3 as a reinforcing phase and MoS2 as a lubricating phase.

[0024] A method for preparing a self-lubricating CoCrNi-based composite material includes the following steps:

[0025] S1. Raw material preparation: Weigh the required raw material powder according to the proportion of the self-lubricating CoCrNi-based composite material as described in claim 1;

[0026] S2. Composite material powder mixing: Place the weighed raw material powder and grinding balls into the ball mill jar, and start the ball mill to mix the composite material powder evenly.

[0027] S3. Sample sintering: The uniformly mixed composite material is subjected to SPS discharge plasma sintering to obtain the self-lubricating CoCrNi-based composite material product.

[0028] The specific steps of the composite material powder mixing process in S2 are as follows: Weigh 165g of stainless steel beads according to a ball-to-material ratio of 3:1, place the weighed raw material powder and stainless steel beads into a ball mill jar, and use a planetary high-energy ball mill to mix the composite material powder evenly for 4 hours at a rotation speed of 180 rpm; the mass of the ball mill jar placed diagonally during mixing in S2 should be more than 100g; the planetary high-energy ball mill in S2 should rotate clockwise and counterclockwise for 20 minutes each, with an interval of 10 minutes;

[0029] The sintering process of the sample in S3 is as follows: the uniformly mixed composite material powder is placed in a graphite mold, a layer of carbon felt is wrapped around the outside of the mold for heat preservation, a pressure of 30 MPa is applied under an argon atmosphere to pre-compress the powder to densify it, then the temperature is raised to 1100℃ at a rate of 100℃ / min and held for 5 min, then water-cooled to 500℃ at a rate of 100℃ / min, and finally cooled to room temperature with the furnace to obtain the target sample; the operation of purging the cavity and then introducing argon gas in S3 needs to be repeated three times; the composite material powder is pre-compressed at room temperature in S3.

[0030] The weighing of raw material powders in S1 is carried out in a glove box, and CoCrNi spherical powder, nano-sized Al2O3 ceramic powder, and nickel-coated molybdenum disulfide powder are used respectively; the nano-sized Al2O3 ceramic powder is dried in an electric heating drying oven before weighing for 2 hours.

[0031] Comparative Example 1:

[0032] A self-lubricating CoCrNi-based bulk material with x wt.% Ni / MoS2 (x=0) is prepared as follows:

[0033] Step 1: Place the nano-sized Al2O3 ceramic powder into an electric heating drying oven and dry it for 2 hours to prevent Al2O3 powder from clumping during the mixing process and affecting the uniformity of the composite powder.

[0034] Step 2: Weigh the required raw material powders according to the component ratios in Table 1 where x = 0;

[0035] Step 3: Weigh 165g of stainless steel beads according to a ball-to-material mass ratio of 3:1. Place the weighed powder and stainless steel beads into a ball mill jar and use an omnidirectional planetary ball mill to thoroughly mix the weighed and proportioned raw materials. Set the mixing time of the planetary ball mill to 4 hours and the rotation speed to 180 rpm. Grind the powder in both clockwise and counterclockwise directions for 20 minutes each, with a 10-minute interval, to obtain a uniformly mixed medium-entropy alloy composite material powder.

[0036] Step 4: Load the powder into a 30mm diameter graphite mold, and wrap the outside of the mold with a layer of carbon felt for insulation. After evacuating the cavity, argon gas is introduced, and the powder is pre-compressed at 30MPa at room temperature to improve its density.

[0037] Step 5: Using the sintering furnace program control, apply a pressure of 30MPa, heat to 1100℃ at a rate of 100℃ / min and hold for 5min, then water cool to 500℃ at a rate of 100℃ / min, and then cool to room temperature with the furnace.

[0038] The above five steps yielded a Φ30mm×5mm CoCrNi-based self-lubricating block material with xwt.%Ni / MoS2 (x=0).

[0039] Example 1:

[0040] A self-lubricating CoCrNi-based bulk material x wt.% Ni / MoS2 (x=10) is prepared by the same method as in Comparative Example 1, except for the composition ratio of the composite material.

[0041] Example 2:

[0042] A self-lubricating CoCrNi-based bulk material x wt.% Ni / MoS2 (x=15) is prepared by the same method as in Comparative Example 1, except for the composition ratio of the composite material.

[0043] Example 3:

[0044] A self-lubricating CoCrNi-based bulk material x wt.% Ni / MoS2 (x=20) is prepared by the same method as in Comparative Example 1, except for the composition ratio of the composite material.

[0045]

[0046] Table 1. Composition ratio of self-lubricating CoCrNi-based composite materials in comparative examples and embodiments.

[0047] This invention provides tribological test results for self-lubricating CoCrNi-based composite materials with different compositions, thereby illustrating the influence of the mass fraction of the lubricating phase on the tribological properties of the samples, as detailed below:

[0048] Figure 1 This is a SEM image of x wt.% Ni / MoS2 (x = 0 and 20) samples sintered by SPS at 1100℃. The hard second phase Al2O3 and the lubricating phase MoS2 are uniformly distributed at the grain boundaries. Al2O3 appears as black granules, while MoS2 appears as gray flakes. The CoCrNi alloy forms a white substrate. No impurities were introduced during the batching, mixing, and sintering processes. Carbon elements from the mold and graphite paper did not diffuse into the sample core during sintering. The 0 wt.% Ni / MoS2 sample has a more irregular grain shape and is relatively dense between grains. The 20 wt.% Ni / MoS2 sample has a slightly smaller grain size, mostly spherical in shape, and the grains are more dispersed due to the introduction of the lubricating phase MoS2. The introduction of MoS2 makes the grain shape more regular and refines the matrix grains to some extent.

[0049] Real-time coefficient of friction (COF) for x wt.% Ni / MoS2 samples (x = 0, 10, 15, and 20) at room temperature is shown in [reference]. Figure 2The average COFs were 0.57, 0.46, 0.45, and 0.42, respectively, and the COFs gradually decreased with increasing lubricant mass fraction. The addition of solid lubricant is beneficial to the friction reduction and lubrication of CoCrNi self-lubricating composites.

[0050] Figure 3 The wear rate is x wt.% Ni / MoS2 (x = 0, 10, 15 and 20) samples at room temperature, which are 9.73 ± 0.885 × 10⁻⁶. -5 mm 3 / Nm, 4.95±0.354×10 -5 mm 3 / Nm, 4.69±0.663×10 -5 mm 3 / Nm and 3.67±0.221×10 -5 mm 3 / Nm, compared to the 0wt.% Ni / MoS2 sample, the 20wt.% Ni / MoS2 sample showed a 62.3% reduction in wear rate. This means that with the increase of solid lubricant phase content, the material's wear rate significantly decreases and exhibits excellent anti-wear properties.

[0051] The coefficients of friction of x wt.% Ni / MoS2 (x = 0 and 20) samples at low temperatures of 0℃, -40℃, -80℃ and -120℃ are as follows: Figure 4 As shown, the surface COFs of the 0wt.% Ni / MoS2 sample gradually decreased with decreasing temperature, with average COFs of 0.73 and 0.56 at 0℃ and -120℃, respectively. The COFs of the 20wt.% Ni / MoS2 sample gradually increased with decreasing temperature. Within the temperature range of 0℃ to -80℃, the COFs of the 20wt.% Ni / MoS2 sample were consistently lower than those of the 0wt.% Ni / MoS2 sample; however, at -120℃, the friction coefficient of the 20wt.% Ni / MoS2 sample reached as high as 0.56, approaching that of the 0wt.% Ni / MoS2 sample without added lubricating phase. At this point, the 20wt.% Ni / MoS2 sample had lost its friction-reducing effect.

[0052] For the wear rates of x wt.% Ni / MoS2 (x = 0 and 20) samples at low temperatures of 0°C, -40°C, -80°C, and -120°C, please refer to [reference needed]. Figure 5 The wear rate of the 0 wt.% Ni / MoS2 sample gradually decreased with decreasing temperature, with wear rates of 78.83 ± 6.07 × 10⁻⁶ at 0℃ and -120℃. -5 mm 3 / Nm and 36.32±0.0418×10 -5 mm 3 / Nm. The wear rate of the 20wt.% Ni / MoS2 sample increased with decreasing temperature, with wear rates of 5.33±0.53×10 at 0℃ and -120℃, respectively. -5 mm 3 / Nm and 6.78±0.37×10 -5 mm 3 / Nm, which is reduced by approximately 93.2% and 81.1% respectively compared to the 0wt.%Ni / MoS2 sample. The comparison revealed that although the wear resistance of the 20wt.%Ni / MoS2 sample slightly increased with decreasing temperature, its wear resistance remained significantly superior to that of the 0wt.%Ni / MoS2 sample.

[0053] In summary, the accompanying drawings of this invention show the SEM morphology and tribological test results of the CoCrNi-based composite material samples, demonstrating that the samples have good friction-reducing and wear-resistant properties after the introduction of the lubricating phase MoS2.

[0054] This invention utilizes spark plasma sintering technology to prepare self-lubricating CoCrNi-based composite materials with fine and uniform microstructure, high density, and excellent tribological properties through composition design and process control. The MoS2 lubricating phase, uniformly distributed at the grain boundaries, has a layered structure with weak intermolecular forces between the layers. During friction, interlaminar shearing easily occurs, forming a lubricating layer with friction-reducing and wear-resistant effects. Furthermore, as the mass fraction of the solid lubricating phase increases, the lubricating layer area becomes larger, and the friction-reducing effect becomes more significant. The self-lubricating CoCrNi-based composite material (20 wt.% Ni / MoS2) exhibits good friction-reducing and wear-resistant properties at low temperatures not lower than -80℃. At -120℃, its coefficient of friction is comparable to that of the sample without the lubricating phase, but its wear resistance is still far superior to that of the 0 wt.% Ni / MoS2 sample. This preparation method has high production efficiency and low energy consumption, expanding the application of medium-entropy alloys at low temperatures.

[0055] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A self-lubricating CoCrNi-based composite material, comprising the composite material, characterized in that: The composite material comprises the following alloy components by mass percentage: x wt.% Ni / MoS2, 0.98·y wt.% CoCrNi and 0.02·y wt.% Al2O3, where x = 10-20 and y = 100-x. The composite material uses hard second-phase Al2O3 as the reinforcing phase and MoS2 as the lubricating phase.

2. The preparation method of the self-lubricating CoCrNi-based composite material as described in claim 1, characterized in that, Includes the following steps: S1. Raw material preparation: Weigh the required raw material powder according to the proportion of the self-lubricating CoCrNi-based composite material as described in claim 1; S2. Composite material powder mixing: Place the weighed raw material powder and grinding balls into the ball mill jar, and start the ball mill to mix the composite material powder evenly. S3. Sample sintering: The uniformly mixed composite material is subjected to SPS discharge plasma sintering to obtain the self-lubricating CoCrNi-based composite material product.

3. The preparation method of the self-lubricating CoCrNi-based composite material as described in claim 2, characterized in that: The specific steps of the composite material powder mixing process in S2 are as follows: Weigh 165g of stainless steel beads according to a ball-to-material ratio of 3:1, put the weighed raw material powder and stainless steel beads into a ball mill jar, and use a planetary high-energy ball mill to mix the composite material powder evenly for 4 hours at a rotation speed of 180 rpm; the mass of the ball mill jar placed diagonally during mixing in S2 should be more than 100g; in S2, the planetary high-energy ball mill should be used to mill in clockwise and counterclockwise directions for 20 minutes each, with an interval of 10 minutes.

4. The preparation method of the self-lubricating CoCrNi-based composite material as described in claim 2, characterized in that: The sample sintering process in S3 is as follows: the uniformly mixed composite material powder is placed in a graphite mold, a layer of carbon felt is wrapped around the outside of the mold for heat preservation, a pressure of 30 MPa is applied under an argon atmosphere to pre-compress the powder to densify it, then the temperature is raised to 1100℃ at a rate of 100℃ / min and held for 5 min, then water-cooled to 500℃ at a rate of 100℃ / min, and finally cooled to room temperature with the furnace to obtain the target sample; the operation of purging the cavity and then introducing argon gas in S3 needs to be repeated three times; the composite material powder is pre-compressed at room temperature in S3.

5. The self-lubricating CoCrNi-based composite material and its preparation method as described in claim 2, characterized in that: The weighing of raw material powders in S1 is carried out in a glove box, and CoCrNi spherical powder, nano-sized Al2O3 ceramic powder, and nickel-coated molybdenum disulfide powder are used respectively; the nano-sized Al2O3 ceramic powder is dried in an electric heating drying oven before weighing for 2 hours.

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