Refrigerator compressor crankshaft and machining process thereof

Abstract

The invention relates to the technical field of compressor crankshafts, in particular to a refrigerator compressor crankshaft and a machining process thereof.The machining process comprises the following steps that impact parameters changing in a staged mode are set through a control unit, and the to-be-machined surface of the crankshaft is treated to form a nanocrystalline layer; secondly, setting atmosphere and electrical parameters which change in a stepped mode through a control unit, and processing the crankshaft processed in the first step so as to form a gradient permeation layer; and step-type changing electrical parameters are set through a control unit, the crankshaft treated in the second step is treated so as to grow a hydrogen-free amorphous carbon layer, the problems that due to internal stress, the coating binding force is poor, the uniformity of the coating on the complex morphology is poor, the coating performance is limited, and the process control precision is not high can be solved, and the application range of the hydrogen-free amorphous carbon layer is widened. Therefore, the comprehensive performance and service life of the crankshaft are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of compressor crankshafts, and more particularly to a refrigerator compressor crankshaft and a processing technology thereof. Background Art

[0002] The compressor is a core component of refrigerators and other refrigeration equipment. Its core moving component, the crankshaft, is subjected to high-frequency cyclic stress, intense friction with bearings and other components, and chemical corrosion from refrigerants, lubricants, and their decomposition products. Therefore, strengthening the crankshaft surface to improve its hardness, wear resistance, fatigue resistance, and chemical stability is a key technology for extending the life and reliability of the compressor.

[0003] Currently, the industry generally uses a method of applying a hard coating to the surface of a crankshaft to improve its performance. Publication No. CN102628154B discloses a method for preparing a wear-resistant compressor crankshaft. This method first plasma nitrides the crankshaft substrate to increase the base hardness. Then, in a vacuum environment, physical vapor deposition (PVD) is used to deposit a layer of metallic chromium (Cr) as a transition layer, followed by a layer of chromium-rich mixed carbon and nitrogen (CrCN) as a gradient layer. Finally, a diamond-like carbon (DLC) coating is deposited on the outermost layer as a wear-resistant layer.

[0004] Due to the huge differences in physical properties such as thermal expansion coefficient and elastic modulus between the steel substrate, metal transition layer and the top hard DLC coating, the coating will accumulate extremely high internal stress during the preparation and cooling process. Although transition layers and gradient layers are used to alleviate this stress, this stress problem is difficult to eradicate. It is the main reason for the coating to crack or even large-scale peeling under complex working conditions (such as vibration, hot and cold shock), seriously affecting the reliability of the product.

[0005] For parts like crankshafts with complex geometries like journals, oil grooves, chamfers, and steps, coating thickness in recesses and corners is often much thinner than on straight surfaces, and may even cause coating non-coating. These areas are precisely where stress concentration and wear occur. Uneven coating thickness can become the "weak link" of the entire protective system, leading to premature failure.

[0006] DLC coatings, produced using acetylene as a carbon source, have limited thermal stability (typically below 350°C) and can degrade under extreme operating conditions with locally elevated temperatures. Furthermore, their relatively weak chemical inertness hinders their long-term corrosion resistance in environments containing refrigerants and lubricants containing moisture and acidic substances. Furthermore, this process makes it difficult to produce thicker coatings (e.g., exceeding 5μm), limiting their wear margin and service life.

[0007] Therefore, there is an urgent need in this field to develop a new crankshaft surface processing technology that can fundamentally solve the internal stress problem, achieve uniform coverage of complex morphologies, and obtain a surface functional layer with better performance. Summary of the Invention

[0008] To this end, the purpose of the present invention is to provide a refrigerator compressor crankshaft and its processing technology, which can solve the problems of poor coating adhesion caused by internal stress, poor coating uniformity on complex morphology, limited coating performance and low process control accuracy, thereby improving the comprehensive performance and service life of the crankshaft.

[0009] To achieve the above object, the present invention provides the following technical solutions:

[0010] A processing technology for a refrigerator compressor crankshaft comprises the following steps:

[0011] S1. The control unit sets the impact parameters in a staged manner to process the surface of the crankshaft to be processed to form a nanocrystalline layer;

[0012] S2 is set by the control unit in a step-by-step change of the atmosphere and electrical parameters, the crankshaft processed in step S1 is processed to form a gradient infiltration layer;

[0013] S3. The control unit sets electrical parameters in a stepwise manner to process the crankshaft processed in step S2 to grow a hydrogen-free amorphous carbon layer.

[0014] The present invention is further configured as follows: Step S1 includes the following steps:

[0015] S11. Initial impact phase: The impact head is driven to impact the surface to be machined at a first frequency range of 20 kHz to 30 kHz for 15 to 20 minutes.

[0016] S12. Interval stage: Stop impacting and let the crankshaft rest for 1 to 3 minutes;

[0017] S13. Refined impact stage: Drive the impact head to impact the surface to be processed at a second frequency range of 30kHz~50kHz, lasting for 10~15 minutes.

[0018] The present invention is further configured as follows: during the execution of steps S11 and S13, the acoustic emission signal generated by the impact is monitored in real time by an acoustic emission sensor; if the amplitude or energy of the signal deviates from the reference value by more than 10%, the control unit adjusts the static load applied by the impact head until the deviation is less than 10%.

[0019] The present invention is further configured as follows: Step S2 includes the following steps:

[0020] S21. Ion cleaning stage: The crankshaft is placed in a vacuum chamber at a vacuum level of 0.1-1 Pa. Argon gas is introduced at a flow rate of 50-100 sccm. A first pulsed electric field with a bias voltage of -600V to -400V is applied to energize the argon plasma. Ion bombardment cleaning of the crankshaft surface is performed for 5-10 minutes.

[0021] S22. Concentration and penetration stage: In a vacuum chamber at a temperature of 400-580°C, nitrogen and methane are introduced as a first reaction gas in a ratio of 1:1 to 3:1. A second pulsed electric field with a bias voltage of -400V to -200V and a duty cycle of 30% to 60% is applied to rapidly form a high-concentration penetration zone on the crankshaft surface.

[0022] S23. Gradient diffusion stage: The reaction gas is adjusted to a second ratio, wherein the flow ratio of nitrogen to methane is 5:1 to 10:1, and a third pulsed electric field with a bias voltage of -200V to -50V is applied to allow the elements in the high-concentration penetration zone to diffuse into the interior of the substrate, forming a gradient penetration layer.

[0023] The present invention is further configured as follows: during the execution of step S22, the spectral line intensity of specific nitrogen ions in the plasma is monitored by a plasma emission spectrometer. When the spectral line intensity reaches a preset concentration threshold, the control unit automatically switches from step S22 to step S23. The concentration threshold is 5 to 10 times the background spectral line intensity in the initial cleaning stage.

[0024] The present invention is further configured as follows: Step S3 includes the following steps:

[0025] S31. Immersing the crankshaft as a cathode in the electrolyte and applying a first series of high-voltage electric pulses with a peak voltage of 2000V to 5000V and a pulse width of 1 to 5 μs to grow a high-adhesion carbon-based nucleation layer with a thickness of 50-200 nm on the surface of the carburized layer;

[0026] S32. After step S31, applying a second series of high-voltage electric pulses with a peak voltage of 500V to 2000V and a pulse width of 10 to 50 μs to grow a main portion of the hydrogen-free amorphous carbon layer on the nucleation layer.

[0027] The present invention is further configured as follows: after step S32, a third series of high-voltage electric pulses with a pulse width of 0.5~2μs, which is smaller than the second series of high-voltage electric pulses, is applied to ion bombard the outermost surface of the hydrogen-free amorphous carbon layer and increase its density.

[0028] The present invention is further configured as follows: during the execution of step S32, a real-time value of the bond ratio of the hydrogen-free amorphous carbon layer is periodically obtained through an in-situ Raman spectroscopy monitoring module; if the real-time value is lower than a first quality threshold of 70%, the control unit increases the peak voltage of the second series of high-voltage electric pulses or reduces its pulse width.

[0029] A refrigerator compressor crankshaft has a composite functional layer on its surface, the composite functional layer comprising, from the inside to the outside, the following:

[0030] a nanocrystallized layer having an average grain size of less than 100 nm;

[0031] a gradient diffusion layer having no interface with the nanocrystallized layer and a thickness of 5 to 20 μm; and

[0032] A hydrogen-free amorphous carbon layer consisting of a nucleation layer, a main body and a densified outer layer with a total thickness of 8 to 30 μm.

[0033] The present invention is further configured as follows: the hydrogen-free amorphous carbon layer in the composite functional layer is a multilayer structure comprising:

[0034] A carbon-based nucleation layer with a thickness of 50 to 200 nm, which is in direct contact with the gradient diffusion layer; and a hydrogen-free amorphous carbon main layer covering the carbon-based nucleation layer and having an outermost surface density higher than that of the inner layer.

[0035] Compared with the shortcomings of the prior art, the beneficial effects of the present invention are:

[0036] Through impact nanostructuring and gradient infiltration, a deeply fused rooted layer is formed on the substrate surface, free of physical interfaces. Liquid-phase electrochemical methods then enable low-temperature, flexible atomic assembly growth, generating virtually no internal stress. This deep fusion and stress-free growth model allows the composite functional layer to seamlessly integrate with the substrate, completely eliminating the risk of failure caused by internal stress.

[0037] Liquid-phase electrochemical growth produces a hydrogen-free amorphous carbon (ta-C) layer with a higher bond content. Its superior hardness, thermal stability, and chemical inertness make it better suited to the harsh operating conditions within the compressor. Furthermore, this process can easily produce a wear-resistant layer far thicker than existing technologies (up to 30μm), providing a significant wear margin and significantly extending the crankshaft's service life. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 Flowchart of the present invention. DETAILED DESCRIPTION

[0039] Reference Figure 1 The examples are further described.

[0040] 40Cr steel was used as the crankshaft substrate, and its surface was treated to prepare a refrigerator compressor crankshaft with a composite functional layer.

[0041] Step 1: The control unit sets impact parameters that change in stages to process the surface to be processed of the crankshaft to form a nano-crystallized layer.

[0042] The purpose of this step is to crush and refine the coarse surface grains to the nanometer scale (average grain size less than 100 nm) through intense localized plastic deformation, without altering the chemical composition of the crankshaft matrix. This step utilizes high-frequency impact processing equipment, the core component of which is an impact system. This system includes a piezoelectric or magnetostrictive transducer that converts high-frequency electrical signals into mechanical vibrations of the same frequency. This vibration is amplified by a horn and then drives an impact head made of cemented carbide (such as YG8). The crankshaft is clamped on a CNC lathe or a specialized fixture, enabling precise rotation and axial feed. A control unit controls the impact head to press against the crankshaft surface to be machined with a specific static load (e.g., 50-200N) and activates the transducer. The impact head impacts the crankshaft surface at a high speed of tens of thousands of times per second, inducing intense plastic deformation in the surface metal.

[0043] The impact head is driven to impact the surface to be machined at a first frequency range of 20kHz to 30kHz for 15 to 20 minutes. After this, the impact is stopped and the crankshaft is allowed to rest for 1 to 3 minutes. This high-frequency impact process generates a large amount of heat and accumulates internal stress. The brief rest period helps dissipate surface temperature and rearrange and eliminate dislocations, facilitating more effective grain refinement in the next stage and preventing surface microcracks caused by overheating and overstress.

[0044] After the crankshaft has been stationary for 1 to 3 minutes, the impact head is driven to impact the surface to be machined at a second frequency range of 30kHz to 50kHz for 10 to 15 minutes. The purpose of this stage is to further transform dislocation cells and subgrain boundaries into large-angle grain boundaries on the basis of the initial impact formation, ultimately forming equiaxed nanograins, and performing a certain degree of "polishing" on the surface to reduce surface roughness.

[0045] While the impact head is driving the crankshaft, an acoustic emission sensor (AE) monitors the acoustic emission (AE) signal generated by the impact in real time. This sensor (such as a piezoelectric ceramic sensor) is placed in close contact with the crankshaft fixture or non-processing area to capture elastic waves generated within the material due to plastic deformation, microcrack initiation, and other factors. The amplitude or energy of the AE signal is directly related to the degree of plastic deformation during the impact process. A stable and uniform nano-processing process should correspond to a smooth AE signal. Sudden increases or decreases in the signal indicate unstable impact energy transfer, which may lead to uneven processing quality or surface damage.

[0046] Step 2: The crankshaft treated in step 1 is processed by setting the atmosphere and electrical parameters in a step-by-step manner through the control unit. The purpose of this step is to form a diffusion layer with a gradient distribution of composition, structure and performance through plasma nitriding and carbonization co-diffusion on the basis of the nanocrystallization layer. The diffusion layer is metallurgically bonded to the substrate without an obvious interface, which can effectively buffer the difference in modulus and thermal expansion coefficient between the subsequent hard coating and the substrate, greatly improving the bonding strength. This step is carried out in a multifunctional plasma surface strengthening device. The main body of the device is a vacuum chamber with a built-in workpiece table that can serve as a cathode, on which the crankshaft is placed. The vacuum system, multi-channel gas mass flow controller (MFC), high-power pulsed DC power supply and a set of plasma emission spectrometer (OES) are the key components of the system.

[0047] Ion cleaning: The crankshaft is placed in a vacuum chamber with a vacuum of 0.1-1 Pa. Argon (Ar) is introduced at a flow rate of 50-100 sccm. A first pulsed electric field with a bias voltage of -600V to -400V is applied to ignite an Ar plasma. Ion bombardment cleans the crankshaft surface for 5-10 minutes. High-energy argon ions (Ar+) bombard the crankshaft surface, removing residual oil, oxides, and adsorbed gas molecules through a physical sputtering effect, exposing a fresh, clean metal surface and creating ideal conditions for subsequent element infiltration. The nanocrystallized surface is more active, making it more conducive to cleaning and subsequent infiltration.

[0048] Enrichment and Permeation Stage: In a vacuum chamber, the temperature is maintained at 400-580°C. Nitrogen (N2) and methane (CH4) are introduced as the first reaction gas mixture, and a second pulsed electric field is applied with a bias voltage of -400V to -200V and a duty cycle of 30% to 60%. This stage is known as the "rapid enrichment" phase. The high methane ratio and moderate electric field intensity cause a large number of active nitrogen and carbon particles to deposit on the crankshaft surface and permeate inward, rapidly forming a highly concentrated nitrogen and carbon compound zone. The presence of nanograin boundaries provides rapid diffusion pathways, resulting in a permeation rate far exceeding that of ordinary grain materials.

[0049] Gradient Diffusion Stage: The reaction gas ratio is adjusted to the second ratio, and a third pulsed electric field with a bias voltage of -200V to -50V is applied. This stage, known as the "inward diffusion" phase, reduces the methane ratio, increases the nitrogen ratio, and significantly reduces the pulse bias voltage, weakening the surface glow discharge and sputtering effects, and shifting to thermal diffusion. This allows the nitrogen and carbon elements enriched in the surface layer during the enrichment and penetration stage ample time to diffuse into the substrate, forming a gradient layer with a smooth transition in concentration from the surface to the core, avoiding the formation of a brittle white layer and achieving an ideal penetration depth of 5 to 20μm.

[0050] During the enrichment and penetration stage, the specific nitrogen ions (such as N2 + The spectral line intensity at 391.4nm). In the plasma, the concentration of gas molecules is proportional to the emission intensity of their corresponding spectral lines. In the enrichment stage, as the surface reaction proceeds, the concentration of nitrogen ions consumed in the plasma will change. When the surface reaches a certain saturation, the consumption rate of nitrogen ions will slow down, resulting in N2 + The spectral line intensity rises back and tends to be stable, and this feature is used to accurately determine the end point of the enrichment stage.

[0051] The switching conditions of the control unit are: ;

[0052] in, , yes Real-time intensity of spectral lines, is the background nitrogen line intensity measured during the argon purge phase (usually from residual gas in the vacuum chamber), is the preset enrichment threshold coefficient (5~10).

[0053] Calibration: During the sub-cleaning phase, OES measures the vacuum chamber background Spectral line intensity It is 50 counting units.

[0054] Setting: Set the enrichment threshold coefficient = 8, the switching threshold is calculated = 400 count units.

[0055] After entering the enrichment and permeation stage, the control unit continuously monitors Spectral line intensity. Initially, the intensity may be low, but as the reaction proceeds, the intensity value changes.

[0056] Switch: When OES detects When the count reaches 401, the control unit determines that surface enrichment has reached the ideal state and automatically executes the program: the gas ratio and electrical parameters are switched to the set values ​​for the gradient diffusion stage. This intelligent control eliminates batch variations caused by manually set fixed time periods, ensuring that every crankshaft achieves the optimal enrichment effect, neither too much nor too little.

[0057] Step 3: The crankshaft treated in step S2 is treated by setting stepwise electrical parameters using a control unit to grow a hydrogen-free amorphous carbon layer. This step aims to deposit an extremely hard, low-friction, and chemically stable hydrogen-free amorphous carbon (ta-C) layer on top of the gradient carburized layer, serving as the final wear- and corrosion-resistant working layer. This step utilizes plasma electrochemical technology in an electrolyte. The crankshaft treated in step 2 serves as the cathode and is immersed in a specific organic electrolyte (such as glycerol or ethylene glycol). A stainless steel or graphite plate serves as the anode. A UHV, microsecond pulsed power supply is connected between the cathode and cathode. When a sufficiently high voltage pulse is applied, the electrolyte surrounding the crankshaft surface is ionized, forming a plasma sheath that envelops the workpiece. Hydrocarbons in the electrolyte are decomposed in the plasma, and carbon ions are accelerated by the high electric field and bombarded, depositing on the crankshaft surface, forming the hydrogen-free amorphous carbon layer.

[0058] Growth of the carbon-based nucleation layer: A first series of high-voltage electric pulses with a peak voltage of 2000V to 5000V and a pulse width of 1 to 5μs is applied. This stage is known as "injection nucleation." The extremely high peak voltage and short pulse width mean that the carbon ions possess very high energy. These high-energy ions are injected into the surface of the gradient diffusion layer and mix with the underlying elements, such as N, C, and Fe, to form a "pseudo-diffusion layer" or "carbon-based nucleation layer" approximately 50-200nm thick, with an atomically crisscross pattern. This layer is crucial for achieving ultra-high adhesion of the subsequent coating.

[0059] Main Body Growth: After the carbon-based nucleation layer grows, a second series of high-voltage pulses with a peak voltage of 500V to 2000V and a pulse width of 10 to 50μs is applied. This stage is called "deposition-based growth." Reducing the peak voltage and increasing the pulse width reduces the ion energy, allowing the deposition rate to exceed the implantation / etching rate, resulting in the rapid growth of the main body of the ta-C layer on the nucleation layer. This layer is primarily composed of a high proportion of sp³ hybridized bonds, which contributes to its high hardness.

[0060] During the growth of the main body, the Raman spectrum of the hydrogen-free amorphous carbon layer is periodically (eg, every minute) acquired through an in-situ Raman spectroscopy monitoring module integrated with an optical fiber probe.

[0061] Raman spectroscopy is a powerful tool for analyzing the bonding structure of carbon materials.

[0062] Surface densification: A third series of high-voltage pulses with a pulse width of 0.5-2μs and a peak voltage lower than that of the second series (e.g., 300V-800V) is applied. This final "ion beam polishing" step uses short-duration, low-voltage pulses to gently bombard the outermost layer of the grown ta-C layer with ions. This treatment effectively closes micropores that may have formed during the growth process and knocks off energetically unstable surface atoms, thereby increasing the density and smoothness of the outermost layer, further enhancing its ability to serve as a corrosion barrier.

[0063] The refrigerator compressor crankshaft obtained by the above process has a composite functional layer on its surface. The composite functional layer specifically includes the following:

[0064] Nanocrystallized layer: This is not a coating, but rather a microstructural change in the crankshaft substrate itself. The average grain size is less than 100nm, resulting in a dramatic increase in the number of grain boundaries, significantly hindering dislocation movement. This significantly increases the crankshaft surface hardness and yield strength. Crucially, it significantly improves the material's fatigue limit, effectively suppressing fatigue crack initiation in stress-concentrated areas (such as journal fillets).

[0065] Gradient diffusion layer: The metallurgical bond between it and the underlying nanocrystallized layer is formed by diffusion, with no physical interface. Therefore, the bonding force is the interatomic force, making it extremely strong. Its thickness ranges from 5 to 20 μm, and its hardness smoothly transitions from approximately 800 HV near the surface to approximately 350 HV at the substrate. This gradient property resolves the mechanical mismatch between the subsequent ultrahard coating and the relatively soft substrate. When the crankshaft is subjected to impact loads, the stress is effectively dispersed and absorbed by this gradient layer, avoiding stress concentration at the interface between the hard coating and the substrate, thereby preventing coating spalling.

[0066] Hydrogen-free amorphous carbon layer (ta-C layer): This layer is connected to the underlying gradient layer via a 50-200nm thick carbon-based nucleation layer. This extremely thin nucleation layer is a hybrid layer formed by high-energy carbon ion implantation. It effectively "pins" the ta-C layer to the gradient layer at the atomic scale, providing unparalleled adhesion.

[0067] Main layer: Overlying the nucleation layer, it forms the bulk of the ta-C layer and can be 8 to 30 μm thick. Its sp³ bonding structure, which accounts for over 70% of the total layer, imparts near-diamond-like hardness and provides excellent resistance to abrasive and adhesive wear. Furthermore, its dense amorphous structure and chemical inertness make it an excellent corrosion barrier, effectively protecting against refrigerant and lubricant decomposition products.

[0068] Densified Outer Layer: The outermost surface of the main body layer undergoes a final ion bombardment treatment, resulting in a higher density and smoothness than the inner layer. It serves as the first line of defense against external corrosive media, and its extremely low surface energy also imparts excellent hydrophobicity, oleophobicity, and anti-adhesion properties.

[0069] When the crankshaft rotates at high speeds within the compressor and is subjected to alternating loads, the outermost ta-C layer, with its low coefficient of friction, reduces frictional power loss and wear, while its high hardness resists scratches from abrasive particles. External loads are smoothly transferred through the ta-C layer to the gradient carburized layer. The gradient carburized layer, with its gradually varying mechanical properties, disperses concentrated stresses and transfers them to the tough nanocrystallized matrix. The nanocrystallized matrix, with its high fatigue strength, withstands cyclic loads and inhibits crack initiation and propagation.

[0070] In order to verify the technical solution of the present invention, the following three embodiments and three comparative examples are set up.

[0071] Crankshaft body: 42CrMo steel bar with a diameter of 20 mm, quenched and tempered, hardness 320 HV.

[0072] Processing equipment: high-frequency impact equipment, plasma nitriding furnace and electrolyte plasma deposition equipment using the integrated feedback control system described above.

[0073] Electrolyte: 99.7% pure glycerol.

[0074] Example 1:

[0075] S1: S11(20kHz, 20min) -> S12(3min) -> S13(30kHz, 15min).

[0076] S2: S21 (Ar:100sccm, -600V, 10min) -> S22 (N2:CH4=1:1, -400V, 30% duty cycle, 400℃, OES feedback) -> S23 (N2:CH4=5:1, -200V).

[0077] S3: S31(2000V, 5μs) -> S32(500V, 50μs, Raman feedback) -> S33(300V, 2μs).

[0078] Example 2 (preferred parameters)

[0079] S1: S11(25kHz, 17min) -> S12(2min) -> S13(40kHz, 12min).

[0080] S2: S21 (Ar:80 sccm, -500 V, 8 min) -> S22 (N2:CH4=2:1, -300 V, 45% duty cycle, 500°C, OES feedback) -> S23 (N2:CH4=7.5:1, -125 V).

[0081] S3: S31(3500V, 3μs) -> S32(1250V, 30μs, Raman feedback) -> S33(500V, 1μs).

[0082] Example 3

[0083] S1: S11(30kHz, 15min) -> S12(1min) -> S13(50kHz, 10min).

[0084] S2: S21 (Ar:50 sccm, -400 V, 5 min) -> S22 (N2:CH4=3:1, -200 V, 60% duty cycle, 580°C, OES feedback) -> S23 (N2:CH4=10:1, -50 V).

[0085] S3: S31(5000V, 1μs) -> S32(2000V, 10μs, Raman feedback) -> S33(800V, 0.5μs).

[0086] Comparative Example 1

[0087] The traditional crankshaft processing technology is adopted: 42CrMo steel is subjected to overall quenching + high temperature tempering treatment.

[0088] Comparative Example 2

[0089] Omit step S1: directly perform the same S2 (gradient carburizing layer) and S3 (ta-C layer) treatments as in Example 2 on the crankshaft in the quenched and tempered state.

[0090] Comparative Example 3

[0091] Omit step S3: After the same S1 (nano-forming) and S2 (gradient diffusion layer) treatments as in Example 2, no ta-C layer deposition is performed.

[0092] Performance testing methods

[0093] Microhardness: Use HV-1000 microhardness tester to measure the hardness gradient distribution by punching points along the cross section from the surface toward the center at a spacing of 20 μm, with a load of 100 g and a holding time of 15 s.

[0094] Membrane-substrate bonding strength: The critical load Lc value was determined by using an MFT-4000 scratch tester with a diamond indenter radius of 200 μm, a loading rate of 100 N / min, and a final load of 100 N. The acoustic emission signal and microscopic observation were used to determine the critical load Lc value.

[0095] Friction and wear properties: Tests were conducted using an HSR-2M reciprocating friction and wear tester with GCr15 steel balls (Ø6 mm) at a load of 10 N, a frequency of 5 Hz, a stroke of 5 mm, and a time of 30 minutes in PAG lubricant containing 3% water. The cross-sectional area of ​​the wear scar was measured using a profilometer to calculate the wear rate.

[0096] Fatigue life: Rotary bending fatigue tests were conducted using a Zwick / Roell Amsler HFP 5100 high-frequency fatigue testing machine with a stress ratio of R = -1 and a frequency of 100 Hz to measure the cycle life under a stress of 800 MPa.

[0097]

[0098] The various performance indicators of Examples 1, 2, and 3, especially the wear resistance and fatigue life, are all superior to those of the traditional quenching process (Comparative Example 1), which proves the great advantages of the composite coating technology of the present invention.

[0099] Comparing Example 2 and Comparative Example 2, while both have similar surface hardness and friction coefficients, the film-substrate bonding strength of Comparative Example 2 (without the nanocrystallized layer) is significantly lower (98N vs. 65N), and the fatigue life is significantly different. This fully demonstrates the indispensable role of the nanocrystallized layer formed in step S1 as a "strong foundation" for improving bonding strength and fatigue resistance.

[0100] Comparing Example 2 and Comparative Example 3, while Comparative Example 3 (without a ta-C layer) boasts superior hardness and fatigue life compared to conventional processes due to nano-scaling and gradient diffusion, its wear resistance is significantly inferior to that of Example 2, which incorporates the ta-C "armor." This demonstrates the critical role of the S3 step in achieving both extremely low friction and high wear resistance.

[0101] Comparison between Examples: Examples 1, 2, and 3 all demonstrated excellent performance. The intermediate parameter combination employed in Example 2 achieved the best overall results in terms of film-substrate adhesion, friction and wear performance, and fatigue life. The parameter combination of Example 1 resulted in a slightly thinner coating, while the parameter combination of Example 3 may have resulted in slightly greater internal stress, resulting in a slight decrease in adhesion. Therefore, the parameter combination of Example 2 is considered the optimal embodiment of the present invention.

[0102] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Common changes and substitutions made by those skilled in the art within the scope of the technical solution of the present invention should be included in the protection scope of the present invention.

Claims

1. A processing technology for a refrigerator compressor crankshaft, characterized in that: The steps include: S1. The control unit sets the impact parameters in a staged manner to process the surface of the crankshaft to be processed to form a nanocrystalline layer; S2 is set by the control unit in a step-by-step change of the atmosphere and electrical parameters, the crankshaft processed in step S1 is processed to form a gradient infiltration layer; S3. The control unit sets electrical parameters in a stepwise manner to process the crankshaft processed in step S2 to grow a hydrogen-free amorphous carbon layer.

2. The processing technology of a refrigerator compressor crankshaft according to claim 1, characterized in that: Step S1 includes the following steps: S11. Initial impact phase: The impact head is driven to impact the surface to be machined at a first frequency range of 20 kHz to 30 kHz for 15 to 20 minutes. S12. Interval stage: Stop impacting and let the crankshaft rest for 1 to 3 minutes; S13. Refined impact stage: Drive the impact head to impact the surface to be processed at a second frequency range of 30kHz~50kHz, lasting for 10~15 minutes.

3. The processing technology of a refrigerator compressor crankshaft according to claim 2, characterized in that: During the execution of steps S11 and S13, the acoustic emission signal generated by the impact is monitored in real time by an acoustic emission sensor. If the amplitude or energy of the signal deviates from the reference value by more than 10%, the control unit adjusts the static load applied by the impact head until the deviation is less than 10%.

4. The processing technology for a refrigerator compressor crankshaft according to claim 1, characterized in that: Step S2 includes the following steps: S21. Ion cleaning stage: The crankshaft is placed in a vacuum chamber at a vacuum level of 0.1-1 Pa. Argon gas is introduced at a flow rate of 50-100 sccm. A first pulsed electric field with a bias voltage of -600V to -400V is applied to energize the argon plasma. Ion bombardment cleaning of the crankshaft surface is performed for 5-10 minutes. S22. Concentration and penetration stage: In a vacuum chamber at a temperature of 400-580°C, nitrogen and methane are introduced as a first reaction gas in a ratio of 1:1 to 3:

1. A second pulsed electric field with a bias voltage of -400V to -200V and a duty cycle of 30% to 60% is applied to rapidly form a high-concentration penetration zone on the crankshaft surface. S23. Gradient diffusion stage: The reaction gas is adjusted to a second ratio, wherein the flow ratio of nitrogen to methane is 5:1 to 10:1, and a third pulsed electric field with a bias voltage of -200V to -50V is applied to allow the elements in the high-concentration penetration zone to diffuse into the interior of the substrate, forming a gradient penetration layer.

5. The processing technology for a refrigerator compressor crankshaft according to claim 4, characterized in that: During the execution of step S22, the spectral line intensity of specific nitrogen ions in the plasma is monitored by a plasma emission spectrometer. When the spectral line intensity reaches a preset concentration threshold, the control unit automatically switches from step S22 to step S23. The concentration threshold is 5 to 10 times the background spectral line intensity in the initial cleaning stage.

6. The processing technology for a refrigerator compressor crankshaft according to claim 1, characterized in that: Step S3 includes the following steps: S31. Immersing the crankshaft as a cathode in the electrolyte and applying a first series of high-voltage electric pulses with a peak voltage of 2000V to 5000V and a pulse width of 1 to 5 μs to grow a high-adhesion carbon-based nucleation layer with a thickness of 50-200 nm on the surface of the carburized layer; S32. After step S31, applying a second series of high-voltage electric pulses with a peak voltage of 500V to 2000V and a pulse width of 10 to 50 μs to grow a main portion of the hydrogen-free amorphous carbon layer on the nucleation layer.

7. The processing technology for a refrigerator compressor crankshaft according to claim 6, characterized in that: After step S32, a third series of high-voltage electric pulses with a pulse width of 0.5 to 2 μs, which is smaller than the second series of high-voltage electric pulses, is applied to bombard the outermost surface of the hydrogen-free amorphous carbon layer with ions and increase its density.

8. The processing technology for a refrigerator compressor crankshaft according to claim 7, characterized in that: During the execution of step S32, a real-time value of the bond ratio of the hydrogen-free amorphous carbon layer is periodically obtained through an in-situ Raman spectroscopy monitoring module. If the real-time value is lower than the first quality threshold of 70%, the control unit increases the peak voltage of the second series of high-voltage electric pulses or reduces its pulse width.

9. A refrigerator compressor crankshaft prepared by the processing method of a refrigerator compressor crankshaft according to any one of claims 1 to 8, characterized in that: Its surface has a composite functional layer, which includes from the inside to the outside: a nanocrystallized layer having an average grain size of less than 100 nm; a gradient diffusion layer having no interface with the nanocrystallized layer and a thickness of 5 to 20 μm; and A hydrogen-free amorphous carbon layer consisting of a nucleation layer, a main body and a densified outer layer with a total thickness of 8 to 30 μm.

10. The refrigerator compressor crankshaft according to claim 9, characterized in that: The hydrogen-free amorphous carbon layer in the composite functional layer is a multilayer structure comprising: A carbon-based nucleation layer with a thickness of 50 to 200 nm, which is in direct contact with the gradient diffusion layer; and a hydrogen-free amorphous carbon main layer covering the carbon-based nucleation layer and having an outermost surface density higher than that of the inner layer.

Images