A surface modification method for key friction pairs of internal combustion engines based on laser cladding and diamond-like carbon composite coating

Abstract

This invention relates to a method for surface modification of key friction pairs in internal combustion engines based on laser cladding and diamond-like carbon (DLC) composite coatings, belonging to the field of surface strengthening and remanufacturing technology for key internal combustion engine components. Two functional transition layers are sequentially prepared on the substrate of the key friction pair using laser cladding technology: first, a Ni60-Cu alloy layer is clad as a toughness buffer layer to alleviate thermal stress and improve the bonding strength with the substrate; then, a WC particle-reinforced Ni-based alloy layer is clad as a reinforcing support layer to provide a high-hardness substrate; after polishing the cladding layers, a DLC coating is prepared on the polished surface using cathodic arc deposition. This invention solves the problems of weak adhesion and easy peeling of DLC coatings on gray cast iron through a gradient material design and sequential process of toughness buffering, reinforcing support, and ultra-hard friction reduction. The prepared friction pair possesses high interfacial bonding strength, excellent fatigue resistance, and friction-reducing and wear-resistant properties, extending the service life of the friction pair under harsh operating conditions.

Description

Technical Field

[0001] This invention belongs to the field of surface strengthening and remanufacturing technology of key internal combustion engine components. It relates to a method for preparing a composite coating to improve the wear resistance and service life of key friction pairs in internal combustion engines. In particular, it is a method for modifying the surface of key friction pairs in internal combustion engines by preparing a gradient functional transition layer through laser cladding and combining it with physical vapor deposition (DLC). Background Technology

[0002] Key friction pairs in internal combustion engines (such as piston rings, piston skirts, cylinder liners, and camshafts) are core moving components that operate under harsh conditions of high temperature, high pressure, high speed, and variable lubrication. Their working surfaces are subjected to severe friction, wear, and corrosion. Friction loss accounts for more than half of the total mechanical losses in an internal combustion engine. Therefore, the surface properties of these key friction pairs directly determine the engine's efficiency, reliability, and service life.

[0003] Currently, gray cast iron is widely used in the manufacture of these critical friction pairs due to its excellent casting properties, thermal conductivity, cost-effectiveness, and good lubricant retention. However, its low hardness and insufficient wear resistance make it difficult to meet the demands of modern high-power-density, long-life engines. To improve its performance, surface modification methods are commonly used in industry. Traditional technologies mainly include electroplating hard chrome and thermal spraying molybdenum. Electroplated chrome layers have high hardness and good wear resistance, but they contain a network of microcracks that can become channels for corrosive media penetration, and the chrome plating process also poses environmental pollution problems. Thermally sprayed molybdenum layers have good resistance to molten wear at high temperatures, but their coefficient of friction is relatively high, and they are prone to oxidation failure in high-temperature, oxygen-rich environments.

[0004] In recent years, physical vapor deposition (PVD) coating technology, especially diamond-like carbon (DLC) coatings, has been considered an ideal choice for coating key friction pairs in next-generation high-performance internal combustion engines due to its extremely high hardness (>2000 HV), extremely low coefficient of friction (0.1-0.2), and excellent chemical inertness. However, directly applying DLC ​​coatings to gray cast iron substrates faces three fundamental technical bottlenecks: First, there's the issue of adhesion. Gray cast iron contains a large amount of flake graphite, resulting in microscopic porosity and defects on the substrate surface. DLC coatings struggle to form a strong bond with this heterogeneous, weakly bonded surface, and are highly susceptible to interfacial delamination under alternating stress.

[0005] Second, there is the issue of internal stress matching. DLC coatings typically contain significant compressive stress, while the coefficient of thermal expansion of gray cast iron differs significantly from that of DLC. Under the thermal cycling loads of an engine during operation, this thermal mismatch generates enormous interfacial shear stress, leading to coating peeling, bulging, and even large-area flaking, thus causing premature failure.

[0006] Third, the issue of substrate support. The gray cast iron substrate itself has low hardness and cannot provide effective rigid support for the ultra-hard DLC coating. Under heavy loads or impact loads, the coating is prone to crushing or premature failure due to plastic deformation of the substrate.

[0007] To improve adhesion, existing technologies typically employ the method of introducing a metal or nitride transition layer (such as Cr or CrN) before depositing DLC. However, the transition layer deposited by PVD methods still exhibits a physical or weak diffusion bond with the gray cast iron substrate, resulting in limited bonding strength. Furthermore, the thin-layer structure is insufficient to alleviate thermal stress mismatch, failing to fundamentally solve the aforementioned problems. On the other hand, while laser cladding technology can form a thick alloy layer with metallurgical bonding on the cast iron surface, significantly improving surface hardness and wear resistance, a single cladding layer often falls short of achieving the extremely low coefficient of friction and optimal anti-adhesive wear performance of DLC coatings.

[0008] Therefore, there is an urgent need to develop an innovative surface modification method to overcome the technical obstacles of weak adhesion and easy peeling when DLC coatings are applied to gray cast iron friction pairs, so as to fully utilize the super friction reduction and wear resistance potential of DLC coatings and significantly improve the comprehensive performance and service life of key friction pairs in internal combustion engines. Summary of the Invention

[0009] In view of this, the purpose of the present invention is to provide a method for surface modification of key friction pairs of internal combustion engines based on laser cladding and diamond-like carbon composite coating, and the key friction pairs of internal combustion engines obtained by surface modification by the method, so as to solve the problems of weak bonding force, internal stress mismatch and insufficient matrix support encountered when DLC is directly applied to the surface modification of key friction pairs of internal combustion engines.

[0010] To achieve the above objectives, the present invention provides a method for surface modification of key friction pairs in internal combustion engines based on laser cladding and diamond-like carbon composite coatings, comprising: Surface pretreatment is performed on key friction pair components; Preheat the key friction pair components, either as a whole or locally, after pretreatment. A laser cladding process is used to clad a first transition layer on the surface of a key friction pair component after preheating. The first transition layer is a mixture of Ni60 alloy powder and Cu powder. A second transition layer is clad onto the surface of the first transition layer using a laser cladding process; the second transition layer is a mixture of Ni60 alloy powder and WC powder. The surfaces of key friction pair components that have undergone laser cladding are ground and polished. The magnetic filter cathode arc deposition process is used to sequentially perform glow discharge cleaning, sputter cleaning, WC bonding layer deposition, and diamond-like carbon coating deposition on the surface of key friction pair components after grinding and polishing.

[0011] Furthermore, in the first transition layer, the mass fraction of Ni60 alloy powder is 95%, and the mass fraction of Cu powder is 5%; in the second transition layer, the mass fraction of Ni60 alloy powder is 90%, and the mass fraction of WC powder is 10%.

[0012] The first transition layer has a cladding thickness of 0.5~1 mm, and the second transition layer has a cladding thickness of 1.5 mm.

[0013] In the first transition layer, the particle size of Ni60 alloy powder is 30~50 μm, and the particle size of Cu powder is 30~50 μm; in the second transition layer, the particle size of WC powder is 10~30 μm.

[0014] Furthermore, the glow discharge cleaning is a Hall source glow discharge cleaning, the cleaning gas is argon, the bias voltage is -800 ~ -1200V, and the cleaning time is 10~30 min.

[0015] Furthermore, the thickness of the WC adhesive layer is 0.1~0.3 μm; the thickness of the diamond-like coating is 1~3 μm.

[0016] On the other hand, the present invention provides a key friction pair component for an internal combustion engine, which is obtained by surface modification using the method described in the first aspect.

[0017] Its structure includes: Key friction pair component substrate; The first transition layer is a mixture of Ni60 alloy powder and Cu powder bonded to the surface of the substrate of the key friction pair component by laser cladding. A second transition layer, consisting of a mixture of Ni60 alloy powder and WC powder, is laser cladding bonded to the surface of the first transition layer; and the second transition layer is formed by laser cladding. A composite coating is bonded to the surface of the two transition layers. The composite coating includes a WC adhesive layer and a diamond-like coating located on the surface of the WC adhesive layer.

[0018] In the first transition layer, the mass fraction of Ni60 alloy powder is 95%, and the mass fraction of Cu powder is 5%; the thickness of the first transition layer is 0.5~1 mm.

[0019] In the second transition layer, the mass fraction of Ni60 alloy powder is 90%, and the mass fraction of WC powder is 10%; the thickness of the second transition layer is 1.5 mm.

[0020] The thickness of the WC adhesive layer is 0.1~0.3 μm; the thickness of the diamond-like carbon coating is 1~3 μm.

[0021] The beneficial effects of this invention are as follows: (1) The interface bonding strength has achieved a qualitative leap: the two gradient transition layers formed by laser cladding and the substrate of the key friction pair components of the internal combustion engine are completely metallurgically bonded, which fundamentally eliminates the original loose surface and provides a dense, firm and chemically compatible "new substrate" for the DLC coating, thereby increasing the bonding strength of the DLC coating several times.

[0022] (2) Excellent stress matching and buffering capacity: The first transition layer (Ni60+Cu) has good plasticity and toughness, while the second transition layer (Ni60+WC) has high hardness and a moderate coefficient of thermal expansion. This "soft-hard" gradient design constitutes an efficient stress buffering system, which can significantly absorb and alleviate the interfacial stress caused by thermal mismatch between the DLC coating and the substrate of the key friction pair of the internal combustion engine, and can suppress the early peeling of the coating.

[0023] (3) Provides strong rigid support: The WC particles dispersed in the second transition layer make its hardness HRC as high as 60 or more, forming a hard "load-bearing skeleton", which effectively resists the plastic deformation of the substrate under heavy load conditions, prevents the crush failure of the DLC coating, and ensures the performance stability of the coating under harsh working conditions.

[0024] (4) Synergistic optimization of tribological properties: The bottom cladding transition layer provides excellent wear resistance and fatigue resistance, while the top DLC coating provides an extremely low coefficient of friction and excellent anti-adhesive wear capability. The synergy of the two enables the composite coating system to have both ultra-high wear resistance and ultra-low coefficient of friction, which can significantly extend the service life of key friction pairs of internal combustion engines.

[0025] (5) Controllable process and strong applicability: This invention combines laser cladding additive manufacturing with physical vapor deposition ultra-precision machining to form a complete and controllable surface modification process chain, which is applicable to high-performance remanufacturing and new product strengthening of various key friction pair components and has significant engineering application value.

[0026] Other advantages, objectives, and features of the invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination, or may be learned from practice of the invention. The objectives and other advantages of the invention can be realized and obtained through the following description. Attached Figure Description

[0027] To make the objectives, technical solutions, and advantages of the present invention clearer, the preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings, wherein: Figure 1 This is a schematic diagram of the composite coating structure; Figure 2 This is a process flow diagram for piston ring surface modification. Figure 3 This is a schematic diagram of the laser cladding process; Figure 4 This is a schematic diagram of a magnetically filtered cathode arc deposition device. Figure 5 This is a schematic diagram of a scratch test.

[0028] Figure reference numerals: 1-1, Piston ring; 1-2, Ni60+Cu composite layer; 1-3, Ni60+WC composite layer; 1-4, WC layer; 1-5, DLC layer.

[0029] 3-1 Laser beam; 3-2 Protective gas; 3-3 Powder feeder; 3-4 Coaxial powder feeding tube; 3-5 Powder flow; 3-6 Molten pool; 3-7 Solidified cladding layer; 3-8 Substrate; 3-9 Scanning direction.

[0030] 4-1 Vacuum chamber; 4-2 Sample stage; 4-3 Plasma path; 4-4 Cooling water system; 4-5 Cathode target; 4-6 Magnetic filter bend.

[0031] 5-1. Coating; 5-2. Scratches; 5-3. Scratching needles; 5-4. Loading direction; 5-5. Scratching direction. Detailed Implementation

[0032] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of the present invention. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0033] The accompanying drawings are for illustrative purposes only and are schematic diagrams, not actual pictures. They should not be construed as limiting the invention. To better illustrate the embodiments of the invention, some parts in the drawings may be omitted, enlarged, or reduced, and do not represent the actual product dimensions. It is understandable to those skilled in the art that some well-known structures and their descriptions may be omitted in the drawings.

[0034] In the accompanying drawings of the embodiments of the present invention, the same or similar reference numerals correspond to the same or similar components. In the description of the present invention, it should be understood that if terms such as "upper," "lower," "left," "right," "front," and "rear" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, they are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, the terms used to describe positional relationships in the drawings are only for illustrative purposes and should not be construed as limiting the present invention. For those skilled in the art, the specific meaning of the above terms can be understood according to the specific circumstances.

[0035] Example 1 This embodiment uses a gray cast iron (HT250) piston ring of a certain type of marine high-performance diesel engine as an example, and applies the method of the present invention for surface modification, as described below: 1. Substrate preparation Component: Gray cast iron piston ring, with the outer working surface requiring reinforcement. While the piston ring base can also be made of steel, gray cast iron is prone to cracking. Therefore, this embodiment uses a gray cast iron piston ring as an example to demonstrate that the method proposed in this invention can eliminate the effects of cracking and achieve multi-faceted reinforcement of the piston ring.

[0036] Preprocessing: Ultrasonic cleaning with alkaline solution for 15 minutes to remove oil; The surface is sandblasted with 80-mesh brown fused alumina until it presents a uniform silver-gray color. Ultrasonic cleaning with anhydrous ethanol for 10 minutes, followed by drying with nitrogen.

[0037] 2. Laser cladding of gradient functional transition layers Equipment: It adopts a 3 kW semiconductor fiber laser, equipped with a coaxial powder feeding system and a high-precision CNC rotary table.

[0038] Powder materials: First layer (toughness layer): 95% Ni60 powder + 5% electrolytic Cu powder, with a powder particle size of 30-50 μm, vacuum dried at 120℃ for 2 hours, and then three-dimensionally mixed for 4 hours.

[0039] The second layer (reinforcing layer) consists of 90% Ni60 powder and 10% spherical WC powder with a particle size of 10-30 μm. After vacuum drying at 120℃ for 2 hours, the powder is three-dimensionally mixed for 4 hours.

[0040] Process: Preheating: Place the piston rings in a heating furnace and preheat to 250±10℃, then keep warm.

[0041] First cladding layer: The preheated piston ring is fixed on a CNC rotary table. Laser power is 1.8 kW, spot diameter is 3.0 mm, scanning speed (i.e., rotary table linear speed) is 10 mm / s, powder feeding rate (toughness layer powder) is 12 g / min, and argon protection is used. A single layer with a thickness of approximately 0.5 mm is clad on the outer surface of the piston ring.

[0042] Second cladding: Without changing the clamping, replace the powder feeder with reinforcing layer powder. Increase the laser power to 2.2 kW, and fine-tune other parameters (scanning speed 8 mm / s, powder feeding rate 18 g / min). Perform multi-pass overlapping cladding with an overlap of 1.8 mm. Control the total cladding layer thickness to 2.0 mm. Slowly cool with the furnace after cladding.

[0043] Post-processing: The cladding layer was precision ground using a CNC cylindrical grinding machine, followed by polishing with diamond polishing paste, resulting in a final surface roughness Ra of 0.4 μm.

[0044] 3. DLC coating deposition Equipment: Magnetic filter cathode arc deposition equipment is used.

[0045] Process: Furnace loading and cleaning: Install the piston rings into the fixture and evacuate to a base vacuum better than 5.0 × 10⁻⁶. - ³ Pa.

[0046] Glow discharge cleaning: Argon gas is introduced into the vacuum chamber to 0.5 Pa, the Hall source is turned on, and a -1000 V pulse bias voltage is applied to perform glow discharge cleaning on the workpiece for 30 minutes to remove surface adsorbed gases and trace contaminants.

[0047] Interface optimization and DLC deposition: a. Sputter cleaning and WC binder layer: Adjust the argon pressure to 0.15 Pa, use WC target material, perform short-time sputter cleaning at -150 V bias, and then deposit a dense WC binder layer of about 0.2 μm thickness.

[0048] b. Deposition of DLC coating: Acetylene gas was introduced, and the flow ratio of acetylene gas to argon gas was adjusted. Under a bias voltage of -80 V, hydrogenated DLC (aC:H) was deposited using a carbon target arc for 120 minutes to obtain a DLC coating with a thickness of about 2.5 μm.

[0049] 4. Effect Verification The prepared composite-coated piston rings were tested: Adhesion: Scratch test critical load (Lc) > 60 N, far exceeding that of coatings directly deposited on gray cast iron.

[0050] Surface properties: The hardness of the cladding layer is HRC 63, and the hardness of the DLC coating is >25GPa. Friction and wear tests (ball-disc type, GCr15 balls) show that the average coefficient of friction is stable at 0.13, and the wear rate is reduced by about 65% compared with the original chrome-plated ring.

[0051] Example 2 This embodiment focuses on the gray cast iron (HT300) cylinder liner of a large excavator engine, and strengthens its inner working surface using the method of this invention.

[0052] 1. Substrate preparation Part: Gray cast iron cylinder liner, inner diameter 120 mm.

[0053] Pretreatment: The process is the same as in Example 1, with the focus on ensuring the uniformity of the inner wall cleaning and sandblasting.

[0054] 2. Laser cladding of gradient functional transition layers Equipment: It adopts a 3 kW disk laser, equipped with a special side powder feeding head for internal holes and a precision CNC machine tool (with spindle rotation and Z-axis linkage function).

[0055] Powder material: Same as in Example 1.

[0056] Process flow (key aspect is the internal cladding strategy): Preheating: A ring-shaped induction heating coil is used to locally preheat the cylinder liner, so that the inner wall temperature is maintained at 280±15℃.

[0057] Cladding path: The cylinder liner is horizontally clamped onto the machine tool spindle. The laser head extends into the inner hole. The program makes the spindle (cylinder liner) rotate at a constant speed, while the laser head moves slowly along the axis to form a spiral cladding path.

[0058] First cladding layer: Laser power 2.0 kW, defocusing amount +10 mm (spot diameter about 4 mm), spindle speed corresponding to scanning linear speed 8 mm / s, powder feeding rate 10 g / min, single-layer spiral cladding, thickness about 0.8 mm.

[0059] Second cladding: Adjust the process parameters (laser power 2.5 kW, linear speed 6 mm / s, powder feeding rate 20 g / min) to perform the second spiral cladding, with an overlap rate of 50%, and the final total thickness of the inner wall cladding layer is 1.6 mm.

[0060] Post-processing: The inner wall of the cylinder liner is precision honed using a special honing machine to achieve Ra 0.4 μm and form a cross-hatching pattern that is conducive to oil storage.

[0061] 3. DLC coating deposition Equipment and process: The basic process is the same as in Example 1. For the inner wall of the cylinder liner, special tooling is required to ensure that it rotates at a uniform speed in the vacuum chamber to ensure the uniformity of coating deposition.

[0062] Parameter Adjustment: To achieve better lubricity, hydrogen-containing DLC ​​(aC:H) was deposited in this embodiment. This was achieved by reducing the acetylene partial pressure and increasing the arc current. The final DLC coating thickness was 2.0 μm.

[0063] 4. Effect Verification Bonding strength: Tested with a dedicated internal hole scratch tester, Lc value > 65 N.

[0064] Compatibility: Cylinder liner-piston ring pair test results show that the friction torque is reduced by about 40% compared to traditional chrome-plated cylinder liners, and the initial break-in time is shortened by about 60%.

[0065] Wear resistance: Wear tests simulating harsh working conditions show that the wear on the inner wall is negligible, and the main wear occurs on the piston rings that are rubbing against each other, thus achieving the design goal of "protecting the core body".

[0066] In summary, the composite surface modification method provided by this invention solves the problem of bonding high-performance coatings with gray cast iron substrates through a synergistic process of "laser cladding gradient functional layer + ultra-precision surface processing + DLC deposition". This method is not only applicable to small rotating parts such as piston rings, but also, by adjusting the tooling and scanning strategy, fully applicable to internal bore parts such as cylinder liners, and even complex curved surface components such as camshaft tips and tappet end faces. It exhibits strong process adaptability and significant effects, providing an effective solution for comprehensively improving the lifespan and reliability of key friction pairs in internal combustion engine power systems.

[0067] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for surface modification of key friction pairs of internal combustion engines based on laser cladding and diamond-like carbon composite coating, characterized by, The method includes: Surface pretreatment is performed on key friction pair components; Preheat the key friction pair components, either as a whole or locally, after pretreatment. A laser cladding process is used to clad a first transition layer on the surface of a key friction pair component after preheating. The first transition layer is a mixture of Ni60 alloy powder and Cu powder. A second transition layer is clad onto the surface of the first transition layer using a laser cladding process; the second transition layer is a mixture of Ni60 alloy powder and WC powder. The surfaces of key friction pair components that have undergone laser cladding are ground and polished. The magnetic filter cathode arc deposition process is used to sequentially perform glow discharge cleaning, sputter cleaning, WC bonding layer deposition, and diamond-like carbon coating deposition on the surface of key friction pair components after grinding and polishing.

2. The method according to claim 1, characterized in that, In the first transition layer, the mass fraction of Ni60 alloy powder is 95%, and the mass fraction of Cu powder is 5%. In the second transition layer, the mass fraction of Ni60 alloy powder is 90%, and the mass fraction of WC powder is 10%.

3. The method according to claim 1, characterized in that, The first transition layer has a cladding thickness of 0.5~1 mm, and the second transition layer has a cladding thickness of 1.5 mm.

4. The method according to claim 1, characterized in that, In the first transition layer, the particle size of Ni60 alloy powder is 30~50 μm, and the particle size of Cu powder is 30~50 μm; In the second transition layer, the particle size of WC powder is 10~30 μm.

5. The method according to claim 1, characterized in that, The glow discharge cleaning is a Hall source glow discharge cleaning, the cleaning gas is argon, the bias voltage is -800 ~ -1200 V, and the cleaning time is 10~30 min.

6. The method according to claim 1, characterized in that, The thickness of the WC adhesive layer is 0.1~0.3 μm; the thickness of the diamond-like coating is 1~3 μm.

7. A key friction pair component for an internal combustion engine, characterized in that, The key friction pair components of the internal combustion engine are obtained by surface modification using the method described in any one of claims 1 to 6.

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