Diamond-like carbon coating for axle differential part and preparation method of diamond-like carbon coating

Abstract

The invention relates to a diamond-like coating for an axle differential part and a preparation method of the diamond-like coating. The preparation method of the diamond-like coating comprises the following steps that the axle differential part is sequentially subjected to surface etching treatment, preliminary chromium deposition, chromium and tungsten carbide transition deposition, tungsten carbide deposition and diamond-like coating treatment; and the preparation of the diamond-like coating is realized. The prepared diamond-like coating has the characteristics of being high in binding force, good in toughness, good in wear resistance and long in service life, and the reliability, the service life and the safety of the axle differential mechanism can be improved.

Description

Technical Field

[0001] This invention relates to the field of coating preparation technology, specifically to a diamond-like carbon coating for axle differential components and its preparation method. Background Technology

[0002] The differential assembly in a vehicle's drive axle is a core component of the powertrain system. The differential cross shaft, as a key load-bearing and friction component, supports the planetary gears and transmits torque, operating in extremely harsh environments. Similarly, with the widespread adoption of new energy vehicles, the splined input shaft of the drive motor needs to transmit high instantaneous torque, resulting in very demanding operating conditions. Under extreme conditions such as slippage, high load, rapid acceleration, or deceleration, these components not only endure enormous alternating shear stress but also face severe friction and wear problems. This places high demands on the wear resistance, coefficient of friction, and anti-galling capabilities of the axle differential cross shaft and input shaft.

[0003] Currently, the traditional methods for improving the wear resistance of differential cross shafts, input shaft splines, and other parts are mainly surface phosphating or electroplating. For example, CN1202286A discloses a high-strength and high-toughness differential cross shaft processing technology, which involves the processing technology of automotive differential cross shafts. The steps are as follows: (1) cleaning the rust and dirt on the surface of the differential cross shaft; (2) carbonitriding; (3) oil cooling; (4) tempering; (5) precision grinding; (6) manganese phosphating; (7) electrostatic spraying and curing of the shaft diameter surface. Phosphating and electroplating can form a film layer on the surface, but they can only play a role in reducing friction in the initial stage. Once the lubricating oil film breaks or the lubrication conditions deteriorate, the lubrication capacity decreases, and the parts and accessories will produce abrasive wear, which will cause changes in the fit clearance and increase noise. Then, the two friction surfaces continue to wear, resulting in welding-separation and forming glue, which eventually leads to failures such as gear breakage.

[0004] Diamond-like carbon (DLC) coating is a type of coating made from sp... 2 and sp 3Amorphous carbon films composed of bonded composites possess the high hardness and wear resistance of diamond and the low coefficient of friction of graphite. Applying them to the surfaces of differential cross shafts, input shaft splines, and other components can fundamentally improve surface wear resistance and anti-galling capabilities, thereby resolving a series of failures caused by wear. For example, CN213776263U discloses a wear-resistant friction plate type limited-slip differential, including a differential housing, half-shaft gears, planetary gears, a planetary carrier, a planetary bearing, a friction plate assembly, and a disc spring. A carbon steel plate is disposed between the disc spring and the friction plate assembly. The outer edge of the carbon steel plate has an external protrusion that engages with the inner wall of the housing, causing the carbon steel plate to rotate synchronously with the housing. A diamond-like carbon coating is disposed on the side of the carbon steel plate that contacts the disc spring. However, directly applying diamond-like carbon (DLC) coatings to such high-stress, high-impact automotive core components still presents problems such as insufficient adhesion between the DLC coating and the substrate, the tendency for microcracks to form when the DLC coating is thick, and insufficient load-bearing capacity of a single DLC coating.

[0005] Therefore, there is an urgent need to develop a method for preparing diamond-like carbon coatings with strong adhesion, low internal stress, good toughness, and long lifespan, which would help improve the reliability, lifespan, and safety of axle differentials. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide a diamond-like carbon coating for axle differential components and its preparation method. The resulting diamond-like carbon coating has strong adhesion, good toughness, good wear resistance, and long service life, which can improve the reliability, lifespan, and safety of axle differentials.

[0007] To achieve this objective, the present invention adopts the following technical solution:

[0008] In a first aspect, the present invention provides a method for preparing a diamond-like carbon coating for axle differential components, the method comprising the following steps:

[0009] The axle differential components are subjected to surface etching, preliminary chromium deposition, chromium and tungsten carbide transition deposition, tungsten carbide deposition, and diamond-like carbon (DLC) coating treatment in sequence to achieve the preparation of the DLC coating.

[0010] The method for preparing diamond-like carbon (DLC) coatings for axle differential components provided by this invention achieves surface cleaning, activation, and micro-roughening of the substrate surface through surface etching. By designing a gradient of composition and structure for the component substrate, pure chromium, chromium / tungsten carbide mixture, tungsten carbide / chromium mixture, pure tungsten carbide, carbon-rich tungsten carbide, and the DLC film, the compatibility between the layers is ensured, ensuring that the final DLC coating has both high hardness and good adhesion to the substrate, thus achieving coating of complex axle differential components at low temperatures.

[0011] Preferably, the surface etching process includes a vacuuming and heating process before the surface etching process.

[0012] Preferably, the temperature endpoint of the heating process is 120-150℃, and the time is 85-95 minutes.

[0013] The endpoint of the heating process is 120-150℃, for example, it can be 120℃, 130℃, 135℃, 140℃ or 150℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0014] The heating process takes 85-95 minutes, for example, 85 minutes, 88 minutes, 90 minutes, 92 minutes or 95 minutes, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0015] Preferably, the surface etching process includes sequential argon pre-etching and argon deep etching.

[0016] This invention achieves the cleaning and activation process through a two-step surface etching process. Argon pre-etching can perform relatively gentle cleaning and preliminary activation, while argon deep etching can achieve high-intensity ion bombardment and activation, thereby effectively removing contaminants from the substrate surface.

[0017] Preferably, the specific steps of the argon pre-etching include: introducing 115-125 sccm of argon gas, setting the bias voltage to 110-130V, the bias current to 15-40A, the bias pulse time to 10-20min, the bias frequency to 30-50Hz, setting the voltage of the three ion sources to 12V, the duty cycle to 65, the heating temperature to 120-150℃, and the argon pre-etching time to 60min.

[0018] The flow rate of the introduced argon gas is 115-125 sccm, for example, it can be 115 sccm, 118 sccm, 120 sccm, 122 sccm or 125 sccm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0019] The bias voltage is set to 110-130V, for example, it can be 110V, 115V, 120V, 125V or 130V, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0020] The bias current is 15-40A, for example, it can be 15A, 20A, 25A, 30A or 40A, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0021] The bias pulse duration is 10-20 min, for example, it can be 10 min, 12 min, 15 min, 18 min or 20 min, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0022] The bias frequency is 30-50Hz, for example, it can be 30Hz, 35Hz, 40Hz, 45Hz or 50Hz, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0023] The heating temperature is 120-150℃, for example, it can be 120℃, 125℃, 130℃, 140℃ or 150℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0024] Preferably, the specific steps of the argon deep etching include: introducing 115-125 sccm of argon gas, setting the bias voltage to 200V, the bias current to 30A, the bias pulse time to 15min, the bias frequency to 40Hz, setting the voltage of the three ion sources to 12V, the duty cycle to 65, the heating temperature to 120-150℃, and the argon deep etching time to 60min.

[0025] The flow rate of the introduced argon gas is 115-125 sccm, for example, it can be 115 sccm, 118 sccm, 120 sccm, 122 sccm or 125 sccm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0026] The heating temperature is 120-150℃, for example, it can be 120℃, 125℃, 130℃, 140℃ or 150℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0027] Preferably, the preliminary chromium deposition includes a first chromium deposition, a second chromium deposition, and a third chromium deposition performed sequentially.

[0028] Preferably, the specific steps of the first chromium deposition include: introducing 275-285 sccm of argon gas, a bias current of 25-30 A, a bias pulse time of 15 min, a bias frequency of 35-40 Hz, setting the current of three chromium targets and two tungsten carbide targets to 5 A each, a heating temperature of 120-150 °C, and a time of 3 min.

[0029] The flow rate of the introduced argon gas is 275-285 sccm, for example, it can be 275 sccm, 278 sccm, 280 sccm, 282 sccm or 285 sccm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0030] The bias current is 25-30A, for example, it can be 25A, 26A, 28A, 29A or 30A, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0031] The bias frequency is 35-40Hz, for example, it can be 35Hz, 36Hz, 38Hz, 39Hz or 40Hz, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0032] The heating temperature is 120-150℃, for example, it can be 120℃, 125℃, 130℃, 140℃ or 150℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0033] Preferably, the specific steps of the second chromium deposition include: introducing 275-285 sccm of argon gas, a bias current of 25-30 A, a bias pulse time of 15 min, a bias frequency of 40 Hz, setting the current of three chromium targets and two tungsten carbide targets to 15 A each, a heating temperature of 120-150 °C, and a time of 1.5 min.

[0034] The flow rate of the introduced argon gas is 275-285 sccm, for example, it can be 275 sccm, 278 sccm, 280 sccm, 282 sccm or 285 sccm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0035] The bias current is 25-30A, for example, it can be 25A, 26A, 28A, 29A or 30A, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0036] The heating temperature is 120-150℃, for example, it can be 120℃, 125℃, 130℃, 140℃ or 150℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0037] Preferably, the specific steps of the third chromium deposition include: introducing 275-285 sccm of argon gas, a bias current of 30 A, a bias pulse time of 15 min, a bias frequency of 40 Hz, setting the current of three chromium targets and two tungsten carbide targets to 25 A each, heating the temperature to 120-150 °C, and heating the time to 2 min.

[0038] The flow rate of the introduced argon gas is 275-285 sccm, for example, it can be 275 sccm, 278 sccm, 280 sccm, 282 sccm or 285 sccm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0039] The heating temperature is 120-150℃, for example, it can be 120℃, 125℃, 130℃, 140℃ or 150℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0040] This invention sets the initial chromium deposition as a series of sequential first, second, and third chromium depositions. Through a progressive deposition process, a transitional layer with varying composition, structure, and stress gradient can be obtained. Specifically, the first chromium deposition allows chromium atoms to begin deposition at a very low rate and energy on a highly activated substrate surface, thereby improving adhesion. The second chromium deposition accelerates the deposition rate on the already well-formed nucleation layer, initiating the construction of the main structure of the chromium layer. The third chromium deposition completes the deposition of the chromium underlayer with maximum efficiency, forming a clean, fine-grained, low-stress, and highly adhesive chromium underlayer, preparing for the next deposition layer.

[0041] Preferably, the chromium and tungsten carbide transition deposition includes sequential stable chromium deposition, preliminary mixed deposition, and mixed deposition;

[0042] Preferably, the specific steps of the stable chromium deposition include: introducing 275-285 sccm of argon gas, a bias current of 25-30 A, a bias pulse time of 15 min, a bias frequency of 40 Hz, setting the current of three chromium targets and two tungsten carbide targets to 30 A each, a heating temperature of 120-150 °C, and a heating time of 180 min.

[0043] The flow rate of the introduced argon gas is 275-285 sccm, for example, it can be 275 sccm, 278 sccm, 280 sccm, 282 sccm or 285 sccm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0044] The bias current is 25-30A, for example, it can be 25A, 26A, 28A, 29A or 30A, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0045] The heating temperature is 120-150℃, for example, it can be 120℃, 125℃, 130℃, 140℃ or 150℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0046] Preferably, the specific steps of the preliminary mixed deposition include: introducing 275-285 sccm of argon gas, a bias current of 30A, a bias pulse time of 15min, a bias frequency of 40Hz, setting the current of the three chromium targets to 20A each, the current of the two tungsten carbide targets to 5A each, a heating temperature of 120-150℃, and a heating time of 15min.

[0047] The flow rate of the introduced argon gas is 275-285 sccm, for example, it can be 275 sccm, 278 sccm, 280 sccm, 282 sccm or 285 sccm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0048] The heating temperature is 120-150℃, for example, it can be 120℃, 125℃, 130℃, 140℃ or 150℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0049] Preferably, the specific steps of the mixed deposition include: introducing 275-285 sccm of argon gas, a bias current of 25-30 A, a bias pulse time of 15 min, a bias frequency of 40 Hz, setting the current of three chromium targets and two tungsten carbide targets to 20 A each, heating the temperature to 120-150 °C, and heating the time to 15 min.

[0050] The flow rate of the introduced argon gas is 275-285 sccm, for example, it can be 275 sccm, 278 sccm, 280 sccm, 282 sccm or 285 sccm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0051] The bias current is 25-30A, for example, it can be 25A, 26A, 28A, 29A or 30A, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0052] The heating temperature is 120-150℃, for example, it can be 120℃, 125℃, 130℃, 140℃ or 150℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0053] This invention incorporates a transitional deposition process for chromium and tungsten carbide, divided into three stages: stable chromium deposition, preliminary mixed deposition, and mixed deposition. This optimizes the quality of the chromium layer and introduces silicon carbide. Stable chromium deposition enables long-term, stable chromium deposition, resulting in a dense, low-stress pure chromium layer. Preliminary mixed deposition introduces carbon elements, achieving a gradual change in composition and avoiding the sharp interface of directly switching from a pure metal layer to a carbide layer, thus strengthening the bond. Mixed deposition forms a mixed interface layer, resolving the compatibility issue between the metallic chromium layer and the tungsten carbide layer, which is beneficial for subsequent tungsten carbide deposition.

[0054] Preferably, the tungsten carbide deposition includes sequential tungsten carbide transition deposition, first tungsten carbide deposition, and second tungsten carbide deposition.

[0055] Preferably, the specific steps of the tungsten carbide transition deposition include: introducing 275-285 sccm of argon gas, a bias current of 25-30 A, a bias pulse time of 15 min, a bias frequency of 40 Hz, setting the current of the three chromium targets to 5 A each, the current of the two tungsten carbide targets to 20 A each, a heating temperature of 120-150 °C, and a heating time of 15 min.

[0056] The flow rate of the introduced argon gas is 275-285 sccm, for example, it can be 275 sccm, 278 sccm, 280 sccm, 282 sccm or 285 sccm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0057] The bias current is 25-30A, for example, it can be 25A, 26A, 28A, 29A or 30A, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0058] The heating temperature is 120-150℃, for example, it can be 120℃, 125℃, 130℃, 140℃ or 150℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0059] Preferably, the specific steps of the first tungsten carbide deposition include: introducing 275-285 sccm of argon gas, introducing 85-95 sccm of acetylene gas, setting the bias voltage to 60V, the bias current to 55A, the bias pulse time to 15min, the bias frequency to 40Hz, turning off the three chromium targets, setting the current of the two tungsten carbide targets to 22A each, the heating temperature to 120-150℃, and the time to 20min.

[0060] The flow rate of the introduced argon gas is 275-285 sccm, for example, it can be 275 sccm, 278 sccm, 280 sccm, 282 sccm or 285 sccm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0061] The flow rate of the acetylene gas introduced is 85-95 sccm, for example, it can be 85 sccm, 88 sccm, 90 sccm, 92 sccm or 95 sccm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0062] The heating temperature is 120-150℃, for example, it can be 120℃, 125℃, 130℃, 140℃ or 150℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0063] Preferably, the specific steps of the second tungsten carbide deposition include: introducing 275-285 sccm of argon gas, introducing 85-95 sccm of acetylene gas, setting the bias voltage to 120V, the bias current to 55A, the bias pulse time to 15min, the bias frequency to 40Hz, turning off the three chromium targets, setting the current of the two tungsten carbide targets to 22A each, the heating temperature to 120-150℃, and the time to 20min.

[0064] The flow rate of the introduced argon gas is 275-285 sccm, for example, it can be 275 sccm, 278 sccm, 280 sccm, 282 sccm or 285 sccm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0065] The flow rate of the acetylene gas introduced is 85-95 sccm, for example, it can be 85 sccm, 88 sccm, 90 sccm, 92 sccm or 95 sccm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0066] The heating temperature is 120-150℃, for example, it can be 120℃, 125℃, 130℃, 140℃ or 150℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0067] This invention employs three steps—tungsten carbide transition deposition, first tungsten carbide deposition, and second tungsten carbide deposition—to deposit a tungsten carbide layer. The tungsten carbide transition deposition transforms the main component of the deposited layer from a chromium-tungsten-carbon mixed phase in the previous deposited layer to tungsten carbide containing trace amounts of chromium, ensuring the continuity of the transformation. The first tungsten carbide deposition achieves the deposition of the main body of the tungsten carbide layer, while the second tungsten carbide deposition optimizes the tungsten carbide layer, making it harder and denser.

[0068] Preferably, after tungsten carbide deposition and before diamond-like carbon coating, a transition treatment step is further included. The transition treatment specifically includes: setting the bias voltage to 0V, the bias current to 55A, the bias pulse time to 15min, the bias frequency to 40Hz, turning off the three chromium targets and the two tungsten carbide targets, heating the temperature to 120-150℃ for 0.5min, and setting the acetylene gas charging volume of the three ion sources to 300sccm.

[0069] The transition process involves stopping all sputtering before the formal start of the diamond-like carbon (DLC) coating process, and allowing acetylene gas to fully fill the vacuum chamber, replacing the previous argon gas, to create a pure carbon source environment for the DLC coating process.

[0070] The heating temperature is 120-150℃, for example, it can be 120℃, 125℃, 130℃, 140℃ or 150℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0071] Preferably, the diamond-like carbon coating process includes a first coating and a second coating performed sequentially.

[0072] Preferably, the specific steps of the first coating include: setting the bias voltage to 200V, the bias current to 55A, the bias pulse time to 15min, the bias frequency to 35-40Hz, the heating temperature to 120-150℃, the time to 50min, setting the voltage of the three ion sources to 12V, the duty cycle to 60-65, and the acetylene gas filling volume to 300sccm.

[0073] The bias frequency is 35-40Hz, for example, it can be 35Hz, 36Hz, 38Hz, 39Hz or 40Hz, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0074] The heating temperature is 120-150℃, for example, it can be 120℃, 125℃, 130℃, 140℃ or 150℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0075] The duty cycle is 60-65, for example, it can be 60, 61, 62, 63 or 65, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0076] Preferably, the specific steps of the second coating include: setting the bias voltage to 450V, the bias current to 55A, the bias pulse time to 15min, the bias frequency to 40Hz, the heating temperature to 120-150℃, the time to 110min, setting the voltage of the three ion sources to 12V, the duty cycle to 60-65, and the acetylene gas filling volume to 300sccm.

[0077] The heating temperature is 120-150℃, for example, it can be 120℃, 125℃, 130℃, 140℃ or 150℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0078] The duty cycle is 60-65, for example, it can be 60, 61, 62, 63 or 65, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0079] This invention divides the diamond-like carbon (DLC) coating process into a first coating and a second coating. First, on a tungsten carbide layer, initial carbon ions are deposited at medium energy to form the first coating layer. Then, the main DLC coating layer is deposited and its performance optimized, increasing the sp... 3 The bond content is increased, and the structure is more compact.

[0080] Preferably, the diamond-like carbon coating process further includes a step of cooling the furnace to ≤100°C, such as 100°C, 90°C, 80°C, 70°C or 60°C, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0081] Preferably, the axle differential components are made of alloy structural steel 20CrMnTi.

[0082] Preferably, the axle differential components include an axle differential cross shaft and / or an axle differential input shaft.

[0083] Preferably, the surfaces of the axle differential components are subjected to carburizing and quenching treatment and grinding.

[0084] Preferably, the hardness of the axle differential components after carburizing and quenching is 58-62 HRC, and the effective hardened layer depth is 0.7-1.1 mm.

[0085] The hardness of the axle differential components after carburizing and quenching is 58-62 HRC, for example, it can be 58 HRC, 59 HRC, 60 HRC, 61 HRC or 62 HRC, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0086] The effective hardened layer depth of the axle differential components after carburizing and quenching treatment is 0.7-1.1mm, for example, it can be 0.7mm, 0.8mm, 0.9mm or 1.1mm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0087] Preferably, the grinding process is performed to a surface roughness Ra ≤ 0.6, for example, it can be 0.6, 0.5, 0.4, 0.3 or 0.2, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0088] Preferably, the grinding process is followed by a cleaning step.

[0089] In a second aspect, the present invention provides a diamond-like coating for axle differential components, wherein the diamond-like coating for axle differential components is prepared by the preparation method of the diamond-like coating for axle differential components described in the first aspect.

[0090] The diamond-like coating for axle differential components includes a preliminary chromium deposition layer, a chromium and tungsten carbide transition deposition layer, a tungsten carbide deposition layer, and a diamond-like coating layer, which are sequentially stacked on the surface of the axle differential components.

[0091] The diamond-like coating provided by this invention, through gradient composition structure design, has the characteristics of strong adhesion, good hardness, low friction coefficient and long service life, and can be used in axle differential components.

[0092] Compared with the prior art, the present invention has the following beneficial effects:

[0093] This invention provides a method for preparing diamond-like carbon (DLC) coatings for axle differential components. The method achieves surface cleaning, activation, and micro-roughening of the substrate through surface etching. By designing a gradient of composition and structure between the component substrate, pure chromium, chromium / tungsten carbide mixtures, tungsten carbide / chromium mixtures, pure tungsten carbide, carbon-rich tungsten carbide, and the DLC film, the compatibility between each layer is ensured. This guarantees that the final DLC coating possesses both high hardness and good adhesion to the substrate, enabling coating of complex axle differential components at low temperatures. The resulting DLC ​​coating has a film thickness within the target range, adhesion meeting the requirements of HF1-HF2 in JB / T 11442 "Test Method for Integral Carbide Coated Tools," a nano-hardness of 20-22 GPa, an elastic modulus ≥148 GPa, and a coefficient of friction ≤0.12. When used on the axle differential cross shaft, it can significantly improve service life. Detailed Implementation

[0094] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0095] Example 1

[0096] This embodiment provides a method for preparing a diamond-like carbon coating for axle differential components, the method comprising the following steps:

[0097] The axle differential cross shaft base is made of 20CrMnTi alloy structural steel. The surface is carburized and quenched to obtain an axle differential cross shaft base with a hardness of 58HRC and an effective hardened layer depth of 0.7mm. After grinding to a surface roughness Ra of 0.6, it is cleaned to obtain the axle differential cross shaft workpiece.

[0098] The cross shaft workpiece of the axle differential was vacuumed and heated to 120℃ for 95 minutes. Then, argon pre-etching was performed, with the following steps: 115 sccm of argon gas was introduced, the bias voltage was set to 110V, the bias current to 15A, the bias pulse time to 20 minutes, the bias frequency to 50Hz, the voltage of all three ion sources was set to 12V, the duty cycle to 65, the heating temperature to 120℃, and the argon pre-etching time to 60 minutes. Finally, argon deep etching was performed, with the following steps: 115 sccm of argon gas was introduced, the bias voltage was set to 200V, the bias current to 30A, the bias pulse time to 15 minutes, the bias frequency to 40Hz, the voltage of all three ion sources was set to 12V, the duty cycle to 65, the heating temperature to 120℃, and the argon deep etching time to 60 minutes.

[0099] The differential cross shaft workpiece of the vehicle axle, after deep argon gas etching, underwent a series of chromium deposition processes, including a first chromium deposition, a second chromium deposition, and a third chromium deposition. The specific steps for the first chromium deposition included: introducing 275 sccm of argon gas, setting a bias current of 25 A, a bias pulse duration of 15 min, a bias frequency of 35 Hz, setting the current for all three chromium targets and two tungsten carbide targets to 5 A, and heating at 120 °C for 3 min. The specific steps for the second chromium deposition included: introducing 275 sccm of argon gas, setting a bias current of... The specific steps for the third chromium deposition include: introducing 275 sccm of argon gas, setting the bias current to 30 A, the bias pulse time to 15 min, the bias frequency to 40 Hz, setting the current for three chromium targets and two tungsten carbide targets to 25 A, the heating temperature to 120 ℃, and the time to 1.5 min;

[0100] The axle differential cross shaft workpiece after the third chromium deposition underwent stable chromium deposition, preliminary mixed deposition, and mixed deposition sequentially. The specific steps for stable chromium deposition included: introducing 275 sccm of argon gas, setting a bias current of 25 A, a bias pulse duration of 15 min, a bias frequency of 40 Hz, setting the current for three chromium targets and two tungsten carbide targets to 30 A each, a heating temperature of 120 °C, and a time of 180 min. The specific steps for preliminary mixed deposition included: introducing 275 sccm of argon gas, setting a bias current of 3... The specific steps for mixed deposition include: introducing 275 sccm of argon gas, setting the bias current to 25 A, the bias pulse time to 15 min, the bias frequency to 40 Hz, setting the current for three chromium targets to 20 A and the current for two tungsten carbide targets to 5 A, the heating temperature to 120 ℃, and the time to 15 min;

[0101] The cross shaft workpiece of the axle differential, after mixed deposition, underwent sequential tungsten carbide transition deposition, first tungsten carbide deposition, and second tungsten carbide deposition. The specific steps for the tungsten carbide transition deposition included: introducing 275 sccm of argon gas, setting the bias current to 25 A, the bias pulse duration to 15 min, the bias frequency to 40 Hz, setting the current for the three chromium targets to 5 A each, the current for the two tungsten carbide targets to 20 A each, the heating temperature to 120 °C, and the time to 15 min. The specific steps for the first tungsten carbide deposition included: introducing 275 sccm of argon gas, introducing 85 sccm of acetylene gas, and setting the bias voltage to 60 V. The bias current is 55A, the bias pulse time is 15min, the bias frequency is 40Hz, the three chromium targets are turned off, the current of the two tungsten carbide targets is set to 22A, the heating temperature is 120℃, and the time is 20min; the specific steps of the second tungsten carbide deposition include: introducing 275sccm of argon gas, introducing 85sccm of acetylene gas, setting the bias voltage to 120V, the bias current to 55A, the bias pulse time to 15min, the bias frequency to 40Hz, turning off the three chromium targets, setting the current of the two tungsten carbide targets to 22A, the heating temperature to 120℃, and the time to 20min.

[0102] The axle differential cross shaft workpiece after the second tungsten carbide deposition is subjected to transition treatment. The specific steps include: setting the bias voltage to 0V, the bias current to 55A, the bias pulse time to 15min, the bias frequency to 40Hz, turning off the three chromium targets and two tungsten carbide targets, heating the temperature to 120℃ for 0.5min, and setting the acetylene gas charging volume of the three ion sources to 300sccm.

[0103] The cross shaft workpiece of the axle differential after transition treatment was subjected to a first coating and a second coating in sequence. The specific steps of the first coating included: setting the bias voltage to 200V, the bias current to 55A, the bias pulse time to 15min, the bias frequency to 35Hz, the heating temperature to 120℃, the time to 50min, setting the voltage of the three ion sources to 12V, the duty cycle to 60, and the acetylene gas filling volume to 300sccm. The specific steps of the second coating included: setting the bias voltage to 450V, the bias current to 55A, the bias pulse time to 15min, the bias frequency to 40Hz, the heating temperature to 120℃, the time to 110min, setting the voltage of the three ion sources to 12V, the duty cycle to 60, and the acetylene gas filling volume to 300sccm. Then, the furnace was cooled to 100℃ to achieve the preparation of the diamond-like carbon coating.

[0104] Example 2

[0105] This embodiment provides a method for preparing a diamond-like carbon coating for axle differential components, the method comprising the following steps:

[0106] The input shaft base of the axle differential is made of 20CrMnTi alloy structural steel. The surface is carburized and quenched to obtain an input shaft base with a hardness of 62HRC and an effective hardened layer depth of 1.1mm. After grinding to a surface roughness Ra of 0.6, it is cleaned to obtain the input shaft workpiece of the axle differential.

[0107] The input shaft of the axle differential was vacuumed and heated to 150°C for 85 minutes. Then, argon pre-etching was performed, with the following steps: 125 sccm of argon gas was introduced, the bias voltage was set to 130V, the bias current to 40A, the bias pulse duration to 10 minutes, and the bias frequency to 30Hz. All three ion source voltages were set to 12V with a duty cycle of 65, the heating temperature to 150°C, and the argon pre-etching time to 60 minutes. Finally, argon deep etching was performed, with the following steps: 125 sccm of argon gas was introduced, the bias voltage was set to 200V, the bias current to 30A, the bias pulse duration to 15 minutes, the bias frequency to 40Hz, all three ion source voltages were set to 12V with a duty cycle of 65, the heating temperature to 150°C, and the argon deep etching time to 60 minutes.

[0108] The input shaft workpiece of the axle differential, after deep argon gas etching, underwent a series of chromium deposition processes, including a first chromium deposition, a second chromium deposition, and a third chromium deposition. The specific steps for the first chromium deposition included: introducing 285 sccm of argon gas, setting a bias current of 30 A, a bias pulse duration of 15 min, a bias frequency of 40 Hz, setting the current for all three chromium targets and two tungsten carbide targets to 5 A, and heating at 150 °C for 3 min. The specific steps for the second chromium deposition included: introducing 285 sccm of argon gas, setting a bias current of... The specific steps for the third chromium deposition include: introducing 285 sccm of argon gas, setting the bias current to 30A, the bias pulse time to 15min, the bias frequency to 40Hz, setting the current for three chromium targets and two tungsten carbide targets to 25A, the heating temperature to 150℃, and the time to 1.5min;

[0109] The input shaft workpiece of the axle differential after the third chromium deposition was subjected to stable chromium deposition, preliminary mixed deposition, and mixed deposition sequentially. The specific steps for stable chromium deposition included: introducing 285 sccm of argon gas, setting the bias current to 30 A, the bias pulse time to 15 min, and the bias frequency to 40 Hz; setting the current for all three chromium targets and two tungsten carbide targets to 30 A; setting the heating temperature to 150 °C; and the time to 180 min. The specific steps for preliminary mixed deposition included: introducing 285 sccm of argon gas, setting the bias current to 30 A, the bias pulse time to 15 min, and the bias frequency to 40 Hz; setting the current for all three chromium targets and two tungsten carbide targets to 30 A; setting the heating temperature to 150 °C; and the time to 180 min. The specific steps for mixed deposition include: introducing 285 sccm of argon gas, setting the bias current to 30A, the bias pulse time to 15min, the bias frequency to 40Hz, setting the current for three chromium targets to 20A and the current for two tungsten carbide targets to 5A, the heating temperature to 150℃, and the time to 15min.

[0110] The input shaft workpiece of the axle differential, after mixed deposition, underwent sequential tungsten carbide transition deposition, first tungsten carbide deposition, and second tungsten carbide deposition. The specific steps for the tungsten carbide transition deposition included: introducing 285 sccm of argon gas, setting the bias current to 30 A, the bias pulse duration to 15 min, the bias frequency to 40 Hz, setting the current for the three chromium targets to 5 A each, the current for the two tungsten carbide targets to 20 A each, the heating temperature to 150 °C, and the time to 15 min. The specific steps for the first tungsten carbide deposition included: introducing 285 sccm of argon gas, introducing 95 sccm of acetylene gas, and setting the bias voltage to 60 V. The bias current is 55A, the bias pulse time is 15min, the bias frequency is 40Hz, the three chromium targets are turned off, the current of the two tungsten carbide targets is set to 22A, the heating temperature is 150℃, and the time is 20min; the specific steps of the second tungsten carbide deposition include: introducing 285sccm of argon gas, introducing 95sccm of acetylene gas, setting the bias voltage to 120V, the bias current to 55A, the bias pulse time to 15min, the bias frequency to 40Hz, turning off the three chromium targets, setting the current of the two tungsten carbide targets to 22A, the heating temperature to 150℃, and the time to 20min.

[0111] The axle differential input shaft workpiece after the second tungsten carbide deposition undergoes a transition treatment. The specific steps include: setting the bias voltage to 0V, the bias current to 55A, the bias pulse time to 15min, the bias frequency to 40Hz, turning off the three chromium targets and two tungsten carbide targets, setting the heating temperature to 150℃ for 0.5min, and setting the acetylene gas charging volume of the three ion sources to 300sccm.

[0112] The input shaft workpiece of the axle differential after transition treatment is subjected to a first coating and a second coating in sequence. The specific steps of the first coating are as follows: the bias voltage is set to 200V, the bias current is 55A, the bias pulse time is 15min, the bias frequency is 40Hz, the heating temperature is 150℃, the time is 50min, the voltage of the three ion sources is set to 12V, the duty cycle is 65, and the acetylene gas filling amount is 300sccm. The specific steps of the second coating are as follows: the bias voltage is set to 450V, the bias current is 55A, the bias pulse time is 15min, the bias frequency is 40Hz, the heating temperature is 150℃, the time is 110min, the voltage of the three ion sources is set to 12V, the duty cycle is 65, and the acetylene gas filling amount is 300sccm. Then, the temperature is lowered to 100℃ in the furnace to achieve the preparation of the diamond-like carbon coating.

[0113] Example 3

[0114] This embodiment provides a method for preparing a diamond-like carbon coating for axle differential components. The difference from Embodiment 1 is that the argon pre-etching step is omitted, while the rest is the same as Embodiment 1.

[0115] Example 4

[0116] This embodiment provides a method for preparing a diamond-like carbon coating for axle differential components. The difference from Embodiment 1 is that the second chromium deposition step is omitted, while the rest is the same as in Embodiment 1.

[0117] Example 5

[0118] This embodiment provides a method for preparing a diamond-like carbon coating for axle differential components. The difference from Embodiment 1 is that the preliminary mixing and deposition step is omitted, while the rest is the same as in Embodiment 1.

[0119] Example 6

[0120] This embodiment provides a method for preparing a diamond-like carbon coating for axle differential components. The difference from Embodiment 1 is that the first and second coatings are adjusted to be a one-step coating, and the bias voltage is adjusted to 400V. All other aspects are the same as in Embodiment 1.

[0121] Comparative Example 1

[0122] This comparative example provides a method for preparing a diamond-like carbon coating for axle differential components. The difference from Example 1 is that the argon pre-etching and argon deep etching steps are omitted, while the rest are the same as in Example 1.

[0123] Comparative Example 2

[0124] This comparative example provides a method for preparing a diamond-like carbon coating for axle differential components. The difference from Example 1 is that the steps of stable chromium deposition, preliminary mixed deposition, and mixed deposition are not included, while the rest are the same as in Example 1.

[0125] The diamond-like carbon coatings on the axle differential components provided in Examples 1-6 and Comparative Examples 1 and 2 were tested using a ball mill for film thickness measurement, JB / T 11442 "Test Method for Integral Carbide Coated Tools" for adhesion testing, nano-hardness testing was performed using a nano-indenter with a loading force of 10 mN, elastic modulus testing was performed using a nano-indenter with a loading force of 10 mN, friction coefficient testing was performed using a tribometer, Raman spectroscopy was performed using a Raman spectrometer, and differential durability testing was conducted (conditions: 60% torque, speed difference 80 rpm). The results are shown in Table 1.

[0126] Table 1

[0127]

[0128] As can be seen from Table 1, the diamond-like carbon coating for axle differential components prepared by the preparation method provided by the present invention can obtain a diamond-like carbon coating with strong adhesion, good hardness, low coefficient of friction, and long service life.

[0129] A comparison of Examples 1 and 3 shows that omitting the argon pre-etching step allows contaminants on the substrate surface to be directly impacted into the interior, and also leads to localized overheating on the surface, forming an unfavorable stress layer and reducing adhesion. A comparison of Examples 1 and 4 shows that omitting the second chromium deposition step makes it impossible to construct a dense transition layer structure. A comparison of Examples 1 and 5 shows that omitting the preliminary mixing deposition step makes it impossible to form a compositional gradient structure, resulting in a sharp interface that directly switches from the chromium layer to the tungsten carbide layer, reducing adhesion. A comparison of Examples 1 and 6 shows that adjusting the first and second coatings to a single coating step leads to a decrease in the interface quality between the tungsten carbide layer and the diamond-like carbon film layer, thereby reducing the overall performance of the coating.

[0130] As can be seen from the comparison between Example 1 and Comparative Example 1, without the surface etching step, it is impossible to remove contaminants from the substrate surface and achieve surface activation. As can be seen from the comparison between Example 1 and Comparative Example 2, without the step of chromium and tungsten carbide transition deposition, it is impossible to form a gradient composition structure, which will significantly reduce the overall performance of the diamond-like carbon coating.

[0131] In summary, the method for preparing diamond-like carbon (DLC) coatings for axle differential components provided by this invention achieves surface cleaning, activation, and micro-roughening of the substrate through surface etching. By designing a gradient of composition and structure between the component substrate, pure chromium, chromium / tungsten carbide mixtures, tungsten carbide / chromium mixtures, pure tungsten carbide, carbon-rich tungsten carbide, and the DLC film, the compatibility between each layer is ensured, guaranteeing that the final DLC coating possesses both high hardness and good adhesion to the substrate. This enables the coating of complex axle differential components at low temperatures. The resulting DLC ​​coating has a film thickness within the target range, adhesion meeting the requirements of HF1-HF2 in JB / T 11442 "Test Method for Integral Carbide Coated Tools," a nano-hardness of 20-22 GPa, an elastic modulus ≥148 GPa, and a coefficient of friction ≤0.12. When used on the axle differential cross shaft, it can significantly improve service life.

[0132] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for preparing a diamond-like carbon coating for axle differential components, characterized in that, The preparation method includes the following steps: The axle differential components are subjected to surface etching, preliminary chromium deposition, chromium and tungsten carbide transition deposition, tungsten carbide deposition, and diamond-like carbon (DLC) coating treatment in sequence to achieve the preparation of the DLC coating.

2. The preparation method according to claim 1, characterized in that, The surface etching process is preceded by a vacuuming and heating process. Preferably, the temperature endpoint of the heating process is 120-150℃, and the time is 85-95 minutes.

3. The preparation method according to claim 1 or 2, characterized in that, The surface etching process includes sequential argon pre-etching and argon deep etching. Preferably, the specific steps of the argon pre-etching include: introducing 115-125 sccm of argon gas, setting the bias voltage to 110-130V, the bias current to 15-40A, the bias pulse time to 10-20min, the bias frequency to 30-50Hz, setting the voltage of the three ion sources to 12V, the duty cycle to 65, the heating temperature to 120-150℃, and the argon pre-etching time to 60min; Preferably, the specific steps of the argon deep etching include: introducing 115-125 sccm of argon gas, setting the bias voltage to 200V, the bias current to 30A, the bias pulse time to 15min, the bias frequency to 40Hz, setting the voltage of the three ion sources to 12V, the duty cycle to 65, the heating temperature to 120-150℃, and the argon deep etching time to 60min.

4. The preparation method according to any one of claims 1-3, characterized in that, The preliminary chromium deposition includes a first chromium deposition, a second chromium deposition, and a third chromium deposition performed sequentially. Preferably, the specific steps of the first chromium deposition include: introducing 275-285 sccm of argon gas, a bias current of 25-30 A, a bias pulse time of 15 min, a bias frequency of 35-40 Hz, setting the current of three chromium targets and two tungsten carbide targets to 5 A each, a heating temperature of 120-150 °C, and a time of 3 min. Preferably, the specific steps of the second chromium deposition include: introducing 275-285 sccm of argon gas, a bias current of 25-30 A, a bias pulse time of 15 min, a bias frequency of 40 Hz, setting the current of three chromium targets and two tungsten carbide targets to 15 A each, a heating temperature of 120-150 °C, and a time of 1.5 min. Preferably, the specific steps of the third chromium deposition include: introducing 275-285 sccm of argon gas, a bias current of 30 A, a bias pulse time of 15 min, a bias frequency of 40 Hz, setting the current of three chromium targets and two tungsten carbide targets to 25 A each, heating the temperature to 120-150 °C, and heating the time to 2 min.

5. The preparation method according to any one of claims 1-4, characterized in that, The chromium and tungsten carbide transition deposition includes sequential stable chromium deposition, preliminary mixed deposition, and mixed deposition. Preferably, the specific steps of the stable chromium deposition include: introducing 275-285 sccm of argon gas, a bias current of 25-30 A, a bias pulse time of 15 min, a bias frequency of 40 Hz, setting the current of three chromium targets and two tungsten carbide targets to 30 A each, a heating temperature of 120-150 °C, and a heating time of 180 min. Preferably, the specific steps of the preliminary mixed deposition include: introducing 275-285 sccm of argon gas, a bias current of 30A, a bias pulse time of 15min, a bias frequency of 40Hz, setting the current of the three chromium targets to 20A each, the current of the two tungsten carbide targets to 5A each, a heating temperature of 120-150℃, and a heating time of 15min. Preferably, the specific steps of the mixed deposition include: introducing 275-285 sccm of argon gas, a bias current of 25-30 A, a bias pulse time of 15 min, a bias frequency of 40 Hz, setting the current of three chromium targets and two tungsten carbide targets to 20 A each, heating the temperature to 120-150 °C, and heating the time to 15 min.

6. The preparation method according to any one of claims 1-5, characterized in that, The tungsten carbide deposition includes sequential tungsten carbide transition deposition, first tungsten carbide deposition, and second tungsten carbide deposition; Preferably, the specific steps of the tungsten carbide transition deposition include: introducing 275-285 sccm of argon gas, a bias current of 25-30 A, a bias pulse time of 15 min, a bias frequency of 40 Hz, setting the current of the three chromium targets to 5 A each, the current of the two tungsten carbide targets to 20 A each, a heating temperature of 120-150 °C, and a heating time of 15 min. Preferably, the specific steps of the first tungsten carbide deposition include: introducing 275-285 sccm of argon gas, introducing 85-95 sccm of acetylene gas, setting the bias voltage to 60V, the bias current to 55A, the bias pulse time to 15min, the bias frequency to 40Hz, turning off the three chromium targets, setting the current of the two tungsten carbide targets to 22A each, the heating temperature to 120-150℃, and the time to 20min; Preferably, the specific steps of the second tungsten carbide deposition include: introducing 275-285 sccm of argon gas, introducing 85-95 sccm of acetylene gas, setting the bias voltage to 120V, the bias current to 55A, the bias pulse time to 15min, the bias frequency to 40Hz, turning off the three chromium targets, setting the current of the two tungsten carbide targets to 22A each, the heating temperature to 120-150℃, and the time to 20min.

7. The preparation method according to any one of claims 1-6, characterized in that, The process after tungsten carbide deposition and before diamond-like carbon coating includes a transition treatment step. The transition treatment specifically includes: setting the bias voltage to 0V, the bias current to 55A, the bias pulse time to 15min, the bias frequency to 40Hz, turning off the three chromium targets and the two tungsten carbide targets, heating the temperature to 120-150℃ for 0.5min, and setting the acetylene gas charging volume of the three ion sources to 300sccm.

8. The preparation method according to any one of claims 1-7, characterized in that, The diamond-like carbon coating process includes a first coating and a second coating performed sequentially. Preferably, the specific steps of the first coating include: setting the bias voltage to 200V, the bias current to 55A, the bias pulse time to 15min, the bias frequency to 35-40Hz, the heating temperature to 120-150℃, the time to 50min, setting the voltage of the three ion sources to 12V, the duty cycle to 60-65, and the acetylene gas filling volume to 300sccm. Preferably, the specific steps of the second coating include: setting the bias voltage to 450V, the bias current to 55A, the bias pulse time to 15min, the bias frequency to 40Hz, the heating temperature to 120-150℃, the time to 110min, setting the voltage of the three ion sources to 12V, the duty cycle to 60-65, and the acetylene gas filling volume to 300sccm. Preferably, the diamond-like carbon coating process further includes a step of cooling the furnace to ≤100°C.

9. The preparation method according to any one of claims 1-8, characterized in that, The axle differential components are made of alloy structural steel 20CrMnTi. Preferably, the surfaces of the axle differential components are subjected to carburizing and quenching treatment and grinding. Preferably, the hardness of the axle differential components after carburizing and quenching is 58-62 HRC, and the effective hardened layer depth is 0.7-1.1 mm. Preferably, the grinding process is performed to achieve a surface roughness Ra ≤ 0.

6.

10. A diamond-like carbon coating for axle differential components, characterized in that, The diamond-like carbon coating for the axle differential components is prepared using the diamond-like carbon coating preparation method for the axle differential components as described in any one of claims 1-9. The diamond-like coating for axle differential components includes a preliminary chromium deposition layer, a chromium and tungsten carbide transition deposition layer, a tungsten carbide deposition layer, and a diamond-like coating layer, which are sequentially stacked on the surface of the axle differential components.

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