A method for preparing a physical vapor deposition coating on the surface of a steel spring

Abstract

This invention discloses a method for preparing a physical vapor deposition coating on the surface of a steel spring, belonging to the field of metal material surface treatment technology. It adopts unbalanced magnetron sputtering technology and high-purity nitrogen as the process gas. By controlling the substrate negative bias voltage, target current and gas introduction parameters in stages, the surface activation, pure Cr transition layer deposition and stable growth of CrN coating are completed sequentially on the surface of the steel spring. The process temperature of this method is lower than the spring tempering temperature, which can maintain the dimensional accuracy of the parts. The prepared CrN coating has excellent microhardness, adhesion and wear resistance, significantly improving the corrosion resistance life of the spring in salt spray environment. It is particularly suitable for surface strengthening of high-load precision parts such as gun compression springs.

Description

Technical Field

[0001] This invention belongs to the field of metal material surface treatment technology, and in particular, it is a method for preparing a physical vapor deposition coating on the surface of a steel spring. By using unbalanced magnetron sputtering technology, a CrN coating is deposited on the surface of a steel spring, which can significantly improve the corrosion resistance and wear resistance of the steel spring. Background Technology

[0002] Gun compression springs endure high-frequency reciprocating loads over extended periods and are prone to corrosion fatigue fracture in harsh environments such as humidity and salt spray. Traditional phosphating processes result in high surface porosity and insufficient salt spray resistance, failing to meet the demands of modern firearms. While zinc-aluminum coatings (such as Dacromet coating) offer good salt spray protection, their low microhardness and high coefficient of friction lead to sluggish dynamic response in the springs. Processes like carburizing and chemical vapor deposition involve high temperatures, causing tempering and softening of the springs, resulting in significant dimensional deformation. In contrast, physical vapor deposition (PVD) processes operate at temperatures below 200°C, eliminating the need for secondary heat treatment and maintaining dimensional accuracy and surface roughness. CrN coatings possess a microhardness greater than 1800 HV, HF1-level adhesion, and a coefficient of friction <0.35; their dense columnar crystalline structure effectively blocks corrosive media penetration. Depositing a CrN coating on the surface of gun compression springs using unbalanced magnetron sputtering technology simultaneously improves both corrosion and wear resistance.

[0003] In view of this, a method for preparing a physical vapor deposition coating on the surface of a steel spring has been invented. Summary of the Invention

[0004] This invention addresses the deficiencies or shortcomings of existing technologies by providing a method for preparing a physical vapor deposition coating on the surface of steel springs. By using unbalanced magnetron sputtering technology, a CrN coating is deposited on the surface of steel springs, which can significantly improve the corrosion resistance and wear resistance of steel springs.

[0005] The technical solution of the present invention is as follows:

[0006] 1. Two Cr targets are used as sputtering targets, and high-purity nitrogen is used as the process gas.

[0007] 2. Evacuate the coating chamber to a vacuum level of 5×10⁻⁶. -3 When the pressure is below Pa, the coating process is started, and the coating process is continuously vacuumed.

[0008] 3. First, increase the negative bias voltage of the substrate to -500V and set the target current to 0.5A. At this time, Ar+ is generated by argon glow discharge. Under the action of electric field, Ar+ will accelerate and bombard the surface of the substrate, cleaning the surface of the workpiece and the target. The purpose is to remove impurities and enhance the adhesion between the coating and the substrate. The cleaning process takes 30 minutes.

[0009] 4. Subsequently, the negative bias voltage of the substrate is reduced to -50 to 70V to prepare a pure Cr substrate to support the harder CrN transition layer. During this process, the Cr target current is 4 to 6A, and the current of other target materials is 0.3A [to remove the sputtered Cr layer on the target material and avoid a decrease in sputtering efficiency]. This process takes about 5 minutes.

[0010] 5. Next, nitrogen gas is gradually introduced, and the flow rate of nitrogen gas is controlled by setting the value of the light emission spectrum monitoring value. At this time, the current of other target materials remains unchanged. This process takes 20 minutes, and the light emission spectrum monitoring value gradually decreases to 60-80.

[0011] 6. Finally, perform the stabilization coating deposition process, which takes 60 minutes.

[0012] The advantages of this invention are:

[0013] 1. The process temperature is low, which does not affect the dimensional accuracy and surface roughness of the parts;

[0014] 2. The coating exhibits excellent corrosion resistance and wear resistance;

[0015] 3. The process has good repeatability and high quality stability. Detailed Implementation

[0017] The example uses a steel spring from a certain firearm as the base material:

[0018] 1. Pretreatment: Alkaline degreasing [50℃×15min] → deionized water rinsing → alcohol dehydration → vacuum baking at 150℃ for 2h;

[0019] 2. Furnace loading: Spring spacing ≥ 3 times wire diameter to ensure uniform plasma coverage;

[0020] 3. Sputter cleaning: Argon flow rate is 15-20 sccm, bias voltage is -500V, and Cr target current is 0.5A;

[0021] 4. Cr transition layer: bias voltage -50 to -60V, Cr target current increased to 4 to 5A, deposition rate reached 15nm / min;

[0022] 5. Gradient film formation: The light emission spectrum monitoring value decreased from 100 to 60-70 within 20 minutes;

[0023] 6. Stable deposition: Maintain the monitored light emission spectrum values; the total coating thickness after deposition is 3.5 ± 0.2 μm.

[0024] 7. Performance Testing: No red rust appeared after 744 hours of salt spray testing; 10 cycles of reciprocating friction... 6 The wear after each cycle is less than 2μm, and the average friction coefficient is approximately 0.33.

Claims

1. A method for preparing a physical vapor deposition coating on the surface of a steel spring, characterized in that: Includes the following steps: 1) Pretreatment: The steel springs are sequentially degreased, ultrasonically cleaned, and vacuum baked dry; 2) Magnetron sputtering preparation: Two Cr targets were used as sputtering targets. The treated spring was installed into the coating chamber, and the vacuum was evacuated to 5×10⁻⁶. -3 Below Pa; 3) Surface activation: Argon gas is introduced at a flow rate of 15-25 sccm, a substrate bias voltage of -500V is applied, the Cr target current is set to 0.5A, and glow discharge cleaning is performed for 30 minutes. 4) Cr transition layer deposition: Reduce the substrate bias voltage to -50 to -70V, set the Cr target current to 4 to 6A, and the current of other target materials to 0.3A, and maintain for 5 minutes; 5) Gradient film formation: Nitrogen gas is introduced, and the nitrogen flow rate is controlled by the light emission spectrum monitoring value. The light emission spectrum monitoring value is gradually reduced from the initial value of 100 to 60-80 for 20 minutes. 6) Stabilized deposition: Deposition for 60 minutes; 7) Post-treatment: After stopping sputtering, cool the furnace to below 80°C and remove.

2. The method according to claim 1, characterized in that... In step 5), the nitrogen purity is ≥99.999%, and the argon-nitrogen flow ratio is adjusted in a gradient of 1:2.

5.

3. The method for preparing a physical vapor deposition coating on the surface of a steel spring according to claim 1, characterized in that: The purity of the Cr target is ≥99.95%, and the target-substrate distance is maintained at 80-100 mm.

4. The method for preparing a physical vapor deposition coating on the surface of a steel spring according to claim 1, characterized in that: The cavity temperature is controlled at 180-220℃ during the deposition process.