Piston Ring CrMoXN Coating for Low Friction and Thick Wear Resistance
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Solution Overview
Problem
Current coatings for piston rings face limitations in reducing friction and wear while maintaining hardness, with existing solutions either having insufficient friction reduction or peeling issues due to high internal stress and thickness constraints.
Innovation Solution
A coating structure comprising an adhesive layer, a transition layer, a gradient layer, and a cyclical function layer with varying Mo content, which reduces internal stress and increases thickness up to 80 μm, enhancing both wear resistance and friction reduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a diamond-like coating is deposited to reduce friction and wear, then the friction coefficient is reduced, but the internal stress increases making the coating prone to peeling when thickness exceeds 10 μm
Solution Approach 1:
The coating is divided into multiple functional layers: a first diamond-like carbon coating layer (10-20 μm thick) for friction reduction, and a second diamond-like carbon coating layer (5-15 μm thick) for wear resistance. This segmentation allows each layer to be optimized for its specific function while reducing overall internal stress through distributed structure.
Solution Approach 2:
The patent uses composite diamond-like carbon coating structure with different deposition parameters for each layer. The first layer is deposited with lower power and higher hydrogen flow ratio to achieve lower internal stress and friction coefficient, while the second layer uses higher power to achieve higher hardness and wear resistance, creating a composite material system that balances multiple properties.
2Duration of action of stationary object
If the coating thickness is increased to extend service life, then the durability is improved, but the internal stress increases causing the coating to peel off
Solution Approach 1:
The thick coating (20-40 μm total) is segmented into two distinct layers with different thicknesses and properties. The first layer (10-20 μm) provides stress distribution and adhesion, while the second layer (5-15 μm) provides additional protection. This segmentation enables the coating to achieve greater thickness without proportional increase in internal stress.
Solution Approach 2:
Different deposition parameters are used for each layer: the first layer uses lower microwave power (800-1200 W) and higher hydrogen flow ratio (30-50%) to reduce internal stress, while the second layer uses higher power (1200-1600 W) to increase hardness. This parameter variation allows thick coating deposition while maintaining adhesion.
3Object-affected harmful factors
If a soft outer coating is added to reduce friction, then the friction coefficient is reduced, but the hardness of the composite coating decreases significantly
Solution Approach 1:
Instead of using a soft outer coating, the patent segments the coating into two diamond-like carbon layers with different properties. The first layer (lower power deposition) provides friction reduction with moderate hardness, while the second layer (higher power deposition) provides high hardness and wear resistance. This segmentation avoids the hardness reduction problem of soft coatings.
Solution Approach 2:
The composite structure uses two diamond-like carbon coatings with different deposition conditions creates a gradient in properties. The first layer has lower internal stress and friction coefficient, while the second layer has higher hardness, forming a composite material system that achieves both friction reduction and high hardness without using soft materials.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The coating achieves a significant reduction in friction coefficient by 10-30% and maintains high hardness, ensuring prolonged durability and lifecycle of the piston ring.
Implementation Method 1
it is reported that physical vapor deposition of a CrTiAlN/MoST composite coating is performed on a cold die steel Cr12MoV
Data Source
AI summary
Provided are a friction reduced and wear resistant coating, a preparation method thereof and a piston ring. The coating includes an adhesive layer, a transition layer, a gradient layer and a function layer in sequence. The gradient layer is a CrMoxN layer in which Mo content progressively increases. The function layer includes at least one cyclical layer. Each cyclical layer includes a first CrMoxN layer and a second CrMoxN layer in sequence from bottom to top. The Mo content of the first CrMoxN layer is lower than the Mo content of the second CrMoxN layer. The coating provided by the present invention has a friction coefficient of 0.3 to 0.45, 10% to 30% lower than a CrN coating, and has an overall hardness of up to 1400 HV to 2600 HV and a thickness of 80 μm, satisfying the required durability for the full lifecycle of the piston ring. The preparation process of the coating is simple and highly operable, and thus is convenient for industrialization.