Piston Ring CrMoN 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, as they either have limited friction reduction due to soft outer layers peeling off or high internal stress leading to coating failure with increased thickness.
Innovation Solution
A multi-layer coating structure comprising an adhesive layer, transition layer, gradient layer, and function layer with cyclical CrMo x N layers, where Mo content progressively increases, reducing internal stress and enhancing inter-layer bonding, allowing for a thicker coating up to 80 µm with improved wear resistance and friction reduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-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 is significantly lower and the coating peels off easily
Solution Approach 1:
The patent applies local quality by creating distinct layers with different properties: the CrTiAlN layer provides hardness and wear resistance, while the MoST layer provides low friction. Each layer is optimized for its specific function rather than trying to make a single layer perform both functions, resolving the contradiction between hardness and friction reduction.
Solution Approach 2:
The patent uses composite materials by combining CrTiAlN (a hard, wear-resistant material) with MoST (a soft, low-friction material) in a laminated structure. This composite approach allows the coating to simultaneously achieve high hardness from the CrTiAlN layer and low friction from the MoST layer, resolving the contradiction between these two properties.
2Strength
If the thickness of diamond-like coating is increased to improve wear resistance, then the wear resistance is improved, but the high internal stress causes the coating to peel off
Solution Approach 1:
The patent segments the coating into multiple thin layers (CrTiAlN and MoST alternating layers) rather than using a single thick layer. This segmentation reduces the internal stress in each individual layer while maintaining overall coating thickness for wear resistance, preventing peeling and improving adhesion reliability.
Solution Approach 2:
The patent changes the parameter of coating structure from a single thick layer to multiple thin alternating layers with different material compositions. This parameter change allows the coating to achieve the required thickness for wear resistance while keeping internal stress manageable through the laminated structure, preventing peeling.
3Strength
If a hard coating is applied to improve wear resistance, then the wear resistance is improved, but the friction coefficient remains high
Solution Approach 1:
The patent applies local quality by creating distinct layers with different properties: the CrTiAlN layer provides hardness and wear resistance, while the MoST layer provides low friction. Each layer is optimized for its specific function rather than trying to make a single layer perform both functions, resolving the contradiction between hardness and friction reduction.
Solution Approach 2:
The patent uses composite materials by combining CrTiAlN (a hard, wear-resistant material) with MoST (a soft, low-friction material) in a laminated structure. This composite approach allows the coating to simultaneously achieve high hardness from the CrTiAlN layer and low friction from the MoST layer, resolving the contradiction between these two properties.
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 10-30% reduction in friction coefficient and maintains high hardness, ensuring durability and extended lifecycle by avoiding defects and stress-related issues, facilitating a thicker, more durable wear-resistant layer.
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
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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.