Sliding Member Carbon Coating for Wear and Chipping Resistance
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Solution Overview
Problem
Existing hard carbon layer coatings for sliding members, such as piston rings, face challenges in achieving both stable chipping resistance and wear resistance, particularly under high loads, due to trade-offs between film thickness, residual stress, and adhesion properties, with CVD methods producing films with low hardness and PVD methods struggling to form thick, durable layers with sufficient adhesion.
Innovation Solution
A coating film comprising alternating layers of black and white hard carbon, with an inclined region on the base material side for enhanced adhesion and a homogeneous region on the surface for consistent wear resistance, where the black layers provide strength and the white layers offer low frictionality, forming a stable and constant chipping and wear resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a hard carbon layer with high hardness is provided to improve wear resistance, then wear resistance is improved, but chipping resistance deteriorates
Solution Approach 1:
The coating film is divided into multiple alternating layers of high-hardness hard carbon layers and low-hardness soft carbon layers. This segmentation allows each layer to perform its specialized function: hard layers provide wear resistance while soft layers provide chipping resistance and stress relief, resolving the contradiction between these two properties.
Solution Approach 2:
The invention uses a composite structure combining materials with different mechanical properties - hard carbon (high hardness, low toughness) and soft carbon (low hardness, high toughness). This composite approach allows the coating to simultaneously achieve wear resistance from the hard layers and chipping resistance from the soft layers, which cannot be achieved with a single material.
2Duration of action of stationary object
If a thick coating film is provided to improve durability, then durability is improved, but residual stress increases causing peeling
Solution Approach 1:
The thick coating film is segmented into multiple thin alternating layers of hard and soft carbon. This segmentation distributes the residual stress across multiple interfaces and prevents stress concentration that would cause peeling, allowing the film to achieve both thickness and adhesion.
Solution Approach 2:
The soft carbon layers have different mechanical properties (lower hardness, higher ductility) compared to hard carbon layers. This parameter change in material properties allows the soft layers to absorb and relieve residual stresses, enabling thick films to be formed without peeling while maintaining durability.
3Reliability
If a hard carbon layer with low hardness is provided to improve chipping resistance, then chipping resistance is improved, but wear resistance deteriorates
Solution Approach 1:
The coating is segmented into alternating hard and soft carbon layers, where soft layers provide chipping resistance and hard layers provide wear resistance. This segmentation allows each material to be used in its optimal performance range without compromising the other property.
Solution Approach 2:
The composite structure combines soft carbon (high toughness, chipping resistance) with hard carbon (high hardness, wear resistance). The soft layers act as a tough matrix that prevents chip formation, while the hard layers provide the wear resistance needed, achieving both properties simultaneously.
4Duration of action of stationary object
If a thick coating film is provided to improve durability, then durability is improved, but adhesion deteriorates due to peeling
Solution Approach 1:
The thick film is segmented into multiple thin layers with alternating hard and soft carbon. This creates multiple bonding interfaces that distribute adhesion stresses, preventing peeling and maintaining adhesion even in thick films, thereby achieving both durability and adhesion.
Solution Approach 2:
The alternating hard and soft layers create variations in mechanical properties through the film thickness. The soft layers have higher ductility and can accommodate thermal and mechanical stresses, improving interfacial adhesion and preventing peeling, which enables thick films to maintain both durability and adhesion.
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 proposed coating film achieves stable and constant chipping and wear resistance, along with improved peeling resistance, even under high loads, by leveraging the strength of black hard carbon layers and low frictionality of white layers, ensuring durability and adhesion.
Implementation Method 1
the hard carbon layers formed by physical vapor deposition (PVD) methods described in Patent Documents 4 and 5
Implementation Method 2
the hard carbon layers formed by chemical vapor deposition (CVD) methods described in Patent Documents 1 to 3
Data Source
AI summary
A sliding member (10) including a coating film (1) composed of a hard carbon layer on a sliding surface (16) of a base material (11). The coating film has, when a cross section thereof is observed by a bright-field TEM image, a thickness within a range of 1 μm to 50 μm, and is configured by repeating units including black hard carbon layers (B), relatively shown in black, and white hard carbon layers (W), relatively shown in white, and laminated in a thickness direction, and comprise an inclined region, provided on a base material side, where thicknesses of white hard carbon layers (W) of the repeating units gradually increase in a thickness direction, and a homogeneous region\, provided on a surface side of the sliding member, where thicknesses of the white hard carbon layers (W) of the repeating units are the same or substantially the same in the thickness direction.