Hard Carbon Piston Ring Coating for Thick-Film Crack Resistance
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Solution Overview
Problem
Existing sliding members with diamond-like carbon (DLC) coatings face challenges in achieving both high peeling resistance and wear resistance, particularly when the coating thickness exceeds 3 μm, as they tend to become brittle and prone to cracking.
Innovation Solution
A DLC coating with a thickness of 3 μm or more, a hydrogen content of 3 atomic % or less, and a Martens hardness to indentation hardness ratio of 0.40 or more is developed, using ion plating with specific bias voltage and arc discharge current settings, and optionally incorporating an intermediate layer of Cr, Ti, Co, V, Mo, or their carbides/nitrides, to enhance peeling and wear resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the DLC coating thickness is increased to 3 μm or more to improve durability, then wear resistance should improve, but the coating becomes prone to cracking and peeling due to excessive brittleness
Solution Approach 1:
The patent applies parameter changes by precisely controlling the hydrogen content (3 atomic % or less) and adjusting the hardness parameters (Martens hardness HM and indentation hardness HIT with HM/HIT ≥ 0.40) of the DLC coating. This resolves the contradiction by modifying the coating's physical parameters to achieve both sufficient thickness (3 μm or more) and adequate flexibility to prevent cracking while maintaining wear resistance.
Solution Approach 2:
The patent introduces an intermediate layer between the base member and the DLC coating, creating a composite structure. This intermediate layer acts as a buffer that reduces stress concentration at the coating-substrate interface, allowing the DLC coating to be thicker without compromising integrity, thus resolving the contradiction between durability and coating strength.
2Strength
If the Young's modulus of the coating is increased to improve hardness, then wear resistance improves, but the coating becomes more prone to cracking and peeling
Solution Approach 1:
The patent resolves this contradiction by changing the hardness evaluation parameters from solely relying on Young's modulus to using Martens hardness (HM) and indentation hardness (HIT) with a specific ratio (HM/HIT ≥ 0.40). This parameter change allows for optimized hardness that balances wear resistance with reduced brittleness, preventing cracking and peeling while maintaining adequate hardness.
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 solution achieves a sliding member with improved peeling and wear resistance, balancing coating rigidity and plastic hardness to prevent brittleness and cracking, while maintaining durability and adhesion.
Implementation Method 1
performing ion plating that effectively regulates the hydrogen content of the coating to 3 atomic % or less
Implementation Method 2
ion plating with specific bias voltage and arc discharge current settings
Data Source
AI summary
A sliding member having a hard carbon coating that has a thickness of 3 μm or more and demonstrates high peeling resistance and high wear resistance is provided. A sliding member 100 according to the present disclosure includes a base member 10 and a hard carbon coating 12 that is formed on the base member 10 and has the hydrogen content of 3 atomic % or less and a thickness of 3 μm or more. When HM represents a Martens hardness of the hard carbon coating 12 and HIT represents an indentation hardness, the ratio HM/HIT is 0.40 or more.