Sliding Element Coating with Layered DLC Structure
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing sliding elements, such as piston rings, face challenges in achieving a balance between low friction and wear resistance, as DLC coatings with layer thicknesses above or below 5 μm alter their properties, and PVD coatings based on hard materials like chromium nitride do not adequately reduce friction while maintaining wear resistance.
Innovation Solution
A sliding element with a coating structure from the inside outwards comprising an adhesive layer, a metal-containing DLC layer with tungsten, and a metal-free DLC layer, where the thickness ratio between the metal-free and metal-containing layers is between 0.7 and 1.5, and the top layer to total layer ratio is between 0.4 and 0.6, optimized for amorphous carbon composition and nanocrystalline tungsten carbide precipitates, ensuring balanced tribological properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If DLC coating layer thickness is increased above 5 μm, then wear resistance is improved, but layer properties alter (structure and composition) such that service life is not achieved
Solution Approach 1:
The coating is divided into multiple functional layers: an adhesive layer for substrate bonding, a metal-containing DLC layer (with tungsten) for stress compensation and wear resistance, and a metal-free DLC layer for low friction. This segmentation allows each layer to optimize its specific function while maintaining overall coating stability and performance.
2Stability of the object's composition
If DLC coating layer thickness is decreased below 5 μm, then coating uniformity is improved, but wear resistance is insufficient
Solution Approach 1:
The coating uses composite material structures combining different DLC types (metal-containing and metal-free) with an adhesive layer. The metal-containing DLC layer provides wear resistance and stress management, while the metal-free DLC layer maintains low friction, creating a composite system that achieves both uniformity and adequate wear protection.
3Strength
If PVD coating based on hard material (chromium nitride) is used, then wear resistance is achieved, but coefficient of friction is not sufficiently reduced
Solution Approach 1:
The invention changes the material parameters by using DLC (diamond-like carbon) instead of traditional PVD chromium nitride coatings. DLC provides inherently lower friction coefficients while maintaining wear resistance. The addition of metal elements (particularly tungsten) in the DLC layer further modifies the tribological parameters to achieve optimal friction and wear performance.
4Use of energy by moving object
If top layer (metal-free DLC) is made thicker to improve friction properties, then coefficient of friction is reduced, but wear values become worse
Solution Approach 1:
Different regions of the coating have different properties optimized for their specific functions. The metal-free DLC top layer provides low friction where it contacts the counterface, while the metal-containing DLC intermediate layer provides wear resistance and stress compensation. This local quality differentiation allows the coating to achieve both low friction and good wear resistance simultaneously.
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 significantly reduced wear and constant low friction coefficients, enhancing the service life of sliding elements by compensating internal stresses and maintaining optimal strength and toughness, particularly when the middle and top layers have similar thicknesses, thereby improving durability and performance in internal combustion engines.
Implementation Method 1
the metal-free DLC layer first introduces into the overall system, i.e. into the coating as a whole, very high internal stresses that, in the case of the metal-containing DLC layer being of a layer thickness similar to the thickness of the outermost layer, can be compensated in such a way that the coating is realised in an optimal manner with regard to the combination between strength and toughness
Implementation Method 2
the friction, which is directly associated with the fuel consumption in the case of internal combustion engines, can be kept to a low level by coatings of DLC (diamond-like carbon)
Implementation Method 3
Although such layers do have the necessary resistance to wear, they nevertheless do not have the required low coefficients of friction
Data Source
AI summary
The invention relates to a sliding element, such as a piston ring, having a coating on at least one running surface, which comprises, from the inside out, an adhesive layer (10), a metal-containing, preferably tungsten-containing, DLC layer (12), and a metal-free DLC layer (14), and is characterized in that the ratio of the thickness of the metal-free DLC layer to the thickness of the metal-containing DLC layer ranges from 0.7 to 1.5 and/or to the overall thickness of the coating ranges from 0.4 to 0.6.