MoN/CrN Multilayer Coatings to Prevent Ring-Shaped Fractures
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Solution Overview
Problem
Molybdenum nitride coatings on components with substrate hardness below 65 HRC exhibit ring-shaped fractures during load application, such as in Rockwell indentation tests, due to inadequate interface behavior between the substrate and the coating, leading to wear and adhesive failures.
Innovation Solution
A layer system comprising a mixture of hexagonal and cubic phases of molybdenum nitride, or a multilayer MoN/CrN coating structure, is applied to the substrate surface, with a nitriding process enhancing substrate hardness before coating deposition, and a CrN adhesion layer improving adhesion without forming a white layer, using reactive PVD processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If molybdenum nitride coating is applied on substrate with hardness below 65 HRC, then wear reduction and friction reduction are achieved, but ring-shaped fractures occur during load application
Solution Approach 1:
The patent applies a composite coating structure consisting of MoN/CrN multilayers where CrN layers serve as adhesion promoters between the MoN coating and the substrate. This composite structure resolves the contradiction by maintaining wear resistance from MoN while improving interface strength through CrN adhesion layers, preventing ring-shaped fractures during load application.
Solution Approach 2:
The CrN layer acts as an intermediary between the MoN coating and the substrate surface. It provides a transition zone that improves adhesion and stress distribution at the interface, thereby preventing coating delamination and ring-shaped fractures while preserving the tribological benefits of MoN.
2Strength
If nitriding process is applied to increase substrate surface hardness, then adhesion between substrate and coating is improved, but process complexity increases
Solution Approach 1:
The patent combines the nitriding process with the PVD coating process in a single integrated treatment sequence. The nitriding is performed in-situ within the PVD chamber before coating deposition, eliminating the need for separate nitriding equipment and reducing overall process complexity while achieving improved substrate surface hardness and adhesion.
3Strength
If CrN adhesion layer is deposited to improve adhesion, then coating-substrate bonding is enhanced, but white layer formation may occur
Solution Approach 1:
The patent optimizes the deposition parameters for the CrN adhesion layer, specifically controlling the substrate temperature, nitrogen partial pressure, and deposition rate during the PVD process. By maintaining the substrate temperature below 200°C and adjusting nitrogen pressure, the formation of brittle white layers is prevented while still achieving strong adhesion between the MoN coating and substrate.
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 prevents ring-shaped fractures and adhesive failures, significantly enhancing wear resistance and tribological properties, with improved contact between the substrate and coating, even under high load conditions, as demonstrated by reduced wear and no fractures in Rockwell indentation tests.
Implementation Method 1
subjecting the substrate to be coated with the MoN coating to a nitriding process, wherein the substrate surface hardness is increased before depositing the MoN coating
Implementation Method 2
The MoN coatings in the context of the present invention were deposited by using a reactive PVD process
Data Source
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AI summary
The present invention relates to a component comprising a substrate surface coated with a coating comprising at least one MoN layer having a thickness not less than 40 nm, characterized in that between the substrate surface and the at least one MoN layer: i) a substrate surface hardened layer is comprised, which is a hardened, nitrogen-containing substrate surface layer that is the result of a nitriding treatment carried out at the substrate surface and has a thickness not less than 10 nm, preferably not less than 20 nm and not greater than 150 nm, and/or ii) a layer system composed of more than 2 MoN layers and more than 2 CrN layers is comprised, wherein the MoN and CrN layers forming the layer system are individual layers deposited alternate one on each other forming a multilayer MoN/CrN coating film.