Multilayer Hard Coating for Cutting Tools
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Solution Overview
Problem
Existing surface coated members, particularly cutting tools, face issues with impurities and structural distortion in hard coatings, leading to reduced service life and performance under high-temperature and high-pressure conditions during metal working.
Innovation Solution
A surface coated member with a hard coating comprising multilayer structures of alternating first and second unit layers, including compounds like TiN and AlN, and an intermediate layer, formed using the CVD method with controlled cooling to enhance wear resistance and stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a hard coating is formed by PVD method with continuous composition change, then wear resistance and toughness are improved, but impurities (droplets) are generated causing coating falling and reduced service life
Solution Approach 1:
The patent changes the deposition method from PVD to CVD, fundamentally altering the physical-chemical parameters of the coating process. This parameter change eliminates droplet formation by using chemical vapor deposition instead of physical vapor deposition, thereby removing the harmful impurities while maintaining coating quality and service life
Solution Approach 2:
The patent replaces the mechanical PVD process with a chemical CVD process. Instead of using physical vapor deposition and ion bombardment, the invention uses chemical reactions of vaporized precursors on the substrate surface, substituting a mechanical-physical system with a chemical system that does not generate droplets
2Stability of the object's composition
If Ti1-xAlxN coating is modified to hexagonal crystal wurtzite structure at high temperature, then distortion is mitigated, but thermal fatigue accelerates modification and causes chipping and fracture
Solution Approach 1:
The patent introduces an intermediate layer with specific composition and structure between the base material and the hard coating. This intermediate layer has different local properties (composition, crystal structure) that gradually transition from the base material to the outer hard coating, creating a gradient structure that reduces thermal stress concentration and prevents chipping while maintaining overall compositional stability
Solution Approach 2:
The patent creates a composite coating structure consisting of multiple layers with different compositions and properties: an intermediate layer and an outer hard coating layer. This composite structure combines the advantages of different materials, where the intermediate layer provides thermal stress relief and the outer layer provides hardness and wear resistance, thereby extending service life
3Reliability
If higher Al content is increased in Ti1-xAlxN coating, then oxidation resistance and hardness are improved, but welding resistance deteriorates
Solution Approach 1:
The patent applies local quality by creating an intermediate layer with specific Al content and composition that is different from the outer hard coating layer. The intermediate layer has optimized local properties that provide good adhesion and welding resistance, while the outer layer has high Al content for oxidation resistance, thereby achieving both requirements through spatial differentiation of material properties
Solution Approach 2:
The patent uses a composite multi-layer coating structure where the intermediate layer and outer hard coating layer have different compositions. The intermediate layer is designed with properties that ensure good welding resistance and adhesion, while the outer layer is optimized for oxidation resistance, creating a composite system that achieves multiple functions 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 solution improves wear resistance, welding resistance, and extends the service life of surface coated members by reducing thermal fatigue and chipping, while maintaining balance between hardness and strength.
Implementation Method 1
a first gas mixture constituted of AlCl3, TiCl4, H2, and argon and a second gas mixture constituted of NH3 and N2 as a nitrogen source are introduced into a CVD reactor vessel
Implementation Method 2
the Ti1-xAlxN coating is modified into a hexagonal crystal wurtzite structure to mitigate the distortion. Particularly, there is a tendency that this modification is accelerated at a high temperature
Data Source
AI summary
A surface coated member having improved stability and a longer service life is provided. The surface coated member includes a base member and a hard coating formed on a surface thereof. The hard coating is constituted of one or more layers. At least one layer among the layers is a layer including hard particles. The hard particles include a multilayer structure having a first unit layer and a second unit layer being layered alternately. The first unit layer includes a first compound. The second unit layer includes a second compound. The first compound and the second compound are respectively made of one or more kind of element selected from the group consisting of a group 4 element, a group 5 element, a group 6 element of a periodic table, and Al, and one or more kind of element selected from the group consisting of B, C, N, and O.