cBN Cutting Tool Coating with (Al,Ti)N Buffer Layer
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Solution Overview
Problem
Coated tools with cBN sintered bodies face insufficient chipping resistance during high-speed cutting due to strain in the crystal lattice and inadequate bonding strength between layers, leading to a short service life.
Innovation Solution
A layered hard coating structure is applied, where an (Al,Ti)N layer acts as a buffer between the cBN body and the (Al,Ti,Si)N layer, controlling the orientation and strain caused by lattice mismatch, and optimizing the composition and thickness of both layers to enhance chipping and wear resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a hard coating layer made of (Al,Ti,Si)N is formed directly on cBN sintered body to improve wear resistance, then wear resistance is improved, but chipping resistance deteriorates due to strain in crystal lattice and insufficient bonding strength
Solution Approach 1:
An (Al,Ti)N intermediate layer is introduced between the cBN sintered body and the (Al,Ti,Si)N hard coating layer. This intermediate layer acts as a mediator that reduces lattice mismatch strain and improves bonding strength, preventing chipping while maintaining wear resistance of the outer (Al,Ti,Si)N layer.
Solution Approach 2:
The coating structure uses a composite layered design combining (Al,Ti)N and (Al,Ti,Si)N layers with specific composition ratios and thicknesses. The composite structure leverages the advantages of both materials: the (Al,Ti)N layer provides strain buffering and bonding, while the (Al,Ti,Si)N layer provides hardness and wear resistance.
2Strength
If Si content is increased in (Al,Ti,Si)N layer to improve wear resistance, then wear resistance is improved, but crystal lattice strain increases reducing chipping resistance
Solution Approach 1:
The (Al,Ti)N intermediate layer serves as a buffer that compensates for the crystal lattice strain introduced by Si atoms in the (Al,Ti,Si)N layer. This allows higher Si content for improved wear resistance while the intermediate layer absorbs the lattice mismatch strain, preventing chipping.
3Strength
If coating layer thickness is increased to improve wear resistance, then wear resistance is improved, but bonding strength between body and coating decreases leading to chipping
Solution Approach 1:
The coating system is segmented into two distinct layers: an (Al,Ti)N intermediate layer for bonding and strain management, and an (Al,Ti,Si)N hard coating layer for wear resistance. This segmentation allows each layer to be optimized for its specific function, with the intermediate layer ensuring strong bonding to the cBN substrate.
Solution Approach 2:
The (Al,Ti)N intermediate layer acts as a bonding mediator between the cBN sintered body and the (Al,Ti,Si)N hard coating layer, ensuring strong adhesion even when the total coating thickness is increased for enhanced wear resistance.
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 excellent chipping resistance and wear resistance over a long period, even under high-load conditions in high-speed cutting processes, such as alloy steel machining, by controlling the orientation and composition of the hard coating layers.
Implementation Method 1
the (Al,Ti)N layer as a buffer layer which buffers the strain caused by a lattice mismatch between the cBN body and the (Al,Ti,Si)N layer
Implementation Method 2
performing physical vapor deposition with respect to a hard coating layer made of an Al—Ti—Si composite nitride layer via a crystalline orientation history layer made of a Ti—Al composite nitride layer
Implementation Method 3
the highest peak appears on a (200) plane in the measurement by an X-ray diffraction device that uses a Cu-Kα X-ray
Data Source
AI summary
In a surface-coated cutting tool, an A layer made of an (Al1-xTix)N layer (0.35≤x≤0.6 by an atom ratio) and a B layer made of a (Al1-y-zTiySiz)N layer (0.35≤y≤0.6 and 0.01≤z≤0.1 by an atom ratio) are layered on a surface of a tool body in which at least a cutting edge is made of a cBN sintered body. A layer thickness ratio of the A layer and the B layer (tB/tA) is 2 to 5, an X-ray diffraction intensity ratio I(200)/I(111) as the entire hard coating layer is more than 3 and 12 or less, a full width at half maximum of a peak of I(200) is 0.3 to 1.0, the IA(200)/IA(111) of the A layer is 2 to 10, and a full width at half maximum of the peak of the IA(200) is 0.3 to 1.0.