Coated Cutting Tool Residual Stress Control Against Peeling
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Solution Overview
Problem
Existing coated tools using cemented carbide with WC as a hard phase face issues of peeling at the interface between the base and coating layer due to mismatched residual stresses, which lowers fracture resistance and adhesion strength.
Innovation Solution
A coated tool design with a base composed of W, C, and Ti phases, and a binding phase of iron group metals, where the residual stress of the hard phase ranges from −2.5 to −0.2 GPa, enhancing adhesion and reducing peeling by controlling the stress ratio between the base and surface to 1.2 or more, and utilizing a multi-layer coating of TiCN, Al2O3, and TiN layers deposited by CVD or PVD methods.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a coating layer is applied on cemented carbide base, then wear resistance is improved, but peeling occurs at the interface between base and coating layer due to residual stress mismatch
Solution Approach 1:
The invention changes the residual stress parameter of the hard phase in the base material from the conventional range to specifically −0.5 to 0 GPa, and controls the coating layer residual stress to −0.2 to 0.2 GPa. This parameter optimization resolves the stress mismatch that causes peeling, while maintaining the wear resistance benefit of the coating layer.
Solution Approach 2:
The invention applies different residual stress characteristics to different regions: the hard phase in the base material has controlled compressive or near-zero stress, while the coating layer has controlled low stress. This localized stress distribution prevents interface peeling while preserving the protective function of the coating.
2Ease of manufacture
If the coating layer has larger heat expansion coefficient than the base material, then coating can be applied, but tensile stress remains in the coating layer after coating completion, lowering fracture resistance
Solution Approach 1:
The invention optimizes the residual stress parameter in the coating layer to be within −0.2 to 0.2 GPa, which compensates for the tensile stress generated by the heat expansion coefficient mismatch. This allows the coating to be successfully applied while maintaining the base material's fracture 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 design improves adhesion strength, reduces peeling, and enhances wear resistance, allowing for stable cutting performance and extended tool life.
Implementation Method 1
multi-layer coating of TiCN, Al2O3, and TiN layers deposited by CVD or PVD methods
Implementation Method 2
multi-layer coating of TiCN, Al2O3, and TiN layers deposited by CVD or PVD methods
Data Source
AI summary
A coated tool in a non-limiting embodiment of the present disclosure includes a base and a coating layer located on a surface of the base. The base includes a hard phase including W and C, a solid solution phase including W, C, and Ti, and a binding phase including an iron group metal. A residual stress of the hard phase in the base is “a,” and the “a” is in a range of −2.5 to −0.2 GPa. A residual stress of the hard phase in the surface of the base is “b,” and the “b” is in a range of −2.0 to 0.0 GPa.