Ti(C,N) Coated Cutting Tool Insert with Stress Gradient
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Solution Overview
Problem
CVD-coated cutting tool inserts exhibit brittleness and low toughness due to cooling cracks and tensile stresses, which limits their performance in interrupted cutting operations, while PVD-coated inserts have higher toughness but lower wear resistance.
Innovation Solution
A CVD-coated cutting tool with a 4-10 μm thick coating comprising two adjacent Ti(C,N) layers, where the inner layer is deposited at a lower temperature and the outer layer at a higher temperature, resulting in a stress difference of 1000 MPa to 2500 MPa, and subjected to wet blasting to enhance toughness and wear resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If CVD coating technique is used, then wear resistance is improved, but toughness deteriorates due to cooling cracks and tensile stresses
Solution Approach 1:
The coating is divided into multiple functional layers: an inner layer deposited at lower temperature to maintain substrate integrity, and an outer layer deposited at higher temperature to provide superior wear resistance. This segmentation allows each layer to optimize its properties without compromising the other, resolving the contradiction between wear resistance and toughness.
Solution Approach 2:
The deposition temperature parameter is varied across different layers of the coating. The inner layer is deposited at a lower temperature to reduce thermal stress and maintain toughness, while the outer layer is deposited at a higher temperature to achieve enhanced wear resistance. This parameter change strategy enables simultaneous optimization of both contradictory properties.
2Reliability
If PVD coating technique is used, then toughness is improved, but wear resistance deteriorates
Solution Approach 1:
The inner layer acts as an intermediary between the substrate and the outer wear-resistant layer. It provides a transition zone that maintains toughness while supporting the outer layer's wear resistance function. This intermediary layer resolves the contradiction by mediating between the substrate's mechanical properties and the coating's protective functions.
Solution Approach 2:
The coating system is designed as a composite structure with distinct layers having different compositions and properties. The inner layer and outer layer are combined to create a composite coating that exhibits both toughness and wear resistance, effectively resolving the contradiction between these two properties that cannot be achieved with a single-material coating.
3Reliability
If high blasting pressure is used, then compressive stresses are increased improving toughness, but coating quality deteriorates with uneven edge line
Solution Approach 1:
Instead of applying uniformly high blasting pressure across the entire coating surface, the patent applies blasting treatment selectively to specific areas or uses moderate pressure that is sufficient to induce compressive stresses without being excessive enough to damage the coating. This partial action approach achieves the desired toughness improvement while maintaining edge line uniformity.
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 significant improvements in both toughness and wear resistance, particularly effective for cutting low alloyed and stainless steel, reducing smearing and coating fragment pull-out, and providing excellent flank wear resistance.
Implementation Method 1
The coatings are most frequently deposited by Chemical Vapour Deposition (CVD) or Physical Vapour Deposition (PVD) techniques
Implementation Method 2
PVD processes run at a significantly lower temperature, 450-650° C. and are performed under strong ion bombardment which leads to crack free layers with high compressive stresses
Implementation Method 3
Every treatment technique that exposes a CVD coating surface to an impact force such as wet- or dry blasting will lower the tensile stresses of the coating and thereby improve the toughness of the coated tool
Data Source
AI summary
A coated cutting tool includes a coating and a substrate. The substrate is at least partly coated with a 4-10 μm thick coating comprising two adjacent Ti(C,N)-layers where the difference (Δ) between the residual stress state of the inner layer and the residual stress state of the outer layer is 1000 MPa≦Δ≦2500 MPa, on at least a part of the cutting edge and/or on at least a part of the rake face. A method to produce such a difference between the residual stress states is also disclosed.