Coated Cemented Carbide Cutting Tool for Comb Crack Resistance
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Solution Overview
Problem
Cutting tools for metal machining often suffer from thermo-mechanically induced 'comb cracks' during intermittent machining, particularly in milling operations, leading to tool failure due to chipping, as existing coatings cannot contract freely and induce tensile stresses, which are exacerbated by cooling cracks.
Innovation Solution
A coated cutting tool with substoichiometric carbon content and the presence of Ti in the metal carbide or nitride coating, combined with a well-distributed eta phase and specific coating layers, is developed to delay and prevent comb crack formation by introducing compressive stresses and optimizing carbon content for even eta phase distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a coating is deposited on the cutting tool substrate, then wear resistance is improved, but cooling cracks are formed and tensile stresses are induced in the coating
Solution Approach 1:
The patent applies shot blasting treatment to change the surface parameters of the substrate, creating compressive stresses that counterbalance the tensile stresses in the coating. This parameter change in the substrate surface state resolves the contradiction by preventing crack formation while maintaining the coating's wear resistance function
Solution Approach 2:
The shot blasting treatment is performed before coating deposition to pre-introduce compressive stresses in the substrate surface. This preliminary anti-action counteracts the tensile stresses that will be induced during cooling, preventing cooling cracks from forming in the first place
2Stability of the object's composition
If the coating contracts during cooling, then coating integrity is maintained, but cooling cracks are formed due to restricted contraction
Solution Approach 1:
The patent introduces compressive stresses in the substrate surface through shot blasting as a counterbalancing force to the tensile stresses generated during coating cooling. This counterweight effect allows the coating to contract freely without forming cracks, maintaining integrity while eliminating the harmful cooling cracks
3Reliability
If compressive stresses are introduced by blasting, then resistance to comb crack formation is improved, but coating surface quality may be affected
Solution Approach 1:
The shot blasting treatment is performed as a preliminary step before coating deposition to establish the desired compressive stress state in the substrate. By performing this action beforehand, the coating is deposited onto a pre-prepared surface that will prevent comb cracks without requiring additional surface treatment after coating, thus maintaining surface quality
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 significantly enhances the resistance to comb crack formation, leading to improved tool life and performance in milling operations by preventing crack propagation and ensuring even eta phase distribution, which is critical for toughness and preventing brittleness.
Implementation Method 1
one way known in the art to increase the resistance to comb crack formation is to delay the crack formation and crack propagation in the coating by introducing compressive stresses in the coating by blasting
Implementation Method 2
a thin coating deposited for the purpose of generally improving wear resistance of the cutting tool
Implementation Method 3
In CVD coatings cooling cracks are formed during cooling after deposition
Implementation Method 4
The cemented carbide in the present invention has a substoichiometric carbon content SCC and an evenly distributed eta phase
Implementation Method 5
These cracks eventually lead to failure of the tool by chipping, being the rate limiting factor for tool life
Data Source
AI summary
The present invention relates to a coated cutting tool comprising a substrate of cemented carbide and a coating, the cemented carbide comprising WC and a binder phase comprising one or more of Co, Fe and Ni, the carbon content in the cemented carbide is a substoichiometric carbon content SCC wherein -0.13 wt%≤SCC<0 wt%, or -0.30 wt% ≤SCC≤ -0.16 wt%, and wherein the coating comprising one or more layers (A) being a metal carbide, metal nitride or metal carbonitride, the metal being at least one of Zr and Hf, optionally Ti is present in an amount of at most 10 at-% of the amount metal, and an aluminum oxide layer, the one or more layers (A) being situated between the substrate and the aluminum oxide layer.