CVD PVD Coated Cutting Tool Stress Management
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current cutting tools face challenges in achieving both high wear resistance and toughness, particularly in interrupted cutting operations, as CVD-coated tools excel in wear resistance but suffer from tensile stresses that reduce toughness, while PVD-coated tools have better toughness but lack wear resistance and adhesion.
Innovation Solution
A method involving a cemented carbide substrate coated with a combination of CVD and PVD layers, where the CVD layer is subjected to wet-blasting to convert tensile stresses to compressive stresses, followed by a diffusion-promoting heat treatment and a PVD coating, resulting in a tool with both high wear resistance and improved toughness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If CVD coating is used, then wear resistance is improved, but toughness deteriorates due to tensile stresses
Solution Approach 1:
The patent applies wet-blasting treatment to the CVD coating, which fundamentally changes the stress state parameter from tensile to compressive stresses. This parameter change resolves the contradiction by maintaining the wear resistance of CVD coating while improving toughness through compressive stresses that prevent crack propagation.
Solution Approach 2:
The patent creates a composite structure by combining CVD coating with PVD coating layers. The CVD layer provides wear resistance while the PVD layers contribute to toughness and compressive stresses. This composite approach allows both materials to contribute their advantageous properties, resolving the contradiction between wear resistance and toughness.
2Reliability
If PVD coating is used, then toughness is improved, but wear resistance deteriorates
Solution Approach 1:
The patent segments the coating system into distinct functional layers: an inner CVD coating layer optimized for wear resistance and outer PVD coating layers optimized for toughness. This segmentation allows each layer to perform its specialized function, with the CVD layer providing abrasion resistance and the PVD layers providing toughness and compressive stresses.
Solution Approach 2:
The patent applies local quality by giving different regions of the coating different properties. The inner CVD layer has high hardness and wear resistance, while the outer PVD layers have higher toughness and compressive stresses. Each layer is optimized for its specific location and function in the coating system.
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 method produces a cutting tool with compressive stresses in both CVD and PVD layers, enhancing toughness and wear resistance, outperforming previous combinations in chip forming machining operations.
Implementation Method 1
CVD-coated inserts show high wear resistance and excellent coating adhesion while PVD-coated inserts are slightly inferior with respect to these properties
Implementation Method 2
Due to the high deposition temperature and to a difference in thermal coefficient of expansion between the deposited coating materials and the cemented carbide tool substrate, CVD produces coatings with cooling cracks and rather high tensile stresses
Implementation Method 3
PVD processes run at a significantly lower temperature, 450-650°C and are conducted under strong ion bombardment which leads to crack free layers with high compressive stresses
Implementation Method 4
subjecting the CVD coating at least partly to an intensive wet-blasting operation such that said one or more Ti(CxNy) layers obtain compressive stresses in the range 600 to 1600 MPa
Implementation Method 5
performing a diffusion promoting heat treating step at 980 to 1030 °C for 1-4 h in an H2/N2-atmosphere, after depositing the CVD coating but before the intensive wet-blasting operation
Implementation Method 6
performing a diffusion promoting heat treating step at 980 to 1030 °C for 1-4 h in an H2/N2-atmosphere
Data Source
Figure 1
AI summary
The invention relates to a method of producing a cutting tool at least partly coated with an inner CVD coating and an outer PVD coating comprising the manufacturing steps of depositing the CVD coating, subjecting the CVD coating at least partly to an intensive wet-blasting operation, followed by depositing the PVD coating. The invention also relates to a coated cutting tool comprising a cemented carbide substrate of 5-14 wt-% Co, 0-8 wt-% cubic carbides of Ti, Ta or Nb or a combination thereof, and balance WC, said substrate being at least partly coated with a 4-14 µm thick coating comprising an inner CVD coating and an outer PVD coating wherein the CVD coating has compressive stresses.