MT-CVD TiCN Coating for Cutting Tool Thermal Crack Resistance
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Solution Overview
Problem
Cutting tools experience limited resistance to wear and thermal cracking during intermittent cutting operations, particularly in milling applications, due to the limitations of existing CVD coatings in handling thermo-mechanical shocks.
Innovation Solution
A multi-layered wear-resistant coating structure comprising a first CVD layer of titanium aluminium nitride followed by a moderate temperature CVD (MT-CVD) layer of titanium carbonitride with specific fiber texture and grain morphology, where the {111} crystallographic planes are preferentially oriented parallel to the substrate, enhancing the coating's resistance to wear and thermal cracking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If columnar microstructure is used, then thermal crack resistance is improved, but grain boundary strength deteriorates
Solution Approach 1:
The invention applies different microstructural qualities to different locations in the coating system. The first CVD layer has a microstructure optimized for wear resistance, while the second MT-CVD TiCN layer has a columnar microstructure optimized for thermal crack resistance. The local quality principle allows each layer to have the microstructure best suited for its specific function without compromising the other
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 coating significantly improves wear resistance and reduces thermal cracking in intermittent cutting operations, particularly in milling, by altering grain boundary growth direction and reducing the layer thickness to average grain diameter ratio, resulting in broader grains with improved mechanical properties.
Implementation Method 1
The hard coating consists of polycrystalline mono-metallic or multi-metallic hard phases. Examples of mono-metallic hard phases are TiN, TiC, TiCN and Al 2 O 3. Examples of multi-metallic hard phases are TiAIN and TiAICN. The hard phase coating layers are deposited on the substrate by CVD or PVD methods.
Implementation Method 2
The MT-CVD process is run in a temperature range of 675 - 950°C, and makes use of nitrile compounds, most commonly acetonitrile, to yield so called MT-TiCN coatings with a columnar microstructure
Data Source
AI summary
A coated cutting tool consisting of a substrate of cemented carbide, cermet, ceramics, steel or cubic boron nitride and a multi-layered wear resistant coating having a total coating thickness from 5 to 25 µm and comprising at least two refractory coating layers deposited by chemical vapour deposition (CVD) or moderate temperature chemical vapour deposition (MT-CVD), the at least two refractory coating layers including a first coating layer and a second coating layer being deposited on top of each other, wherein the first coating layer consists of titanium aluminium nitride or carbonitride Ti1-uAluCvNw, with 0.2 ≤ u ≤ 1.0, 0 ≤ v ≤ 0.25 and 0.7 ≤ w ≤ 1.15, and is deposited by CVD at a reaction temperature in the range from 600°C to 900°C, the second coating layer consists of titanium carbonitride TixCyN1-y, with 0.85 ≤ x ≤ 1.1 and 0.4 ≤ y ≤ 0.85, and is deposited on top of the first coating layer by MT-CVD at a reaction temperature in the range from 600°C to 900°C, wherein the second TixCyN1-y coating layer has a columnar grain morphology and the overall fiber texture of the TixCyN1-y coating layer is characterized by a texture coefficient TC (1 1 1) > 2, the TC (1 1 1) being defined as follows: wherein (h k l) = measured intensity of the (hkl) reflection I0 (h k l) = standard intensity of the standard powder diffraction data according to JCPDF- card no. 42-1489 n = number of reflections used in the calculation, whereby the (hkl) reflections used are: (1 1 1), (2 0 0), (2 2 0) and (3 1 1).