AlTiN Layered Coating for Chipping-Resistant Cutting Tools
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Solution Overview
Problem
Existing surface-coated cutting tools face challenges with chipping resistance and tool life due to excessive quenching causing tensile residual stress at the interface between TiN and AlN layers, and composite nitride or carbonitride layers lack sufficient chipping resistance despite high hardness and toughness.
Innovation Solution
A surface-coated cutting tool with a first hard coating layer having a sodium chloride-type crystal structure, where Al x Ti 1-x and Al y Ti 1-y layers are alternately stacked with varying atomic ratios, and a second hard coating layer with controlled thickness, enhancing adhesiveness and wear resistance, and applying compression residual stress to improve toughness and chipping resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If AlN layer thickness is increased to increase Al content in AlTiN coating, then Al content increases, but layer structure changes to wurtzite crystal structure resulting in reduction of hardness
Solution Approach 1:
The patent applies local quality by creating distinct regions within the coating layer with different Al contents. The AlN layer is designed with specific thickness (1-5 nm) to provide high Al content locally for oxidation resistance, while the TiN layer (3-10 nm) provides hardness. This local differentiation allows the coating to achieve both high Al content and maintained hardness without transitioning to wurtzite structure.
Solution Approach 2:
The coating is segmented into alternating TiN and AlN layers, with each layer having controlled thickness. This segmentation allows independent optimization of each layer's properties: TiN layers provide hardness and wear resistance, while thin AlN layers provide oxidation resistance. The total Al content can be increased by adjusting the ratio of AlN layer thickness to total coating thickness without compromising the hardness of TiN layers.
2Strength
If TiN and AlN layers are alternately layered to form hard coating, then wear resistance improves, but excessive quenching causes tensile residual stress at interface resulting in chipping
Solution Approach 1:
The patent applies parameter changes by carefully controlling the thickness parameters of TiN and AlN layers, as well as the cooling rate during deposition. The AlN layer thickness is limited to 1-5 nm and TiN layer to 3-10 nm to prevent excessive quenching. By adjusting these dimensional parameters and the cooling rate parameter, the patent reduces tensile residual stress at interfaces while maintaining the wear resistance benefits of the layered structure.
3Strength
If composite nitride or carbonitride layers are used to achieve high hardness and toughness, then mechanical properties improve, but chipping resistance remains insufficient
Solution Approach 1:
The patent uses composite materials by combining TiN and AlN in a layered structure. TiN provides hardness and wear resistance, while AlN contributes to oxidation resistance and toughness. The composite structure leverages the complementary properties of both materials to achieve high hardness and toughness while improving chipping resistance through controlled layer thickness and reduced residual stress.
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 high hardness, excellent toughness, and improved chipping resistance, leading to a longer tool life and enhanced wear resistance, particularly in high-speed cutting applications.
Implementation Method 1
a first hard coating layer including crystal grains having a sodium chloride-type crystal structure, where a first layer composed of nitride or carbonitride of AlxTi1-x and a second layer composed of nitride or carbonitride of Al 1-xTi x are stacked alternately into one or more layers
Data Source
Figure 1A~1B
Figure 2
Figure 3A~3B
AI summary
A surface-coated cutting tool includes a base material and a coating formed on a surface of the base material. The coating includes a first hard coating layer including crystal grains having a sodium chloride-type crystal structure. The crystal grain has a layered structure in which a first layer composed of nitride or carbonitride of AlxTi1-x and a second layer composed of nitride or carbonitride of AlyTi1-y are stacked alternately into one or more layers. The first layer each has an atomic ratio x of Al varying in a range of 0.76 or more to less than 1. The second layer each has an atomic ratio y of Al varying in a range of 0.45 or more to less than 0.76. The largest value of difference between the atomic ratio x and the atomic ratio y is 0.05≤x-y≤0.5. The first layer and the second layer adjacent to each other have a total thickness of 3 to 30 nm.