Polycrystalline cBN Composition for Crack-Resistant Cutting Tools
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Solution Overview
Problem
Polycrystalline cubic boron nitride (cBN) sintered materials exhibit poor crack resistance, leading to easy chipping of cutting edges in tools due to their low elastic limit and susceptibility to tensile stress.
Innovation Solution
The development of polycrystalline cBN with a ratio of second length to first length (d2/d1) of 0.99 or less, measured through a Knoop hardness test, enhances the elastic limit and crack resistance by allowing for elastic deformation, reducing the occurrence of cracks and chipping.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If polycrystalline cubic boron nitride sintered materials are used for cutting tools, then high hardness is achieved, but crack resistance deteriorates leading to easy chipping of cutting edges
Solution Approach 1:
The invention changes the elastic limit parameter of polycrystalline cBN by controlling the ratio of second length to first length (d2/d1) to be 0.99 or less during sintering. This parameter change allows the material to exhibit elastic deformation capability while maintaining high hardness, thereby resolving the contradiction between hardness and crack resistance
Solution Approach 2:
The invention utilizes phase transition during sintering to transform the microstructure of polycrystalline cBN. By controlling the sintering process, the material undergoes phase transition that results in a specific d2/d1 ratio, enabling elastic deformation and improving crack resistance while maintaining the hard cubic boron nitride phase
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 improved crack resistance and elastic limit of polycrystalline cBN result in reduced chipping and enhanced performance of cutting tools, with a first Knoop hardness of 40 GPa or more and less than 54 GPa, facilitating better processing accuracy and tool durability.
Implementation Method 1
A ratio of a second length to a first length is 0.99 or less. Each of the first length and the second length is a value measured on a surface of the polycrystalline cubic boron nitride with an indentation formed by a Knoop hardness test under conditions specified in ISO4545-1 and ISO4545-4.
Implementation Method 2
The streaky indentation is measured by observing the surface of the polycrystalline cubic boron nitride with a field emission scanning electron microscope at a magnification of no less than 5000 times and no more than 10000 times.
Implementation Method 3
The second length is measured by observing the surface of the polycrystalline cubic boron nitride with an optical microscope at a magnification of no less than 500 times and no more than 1000 times.
Data Source
AI summary
A polycrystalline cubic boron nitride includes a cubic boron nitride particle group. The ratio of a second length to a first length is 0.99 or less. Here, each of the first length and the second length is a value measured on a surface of the polycrystalline cubic boron nitride with an indentation formed by a Knoop hardness test under conditions specified in ISO4545-1 and ISO4545-4. The second length represents the length of the longer diagonal of the indentation. The first length represents the sum of the second length and the length of the streaky indentation.