Binder-Free cBN Polycrystal Sintering for Tough Cutting Tools
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Solution Overview
Problem
Cubic boron nitride sintered materials with small grain sizes for cutting tools face challenges in strength and toughness due to impurities and binder presence, leading to low hardness and heat resistance, and high sintering temperatures result in low sinterability and chipping during machining.
Innovation Solution
A method to produce a cubic boron nitride polycrystal with an average grain size of not more than 100 nm, incorporating wurtzite type boron nitride and compressed hexagonal boron nitride, under specific high-pressure and high-temperature conditions, without binders or catalysts, to enhance density and toughness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If binder is added to cBN sintered material to improve sinterability, then sintering process becomes easier, but strength, heat resistance, and thermal diffusion property are reduced
Solution Approach 1:
The invention extracts and eliminates the binder component from the cBN sintered material composition. By using a catalyst-free sintering process, the material achieves bonding without organic binders, thereby maintaining high strength and heat resistance while still achieving adequate sinterability through the sintering process itself.
Solution Approach 2:
The invention changes the sintering parameters (temperature, pressure, atmosphere) to enable binder-free sintering. Specifically, sintering is performed at high temperature (1000-2000°C) in a nitrogen atmosphere without catalysts or binders, allowing direct bonding of cBN particles while preserving material properties.
2Volume of stationary object
If high sintering temperature is applied to improve density, then density increases, but sinterability decreases and chipping occurs during machining
Solution Approach 1:
The invention optimizes the combination of temperature and pressure parameters during sintering. By performing sintering at high temperature (1000-2000°C) combined with high pressure (3-10 GPa) in a nitrogen atmosphere, the process achieves both high density and good sinterability simultaneously, avoiding the chipping issue that occurs with temperature alone.
Solution Approach 2:
The invention creates a composite structure at the micro level by incorporating wurtzite-type BN and compressed hBN phases alongside cubic BN. This multi-phase composite approach improves overall sinterability and toughness while maintaining high density, as the different phases complement each other's properties.
3Speed
If grain size is reduced to improve hardness, then hardness increases, but toughness and resistance to cracking are reduced
Solution Approach 1:
The invention creates a composite microstructure containing cubic BN (for hardness), wurtzite-type BN (for toughness), and compressed hBN (for crack resistance). This multi-phase composite at the micro level achieves both high hardness from the fine cubic BN grains and high toughness from the other phases that can absorb and distribute stress.
Solution Approach 2:
The invention creates local quality variations in the material structure by having different phases distributed throughout the sintered body. The cubic BN provides local hardness, while wurtzite-type BN and compressed hBN provide local toughness and crack resistance, achieving overall balanced properties.
4Productivity
If catalyst is used to improve sintering efficiency, then sintering process becomes more efficient, but thermal expansion difference causes fine cracks under heat application
Solution Approach 1:
The invention extracts and eliminates the catalyst component from the sintering process. By performing catalyst-free sintering at high temperature and pressure in a nitrogen atmosphere, the process achieves adequate sintering efficiency without introducing foreign materials that would cause thermal expansion mismatch and cracking during subsequent heat application.
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 resulting cubic boron nitride polycrystal exhibits improved strength, toughness, and resistance to cracking, making it suitable for high-load cutting and precision machining applications with reduced wear and increased tool life.
Implementation Method 1
converting hexagonal boron nitride into cubic boron nitride under high pressure and high temperature
Implementation Method 2
sintering it at the same time
Data Source
AI summary
A cubic boron nitride polycrystal includes cubic boron nitride, the cubic boron nitride having an average grain size of not more than 150 nm, the cubic boron nitride polycrystal having a crack generation load of not less than 25 N in a breaking strength test in which an R200µm diamond indenter is used to apply a load at a rate of 100 N/min.