Polycrystalline cBN Tool Grain Refinement
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Solution Overview
Problem
Polycrystalline cubic boron nitride tools used in precision machining suffer from short tool life due to damage and lattice defects, which reduces their effectiveness and durability.
Innovation Solution
A method involving the preparation of hexagonal boron nitride powder with a median diameter of 0.3 μm or less, followed by heating and pressurizing to temperatures between 1500°C and 2200°C and pressures of 10 GPa or more, passing through a stable region of wurtzite boron nitride, to produce a polycrystalline cubic boron nitride with a dislocation density of 8×10^15/m² or less and crystal grains smaller than 100 nm, thereby enhancing tool life.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a binder is added to cubic boron nitride sintered body to improve strength, then strength is improved, but thermal diffusivity decreases
Solution Approach 1:
The invention removes the binder component from the sintered body composition entirely. By using pure cubic boron nitride powder without any binder additives, the patent eliminates the trade-off between strength and thermal diffusivity that binders create, achieving both high strength and high thermal diffusivity simultaneously.
Solution Approach 2:
The invention changes the compositional parameter from a composite material (cubic boron nitride + binder) to a pure material (100% cubic boron nitride). This parameter change resolves the contradiction by eliminating the harmful effect of binders on thermal diffusivity while maintaining strength through pure cubic boron nitride consolidation.
2Reliability
If sintering is conducted at ultrahigh pressure and high temperature to directly convert hexagonal boron nitride into cubic boron nitride without binder, then thermal diffusivity is improved, but manufacturing complexity increases
Solution Approach 1:
The invention utilizes the phase transition from hexagonal boron nitride (hBN) to cubic boron nitride (cBN) under ultrahigh pressure and high temperature conditions. By controlling the heating and pressurizing path to pass through the stable region of wurtzite boron nitride, the patent achieves complete phase conversion without requiring binders, thereby improving thermal diffusivity while managing manufacturing complexity through precise parameter control.
3Reliability
If heating and pressurizing path passes through stable region of wurtzite boron nitride, then dislocation density is reduced, but processing time increases
Solution Approach 1:
The invention performs preliminary heating to raise the temperature to 900°C or higher before applying ultrahigh pressure, ensuring the material enters the stable region of wurtzite boron nitride. This preliminary thermal preparation facilitates subsequent phase transition to cubic boron nitride with low dislocation density, reducing the need for prolonged processing time during the actual pressurization phase.
Solution Approach 2:
The invention optimizes the heating and pressurizing parameters by defining specific ranges: temperature of 1500-2200°C and pressure of 10 GPa or more. By controlling the heating rate and holding time at critical temperatures, the patent achieves low dislocation density while minimizing total processing time through efficient parameter management.
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 polycrystalline cubic boron nitride exhibits improved strength, thermal diffusivity, and resistance to damage, leading to extended tool life and better performance in precision machining applications.
Implementation Method 1
heating and pressurizing the hexagonal boron nitride powder to a temperature greater than or equal to 1500° C. and less than or equal to 2200° C. and to a pressure greater than or equal to 10 GPa, with the temperature and the pressure passing through a temperature and a pressure in a stable region of a wurtzite boron nitride to obtain the polycrystalline cubic boron nitride
Data Source
AI summary
A polycrystalline cubic boron nitride comprising 96% by volume or more of cubic boron nitride, wherein the cubic boron nitride has a dislocation density of 8×1015/m2 or less, the polycrystalline cubic boron nitride comprises a plurality of crystal grains, and the plurality of crystal grains have a median diameter d50 of an equivalent circle diameter of less than 100 nm.