Polycrystalline CBN Composition for Binder-Free Cutting Edges
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Solution Overview
Problem
Conventional cubic boron nitride sintered bodies used in machining tools suffer from reduced strength and thermal diffusivity due to the presence of binders, and have shorter tool life when machining difficult-to-cut materials like Ti alloys, leading to blade edge damage and reduced tool life.
Innovation Solution
A polycrystalline cubic boron nitride with a dislocation density of more than 8×10^15/m² and a method for manufacturing it by heating and pressurizing hexagonal boron nitride powder to a temperature of 1700°C to 2500°C under 8 GPa, holding in the stable region of wurtzite boron nitride for 3 minutes to 60 minutes, without using a binder, to achieve a high cubic boron nitride content and improved dislocation density.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a binder is added to cubic boron nitride sintered body, then the sintered body can be manufactured, but the strength and thermal diffusivity of the sintered body decrease
Solution Approach 1:
The invention extracts and removes the binder component from the sintered body composition. By using a binder-free sintering process where hexagonal boron nitride is directly converted to cubic boron nitride under ultrahigh pressure and temperature, the harmful binder is completely eliminated, thereby maximizing strength and thermal diffusivity without compromising manufacturability
Solution Approach 2:
The invention changes the physical and chemical parameters of the sintering process by applying ultrahigh pressure (above 8 GPa) and high temperature (above 1700°C) to enable direct phase transformation from hexagonal to cubic boron nitride. This parameter change allows binder-free sintering, resolving the contradiction between manufacturability and strength
2Ease of manufacture
If a binder is added to cubic boron nitride sintered body, then the sintered body can be manufactured, but the tool life is shortened due to blade edge damage
Solution Approach 1:
The invention extracts and removes the binder component that causes blade edge damage during machining. The binder-free composition eliminates the source of damage, thereby extending tool life while maintaining ease of manufacture through direct sintering
Solution Approach 2:
The invention applies ultrahigh pressure and high temperature parameters to achieve binder-free sintering, which produces a denser, more durable sintered body structure that resists blade edge damage and extends tool life
3Strength
If the crystal grain size is reduced to increase strength, then the strength increases, but the manufacturing complexity increases due to precise control requirements
Solution Approach 1:
The invention changes the sintering parameters to ultrahigh pressure (above 8 GPa) and high temperature (above 1700°C), which naturally produce fine crystal grain structures without requiring complex control mechanisms. The extreme parameters simplify the process by achieving grain refinement through thermodynamic conditions rather than mechanical control
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 enhanced strength, toughness, and crack propagation resistance, leading to a longer tool life even in high load machining of iron and difficult-to-cut materials, with improved resistance to damage and reduced blade edge wear.
Implementation Method 1
heating and pressurizing the hexagonal boron nitride powder to a temperature greater than or equal to 1700° C. and less than or equal to 2500° C. and to a pressure greater than or equal to 8 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 a boron nitride polycrystalline body
Data Source
AI summary
A polycrystalline cubic boron nitride comprising 98.5% by volume or more of cubic boron nitride, wherein the cubic boron nitride has a dislocation density of more than 8×1015/m2, 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 0.1 μm or more and 0.5 μm or less.