cBN Polycrystal Toughness via Granular-Tabular Microstructure
Solution Overview
Problem
Cubic boron nitride (cBN) polycrystals synthesized for cutting tools and wear-resistant tools have grain sizes that are either too large for microfabrication applications or, when reduced, become prone to cracking and lack toughness under high load processing.
Innovation Solution
A manufacturing method involving the direct conversion of hexagonal boron nitride to cubic boron nitride at ultra-high pressure and temperature, with a combination of granular and tabular cBN structures, and inclusion of wurtzite-type boron nitride, results in a polycrystal with high hardness and small grain size, inhibiting crack development and enhancing toughness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the grain size of cBN polycrystal is reduced for microfabrication applications, then the suitability for microfabrication is improved, but the toughness and resistance to cracking under high load processing deteriorates
Solution Approach 1:
The patent applies local quality by creating a heterogeneous microstructure with two distinct grain types: fine granular grains (50-200 nm) providing hardness and toughness, and coarse tabular grains (1-10 μm) providing crack resistance. Each grain type is optimized for its specific function within the composite structure, resolving the contradiction between fine grain size and toughness.
Solution Approach 2:
The patent creates a composite microstructure combining two different grain morphologies (granular and tabular) within the same cBN polycrystal. This composite structure integrates the advantages of both grain types: fine granular grains for hardness and toughness, and coarse tabular grains for crack resistance, thereby resolving the contradiction between grain size reduction and toughness maintenance.
2Strength
If a binding agent is added to cBN sinter to improve strength, then the strength is improved, but the heat resistance and heat diffusion deteriorate
Solution Approach 1:
The patent extracts and eliminates the binding agent component from the cBN sinter composition. By achieving strong intergranular bonding through direct cBN-cBN contact in a dense microstructure without organic or metallic binders, the patent removes the source of heat resistance deterioration while maintaining strength through the inherent properties of cBN and optimized microstructure.
3Volume of stationary object
If a catalyst is used in cBN sinter manufacturing to improve density, then the density is improved, but the heat-resistant temperature deteriorates due to thermal expansion difference
Solution Approach 1:
The patent extracts and eliminates the catalyst component from the final sinter structure. By achieving complete conversion of hBN to cBN and creating a dense microstructure through optimized pressure-temperature treatment without residual catalyst particles, the patent removes the source of thermal expansion mismatch while maintaining density through direct cBN grain contact.
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 complex polycrystal exhibits high hardness and toughness, suitable for cutting tools, wire-drawing dies, and grinding tools, with improved performance in microfabrication and high-load processing applications.
Implementation Method 1
the direct conversion of hexagonal boron nitride to cubic boron nitride at ultra-high pressure and temperature
Implementation Method 2
A manufacturing method involving the direct conversion of hexagonal boron nitride to cubic boron nitride at ultra-high pressure and temperature
Data Source
Figure 1
AI summary
A cubic boron nitride complex polycrystal comprising wurtzite-type boron nitride at 10 to 95 v/v%; and cubic boron nitride and unavoidable impurities as the remainder, the average grain size of said cubic boron nitride being 200 nm or less.