Polycrystalline CBN Compact Bimodal Particle Distribution
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Solution Overview
Problem
High CBN content polycrystalline compacts require a strong binder phase to achieve high abrasion resistance, edge integrity, strength, and heat resistance, but existing methods struggle to maintain a high CBN content while ensuring effective bonding and minimizing flaws in the material structure.
Innovation Solution
A method involving attrition milling of CBN particles with a binder phase to produce a bimodal particle size distribution, followed by high energy mixing and vacuum heat treatment, to create a polycrystalline CBN compact with at least 75% CBN content, where the binder phase forms a strong, ceramic bond with CBN grains, enhancing toughness and strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If CBN content is increased to exceed 75 percent by volume of the compact, then abrasion resistance and edge integrity are improved, but bonding between particles becomes insufficient due to limited CBN-to-CBN contact
Solution Approach 1:
The invention changes the particle size distribution parameter of CBN, using a bimodal distribution with fine particles (0.5-2 μm) and coarse particles (3-10 μm). The fine particles fill gaps and create numerous contact points, while coarse particles provide structural framework, enabling both high CBN content (>75 vol%) and sufficient bonding through optimized particle packing and contact geometry.
Solution Approach 2:
The invention creates a composite particle structure where fine CBN particles and coarse CBN particles work synergistically. The fine particles act as bonding mediators between coarse particles, forming a dense network with multiple contact points that provides both structural integrity and abrasion resistance while maintaining high overall CBN content.
2Reliability
If CBN content is decreased to the region of 40 to 60 percent by volume, then bonding is improved through increased matrix material, but abrasion resistance and hardness are reduced
Solution Approach 1:
The invention optimizes the particle size distribution parameters to achieve dense packing with minimal matrix material. The bimodal distribution allows fine particles to fill interstices between coarse particles, maximizing CBN volume fraction (>75%) while maintaining sufficient contact points for bonding, thereby achieving both high abrasion resistance and adequate bonding without excessive matrix material.
3Stability of the object's composition
If conventional high energy mixing methods are used to mix CBN particles and binder phase, then mixing homogeneity is achieved, but particle size distribution is not optimized and bonding flaws occur
Solution Approach 1:
The invention segments the CBN particles into two distinct size groups (fine: 0.5-2 μm and coarse: 3-10 μm) and processes them through a two-stage mixing method. First, fine particles are mixed with binder phase using attrition milling to ensure homogeneous distribution, then coarse particles are added and gently mixed. This segmentation approach achieves both mixing homogeneity and optimized particle size distribution without creating bonding flaws.
Solution Approach 2:
The invention performs preliminary mixing of the fine CBN particles with the binder phase using attrition milling before adding the coarse particles. This preliminary action ensures that the fine particles and binder are thoroughly homogenized, creating a uniform matrix that will properly bond the subsequently added coarse particles, thereby achieving both homogeneity and optimized particle distribution.
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 method results in polycrystalline CBN compacts with improved toughness, strength, and reduced flank wear rates during machining, suitable for applications in machining hard metals like grey cast iron and powder metallurgy steels, with a high CBN content and effective bonding.
Implementation Method 1
the binder phase forms a strong, ceramic bond with CBN grains
Implementation Method 2
subjecting a mixture of first CBN particles having an average particle size of 0.1 to 2 μm and a powdered binder phase to attrition milling
Implementation Method 3
subjecting the powdered composition to conditions of elevated temperature and pressure suitable to produce such a compact
Data Source
AI summary
A method of making polycrystalline CBN compacts, high in CBN content, is provided. The method includes making a powdered composition by subjecting a mixture of CBN, present in an amount of at least 80 volume percent of the mixture, and a powdered binder phase to attrition milling. This powdered mixture is subjected to conditions of elevated temperature and pressure suitable to produce CBN compacts.