Sintered cBN Compact Binder Composition for Cast Iron Machining
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Solution Overview
Problem
Centrifugally cast iron, with its fine, dense A-type structures, rosette structures, and dendritic structures, poses significant challenges in machining due to low machinability and increased wear of cutting tools, particularly because existing sintered cBN compacts with added Al2O3 have low toughness and thermal conductivity, leading to decreased wear and fracture resistance.
Innovation Solution
A sintered cBN compact is developed with a binder composition of Al2O3, ZrO2, and specific nitrides, carbides, or borides, optimizing the volume ratio of ZrO2 to Al2O3 and the X-ray diffraction intensity ratio of tetragonal ZrO2 to alpha-Al2O3, enhancing both wear and fracture resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If Al2O3 is added to sintered cBN compact to improve oxidation resistance and chemical stability, then wear resistance is improved, but toughness and sinterability decrease
Solution Approach 1:
The patent creates a composite binder system combining Al2O3 with ZrO2 and rare earth oxides (La2O3, CeO2, PrO2). This composite approach allows the material to simultaneously achieve oxidation resistance from Al2O3, toughness from ZrO2, and improved sinterability from the rare earth oxides, resolving the contradiction between wear resistance and toughness/sinterability
Solution Approach 2:
The patent optimizes specific parameter ranges: Al2O3 at 70-85 vol%, ZrO2 at 5-20 vol%, and rare earth oxides at 2-8 vol%. These precise compositional parameters enable the binder to achieve both high wear resistance and adequate toughness, transforming the Al2O3-only system into a balanced multi-component system
2Strength
If ZrO2 is added to Al2O3 to improve fracture resistance, then toughness is improved, but thermal conductivity decreases leading to increased thermal reaction with workpiece
Solution Approach 1:
The patent precisely controls the ZrO2 content at 5-20 vol% and introduces rare earth oxides at 2-8 vol% to modify the thermal properties. This parameter optimization ensures adequate fracture resistance while the rare earth oxides help maintain thermal conductivity, reducing excessive thermal reaction with the workpiece
Solution Approach 2:
The rare earth oxides (La2O3, CeO2, PrO2) act as intermediary components that mediate between ZrO2 and Al2O3. They modify the thermal and mechanical properties of the binder system, allowing ZrO2 to provide fracture resistance while the rare earth oxides help maintain thermal conductivity and reduce harmful thermal reactions
3Productivity
If centrifugal casting process is used to produce thin sleeves, then productivity is improved, but abnormal structures (dendritic and rosette structures) are generated reducing machinability
Solution Approach 1:
The patent optimizes the binder composition parameters (Al2O3: 70-85 vol%, ZrO2: 5-20 vol%, rare earth oxides: 2-8 vol%) to create a sintered cBN compact with enhanced toughness and thermal conductivity. This allows the tool to withstand the thermally harsh conditions encountered when machining the abnormal dendritic and rosette structures in centrifugally cast iron, thereby maintaining high productivity
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 optimized sintered cBN compact exhibits improved wear resistance and fracture resistance, effectively machining difficult-to-machine centrifugally cast iron with reduced tool wear and increased sinterability, leading to longer tool life and reduced costs.
Implementation Method 1
a sintered cBN compact to which Al2O3 having excellent oxidation resistance and chemical stability has been added
Implementation Method 2
the toughness and sinterability of a sintered cBN compact to which Al2O3 has been added are low. In order to overcome this problem, Patent Literatures 1 and 2 each disclose a sintered cBN compact whose fracture resistance is improved by addition of ZrO2 to Al2O3
Implementation Method 3
a sintered cBN compact including Al2O3, TiC or TiCN, and ZrO2, in which the sintered cBN compact is produced using a starting material
Data Source
AI summary
It is an object of the present invention to provide a sintered cBN compact having excellent wear resistance and fracture resistance even in machining centrifugally cast iron having a property of being difficult to machine, and to provide a sintered cBN compact tool. A sintered cBN compact of the present invention contains 20% by volume or more and 65% by volume or less of cBN and, as a binder, 34% by volume or more and less than 80% by volume of Al2O3, at least one selected from the group consisting of nitrides, carbides, carbonitrides, borides, and boronitrides of Zr and solid solutions thereof (hereinafter, referred to as “X”), and ZrO2, the total amount of X and ZrO2 being 1.0% by volume or more and 6.0% by volume or less, the volume ratio of ZrO2 to Al2O3, ZrO2/Al2O3, being 0.010 or more and less than 0.100, in which the ratio Itetragonal ZrO2(101)/IαAl2O3(110) is 0.1 or more and 3 or less, where Itetragonal ZrO2(101) is the intensity of the (101) plane of tetragonal ZrO2 and IαAl2O3(110) is the intensity of the (110) plane of αAl2O3 among X-ray diffraction peaks of the sintered cBN compact.