Cubic Boron Nitride Coating Adhesion via Tungsten Intermediary
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Solution Overview
Problem
The existing surface-coated cubic boron nitride tools exhibit poor toughness and adhesion when subjected to large impact or varying loads, leading to short tool lifetimes due to inadequate bonding between the hard coating layer and the substrate.
Innovation Solution
A surface-coated sintered body with a sintered body of cubic boron nitride and a surface coating layer, where the adhesion layer is formed of amorphous W or ultrafine W particles, and a hard coating layer with specific stress and composition, enhancing adhesion and mechanical properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a hard coating layer is formed on a sintered body of cubic boron nitride, then wear resistance is improved, but toughness deteriorates and the coating may exfoliate under impact load
Solution Approach 1:
An intermediate layer comprising a metal layer and a gradient layer is introduced between the hard coating layer and the sintered body of cubic boron nitride. The metal layer (containing W, Mo, or Re) provides ductility and impact resistance, while the gradient layer with gradually changing composition ensures strong bonding to both the substrate and the hard coating, preventing exfoliation under impact loads while maintaining wear resistance.
Solution Approach 2:
The intermediate layer utilizes a gradient in metal content from the metal layer to the gradient layer, creating a gradual transition in mechanical properties. This parameter change in composition and structure allows the coating system to accommodate impact stresses without exfoliation while maintaining the hardness and wear resistance of the outer coating layer.
2Reliability
If an intermediate layer of metal compounds or metals is formed to enhance adhesion, then bonding between hard coating and substrate is improved, but insufficient chemical bonding occurs at the covalent interface under large impact loads
Solution Approach 1:
The gradient layer acts as a compositional intermediary between the metal layer and the sintered body of cubic boron nitride. Its gradual transition in metal content creates a continuum of bonding characteristics, enabling strong chemical bonding to the covalent substrate while maintaining compatibility with the metallic adhesion layer, thereby achieving robust interfacial bonding under impact loads.
Solution Approach 2:
The intermediate layer forms a composite structure combining metallic phases and gradient composition regions. This composite architecture provides both the ductility needed for impact resistance and the chemical bonding capability required for strong adhesion to the covalent cubic boron nitride substrate, overcoming the limitations of single-phase intermediate layers.
Data Source
AI summary
There is provided a surface-coated sintered body formed of a sintered body of cubic boron nitride with a sufficiently adhesive surface coating layer thereon. The present surface-coated sintered body includes a sintered body of cubic boron nitride and a surface coating layer formed on a surface thereof, the sintered body of cubic boron nitride including 20-99.5% by volume of cubic boron nitride and a binder, the surface coating layer including an adhesion layer and at least one hard coating layer, the adhesion layer being a metal layer including at least W, and being formed to cover a surface of the sintered body of cubic boron nitride, the hard coating layer being formed to coat the adhesion layer, the adhesion layer being configured of an amorphous state and/or ultrafine particles having an average particle size equal to or smaller than 5 nm.