Diamond Coated WC-Co Substrates via CrN Interlayer
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current diamond coating technologies face challenges with poor adhesion of diamond films to cemented carbide substrates due to thermal expansion mismatch and chemical incompatibility, leading to residual stress and delamination, especially with substrates like tungsten carbide cobalt (WC—Co) where cobalt acts as a catalyst converting diamond to graphite.
Innovation Solution
A novel methodology involving the formation of a crystalline stoichiometric chromium nitride (CrN) interlayer prior to diamond deposition, which serves as a diffusion barrier and promotes adhesion by maintaining high crystallinity and acting as a barrier for cobalt and carbon diffusion, thereby enhancing the bonding between the diamond film and the WC—Co substrate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If diamond film is deposited directly on WC-Co substrate, then carbon absorption occurs, but adhesion deteriorates due to thermal expansion mismatch and chemical incompatibility
Solution Approach 1:
A chromium nitride (CrN) interlayer is introduced between the WC-Co substrate and the diamond film. This interlayer acts as a mediator that reduces thermal expansion mismatch and prevents direct chemical interaction between cobalt and carbon, thereby reducing residual stress and improving adhesion without causing delamination.
Solution Approach 2:
The harmful cobalt binder is extracted or removed from the substrate surface through selective etching or plasma treatment before diamond deposition. This eliminates the catalytic conversion of diamond to graphite and reduces harmful chemical interactions at the interface.
2Stability of the object's composition
If cobalt binder is present in WC-Co substrate, then substrate integrity is maintained, but diamond formation is inhibited due to catalytic conversion to graphite
Solution Approach 1:
The chromium nitride interlayer serves as a protective barrier that prevents direct contact between cobalt and carbon during diamond deposition. This allows the cobalt binder to remain in the substrate for maintaining integrity while preventing its harmful catalytic effect on diamond formation.
Solution Approach 2:
The substrate structure is segmented into distinct functional layers: the WC-Co substrate maintains mechanical integrity, the CrN interlayer provides chemical protection and stress management, and the diamond film delivers wear resistance. This segmentation allows each layer to fulfill its specific function without interfering negatively with others.
3Strength
If thicker diamond coating is applied, then wear resistance improves, but adhesion deteriorates due to increased residual stress
Solution Approach 1:
The chromium nitride interlayer is applied beforehand as a cushioning layer that accommodates thermal expansion differences and stress buildup. This pre-prepared stress management layer allows thicker diamond coatings to be applied without causing delamination, as the interlayer absorbs and distributes mechanical stresses.
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 approach results in excellent adhesion of the diamond film to the WC—Co substrate, maintaining fine structural features and extending the life of diamond-coated tools by reducing residual stress and graphite formation, allowing for thicker diamond coatings without delamination.
Implementation Method 1
serves as a diffusion barrier and promotes adhesion by maintaining high crystallinity and acting as a barrier for cobalt and carbon diffusion
Implementation Method 2
face challenges with poor adhesion of diamond films to cemented carbide substrates due to thermal expansion mismatch and chemical incompatibility, leading to residual stress and delamination
Implementation Method 3
Carbon CVD is essentially based on contacting a surface of a substance susceptible to carbon vapors, namely to a carbon-containing gas
Data Source
AI summary
A composite structure, comprising a cemented carbide substrate (e.g., tungsten carbide substrate cemented with cobalt, such as WC—Co), a thin interlayer disposed over the substrate, and a contiguous diamond film disposed over the interlayer, as well as processes of preparing such a composite structure and uses thereof, are provided. The composite structure is characterized by at least one of a substrate binder concentration of at least 2 percents by weight, interlayer thickness less than 20 microns, a homogenous interlayer made substantially of crystalline chromium nitride, a low to null binder concentration in the interlayer, and a high co-adhesion of the diamond film to the interlayer and the interlayer to the substrate.