OPTIMIZATION OF CHEMICAL PRETREATMENT FOR REMOVING COBALT ON TUNGSTEN CARBIDE SUBSTRATE USING RESPONSE SURFACE METHODOLOGY

At a Glance

Metadata	Details
Publication Date	2016-05-30
Journal	Jurnal Teknologi
Authors	A. Shah, S. Izman, Mas Ayu Hassan, Ramlee Mustapha
Institutions	Sultan Idris Education University, Universiti Malaysia Pahang Al-Sultan Abdullah
Citations	1
Analysis	Full AI Review Included

Technical Documentation & Analysis: MPCVD Diamond on Pretreated WC-Co Substrates

Executive Summary

This research focuses on optimizing the chemical pretreatment of Tungsten Carbide (WC) substrates to ensure superior adhesion and quality of subsequent diamond coatings—a critical step for high-performance cutting tools and microelectronic applications.

Core Challenge Addressed: Eliminating residual Cobalt (Co) binder from WC substrates, which severely inhibits diamond nucleation and growth during MPCVD.
Methodology: Full Factorial Design and Response Surface Methodology (RSM) were successfully employed to model and optimize the single-step etching process.
Etching Parameters: Caro acid (H${2}$O${2}$ + H${2}$SO${4}$) was used, with Etching Time (B) identified as the most significant factor influencing Co removal, followed by Temperature (A).
Optimal Process Window: Minimum residual cobalt content was achieved by etching at 48°C to 50°C for 3 minutes.
Performance Achievement: The pretreatment reduced the initial cobalt content (6% wt) to a minimum residual content of approximately 0.34% to 0.41%, meeting the critical requirement of <1% residual Co for high-adhesion diamond films.
Model Reliability: The developed quadratic empirical model demonstrated high accuracy, with an R² value of 0.9878.

Technical Specifications

The following hard data points were extracted from the experimental optimization of the WC-Co substrate pretreatment process.

Parameter	Value	Unit	Context
Substrate Material	WC with 6% wt Co	-	Standard cemented carbide
Initial Cobalt Content	6	%	Before chemical pretreatment
Target Residual Cobalt	< 1	%	Required for high-quality diamond adhesion
Achieved Minimum Co Content	0.336608	%	Optimal predicted result (Table 8)
Optimal Etching Temperature (A)	48 to 50	°C	Working temperature range
Optimal Etching Time (B)	3	minutes	Most significant factor
Etchant Composition (H${2}$O${2}$)	88 (30%)	ml	Caro acid component
Etchant Composition (H${2}$SO${4}$)	3 (95%)	ml	Caro acid component
R² Value (Quadratic Model)	0.9878	-	Model fit accuracy
Substrate Dimensions	ø12 x 3	mm	Cylindrical sample size
Surface Roughening Abrasive	Al${2}$O${3}$ (#180 grit)	-	Used prior to etching

Key Methodologies

The experiment utilized a systematic approach combining mechanical roughening, chemical etching, and statistical optimization (RSM) to achieve optimal cobalt removal.

Workpiece Preparation: Tungsten Carbide (WC) samples (6% wt Co) were cut into cylindrical dimensions (ø12mm x 3mm).
Surface Roughening: Samples were blasted for 10 seconds using a Blasting Wear Tester (BWT) with Al${2}$O${3}$ (#180 grit) to enhance surface area for etching and subsequent diamond nucleation.
Cleaning: Samples were cleaned with acetone to remove surface contaminants prior to chemical treatment.
Etchant Preparation: Caro acid was prepared by mixing 88ml of 30% Hydrogen Peroxide (H${2}$O${2}$) and 3ml of 95% Sulfuric Acid (H${2}$SO${4}$).
Etching Process: Samples were etched in the Caro acid solution under ultrasonic vibration at varied temperatures (35°C to 55°C) and times (1 to 3 minutes).
Analysis: Residual cobalt content was quantified using Energy Dispersive X-ray (EDAX) integrated within a Scanning Electron Microscopy (SEM) system.

6CCVD Solutions & Capabilities

6CCVD is the ideal partner for researchers and engineers seeking to translate optimized substrate preparation (like this WC-Co etching process) into high-performance diamond coatings for demanding applications such as cutting tools, microelectronics, and thermal management.

Applicable Materials

To replicate or extend this research, 6CCVD recommends materials optimized for high wear resistance and thermal stability, leveraging the successful substrate pretreatment:

High-Purity Polycrystalline Diamond (PCD): Ideal for cutting tools and wear parts, offering exceptional hardness and thermal conductivity on pretreated WC substrates. 6CCVD provides PCD plates up to 125mm in diameter.
Electronic Grade Single Crystal Diamond (SCD): Required for high-power microelectronics and thermal management systems where the substrate preparation is critical for minimizing interface defects and maximizing heat dissipation.
Boron-Doped Diamond (BDD): For electrochemical or sensing applications where the diamond coating must be conductive. BDD can be deposited directly onto pretreated WC-Co substrates, leveraging the improved adhesion.

Customization Potential

The success of this pretreatment relies on precise material handling and subsequent diamond deposition. 6CCVD offers comprehensive customization services that directly support the requirements of this research:

Requirement from Paper	6CCVD Capability	Technical Specification
Substrate Dimensions	Custom wafer/plate fabrication	Plates/wafers up to 125mm (PCD); Substrates up to 10mm thick.
Diamond Layer Thickness	Precision growth control	SCD (0.1µm - 500µm); PCD (0.1µm - 500µm).
Surface Quality	Advanced polishing services	SCD: Ra < 1nm; Inch-size PCD: Ra < 5nm.
Post-Processing	Custom metalization	Internal capability for Au, Pt, Pd, Ti, W, Cu contacts/interlayers, crucial for electronic applications.
Logistics	Global supply chain	Global shipping (DDU default, DDP available) ensures rapid delivery of custom materials.

Engineering Support

The optimization of the WC-Co interface is paramount for diamond coating quality. 6CCVD’s in-house PhD team specializes in interface engineering and material selection for similar High-Adhesion Diamond Coating projects. We provide consultation on:

Nucleation Enhancement: Selecting optimal diamond seeding methods post-etching to maximize nucleation density on the cobalt-depleted surface.
Process Scaling: Assisting clients in scaling the optimized pretreatment parameters (48°C - 50°C, 3 min) to larger industrial-scale MPCVD processes.
Adhesion Testing: Providing materials compatible with industry-standard adhesion tests (e.g., Rockwell indentation, scratch testing) to validate the effectiveness of the pretreatment/coating combination.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

View Original Abstract

Diamond coating are commonly used in industries especially for application such as cutting tools, biomedical components, optical lenses, microelectronics, engineering, and thermal management systems. The diamond coating quality is strongly depending on substrate preparation prior to diamond coating. Thus, the several process parameters must be studied to obtain optimal parameters which lead high quality diamond coating. In this present work, an attempt was made to optimize pretreatment parameters namely temperature and time on cobalt removal of tungsten carbide. Full factorial experimental designs followed by Response Surface Methodology (RSM) were employed in this study to plan and analyze the experiment. The cobalt removal was the independent response variables. Empirical model was successfully developed to predict amount of cobalt removal on the substrate after single step etching process. Experimental results have shown that the temperature, time and time2 are found to be the most significant factors for cobalt removal. Whereas for interaction of time and temperature were insignificant factors to influence cobalt removal. According to this study, the minimum cobalt content can be obtained at working temperature from 48 to 50C for 3 minute.

Tech Support

Original Source

DOI: https://doi.org/10.11113/jt.v78.8830