Cobalt-Free Tungsten Carbide Sintering via Discharge Plasma
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Solution Overview
Problem
Conventional methods for preparing tungsten carbide (WC) sintered bodies for friction stir welding tools, such as powder metallurgy, require multiple stages, lead to increased costs, reduced hardness, and a short lifespan due to the addition of cobalt, and result in differences between internal and external physical properties.
Innovation Solution
A single-process discharge plasma sintering method using pulsed current activation to produce a WC sintered body with high density, strength, and abrasion resistance without cobalt, controlling particle growth and maintaining uniform internal and external properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If cobalt is added to tungsten carbide to improve toughness, then toughness is improved, but hardness is reduced and process cost is increased
Solution Approach 1:
The invention extracts and removes cobalt from the traditional WC-Co composite material system, creating a pure tungsten carbide sintered body. This eliminates the need for cobalt addition while maintaining or improving mechanical properties through optimized sintering processes and particle morphology control.
Solution Approach 2:
The invention changes the sintering parameters including using pulsed electric current sintering with specific temperature profiles (heating rate of 10-100°C/min, holding at 1400-2000°C), pressure conditions (30-100 MPa), and atmosphere control to achieve dense sintering of pure WC without cobalt, thereby improving hardness while maintaining toughness.
2Stability of the object's composition
If conventional powder metallurgy methods are used, then uniform phase distribution is achieved, but the process requires multiple stages and takes a long time
Solution Approach 1:
The invention merges multiple conventional process stages (mixing, molding, sintering, heat treatment) into a single integrated pulsed electric current sintering process. The simultaneous application of pressure, temperature, and electric current achieves both densification and phase uniformity in one step, dramatically reducing process time.
Solution Approach 2:
The invention employs continuous pulsed electric current sintering where pressure and temperature are applied continuously throughout the sintering process without intermediate steps. The pulsed current provides continuous heating and activation, maintaining useful action throughout the entire process duration.
3Temperature
If external heating systems are used in conventional methods, then sintering is achieved, but difference between internal and external physical properties occurs and cost increases
Solution Approach 1:
The invention replaces the conventional external heating system (thermal conduction from furnace walls) with direct internal heating through pulsed electric current passing through the compacted powder. This generates heat internally within the material itself, ensuring uniform temperature distribution and eliminating thermal gradients between internal and external regions.
Solution Approach 2:
The material itself serves as the heating element through resistive heating from the pulsed electric current. The compacted WC powder acts as both the workpiece and the heating source, eliminating the need for external heating systems and ensuring uniform self-heating throughout the material volume.
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 achieves a high relative density of 99.5% or more, with improved toughness, strength, and abrasion resistance, reducing process costs and extending tool lifespan while maintaining uniform physical properties across the sintered body.
Implementation Method 1
molding the WC powder in the mold while maintaining a constant pressure inside the mold and increasing a temperature according to a set heating pattern until the temperature reaches a final target temperature
Implementation Method 2
a preparation method of a tungsten carbide sintered body for a friction stir welding tool using a discharge plasma sintering process
Data Source
AI summary
The present invention relates to a preparation method of a tungsten carbide sintered body for a friction stir welding tool used in a friction stir welding tool of a high melting point material such as steel, titanium and the like or a dissimilar material such as aluminum, magnesium-steel, titanium and the like. The preparation method comprises the following steps: filling a tungsten carbide (WC) powder in a mold made of a graphite material; mounting the mold filled with tungsten carbide powder in a chamber of a discharge plasma sintering apparatus; making a vacuum inside of the chamber; molding the tungsten carbide powder while maintaining a constant pressure inside the mold and increasing the temperature according to a set heat increase pattern until the temperature reaches a final target temperature; and cooling the inside of the chamber while maintaining the pressure pressurized in the mold after the molding step.