Powder Consolidation via Pulsed Electric Field Sintering
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional sintering methods face inefficiencies in heating rate and grain growth, leading to difficulty in achieving materials with densities above 90% and grain sizes below 100 nm, and existing electric field-activated sintering methods are unreliable due to high-voltage issues and complex power supply constructions.
Innovation Solution
A two-step consolidation method using a device with a gastight chamber and electrodes, applying current pulses with peak voltages between 50 V to 900 V and durations shorter than 300 µs, initially vacuuming the chamber to facilitate arc discharges for purification, then increasing pressure for proper consolidation, allowing for precise control of temperature and shrinkage to achieve high-density, small-grain materials.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional thermal sintering is used, then the sintering process is simple and equipment is basic, but heating rate is low and grain growth occurs leading to difficulty achieving density above 90% and grain size below 100 nm
Solution Approach 1:
The patent replaces conventional thermal conduction heating with electric field-activated heating. Current pulses are applied directly to the powder compact, generating heat through Joule heating and arc discharges within the material volume, achieving rapid heating rates and precise grain size control below 100 nm while reaching densities above 90%.
Solution Approach 2:
The patent employs periodic current pulses with specific duration (microsecond to millisecond range) and frequency characteristics. This pulsed electric field activation enables controlled heating cycles that achieve rapid densification while limiting grain growth, resolving the contradiction between heating rate and grain size control.
2Manufacturing precision
If high voltage is applied to enable arc discharges for purification, then powder surface purification is achieved, but power supply construction becomes complex and reliability decreases
Solution Approach 1:
The patent optimizes the voltage parameter to a specific range (50-900 V peak) that is sufficient to initiate arc discharges for powder surface purification but low enough to avoid the complexities and reliability issues associated with high-voltage power supplies. This parameter optimization enables purification while maintaining system reliability.
Solution Approach 2:
The patent employs dynamic current pulsing with variable amplitude and duration rather than continuous high voltage. The pulsed nature of the electric field allows arc discharges to occur during peak pulses for purification, while the low average voltage maintains power supply reliability and simplicity.
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
This method enables efficient sintering with reduced voltage requirements, simpler power supply units, and controlled consolidation, resulting in materials with high density and small grain size, such as a WC sinter with 99.8% relative density and 50 nm grain size, while preventing fracturing through controlled cooling.
Implementation Method 1
heating is realised by means of pulsed current only in the first compaction period, or in the first and the second sintering step, as is in the case of the SPS method
Implementation Method 2
the heating of powder is much more complicated. This is due to many possible current flow paths through the consolidated powder subjected to pressing. The current flow can occur: in result of arc discharges in pores between consolidated powder particles
Implementation Method 3
To provide conditions favouring the occurrence of electric breakdown in regions between powder particles it is recommended to use pressing at a low pressure. Electric breakdown is a discharge in surrounding gaps between particles, revealing itself by presence of arcing.
Data Source
Figure 1
AI summary
The object of the invention is a method of consolidation of powder materials by means of a device provided with a gastight operating chamber (1), a press connected (11) to a first electrode (3) and to a second electrode (6), wherein between the electrodes there is located in a die (4) the consolidated powder (5), wherein the press (11) exerts pressure on the consolidated powder with the first electrode (3) and the second electrode (6). To the first electrode (3) and the second electrode (6) there is connected a circuit comprising a power supply unit (9) so that the flow of current provided by the power supply unit (9) is closed through the first electrode (3) and the second electrode (6), and the consolidated powder (5). Simultaneously, the consolidated powder (5) is subjected to pressure and stimulated by current pulses. The voltage applied to the powder (5) in pulse peak fits within the range of 50 V to 900 V, and pulse duration is shorter than 300 ]is. The consolidation of powder (5) is performed in at least two steps. In the first step a pressure of the press (11) corresponding to pressure on the powder (5) within the range of 2 MPa to 15 MPa is applied, while the values of pulse current, pulse duty cycle and repetition frequency are chosen such that the temperature of the powder was constantly in the range of 0.05 do 0.3 of melting temperature of the powder. In the second step a pressure of the press (11) corresponding to pressure on the powder (5) within the range of 15 MPa to 200 MPa is applied, while the values of pulse current, pulse duty cycle and repetition frequency are chosen such that the temperature of the powder (5) was constantly in the range of 0.6 to 0.9 of melting temperature of the powder (5). Furthermore, the object of the invention is a device for consolidation of powder materials, provided with a gastight operating chamber (1), a press (11) connected to a first electrode (3) and to a second electrode (6), wherein between the electrodes there is located in a die (4) the consolidated powder (5), wherein the press (11) exerts pressure on the consolidated powder with the first electrode (3) and the second electrode (6), wherein to the first electrode (3) and the second electrode (6) there is connected a circuit comprising a power supply unit (9) and switching means so that the flow of current provided by the power supply unit (9) is closed through the first electrode (3) and the second electrode (6), the consolidated powder (5) and the switching means. Furthermore, the device is provided with a vacuum pump and means for measuring the temperature (8) of the consolidated powder. Furthermore, the voltage of the power supply unit (9) is within the range of 50 V to 900 V, and the switching means are configured to close the current flow path for a time shorter than 300 μs. A substance according to the invention is a result of consolidation of the substance comprising at least one of the group including A1203, SiC, Si3N4, WC, Ta, ReB2, Zr02, TiC, TiN using the method according to the invention.