[Disclosure] Full analysis of copper particle sintering method: depth analysis of four processes

Copper particle sintering technology is a process in which dispersed copper particles are treated at high temperature to achieve metallurgical bonding between particles in solid phase or partial liquid phase to form sintered bodies with certain density and specific properties. The basic principle is to use the diffusion between particles, plastic flow, grain boundary migration, recrystallization and other mechanisms, as well as the liquid phase that may be generated during the sintering process to promote sintering, so that the gap between particles is reduced, and finally achieve the expected physical and chemical properties and mechanical properties.

Classification and characteristics of sintering methods for copper particles

• Atmospheric sintering method
  Process flow and key parameters
  The atmospheric sintering process follows the following typical process:

1. Raw material preparation: Select the copper powder raw material that meets the requirements, which may involve pure copper powder, copper alloy powder or composite powder doped with specific additives. The raw material should have good particle size distribution, chemical purity and low oxygen content.
2. Pre-mixing: The copper powder is evenly mixed with the necessary sintering additives and lubricants (such as graphite) to improve the sintering behavior and pressing performance.
3. Pressing molding: Use hydraulic press, isostatic press or cold isostatic press equipment to press the mixed powder into the desired shape of the body, control the pressing pressure, holding time and release speed, to ensure that the body has the appropriate density and strength.
4. Degreasing (if necessary) : For systems containing organic additives, degreasing is required to remove organic matter. Common methods include thermal degreasing, solvent degreasing, or chemical degreasing.
5. Sintering: the degreased billet is placed in the sintering furnace and heated according to the predetermined temperature curve. Key parameters include sintering temperature, holding time, heating rate and cooling rate. During the sintering process, the furnace atmosphere should be monitored to ensure that no oxidation occurs.
6. Post-treatment: After the sintering is completed, the necessary cooling, cleaning, grinding, heat treatment (such as age hardening) and other steps are carried out to obtain the final desired performance and surface quality.
7. Advantages and disadvantages analysis and scope of application

Advantages: relatively low equipment cost, mature process, easy to implement. Suitable for mass continuous production, with good economy. Parts with relatively complex shapes can be prepared, and high precision can be achieved without subsequent machining.

Disadvantages: Affected by gravity, the sintered body is prone to the "stratification" phenomenon of dense bottom and loose top, resulting in uneven density. High sintering temperature and high energy consumption may cause copper volatilization or abnormal grain growth. For composite materials containing multiple components, component segregation is difficult to avoid during sintering.

Scope of application: The atmospheric pressure sintering method is suitable for the manufacture of copper based parts with low density and medium strength requirements, such as electronic packaging components, conductive connectors, heat exchangers, etc.

• Hot isostatic pressing sintering method

1. Process principle and process control principle: Hot isostatic pressing sintering (HIP) is the use of high pressure gas (such as argon) or inert liquid (such as oil) as a pressure transfer medium in a closed container at high temperature (up to 2000℃ or more) and high pressure (up to 200 MPa or more), to apply isotropic pressure to the preformed body, so that it can be uniformly pressurized at high temperature sintering.

Process control:

Pressure control: precisely adjust and maintain the working pressure to ensure that the pressure fluctuation is within the allowable range.

Temperature control: Advanced thermocouple and temperature control system are adopted to achieve precise setting and stability of sintering temperature.

Gas purity and flow: to ensure the high purity of the pressure transfer medium, control the gas circulation rate to ensure uniform heating and pressure transfer.

Furnace loading and unloading: strict operation to avoid seal damage and media pollution.

2. Features and application advantages
3. Features:

High uniformity: HIP sintering can achieve isothermal and isobaric sintering of all parts inside the body, significantly reducing density gradient and component segregation.

Excellent density: almost completely eliminate the pores, obtain close to the theoretical density of the sintered body, significantly improve mechanical properties and corrosion resistance.

 Excellent microstructure: promote grain refinement and uniform distribution of the second phase, which is conducive to improving material properties.

1. Application advantages:

High-end applications: suitable for aerospace, nuclear energy, precision instruments and other areas with high material performance and reliability requirements.

Refractory materials and composite materials: The sintering effect of refractory metals, multi-component composite materials and a large number of non-metallic phases is particularly outstanding.

Defect Repair and Additive Manufacturing: Can be used to repair defects in castings, weld joints, and sintered 3D-printed metal parts in additive manufacturing.

• Induction heating sintering method

1. Process principle and equipment requirements

Principle: induction heating sintering uses high-frequency alternating electromagnetic fields to induce eddy current inside copper particles, and the Joule heat generated by eddy current causes particles to rapidly heat up to sintering temperature.

Equipment requirements:

High-frequency power supply: to provide stable high-frequency electrical energy, the frequency is generally in the range of kHz to MHz.

Induction coil: Designed to match the shape of the workpiece to be sintered, ensuring effective magnetic field coupling.

Temperature control system: equipped with high precision temperature measuring elements and fast response temperature controller.

Cooling device: Ensure stable operation of coil and power system under high temperature operation.

2. Technical features and application scenarios

Technical features:

Rapid heating: induction heating has a high thermal efficiency, which can achieve rapid heating and significantly shorten the sintering time.

Local precision heating: By adjusting coil design and power distribution, precise heating of specific areas is achieved for complex shapes and local sintering.

Accurate temperature control: real-time monitoring and control of sintering temperature is conducive to preventing overburning and underburning.

Energy saving and environmental protection: due to the fast heating speed, high thermal efficiency, low energy consumption, in line with the green manufacturing concept.

Application scenario:

Thin-wall and small parts: It is suitable for rapidly sintering thin-wall or small complex shape copper based parts, such as electronic packaging components, miniature heat pipes, etc.

Micro and nano materials: For nano copper powder, ultra-fine copper powder and other materials with high specific surface area, induction heating can effectively reduce oxidation, which is conducive to maintaining nano characteristics.

Heat sensitive materials: For copper matrix composites with poor thermal stability or sensitive thermal history, induction sintering can reduce the heat affected zone and maintain material properties.

• Microwave assisted sintering method

1. Microwave sintering principle and mechanism

Principle: microwave sintering uses microwave energy to interact with the dielectric loss of the material, so that the material directly absorbs microwave energy into heat energy, to achieve rapid and uniform "volume heating".

Mechanism:

Rotating dipole heating: Free electrons inside metal particles oscillate at high speed under the action of alternating electric fields to generate heat.

Interface polarization heating: In the contact area between particles, the charge accumulation caused by the difference in electrical conductivity forms a strong electric field and triggers local heating.

Heat conduction and convection: Heat generated by microwave heating is transferred between particles through heat conduction and convection, which promotes the sintering process.

2. Technical advantages and innovative application

Technical advantages: fast and efficient: microwave can directly act on the inside of the particle, the heating speed is fast, and the sintering time is significantly shortened.

Low temperature sintering: Because of uniform heating and high efficiency, sintering can be achieved at a lower temperature, which is conducive to maintaining the original characteristics of the material.

Environmental protection and energy saving: The microwave sintering process has no open flame, no emission, and high thermal efficiency, which meets the environmental protection requirements.

Microstructure control: microwave sintering helps to inhibit grain growth and achieve fine microstructure control.

Innovative applications:

Nano copper sintering: In the field of electronic packaging, nano devices, microwave sintering is used to achieve rapid low temperature connection of nano copper particles.

Special composites: For copper matrix composites containing dielectric or magnetic phases, microwave sintering utilizes its special interaction with microwave to achieve efficient sintering.

Functionally graded materials: Copper based functionally graded materials with continuously varying properties are prepared by using the local controllability of microwave heating.

In summary, copper particle sintering methods include normal pressure sintering, hot isostatic sintering, induction heating sintering and microwave assisted sintering, each of which has its own unique process flow, key parameter control, characteristics and advantages, and is suitable for different application scenarios. Through the in-depth understanding and reasonable selection of these methods, copper based sintered materials with excellent properties can be prepared according to specific needs.