Advantages and Selection Guide of Vacuum Sintering

Vacuum sintering involves heating powder, powder compacts, or other materials in a vacuum environment at an appropriate temperature to achieve inter-particle bonding through atomic migration. The goal of vacuum sintering is to impart a desired structure and properties to a porous powder compact.

Advantages of Vacuum Sintering

1. Under vacuum sintering conditions, the carbon content of the alloy is easily controlled. At the sintering temperature, the furnace pressure is only tens of Pa (Pa), or even lower. The presence of O₂, N₂, H₂, and H₂O molecules is minimal, making many reactions negligible and minimizing the influence of the medium. As long as the dewaxing process is strictly controlled, the carbon content of the alloy will vary minimally during vacuum sintering, resulting in highly stable properties and microstructure.

2. Under vacuum sintering conditions, the purity of cemented carbide can be improved. Vacuum sintering facilitates the reduction of metal oxides; the furnace door does not need to be opened during the entire sintering cycle, preventing air from entering, and virtually eliminating reactions involving N₂ and O₂.

3. Under vacuum sintering conditions, impurities adsorbed on the surface of the hard phase are reduced, improving the wettability of the drill with the hard phase and increasing the strength of the alloy, especially TiC-containing alloys. 4. Vacuum sintering allows for simple process operation. Since vacuum sintering eliminates the need for fillers, this not only simplifies the process but also prevents the adverse effects of fillers on the sintered body surface.
5. Integrated dewaxing and sintering reduces product oxidation and eases carbon control, while also reducing equipment footprint and labor intensity.
6. Multi-atmosphere integrated dewaxing and sintering allows for separate temperature control of temperature, atmosphere, and furnace pressure, enabling isothermal sintering (insulation) at any temperature and facilitating a variety of applications, such as gradient alloy sintering.

Advantages of Vacuum Sintering

1. Vacuum sintering reduces contamination of the material by harmful atmospheric components (water, oxygen, nitrogen, and other impurities), preventing a series of reactions such as decarburization, carburization, reduction, oxidation, and nitriding. This vacuum environment is unique to other sintering methods (when the furnace vacuum reaches 1.3 x 10-1 Pa, the residual gas in the furnace is equivalent to 99.99987% pure argon).
2. Vacuum sintering completely removes the oxide film from the particles before the liquid phase appears, thereby improving the wettability of the liquid phase with the carbide phase, enhancing the alloy structure, and improving alloy properties.
3. Because the amount of gas in the pores of the compact is reduced under vacuum, gas products are more easily expelled from the pores and gases dissolved in the metal are removed, resulting in a higher density of the material.
4. Vacuum sintering enhances the wear resistance and strength of the material.
5. Vacuum sintering also significantly reduces product costs.

Uses and Classifications of Vacuum Sintering Furnaces

Vacuum sintering furnaces are primarily used for sintering powder metallurgy products, metal injection molded products, stainless steel bases, cemented carbides, superalloys, high-density golds, ceramics, magnetic materials, and neodymium iron boron.
There are two main types of vacuum furnaces: the first is categorized by temperature, including ordinary sintering furnaces (1300°C and below), medium-temperature sintering furnaces (1300°C to 1600°C), and high-temperature sintering furnaces (1600°C to 2400°C). The second is categorized by the degree of vacuum, which can be divided into low-vacuum, high-vacuum, and ultra-high-vacuum sintering furnaces.

How to Choose a Vacuum Sintering Furnace?

The primary function of a vacuum furnace is heating. A fast heating rate is required, and the selected heating material must have good thermal conductivity and resist deformation and excessive heat loss at high temperatures. Performance must also be stable over time during operation. When selecting heating elements, consider the chemical properties of the product being processed to prevent the material from affecting the quality of the workpiece. Therefore, it’s crucial to choose the right heating element.

The heat shield is a key component of the vacuum furnace’s heating chamber. Its primary functions are insulation, heat preservation, and heat loss reduction. It also serves as the structural foundation for securing the heater. Therefore, the structure and material of the heat shield significantly impact the furnace’s power and performance (such as vacuum level and outgassing rate).

Heat shields are generally categorized into two types: metal and non-metallic. The choice of heat shield is primarily determined by the sintering temperature, the physical and chemical properties of the product, and the required vacuum level. Compared to heat shields made of other materials, those made of tungsten and molybdenum offer superior heat protection and more effectively block heat convection.