The sintering process of tungsten-nickel-iron alloy is a heat treatment process for the formed green body at high temperature, which makes the powder particles diffuse, bond and densify, and finally form an alloy product with certain mechanical properties and structure, which is the core process in powder metallurgy preparation. The key parameters of this process include sintering temperature, holding time, atmosphere control, etc., which directly affect the density, grain size and mechanical properties of the alloy.
Sintering temperature is the most critical parameter in the sintering process. The sintering temperature of tungsten-nickel-iron alloy is usually controlled between 1400 – 1600℃. When the temperature is too low, the diffusion between powder particles is insufficient, and a firm bond cannot be formed, resulting in low alloy density and insufficient strength; too high temperature will lead to excessive growth of tungsten particles and even liquid phase exudation, making the alloy structure uneven and performance degradation. In actual production, the sintering temperature needs to be adjusted according to the composition ratio of the alloy (especially the tungsten content). When the tungsten content is high, a higher sintering temperature is usually required to promote diffusion.
Holding time refers to the time that the green body is kept at the sintering temperature, generally 1 – 4 hours. Appropriate holding time can ensure sufficient diffusion and reaction between powder particles, gradually increasing the alloy density; too short holding time results in incomplete diffusion and failure to reach the required density; too long holding time may lead to coarse grains, affecting the toughness of the alloy. Therefore, it is necessary to reasonably set the holding time according to the size, composition and required performance of the green body to achieve a balance between density and grain size.
Atmosphere control is crucial to sintering quality. The sintering of tungsten-nickel-iron alloy is usually carried out in hydrogen or vacuum atmosphere. Hydrogen atmosphere is reducing, which can prevent the green body from oxidizing at high temperature, and can also reduce the oxide film that may exist on the powder surface, promoting the bonding between particles; vacuum atmosphere (vacuum degree is generally higher than 10⁻³Pa) can avoid pollution by gas impurities and reduce the generation of pores, especially suitable for alloy products with high purity requirements. During the sintering process, the stability of the atmosphere must be ensured to prevent air from entering the furnace and causing oxidation of the alloy.
The cooling rate after sintering also affects the alloy performance. Generally, furnace cooling or slow cooling is adopted to reduce the generation of internal stress. For some alloys with special performance requirements, heat treatment processes such as aging treatment can be carried out after sintering to further optimize their mechanical properties.
By optimizing the sintering process parameters, the density of tungsten-nickel-iron alloy can reach more than 95%, even close to the theoretical density, thus ensuring that it has excellent comprehensive properties such as strength, hardness and toughness, meeting the application needs of different fields.
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