There are various methods for preparing molybdenum copper alloy, among which powder metallurgy process has become one of the most commonly used methods in industrial production because of its strong process controllability, low cost, and the manufacture of parts with complex shapes.
The powder metallurgy process mainly includes several key steps such as raw material powder preparation, powder mixing, molding, sintering and post-treatment.
1.1 Preparation of raw material powder
To prepare high-performance molybdenum copper alloy, it is first necessary to obtain molybdenum powder and copper powder with high purity and suitable particle size. Molybdenum powder is usually prepared by hydrogen reduction, while copper powder can be obtained by electrolysis or chemical reduction.
Molybdenum powder: molybdenum oxide (MoO?) is obtained by hydrogen reduction at high temperatures. The purity, particle morphology and particle size distribution of molybdenum powder have a significant impact on the properties of the final alloy. In general, ultrafine molybdenum powder helps to improve the uniformity and density of the alloy.
Copper powder: can be prepared by electrolytic deposition, gas atomization or chemical precipitation. The particle size of the copper powder affects the liquid phase fluidity during the sintering process and the final alloy structure.
1.2 Powder mixing
Powder mixing is an important step in determining the uniformity of the alloy. Molybdenum and copper powder are mixed in a certain proportion, and ball milling, mechanical stirring and other methods are used to improve the uniformity of the powder. In order to avoid particle agglomeration and component segregation during the mixing process, it is often necessary to add the right amount of additives or use wet mixing.
1.3 Forming
The mixed powder is pressed into shape to obtain the desired geometry. Common molding methods include:
Cold isostatic pressing (CIP): The powder is pressed by uniform pressure in all directions, so that the density of the green body is relatively uniform, and the density of the subsequent sintering is improved.
Mold pressing: Applying pressure in a specific mold to make the powder form. This method is suitable for producing parts with regular shapes.
Hot Pressing (HP): Pressing at high temperatures helps to increase the density of the green body and reduce sintering shrinkage.
1.4 Sintering
Sintering is a core step in the powder metallurgy process, which is mainly used to increase the density of materials and achieve the effective bonding of molybdenum-copper particles. The sintering methods of molybdenum copper mainly include solid-phase sintering and liquid-phase sintering:
Solid-phase sintering: Performed at temperatures below the melting point of copper (1083°C), it relies mainly on diffusion bonding between molybdenum particles. This method can control the microstructure uniformity of the material well, but the sintering density is low, and subsequent treatment is usually required to improve the density.
Liquid-phase sintering: At a temperature higher than the melting point of copper (usually between 1100~1300 °C), the copper partially melts and penetrates between the molybdenum particles during the sintering process, which makes the density of the material significantly increased. This method is able to obtain high thermal conductivity and mechanical strength, but requires strict control of the sintering temperature and time to avoid excessive copper loss.
The sintering process is usually carried out in hydrogen or an inert atmosphere, such as argon, to prevent copper oxidation. At the same time, by optimizing the sintering temperature, holding time and heating rate, the microstructure of molybdenum copper can be improved and the comprehensive properties of the material can be improved.
1.5 Post-processing
To further optimize the microstructure and properties of the material, sintered molybdenum copper typically undergoes post-treatment processes including:
Hot Isostatic Pressing (HIP): Further densification in high temperature and high pressure environments, reducing porosity and improving the strength and thermal conductivity of the material.
Machining: Because molybdenum copper is brittle and hard, traditional machining is more difficult, so electrical discharge machining (EDM) or laser processing is often used for accurate forming.
Surface treatment: The surface of the material is nickel or silver plated to improve its corrosion resistance and welding performance.
