The performance and application range of powder metallurgy raw materials largely depend on their preparation methods. Different powder preparation processes determine the morphology, particle size distribution, purity, and internal structure of the powder, thus affecting subsequent forming and sintering behavior. Mastering the principles and characteristics of various preparation methods is a prerequisite for achieving accurate raw material selection and process optimization.
The preparation of metal powders is mainly divided into two categories: physical methods and chemical methods. Among physical methods, atomization is the most widely used, including gas atomization and water atomization. Gas atomization uses a high-speed airflow to disperse molten metal into droplets and rapidly solidify them, resulting in powders that are mostly spherical with good flowability, suitable for high-precision pressing. Water atomization uses high-pressure water jets to impact the melt, resulting in high cooling rates, producing powders that are mostly irregular in shape, with rough surfaces and strong green body bonding. The plasma rotating electrode method melts and atomizes spherical powders using a high-speed rotating electrode, producing powders with excellent purity and sphericity, often used in high-performance alloys. Chemical methods include reduction methods, electrolysis methods, and carbonyl methods. Reduction methods use metal oxides as raw materials, reducing them with hydrogen or carbon to obtain powder. This process is mature, low-cost, and suitable for bulk products such as iron powder. Electrolysis methods obtain high-purity powders through electrochemical deposition, with controllable morphology, and are often used for conductive materials such as copper and nickel. Carbonyl methods utilize the thermal decomposition of metal carbonyl compounds to produce ultrafine, high-purity powders, suitable for special functional applications.
The preparation of non-metallic powders encompasses methods such as mechanical grinding, chemical synthesis, and high-temperature reactions. Ceramic and carbide powders are often obtained through high-temperature solid-state reactions or vapor-phase deposition, with particle size and crystallinity controllable according to reaction conditions. Graphite powders are mostly obtained from natural flake graphite through mechanical grinding and classification; lattice defects must be controlled to prevent performance degradation.
The preparation of auxiliary materials emphasizes the uniformity and stability of the formulation. Lubricants are often obtained through melt mixing and spray drying, while binders can achieve the required viscoelasticity through polymerization or blending processes.
In general, the preparation methods for powder metallurgy raw materials are diverse, each with its own advantages and limitations. By rationally selecting and combining subsequent processing methods, an optimal balance can be achieved between morphology, purity, and performance, providing a solid raw material guarantee for high-quality products.