Classification and application of powder metallurgy materials
Powder metallurgy materials are metal or composite materials manufactured through processes such as powder preparation, forming, and sintering. They possess characteristics such as uniform composition, controllable structure, and near-net shape. They can produce materials difficult to prepare using traditional casting or forging methods, such as porous materials and refractory metals. Powder metallurgy materials can be classified in various ways: by material, they can be divided into metal powder metallurgy materials, cermet materials, and powder metallurgy composites; by structure, they can be divided into dense materials and porous materials; and by function, they can be divided into structural materials, friction materials, and functional materials. Different types of powder metallurgy materials have unique properties and are widely used in fields such as machinery manufacturing, the automotive industry, and aerospace, becoming an essential component of modern materials engineering.
Metal powder metallurgy is the most commonly used powder metallurgy material, primarily including iron-, copper-, and nickel-based series. Iron-based powder metallurgy is the most widely used. Iron-based powder metallurgy uses iron powder as its primary raw material, with alloying elements such as carbon, copper, and nickel added. Through sintering, it forms a material with a certain porosity (generally 5%-20%). Its strength can reach 300-800 MPa, with a hardness of HB100-250, and its cost is only 60%-70% of that of forged steel. It is suitable for manufacturing structural parts such as gears and bearing seats. Copper-based powder metallurgy, made from copper powder or copper alloy powder, exhibits excellent electrical and thermal conductivity and wear resistance. Its porosity can be controlled at 10%-30%, making it commonly used in the manufacture of oil-containing bearings, electrical contacts, and other parts. Oil-containing bearings are self-lubricated during operation through the lubricating oil in their pores, extending their service life by 2-3 times that of ordinary sliding bearings. Nickel-based powder metallurgy materials have excellent high-temperature strength and corrosion resistance, and are suitable for manufacturing high-temperature components such as turbine blades and combustion chambers of aircraft engines, but their cost is relatively high and their application range is relatively limited.
Cermets are powder metallurgy materials composed of a composite of metal and ceramic. They combine the toughness of metal with the high hardness and high-temperature resistance of ceramic. They primarily include cemented carbide and ceramic tool materials. Cemented carbide, composed of carbides such as WC and TiC as the hard phase and Co as the binder phase, boasts a hardness of up to HRA85-93 and wear resistance 5-10 times that of high-speed steel . They are widely used in cutting tools, molds, and mining tools. For example, WC-Co cemented carbide tools can cut hardened steels below HRC60 , while TiC -based cemented carbide is suitable for machining difficult-to-machine materials such as stainless steel and high-temperature alloys. Ceramic tool materials (such as Al₂O₃-ZrO₂ composite ceramics) offer even higher hardness ( HRA90-95 ) and excellent high-temperature resistance (operating temperatures exceeding 1200 °C), but they have lower toughness. They are therefore suitable for high-speed precision turning and continuous cutting. In automotive engine block machining, they can achieve cutting speeds of 300-500 m/min, increasing efficiency 2-3 times that of cemented carbide tools.
Powder metallurgy composites are formed by combining powders of two or more different materials, achieving optimized performance through synergistic effects. They primarily include particle-reinforced composites, fiber-reinforced composites, and layered composites. Particle-reinforced composites use a metal matrix (such as aluminum and magnesium) reinforced with ceramic particles (such as SiC and Al₂O₃ ). They exhibit high strength, high stiffness, and low density. For example, SiC particle-reinforced aluminum-based composites have a specific strength twice that of steel , making them suitable for manufacturing automotive wheels and aerospace structures. Fiber-reinforced composites use carbon fibers, boron fibers, and other materials as reinforcements in a metal or alloy matrix. They exhibit excellent mechanical properties and high-temperature resistance. For example, carbon fiber-reinforced titanium-based composites can be used in aircraft engine fan blades, achieving a 30% reduction in weight and a 50% increase in strength compared to pure titanium blades. Layered composites achieve functional integration through the layering of materials with different properties. For example, a steel-copper-steel three-layer composite combines the strength of steel with the conductivity of copper, making it suitable for manufacturing parts such as motor brushes and heat sinks.
Porous powder metallurgy materials are specialized materials with a large number of pores, typically with a porosity ranging from 20% to 60%. Based on their pore structure, they can be categorized as open-pore and closed-pore materials. They have important applications in filtration, vibration reduction, and energy storage. Open-pore powder metallurgy materials (such as porous copper and porous nickel) have interconnected pore structures, offering excellent air permeability and are suitable for liquid and gas filtration. For example, porous stainless steel used in automotive exhaust filters can effectively filter over 90% of particulate matter. Porous titanium, due to its excellent biocompatibility, can be used in bone repair, where its pore structure facilitates the growth and fusion of bone cells. Closed-pore powder metallurgy materials (such as porous aluminum alloys) have discrete pores, resulting in lightweight, sound-insulating, and vibration-damping properties. They are suitable for manufacturing thermal insulation layers for spacecraft and shock-absorbing components for automobiles. Their density is only 50%-70% of that of solid materials, significantly reducing structural weight. With the advancement of powder metallurgy technology, the porosity and pore size distribution of porous materials can be precisely controlled, further expanding their application prospects in energy and environmental protection.
