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What is powder metallurgy

Powder metallurgy, as an ancient and dynamic advanced material preparation and forming technology, originated from ancient ceramic preparation technology and ironmaking technology until 1909, when the powder metallurgy method for ductile tungsten was introduced, marking the advent of the modern powder metallurgy era. For over a hundred years, powder metallurgy technology has flourished, with various important new materials and critical products constantly emerging, becoming one of the indispensable engineering technologies in today's national economy and science and technology.

Characteristics and advantages of powder metallurgy

Powder metallurgy is a technology that uses metal powders (or mixtures of metal and non-metal powders) as raw materials, and through processes such as molding and sintering, manufactures metal materials, composite materials, and various types of products.

Compared with traditional smelting and casting processes, powder metallurgy has many advantages. On the one hand, it can effectively avoid possible component segregation during the melting process, ensure uniform material composition, and thus obtain more stable and excellent performance. On the other hand, powder metallurgy can achieve near net forming, greatly reducing subsequent processing steps and material waste. According to relevant data statistics, the material utilization rate of parts manufactured using powder metallurgy technology can reach over 90%, while the material utilization rate of traditional mechanical processing methods is usually only 30%~50%. This not only reduces production costs but also improves production efficiency, which is in line with the development concept of green and environmental protection in modern manufacturing industry. In addition, by adjusting the powder composition, particle size, and preparation process, precise control of material properties can be achieved to meet the special performance requirements of materials in different fields, such as high strength, high hardness, high temperature resistance, and corrosion resistance.

Main processes of powder metallurgy technology

（1） Powder preparation

Mechanical crushing method: It relies on mechanical force to crush block metal or alloy into powder. The equipment is simple, the cost is low, and the output is large. However, the powder shape is irregular, the particle size distribution is wide, and impurities are easily introduced.

Atomization method: Spray molten metal liquid into small droplets with high-pressure gas (nitrogen, argon) or high-speed water flow, cool and solidify into powder. Gas atomization method has high sphericity and good flowability of powder, suitable for manufacturing high-performance parts; The water atomization method has low cost, high efficiency, irregular powder shape, and is commonly used for ordinary steel powder and products with low performance requirements.

Reduction method: Metal oxides are reduced to powder using reducing agents such as hydrogen and carbon monoxide, which has high purity, high activity, high sintering activity, and can be densified at low temperatures. However, production requires high temperatures and specific atmospheres, and equipment investment and cost are high.

Electrolysis method: electrolyzing metal salt solution or molten salt to precipitate metal ions into powder at the cathode, with extremely high purity, fine and uniform particle size, suitable for fields with high requirements for purity and particle size, such as electronic materials, but with low production efficiency, high energy consumption, and high cost.

（2） Forming

Compression molding: Place the pre treated metal powder into a mold, apply pressure and compact it into shape, including powder loading, pressing, and demolding. It is suitable for products with simple shapes and high precision requirements, such as gears. The advantages are simple equipment, high efficiency, low cost, and the ability to produce on a large scale; The disadvantage is that it is difficult to design and manufacture complex product molds, and it is difficult to ensure density uniformity.

Isostatic pressure forming: Using liquid to uniformly transmit pressure, the powder is loaded into an elastic mold and placed in a high-pressure container for pressure forming. Cold isostatic pressing is carried out at room temperature, suitable for products with complex shapes and high density requirements; Hot isostatic pressing with high temperature and high pressure is used for high-performance aerospace materials. The advantage is that the density of the product is uniform in all directions, suitable for large and complex products; The disadvantages are expensive equipment, long cycle time, and high cost.

Injection molding: Mixing metal powder with a binder to form an injection material, injecting it into the mold cavity using an injection machine for molding. It is suitable for manufacturing high-precision, complex, and small parts, such as electronic components. Its advantages are high molding efficiency and precision, making it suitable for large-scale production; The disadvantage is that the selection and removal of adhesives are difficult, and improper handling can affect the performance of the product.

（3） Sintering

Conventional sintering: Heating the formed body at a suitable temperature and atmosphere (hydrogen, nitrogen, vacuum, etc.) to bond the powder particles and increase density and strength. Hydrogen atmosphere removes impurities, nitrogen prevents oxidation, and vacuum is suitable for materials with high oxygen content requirements.

Hot pressing sintering: During sintering, pressure is applied and carried out in specialized equipment, using materials such as graphite for the mold. It can reduce sintering temperature, shorten time, and obtain products with higher density and performance, commonly used in the preparation of high-performance ceramics and other materials.

Spark Plasma Sintering (SPS): Spark plasma is generated by pulsed current and rapidly heated by Joule heating for sintering. It can remove surface impurities of particles, activate the surface, quickly heat up (100-1000 ℃/min), short time (several minutes to tens of minutes), inhibit grain growth, and is used for the preparation of nanomaterials.

Application field of powder metallurgy technology

（1） Aerospace field

Aerospace has strict requirements for material performance, and powder metallurgy technology precisely meets the needs. Powder metallurgy high-temperature alloys are used to manufacture key components such as turbine disks and blades for aircraft engines. For example, the turbine disk of Pratt&Whitney F119 engine in the United States uses powder metallurgy nickel based high-temperature alloys to improve engine performance and reliability. Powder metallurgy titanium alloy, with its low density, high strength, and corrosion resistance, is used to manufacture structural components such as aircraft wing beams and fuselage frames, reducing aircraft weight, improving fuel efficiency, and flight performance.

（2） Automotive manufacturing field

Powder metallurgy parts are widely used in automotive engines, transmissions, and braking systems. The valve seat rings, guide pipes, and piston rings in the engine are made of copper based or iron-based alloys, which can withstand high temperature and high pressure, improve engine performance and service life; The gears of the transmission and the hub of the synchronizer have high precision and good strength, making gear shifting smoother and improving transmission efficiency; The brake pads and discs of the braking system are made of special friction materials, which have good friction and wear resistance, ensuring braking safety.

（3） In the field of electronic information

With the development of electronic devices towards small, lightweight, and high-performance, powder metallurgy technology is being applied more widely. Soft magnetic powder metallurgy materials are used to manufacture electronic components such as transformers and inductors; Powder metallurgy metal based composite materials such as copper tungsten and copper molybdenum are used for heat dissipation substrates and packaging shells of high-power electronic devices; Powder metallurgy contact materials are used for electrical switches and relays to ensure safe circuit switching.

Iron silicon nickel magnetic powder core (KNF)

（4） Mechanical manufacturing field

Powder metallurgy technology is used to manufacture mechanical parts such as gears and bearings. Powder metallurgy gears have high precision, smooth transmission, and high material utilization rate; Powder metallurgy bearings are self-lubricating and wear-resistant, suitable for low-speed, heavy-duty, and low-noise applications. Under special working conditions, oil containing bearings can maintain good performance, improve equipment reliability and service life.

（5） Medical device field

In terms of implants, powder metallurgy titanium alloys are used to manufacture artificial joints, etc. Their porous structure can promote bone cell growth and reduce the risk of implant loosening. Surgical instruments are made of powder metallurgy high-speed steel and stainless steel, with higher hardness, wear resistance, and corrosion resistance, and can also manufacture complex shaped instruments. In dental materials, dentures have good strength, toughness, and aesthetics. Dental implants are made of powder metallurgy titanium or titanium alloy, which can improve the success rate of implantation. orthodontic brackets are made of powder metallurgy stainless steel or nickel titanium alloy, which can accurately apply force.

（6） In the field of new energy

In the field of lithium-ion batteries, positive electrode materials such as lithium iron phosphate and ternary materials prepared by powder metallurgy technology can improve battery energy density and charge discharge efficiency. In the field of fuel cells, metal bipolar plates and catalyst carriers with high specific surface area manufactured by powder metallurgy technology have improved the performance of fuel cells and reduced costs. In wind power generation, components such as gearboxes and bearings manufactured by powder metallurgy can maintain stable performance in harsh environments and extend the service life of equipment.

Progress in Powder Metallurgy Technology

（1） The integration of metal additive manufacturing (3D printing) and powder metallurgy

Metal additive manufacturing technology has developed rapidly in recent years, and its combination with powder metallurgy has brought new breakthroughs to the manufacturing of complex components. Through 3D printing technology, metal powder can be directly stacked layer by layer to produce parts with complex internal structures and personalized designs. This technology not only reduces material waste and processing steps, but also enables the manufacturing of parts that are difficult to produce using traditional processing methods, such as complex blades for aircraft engines.

  （2） Nano powder metallurgy technology

With the development of nanotechnology, nanometer powder metallurgy technology came into being. Nanoscale metal powders have the characteristics of large specific surface area, high activity, and strong sintering driving force, which can prepare nanostructured materials with excellent mechanical, electrical, and magnetic properties. At present, nano powder metallurgy technology has made remarkable progress in the preparation of high-performance magnetic materials, superconducting materials and high-strength alloys.

Schematic diagram of the preparation process of spherical nano Ti TiBw composite powder at Xi'an University of Technology

（3） Innovation of Powder Metallurgy Composite Materials

By adding various reinforcing phases (such as ceramic particles, fibers, etc.) to metal powders, high-performance powder metallurgy composite materials are prepared. These composite materials combine the advantages of metals and reinforcing phases, with high strength, high hardness, good wear resistance, and high temperature resistance, and are widely used in fields such as aerospace, automotive manufacturing, and mechanical engineering. For example, aluminum based composite materials prepared by adding silicon carbide particles to aluminum alloy powder have significantly improved strength and hardness while maintaining the low-density characteristics of the aluminum alloy. 

Conclusion: 

Looking ahead to the future, with the continuous advancement of technology, powder metallurgy technology is expected to achieve breakthroughs in more emerging fields, and its integration with other cutting-edge technologies will further deepen. In the fields of intelligent manufacturing, quantum materials, biomedical engineering, etc., powder metallurgy technology has the potential to create more high-performance and multifunctional materials and components, providing innovative solutions to global challenges such as energy crisis, environmental protection, and human health. It can be foreseen that powder metallurgy technology will play a more important role in the future industrial development and social progress.