What Is Powder Metallurgy, Do You Know What?

Powder metallurgy, as an ancient and dynamic advanced material preparation and forming technology, originated from the ancient ceramic preparation technology and iron making technology, until 1909, the advent of powder metallurgy ductile tungsten marked the advent of the modern powder metallurgy era. For more than one hundred years, powder metallurgy technology has developed vigorously, and a variety of important new materials and key products have emerged continuously, becoming one of the indispensable important engineering technologies in the national economy and science and technology.

Characteristics and advantages of powder metallurgy

Powder metallurgy is a technology that uses metal powder (or a mixture of metal and non-metal powder) to manufacture metal materials, composite materials and various types of products by molding and sintering processes as raw material.

Compared with the traditional smelting and casting process, powder metallurgy has many advantages. On the one hand, it can effectively avoid the possible component segregation in the smelting process, and ensure the uniform material composition, so as to obtain more stable and excellent performance. On the other hand, powder metallurgy can achieve near-net forming, greatly reduce the subsequent processing process and material waste. According to relevant data statistics, the material utilization rate of the parts manufactured by powder metallurgy process can reach more than 90%, while the material utilization rate of the traditional machining method is usually only 30% -50%, which not only reduces the production cost, but also improves the production efficiency, and fit the green development concept of modern manufacturing industry. In addition, by adjusting the powder composition, particle size and preparation process, the precise regulation of the material properties can be realized to meet the needs of different fields for the special properties of the material, such as high strength, high hardness, high temperature resistance, corrosion resistance, etc.

Main process of powder metallurgy process

(I) Powder preparation

Mechanical crushing method: rely on mechanical force to block metal or alloy broken into powder, simple equipment, low cost, large yield, but the powder shape is irregular, wide particle size distribution, easy to introduce impurities.

Abulization method: the molten metal liquid with high-pressure gas (nitrogen, argon) or high-speed water flow spray into small droplets, cooled and solidified into powder. Gas atomization powder has high spherical shape, good fluidity, suitable for high performance parts; water atomization method with low cost, high efficiency, irregular powder shape, which is often used in ordinary steel powder and products with low performance requirements.

Reduction method: using hydrogen, carbon monoxide and other reducing agents to reduce metal oxide into powder, high purity, high activity, high sintering activity, low temperature compaction, but the production needs high temperature and specific atmosphere, equipment large investment, high cost.

Electrolysis method: electrolysis metal salt solution or molten salt, so that metal ions in the cathode precipitation into powder, high purity, fine and uniform, suitable for the field of high purity and particle size requirements, such as electronic materials, but low production efficiency, high energy consumption, high cost.

(2) Forming

Molding: put the pretreatment metal powder into the mold, pressure compaction molding, steps including powder, pressing, release, suitable for simple shape, high precision requirements of products, such as gear. The advantages are simple equipment, high efficiency, low cost, mass production; complex products are difficult to design and manufacture, density uniformity.

Isostatic pressure molding: the use of liquid uniform pressure transmission, the powder loaded elastic mold put high pressure vessel pressure molding. Cold isostatic pressure at room temperature is suitable for products with complex shape and high density requirements; Thermal isostatic pressure acts at high temperature and high pressure simultaneously for high-performance aerospace materials. The advantage is that the product density is uniform, suitable for large complex products; the equipment is expensive, long cycle and high cost.

Injection molding: mixing metal powder and adhesive into injection material and injecting machine into mold cavity, it is suitable for manufacturing high precision complex small parts such as electronic components. The advantages are high molding efficiency and precision, suitable for mass production; the selection and removal of adhesive are difficult, and improper treatment affects the performance of products.

(3) Billing

Conventional sintering: heat the billet at the appropriate temperature and atmosphere (hydrogen, nitrogen, vacuum, etc.) to combine the powder particles and improve the density and strength. Hydrogen atmosphere to remove impurities, nitrogen oxidation, vacuum is suitable for high oxygen content requirements.

Hot pressure sintering: sintering pressure, in the special equipment, mold with graphite and other materials. Products that can reduce the sintering temperature, shorten the time, and obtain higher density and performance are often used in the preparation of high-performance ceramics and other materials.

Discharge plasma sintering (SPS): generate discharge plasma and joule heat rapid heated sintering by pulse current. It can remove impurities on the surface of particles, activate the surface, heat up quickly (100-1000℃ / min), short time (a few minutes to a few minutes), can inhibit grain growth, and is used to prepare nanomaterials.

Application field of powder metallurgy technology

(1) Aerospace field

Aerospace has strict requirements on material performance, and powder metallurgy technology just meets the requirements. Powder metallurgy superalloy is used to manufacture key components such as turbine disks and blades, such as the turbine disk of F119 engine of Pucompany, and powder metallurgy nickel based superalloy is used to improve the engine performance and reliability. With low density, high strength and corrosion resistance, powder metallurgy titanium alloy is used to manufacture structural parts such as aircraft wing girder and fuselage frame to reduce the weight of aircraft and improve fuel efficiency and flight performance.

(2) Automobile manufacturing field

Powder metallurgy parts are widely used in automotive engine, transmission and braking systems. The valve ring, catheter and piston ring in the engine are made of copper base or iron base alloy, which can withstand high temperature and high pressure and improve the performance and life of the engine; the transmission gear and synchronizer have high precision and good strength, make the gear shift more smoothly and improve the brake efficiency, with good friction and wear resistance, and brake safety.

(3) The field of electronic information

With the development of electronic equipment to small, lightweight and high performance, powder metallurgy technology is more widely used. Soft magnetic powder metallurgy materials are used to manufacture electronic components such as transformers and inductors; powder metallurgy metal matrix composites such as copper-tungsten and copper-molybdenum are used for heat dissipation substrate and packaging housing of high-power electronic devices; powder metallurgy contact materials are used for electrical switches and relays to ensure safe circuit opening and breaking.

Fe-silicon-nickel magnetic powder core (KNF)

(4) Mechanical manufacturing field

Powder metallurgy technology is used to manufacture gears, bearings and other mechanical parts. Powder metallurgy gear has high accuracy, smooth transmission and high material utilization rate; Powder metallurgy bearing is self-lubrication and wear-resistant, suitable for low speed, heavy load and low noise. Under special working conditions, oil bearing can maintain good performance and improve the reliability and service life of equipment.

(5) Medical devices field

In terms of implants, powder metallurgy titanium alloy is used to make artificial joints, etc., whose porous structure can promote the growth of bone cells and reduce the risk of implant loosening. Surgical instruments are made from powder metallurgy high-speed steel and stainless steel, with higher hardness, wear resistance and corrosion resistance, and can also make complex shape devices. In dental materials, dentures have good strength, toughness and aesthetics. Dental implants use powder metallurgy titanium or titanium alloy, which can improve the success rate of implant. The orthodontic bracket uses powder metallurgy stainless steel or nickel-titanium alloy, which can accurately apply force.

(6) New energy sector

In terms of lithium-ion batteries, cathode materials such as lithium iron phosphate and ternary materials prepared by powder metallurgy technology can improve the energy density and charge and discharge efficiency of batteries. In the field of fuel cells, metal bipolar plates manufactured by powder metallurgy process and catalyst carriers with high specific surface area can improve fuel cell performance and reduce costs. In the wind power generation, the gear boxes, bearings and other parts manufactured by powder metallurgy can maintain the stable performance in the harsh environment and prolong the service life of the equipment.

Progress in powder metallurgy technology

(1) Fusion 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 a new breakthrough for the manufacturing of complex parts. Through 3D printing technology, the metal powder can be directly accumulated and formed layer by layer to produce parts with complex internal structure and personalized design. This technology not only reduces material waste and processing processes, but also enables the manufacture of parts that are difficult to manufacture, such as complex blades of aero engines.

(2) Nano-powder metallurgy technology

With the development of nanotechnology, nano-powder metallurgy technology has emerged. Nanoscale metal powder has the characteristics of large specific surface area, high activity, large sintering driving force, and 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.

(3) Innovation of powder metallurgy composites

By adding various enhanced phases (such as ceramic particles, fibers, etc.) to the metal powder, the powder metallurgical composite material with excellent performance is prepared. These composite materials combine the advantages of metal and enhanced phase, have the characteristics of high strength, high hardness, good wear resistance, high temperature and other resistance, and are widely used in aerospace, automotive manufacturing, mechanical engineering and other fields. For example, the aluminum matrix composite material prepared by the addition of silicon carbide particles to the aluminum alloy powder significantly improves the strength and hardness, while maintaining the low density characteristics of the aluminum alloy.

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