Materials Used for Manufacturing Sintered Bushings/Bearings
The powder metallurgy process begins with a collection of metal powder particles.
Metal powders are engineered materials that meet a wide range of performance requirements. Understanding the powder is crucial in powder metallurgy as this is the key input to the production of a final metal component.
The powder is produced through either solid-state reduction, atomization (gas, water, or centrifugal), electrolysis, or chemical treatments of the metallic material.
Atomization is the typical method used today. It involves the conversion of molten metal in a spray of droplets that solidify into powder. Water atomization is the most common form of atomization as it results in irregularly shaped particles, which is beneficial in the compaction of powder metal component production.
Metal powders are classified as elemental, partially-alloyed, or pre-alloyed. Elemental powder is a granular form of pure metal powder. They are the building blocks of creating alloys and composite materials. Partially-alloyed powders are a mixture of elemental powders of different materials blended together, and a prealloyed material is in an alloyed state as produced by atomizing a combination of metals.
In most cases, the powder mixture, whether elemental or prealloyed, also contains additives (lubricants or binders) for increased tool life, to assist in the ejection of the component from the compaction die or to hold the metal part together before the sintering process. These additives are removed from the component desiring the sintering process.
The geometry of the individual powder is defined by particle shape and internal structure, particle size and distribution, and surface area. Particles come in a variety of shapes, from spherical, irregular, flake, dendritic, and sponge. The distribution of particle sizes in the powder influences compaction as smaller particles will fill in the void between larger particles. This combination of sizes improves compaction density and material properties.
These are critical parameters in powder metallurgy as they determine how the powder performs when filling the die, during compaction, and in sintering. These factors must be optimized to achieve the desired strength and density in the green stage and in the final sintered component.
