What is Infiltration of Powdered Metals?December 13, 2018
Imagine the powder metallurgical process as a series of illustrated steps. The powders and additives mix, then they’re formed and sintered. The process is clearly marked out in the various illustrations. Adding another illustrated block to the process, infiltration action strengthens powder metal components. Basically, the technique adds a second metal to the part, and that alloy fills the part’s porous structure. The metal “infiltrates” the pores.
Pore Infiltration Technology
So, what’s the big idea? Powdered metals use their pores to store lubricating agents and other additives. That’s the whole purpose of this process, right? Well, there are some applications where powdered metallurgy is desired, but it can’t be properly applied because the pores undermine a product’s load-bearing capabilities. The product engineer wants porosity, wants powdered metals and all the benefits they carry, but he doesn’t want that slightly reduced material density. To overcome this drawback, infiltration technology is recruited. The goal is to fill the pores with a liquid metal, an alloy that has a lower melting point than the powdered metal.
Low Melting Point Alloy Infiltration
And that’s the key point here, the low melting point of the infiltrating alloy. Heated, the powdered metal retains its compacted and sintered outlines. Meanwhile, the second metal melts and flows. It uses capillary action to penetrate a component’s pore system and densify the P/M manufactured product. Temperature management programs are essential when carrying out this action, as is a precisely administered sequence of time-based steps. There are hold times and metal fluidizing periods to manage, plus a number of other highly sensitive flow issues to handle. Next, let’s move onto the base metals and the low-temperature flow agents.
Determining the Penetration Alloy
For ferrous-rich alloys, the melting temperature of a sintered component is high. A great deal of energy was expended when the component was compacted and sintered, but its pore system is undermining a normally superhard structure. Injecting molten copper as a pore-penetrating medium, the iron gains a brownish tint. It’s harder, denser, more corrosion resistant, and it’s also now a weldable material. Those mechanical and chemical enhancements wouldn’t exist, not without the copper infiltration stage working its densifying magic.
Reinforcing P/M manufactured components, infiltration procedurals rely on the properties of a low temperature penetrant. Copper is one such material, which improves the corrosion and strength of powdered iron. Then there are ceramic slurries and other exotic materials, which alter the behaviour of formerly porous metal bases. Essentially, used as a secondary property-enhancing operation, infiltration technology is used to fill pore systems. The process seals or strengthens sintered components, makes the part corrosion resistant and/or makes the part more machinable.
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