How Powdered Metals Convert for the Strength You NeedNovember 21, 2018
Historically speaking, powdered metals are recognized as moderately strong materials. They form relatively hard bearings and other self-lubricating items. By heat treating sintered metal parts, they become even tougher. In point of fact, the sintering process uses thermal energy and pressure, so some heat treated hardenability is applied during the production phase. Okay, this strength-conversion methodology feels a little nebulous. Just think, wouldn’t it be better if powdered metal parts could be strengthened, toughened and made fatigue resistant with the flip of a switch?
Injecting Alloying Materials
Well, it’s not a physical switch, but this material-strengthening approach does add a process controlling edge to the production line. It goes something like this: Since powdered metals use special engineering recipes, why not add hardenability ingredients to the blend? Molybdenum is considered a hardness agent, as is nickel. Like the alloys that strengthen stainless steel, those metallic elements create generously toughened powder metal parts. Of course, such metals force production costs higher, which is a problem. One answer to this conundrum is to substitute chromium, a capable but affordable metal hardener, into the powder blend. Unfortunately, this approach isn’t without problems, including oxidizing issues. Let’s move onto a second product strengthening technique, one that’ll satisfy the most demanding customers.
Compaction Control Mechanics
Microscopically assessing the atomized powders, the engineers in charge observe the powder’s morphology. It’s a spheroidal mass of tiny particles. Using the latest chemical and mechanical pulverization methods, those that assure featureless particle geometries, the fine-grained load enters the sintering tumbler as a liquid metal stream. In truth, the mass is made of tiny particles, not a liquid base, but it’s so finely atomized that it behaves like a fluid. Now, extreme pressures are applied, thermal curves are controlled, and the sintering process is executed. Because of the particle morphology, that featureless spheroid shape, the particles weld together. Capillary action and porous voids are still part of the design here, but the compaction stage favours strength over material porosity. Essentially, because the particles are finer and smoother, they weld together more easily. Fewer gaps are left behind, so the material becomes denser and harder.
Pressing and sintering control mechanisms regulate powdered metal strength. There are also strengthener additives and hardness heat treatment cycles to further reinforce their strength. Converting to match a client’s design specs, resilient alloys also imbue sintered products with a high degree of durability and fatigue-resisting power. However, such alloys can be expensive, so much so that the process becomes exorbitantly pricey. Currently, chromium is the most cost-effective option here, although the process then must account for oxidization issues.
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