Hardening Methods of Powder Metallurgy PartsAugust 27, 2018
On occasion, when sintered components need to exhibit a predetermined quantity of mechanical toughness, the parts are subjected to special supplementary operations. The finishing service, which is typically carried out in-house, further hardens a sintered component’s internal structure. Now, heat treatment principles obviously dominate this post-production phase, but there are other secondary hardening methods of interest here, which also take place at the end of the production run.
A newly sintered part, having completed the entire powder metallurgy process, balances its ingrained hardness classification against a desired porosity ratio. Alternatively, the component can be densified. Exposed to a secondary repressing phase, the component is placed inside a closed die, pressed uniformly, and heated. As the sintered material becomes denser, it hardens.
Viewed as a heat treatment offshoot, near melting point thermal curves are not required here, yet the powder-manufactured components do gain a case-hardened finish. Essentially, the process uses steam and heat to oxidize the metal’s surface. By applying more steam and sustaining the thermal energy for a predetermined period, the hardened finish goes deeper.
In this supplementary hardening procedure, powder metallurgy parts no longer use their porous structures as an oil-filled system. However, the component can still deliver a powerful quantity of self-lubricating might if the right filler is employed. For example, fluoropolymer fillers seal the pores while simultaneously providing a Teflon-coated lubricating feature. Otherwise, a second metal can be used as the filler, one that again densifies the normally porous material base.
Carried out in a vacuum furnace or a heated enclosure that pumps in an inert gas atmosphere, a single-phase solution takes form within the PM manufactured metal. Precipitates are produced as the thermal energy in the furnace climbs. Locking this metallic phase in place, the sintered parts are rapidly cooled in water or oil. The fine-grain metal still contains a porous sub-structure, but that metal grain is finer and harder.
Precipitation technology works well on certain alloys. However, in powder metallurgy work, there’s a need for niobium or some other exotic metal, which facilitates the precipitate formation stage. Unlike this exacting heat treatment method, case hardening tech is a little more flexible. Available hardening methods here include induction hardening, plasma nitriding, and carbonitriding.
Powder metallurgy tech creates hardened components. If a client or application requires a harder metal, then repressing or steam treatment work provide a cost-effective avenue. Then, for those applications that absolutely demand the services of a heat treatment process, there’s case hardening work or the even denser precipitation hardening process.
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