Factors that Affect the Sinterability of Metal Powders

July 2, 2019

No matter how well a line of sintering equipment is configured, how high-performing the equipment has proven to be in the past, particle coalescing challenges can occur. Perhaps randomly, without any obvious source of concern, the Green Compact doesn’t fully fuse into one single workpiece. To fix this process-impeding state of affairs, a veteran trouble-shooter cooks up a sinterability problem solver, which lists the possible reasons for the coalescence-inhibiting failure.

Tracking DownSinterability Inhibitors

Let’s open up the problem-solving guide and get to work. Presumably, the flaw is inside the equipment. The compaction stage created a dimensionally and geometrically accurate Green Compact, but now the process is running aground just as the powdered metal compact enters the sintering chamber. There’s a high-temperature thermal envelope flowing uniformly throughout the enclosed compartment. If the seal in that chamber is damaged, the heat escapes and the necking phase doesn’t happen, at least not as specified by the imposed manufacturing parameters. Basically, the temperatures in there must be maintained. If they’re too high, the metal powder melts. Held too low, the particle necking phase is performed in a materially inefficient manner. Seal failures, heat element damage or gas fuel shortfall, the result is the same: the thermal envelope is applied unevenly, if at all.

All About Sintering Atmospherics

The trouble-shooters are halfway down the problem-solving guide, and they’ve yet to fix the problem. The seals are secure, the thermal energy is being applied just-so, and the process cycle is being timed to the split-second. Despite all of this, there’s another sinterability factor, and it’s still stopping the workpieces from coalescing. Even if the powder metal is fusing completely, the tiny capillary network inside the permeable metal part isn’t large enough to act as a support system for a stored lubricant. Okay, let’s check the furnace atmosphere. Is the vacuum inside the chamber forming properly? If there’s a gas replacing the evacuated air, is the gas mixture set as required? If the gas ratio is “off,” even slightly, the sintering process could be impacted.

If all of these equipment factors check out, it’s time to go back further. Before the sintering furnace, before even the compaction phase, the mixing chamber and powder atomization section require inspection. Are all the additives and oils mixing with the powdered metal to produce a fully homogenized mass? Perhaps the shape of the discrete metal particles isn’t being applied to the atomized grains of metal. If that’s the case, it might be a good idea to check out the powder atomization mechanism and make sure the particles are receiving the correct, process-desired grain profile.

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