I used an ultrasonic bath at work once to clean some aluminium brake levers that I had hand-polished. The idea was to use the ultrasonic bath to get every last trace of autosol out of the nooks and crannies in the levers. My plan went wrong when I pulled the levers out of the ultrasonic bath, and realised that the ultrasonic process, in combination with washing up liquid, had dulled my lovely hand-polished mirror finish. I didn't use the ultrasonic bath again. I re-polished the levers, and blasted them with lots of WD40, then wiped them down with some kitchen towel.
I'm telling this story because ultrasonic baths can be quite an aggressive method of cleaning. The process generates huge numbers of tiny bubbles (this is technically termed cavitation), which then suddenly collapse. When these bubbles collapse next to the metal surface you're trying to clean, the pressures generated can be quite large, which is what produces the cleaning effect. This may not be much of a problem for objects such as chains, but could damage sensitive finishes when placed in large, powerful, industrial cleaning units.
If I recall correctly, one of the instruction manuals I once read for an ultrasonic bath stated that you can test the unit by suspending a strip of aluminium foil in the bath (knowing that the unit is working correctly is important when cleaning surgical equipment). If the ultrasonic bath is working correctly, the aluminium foil should start perforating after a few minutes. Of course that's an extreme example, because aluminium foil is very thin. So when a bubble collapses nearby, there is not enough thickness of material to resist the extreme pressures generated, causing the foil to deform, and then perforate.
A similar effect can occur in pumps, and can lead to a sound being generated that sounds like gravel is circulating around the pump. This effect is a well known problem in the pumps industry, as the cavitation voids are much larger, and so the pressures generated when the voids suddenly collapse are much greater. In pumps that are poorly designed or poorly setup, cavitation can rapidly cause serious damage and destroy pump impellers.
Cavitation damage on a pump impeller (picture from
here)