Electron beam deposition on naval propellers

Post-cold-war research contract using nickel-manganese-aluminum bronze samples to demonstrate ridge buildup on propeller-grade castings. Surface tension defects and residual stress limit buildup to about half an inch.

[Tom passes a small sample around the class and holds up a larger one.] Since they were trying to find a use for their technology, we had a research contract and we tried electron beam deposition. This is a piece of nickel manganese aluminum bronze. Anybody know what this alloy is used for in the Navy? Propellers. Propellers are circular and you could potentially build up structure. So this is a piece cut from that, and we built up this ridge with an electron beam. This is a piece of stainless steel where we were building up a ridge just going around and around. But sometimes you end up getting solidification defects, surface tension defects, and they tend to propagate and it's hard to get rid of them. The other problem is you develop residual stresses. As you build up bigger and bigger things, you have these small little weld zones and you put one on top of another, and the residual stresses get worse and worse. Typically you get to about more than a half an inch and you find that you end up cracking.