Army helicopter rotor casting weld repair (early 1980s)

Tom's student "Gordon" worked at Watertown Arsenal on whether weld repairs of titanium helicopter rotor castings would be acceptable. Result: welds were better than the base metal because of faster cooling and finer Widmanstätten structure. Used to make the point that in titanium, welds can outperform base material in fatigue strength.

It turns out the welds in titanium have better fatigue strength than the base metal because they have a finer structure. I had a student in the early 80s working on helicopter rotors over here at Watertown Arsenal. The Army wanted to use castings. You cast titanium or anything else, you're gonna have defects in the casting. You can't throw out a fifty-thousand-dollar casting, you've got to weld-repair it. The question was, would the weld repair be any good. Gordon proved the welds were better than the base metal, because you've got a better cooling rate, gave you a finer structure. We don't have time to go through all the metallurgy, but the point is, titanium is relatively easy to get a good structure in the weld.