It's more than metallurgy and aero design.
Manufacturing processes are hard to understand, let alone replicate, when you're on the outside looking in. 3+ decades ago Brand A was building an engine on a gov't contract, so the gov't owned the drawings. The gov't decided to second-source the engine, and turned drawings over to Brand B.
A vs B Parts looked alike, measured alike, but B's parts failed endurance tests. They differed at the intergranular level, which B was unable to achieve.
