As successive layers are deposited, heat can build-up within an additive part that could lead to grain or microstructure coarsening. The EBM process can take 5 to 80 hours to cool below 100° C after layer melting is completed, depending on part size and geometry, so an additive manufactured-part may experience a significant amount of annealing and recrystallization within the AM process chamber.
Heating certain metal powders or parts in an air atmosphere can result in oxidation or oxide scale formation, so the melting processes (LM, EBD, DED) use inert or vacuum atmospheres. If the atmosphere is not controlled within the metal deposition chamber, then oxidation and contamination of the deposited metal can occur, which can embrittle alloys like titanium. Oxidation can also result in brittle oxide inclusions, which introduces a surface where cracks can initiate. Aircraft grade alloys are often vacuumed arc remelted (VAR) to produce a cleaner, more uniform alloy product with the superior properties required for critical service applications. Current AM equipment from some suppliers makes the fabrication of parts from oxidation-prone materials difficult. In many systems, the metal powder is frequently loaded in open air.
