Electron beam melting of Inconel 718: effects of processing and post-processing

This study reports the effect of process temperature on microstructure evolution of electron beam melted Inconel 718. Samples fabricated at 915 degrees C had fine grain boundary delta (similar to 200 nm) along with coarse intragranular delta spanning through the length of the grains. On the other hand, samples fabricated at 990 degrees C, only had grain boundary delta along with secondary carbides. During hot isostatic pressing, the distribution of carbides governs the grain growth vs. lack of it. The samples fabricated at 990 degrees C having grain boundary carbides had no grain growth owing to the pinning effect of carbides. In contrast, the sample processed at 915 degrees C had significant grain growth owing to dissolution of grain boundary delta phase and absence of grain boundary carbides.