My thinking is that additive 3d printed parts will only become as strong as things that have been forged then machined, once they figure out how to bombard the part being grown with hundreds perhaps thousands of laser or plasma streams at the same time from as many angles of attack as there are laser emitters or plasma nozzles, with overlapping depths in a high-pressure chamber. If you think about how 3d printers function the growth currently comes from a single point of contact. if they come up with a way of creating multiples of these in varying frequencies of application while randomly controlling the depth of the penetration the cellular growth of the crystalline grains will be forced into the voids of adjacent crystals. Very similar to how metal ores were turned into useable metals by heating and beating the impurities out of the molten blobs called sponge.