The authors were able to fine-tune the composition of the steel to find a set of compositions consisting of only iron, nickel, copper, niobium, and chromium that worked because they now had a good understanding of the structural dynamics during printing for reference. .
“Composition control is truly the key to 3D printing alloys. By controlling the composition, we can control how it solidifies. We also showed that, over a wide range of cooling rates, say between 1000 and 10 million degrees Celsius per second, our compositions consistently result in fully martensitic 17-4 PH steel,” said Zhang.
Recent work could also be influential beyond 17-4 PH steel. Information gained from the XRD-based method could be used to develop and test computer models to predict the quality of printed items, as well as optimize other alloys for 3D printing.
“Our 17-4 is reliable and reproducible, lowering the barrier to commercial use. By following this composition, manufacturers should be able to print 17-4 structures that are just as good as conventionally manufactured parts,” Chen said.
Fusion-based additive manufacturing technologies enable the manufacture of geometrically and compositionally complex parts that cannot be achieved with conventional manufacturing methods. However, non-uniform and far from equilibrium heating/cooling conditions pose a significant challenge in consistently obtaining desirable phases in printed parts. Here we report a development of martensitic stainless steel guided by phase transformation dynamics revealed by high-speed, high-energy, high-resolution X-ray diffraction in situ. This engineered stainless steel consistently forms the desired fully martensitic structure over a wide range of cooling rates (102–107 ℃/s), allowing direct printing of parts with a fully martensitic structure. The printed material exhibits a yield strength of 1157 ± 23 MPa, comparable to its forged counterpart after precipitation hardening heat treatment. The printable property is attributed to the fully martensitic structure and fine precipitates formed during heat treatment intrinsic in additive manufacturing. The phase transformation dynamics-driven alloy development strategy shown here paves the way for developing reliable, high-performance alloys specifically for additive manufacturing.