We plan to i) map the strain and 3-D position of different phases in an additively manufactured Fe-9Cr steel using x-ray computed tomography and ii) obtain 2-D diffraction data sets for the same material that has been ion irradiated to determine stability to irradiation. From initial SEM and TEM characterization of the unirradiated material we observed a heterogeneous microstructure containing a network of martensite surrounding and carbides within a predominantly ferrite material. Strain and phase mapping will 1) measure the 3-D distribution of the high strain martensite and 2) determine the distribution of martensite and carbide phases with position in the build (i.e. top to bottom). Comparison to the heavy ion irradiated material will reveal the stability of the different phases, though mapped in 2-D for the irradiated material.
Prior investigation of the room and high temperature mechanical properties of this AM Fe-9Cr steel found higher yield strength than wrought material while maintaining work hardening and ductility. We hypothesize the distribution of the harder martensite and carbide phases surrounding and within the ductile ferrite phase leads to the combination of strength and ductility. A key outcome of measuring the 3-D distribution of the high strain martensite is to form or use an existing model for the meso-scale-microstructural contributions to material strength. The model could then be used to enhance mechanical properties through microstructure, which is easily controlled by minor changes to the AM processing conditions. The secondary outcome is determining differences in the martensite and carbide distribution as a function of position in the build, which is an important consideration for applying advanced manufacturing to engineering components. Finally, the stability of the phases measured will be determined with investigation of the ion irradiated material.
The proposed experiments support an ongoing investigation at LANL supported previously by internal funding and currently by DOE-NE through a NEET-1 award. The proposed experiments include 3 days. The project is flexible whether the days are continuous or separate. A total of 7 experiments are expected to be completed. The results obtained through the RTE are expected to be combined with previously acquired data and published in an academic journal within 18 months.
The proposed research advances DOE’s Office of Nuclear Energy mission specifically regarding advanced manufacturing of materials for nuclear applications. The research will lead to an improved understanding of additive manufactured materials correlating the complex microstructures to improved mechanical properties. Additive manufacturing is one of the leading advanced manufacturing methods being investigated to produce certain nuclear reactor components in micro- and traditional nuclear reactors. Ferritic/Martensitic steels are nuclear reactor relevant structural materials due to high thermal conductivity, excellent corrosion resistance, radiation tolerance and mechanical properties.
There remains a knowledge gap in the microstructure and mechanical properties of additively manufactured FM steels (unlike additively manufactured austenitic steels where there is a wealth of knowledge). The gap we are specifically probing is the link between microstructure and mechanical properties.
