Additive manufacturing (AM) enables the unique fabrication of parts using an optimum amount of feedstock material [1,2]. Amongst the different types of AM processes for metals, laser powder bed fusion (LPBF) is widely used for steels [3]. In LPBF, a powder layer of a given thickness is deposited on top of previously melted and solidified layers, which is then fused by a laser. Parameters like power, speed, beam diameter, wavelength, or emission mode are typically varied. Optimum selection of the process parameters can help to reduce defects like porosity, thus improving a part’s mechanical properties [4].

Maraging steels are characterised by low carbon contents and high amounts of substitutional elements that precipitate when subjecting the as-quenched condition to an ageing treatment [5]. The outstanding weldability and mechanical properties (ultrahigh strength and fracture toughness) of maraging steels make them ideal for applications that require high strength-to-weight ratios, such as landing gear and slat tracks for the aerospace industry, as well as high-performance parts in power plant and injection moulding industries. Maraging steels produced by AM have shown different resultant microstructures compared to ones obtained by conventional processing [6]. Indeed, it has been shown that the microstructure of as-built, LPBF-produced maraging 300 steels consist of martensite without precipitates [6]; they also contain between 2-8 ± 3% of retained austenite. Ageing treatments typically used for these kind of steels produced by AM also precipitate particles, although the differences with respect to particles produced by conventional processing have still not been fully assessed in the literature. In this work, the difference in chemical homogeneity on the micro- and nanoscale and phase distribution of AM-produced maraging 300 steel and the effect on microstructural evolution during ageing was investigated by atom probe tomography and complementary characterization. Results revealed that aged microstructures are comparable to that obtained by conventional manufacturing methods.

References

[1] H. Fayazfar, M. Salarian, A. Rogalsky, D. Sarker, P. Russo, V. Paserin, E. Toyserkani, A critical review of powder-based additive manufacturing of ferrous alloys: Process parameters, microstructure and mechanical properties, Mater. Des., 2018, 144, 98–128.

[2] I. Gibson, D.W. Rosen, B. Stucker, M. Khorasani, Additive manufacturing technologies, Springer, 2021.

[3] M.J. Mirzaali, F.S.L. Bobbert, A.A. Zadpoor, Y. Li, Additive Manufacturing of Metals Using Powder Bed-Based Technologies, in: A. Bandyopadhyay, S. Bose (Eds.), Addit. Manuf., CRC Press, 2019.

[4] I. Koutiri, E. Pessard, P. Peyre, O. Amlou, T. De Terris, Influence of SLM process parameters on the surface finish, porosity rate and fatigue behavior of as-built Inconel 625 parts, J. Mater. Process. Technol., 2018, 255, 536–546.

[5] P. Bajaj, A. Hariharan, A. Kini, P. Kürnsteiner, D. Raabe, E.A. Jägle, Steels in additive manufacturing: A review of their microstructure and properties, Mater. Sci. Eng. A., 2020, 772, 138633.

[6] E.A. Jägle, P. Choi, J. van Humbeeck, D. Raabe, Precipitation and austenite reversion behavior of a maraging steel produced by selective laser melting, J. Mater. Res., 2014, 29, 2072–2079.