Abstract
Powder and selective laser melting (SLM) additively manufactured parts of X5CrNiCuNb17-4 maraging steel were systematically investigated by electron microscopy to understand the relationship between the properties of the powder grains and the microstructure of the printed parts. We prove that satellites, irregularities and superficial oxidation of powder particles can be transformed into an advantage through the formation of nanoscale (AlMnSiTiCr) oxides in the matrix during the printing process. The nano-oxides showed extensive stability in terms of size, spherical morphology, chemical composition and crystallographic disorder upon in situ heating in the scanning transmission electron microscope up to 950 °C. Their presence thus indicates a potential for oxide-dispersive strengthening of this steel, which may be beneficial for creep resistance at elevated temperatures. The nucleation of copper clusters and their evolution into nanoparticles, and the precipitation of Ni and Cr particles upon in situ heating, have been systematically documented as well.
Highlights
Maraging steels are low-carbon, precipitation-hardenable martensitic steels with high strength and toughness, high temperature creep resistance and low temperature properties, but are corrosion resistant
In order to clarify whether the oxides are stable at elevated temperatures and to observe the nucleation of the nanosized Cu, Cr and Ni precipitates, we performed simultaneous thermal analysis (STA) measurements of the as-built sample, and scanning transmission electron microscopy (STEM) in situ heating experiments accompanied by EDX analyses
Correlative electron microscopy and STA investigations were performed for X5CrNiCuNb174 maraging steel to better understand the microstructural characteristics of the final additively manufactured parts and their evolution upon in situ heating up to 950 ◦ C
Summary
Maraging steels are low-carbon, precipitation-hardenable martensitic steels with high strength and toughness, high temperature creep resistance and low temperature properties, but are corrosion resistant. Depending on the printing parameters and powder characteristics (e.g., uniformity of grain size and natural surface oxidation), element segregations and rather large oxide inclusions (TiO2, Al2O3 of about 10–20 μm, or other oxides containing Ti, Mo, Al and Si in various ratios) [4] have been observed at melt pool boundaries Their presence, due to consistently high density of the part (absence of pores), is generally considered to have an unfavorable influence on the mechanical properties of the printed part [4,5,6,7] because of crack initiation. To the best of our knowledge, only been reported for AlSi10Mg alloy [19]
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