Speaker
Description
Laser Powder Bed Fusion (LPBF) is an established technique for additive manufacturing. However, not all alloys are manufacturable with LPBF. Especially high-strength aluminum alloys that can be precipitation hardened are difficult to weld and thus difficult to process with LPBF. The growth of elongated grains and build-up of residual stress lead to anisotropic macroscopic mechanical properties of the printed part and higher risk of crack formation at grain boundaries. Processing at elevated environment temperatures can reduce the problems but is not economical due to long cooldown times. To mitigate these problems the relatively new approach of reactive additive manufacturing (RAM) is being investigated in cooperation of Colibrium Additive, Friedrich-Alexander-Universität Erlangen-Nürnberg and Technical University of Munich.
Here reactive particles are mixed with the pre-alloyed aluminum powder that react exothermally during melting and form ceramic nanoparticles that inhibit grain growth and act as nucleation points to form smaller grains and therefore reduce cracking.
To assess the bulk microstructure and distribution of RAM particles neutron imaging studies were performed on samples printed with different process parameters using different laser powers.
Both transmission and dark-field contrast from neutron grating interferometry were used to show the homogeneity of the printed parts.
Due to the high boron content in the added RAM particles their distribution can be seen in transmission contrast.
The sensitivity of the dark-field signal to scattering of micrometer-sized structures enables the spatially resolved assessment of defects like porosity and anomalies such as unreacted RAM particles.
