Thermal stability and Ar + ion irradiation behaviour of SLM AlSi10Mg alloy post-processed via KOBO extrusion method

Abstract

Ultra-fine-grained (UFG) and nanotwinned (NT) materials are anticipated to exhibit exceptional resistance to irradiation due to their significant volume fraction of grain boundaries. However, a notable drawback is their susceptibility to grain coarsening at elevated temperatures, which significantly limits their practical application as irradiation-resistant materials, particularly in high-temperature environments. In this study, an AlSi10Mg alloy, prepared using laser powder bed fusion (LPBF), underwent post-processing via the KOBO extrusion method, resulting in an ultra-fine-grained microstructure with an enhanced fraction of coincident site lattice (CSL) twin boundaries. The investigation was conducted in three phases. The first phase involved modelling radiation damage to gain insights into the expected behaviour of the microstructures under irradiation. The second phase included a comprehensive analysis of the microstructures of both as-built and KOBO-processed samples using light, scanning, and transmission electron microscopy. This analysis revealed an ultra-fine-grained microstructure with a mean grain size of approximately 0.8 µm and an increase in the fraction of CSL boundaries from 30% in the as-built state to 42% following KOBO extrusion. In the third phase, the thermal stability of both samples was assessed through annealing experiments conducted for 1 h across a temperature range of 300–500 °C, with 50 °C intervals. To further explore the impact of the nanotwinned microstructure on thermal stability, irradiation experiments were conducted using 60 keV He⁺ ions to a dose of 5 × 10¹⁷ ions cm⁻² at 130 °C. The results indicated an improved irradiation resistance in the KOBO-processed sample, as evidenced by a thinner sponge-like structure formation upon Ar⁺-ion irradiation compared to the as-built counterpart.