Influence of the graphene incorporation on nanostructure and thermal properties of the laser powder bed fusion processed AlSi12 matrix composites

The successful fabrication and implementation of graphene-reinforced aluminum (Al) matrix composites (AMCs) have been obstructed by the undesirable graphene-Al reactions during their casting or inability of complex part manufacturing through powder metallurgy techniques. The emergence of the laser powder bed fusion (L-PBF) process with extremely short melt duration and almost no limitations in terms of the manufacturing of intricate features has renewed the interests for fabrication of graphene-reinforced AMCs. In this study, the influence of graphene incorporation into AlSi12 on L-PBF processability and defect formation is studied. The specific heat capacity, coefficient of thermal expansion, thermal diffusivity and thermal conductivity of composites were compared to those of the monolithic AlSi12 alloy. Microstructure-thermal properties relationship was studied through transmission electron microscopy (TEM), high-resolution TEM (HRTEM), electron backscatter diffraction (EBSD), electron dispersive spectroscopy (EDS) and Raman spectroscopy. This study provides valuable insights into (i) the chance of survival of graphene, (ii) possibility of graphene changing into other forms of carbon, and (iii) graphene-Al reactions during the L-PBF process. It was found that most of the graphene/graphite particles transformed into Al4C3. Among the survived carbon material, it appears they are more disordered than the initial graphene/graphite, though highly ordered ones with almost no defects were also detected. Thermal expansion measurements showed that the coefficient of thermal expansion decreased from 27.5×10–6/˚C for AlSi12 to 25.3×10–6/˚C for AlSi12–0.25 Gr and 25.5×10–6/˚C for AlSi12–0.5 Gr. Regarding thermal conductivity, in the case of AlSi12–0.5 Gr, it either matched or was lower than that of pure AlSi12 within the tested temperature range. In contrast, AlSi12–0.25 Gr exhibited higher thermal conductivity than AlSi12 in the temperature range of 150–350 ˚C.