Preparation of ferrosilicon-aluminium coating using a mechanical alloying technique: Study of thermal annealing on their structural characteristics

In the present study, ferrosilicon-aluminium coating was successfully deposited on the surface of low‑carbon steel using mechanical alloying (MA) technique. The coating structures after MA and annealing were studied using X-ray diffraction (XRD), scanning electron microscope (SEM) equipped with energy disperse X-ray spectroscopy (EDX) and electron backscatter diffraction (EBSD). The roughness and hardness of the coatings were measured by Surfcorder SE300 and microhardness tester, respectively. The coating thickness after mechanical alloying is in the range of 65 μm to 100 μm and the surface roughness is around 11.581 μm. Phase analysis showed that ferrosilicon-aluminium coating was composed by FeSi2, Si and Al0.8Si0.2 phases. While the thermal annealing led to the formation of FeAl3Si2 and Fe2Al3Si3 phases. Further cross-sectional observation of annealed samples showed that the coating consisted of four layers structures with the thickness of each layer depended on annealing temperature. The first top layer was composed of porous structure of FeAl3Si2 and Fe2Al3Si3 phases. The second and third layers possess a dense structure consisting of Fe3Al2Si3 and Fe2Al5 phases, respectively. The fourth layer at the coating/substrate interface was rich in Si, namely Si-rich layer. As annealing temperature increased, the thickness of Fe3Al2Si3 and Si-rich layer increased, but the thickness of Fe2Al5 layer decreased. The optimum microhardness value of ferrosilicon-aluminium coating after mechanical alloying and diffusion layer of annealed samples were 481 HV and 1170 HV, respectively.