Phase Evolution and Structure–Property Relationships of Fe79Zr6Si14Cu1 Coatings with Low GFA Produced by Atmospheric Plasma Spraying

The phase evolution of low-glass-forming-ability (low-GFA) Fe-Zr-Si alloys under atmospheric plasma spraying (APS) conditions remains insufficiently understood. In the present study, Fe79Zr6Si14Cu1 coatings were deposited by APS in order to investigate the influence of spray distance on microstructural development and structure–property relationships. Despite the rapid solidification conditions associated with APS, all coatings exhibited predominantly crystalline multiphase microstructures composed of α-Fe(Si) and Fe-Zr intermetallic phases, with no detectable amorphous fraction in the XRD patterns. The coatings developed a characteristic lamellar morphology with porosity ranging from 2.2 to 4.9%, strongly dependent on spray distance and particle thermal history. Increasing spray distance promoted higher hardness and improved wear resistance but simultaneously deteriorated corrosion resistance due to increased porosity and interlamellar defect population. Among the investigated conditions, the coating deposited at 90 mm exhibited the most favourable balance of hardness, wear resistance, and electrochemical behaviour owing to its relatively dense and cohesive microstructure. The results demonstrate that phase evolution in low-GFA Fe-Zr-Si-Cu alloys processed by APS is governed not only by rapid cooling rates but also by splat-based solidification, repeated thermal cycling, and heterogeneous nucleation during coating build-up.