Phase Transformations in a Fe-Ni-Cr-Cu-Si-B-C Composition during Mechanochemical Alloying

To investigate the possibility of preparation of a surfacing powder for gas-plasma facing, mechanochemical alloying of a mixture of Fe, Ni, Cr, Cu, B, and C powders is performed in a MPP-2-1K planetary mill for 15 min. To determine the chemical interaction between charge components and the sequence and character of formation of the phase composition in granulated alloys during mechanochemical alloying (MCA), X-ray diffraction (XRD) analysis of the powder material is performed using a D8 ADVANCE (BrukerElementalGmbH) diffractometer. The morphology of granules after mechanical alloying is studied by scanning electron microscopy (SEM) using a JEOLJXA-8230 scanning electron microscope. To determine the melting temperature of the prepared composition, thermal gravimetric analysis is carried out using a TG-DTA/DSC STA 449 F3 Jupiter (NETZSCH) synchronous thermal analyzer equipped with a quadrupole mass spectrometer. The experimental results of show that, upon mechanical activation of an Fe-Ni-Cr-Cu-Si-B-C composition, the formation of both stable and metastable phases takes place. It is found that, already after 1-min mechanochemical alloying, numerous new phases form; after 15-min alloying, a multiphase system forms, which includes intermetallics (Fe0.95Ni0.05, Cr1.07Fe18.93, etc.), carbides (Fe3C, Cr15.58Fe7.42C6, etc.), borides (Ni75Si24B0.04, etc.), and silicides (Ni0.92Si0.08, Cr5Si3). The main cause for the phase formation upon mechanochemical alloying is the shock action of milling bodies (balls), which results in the plastic deformation of starting component particles, their breaking, and welding along formed juvenile surfaces, which is accompanied by exothermic effects and the formation of intermediate liquid phases. As a result, the contact surface of the reagents abruptly increases and composite particles form. Upon shock action, complex and poorly understood chemical processes, diffusion of components, and phase- and structure-formation occur.