Design, preparation and characterization of iron nitride magnetic abrasives

In order to effectively polish the surface of the titanium alloy workpiece, a novel type of iron nitride magnetic abrasives was designed, prepared and characterized. Theoretically, first-principles were used to analyze the effects of phase compositions of iron nitrogen compounds on the mechanical and magnetic properties of the abrasive, and ε-Fe3N and γ′-Fe4N were determined as the grinding phase compositions with the simultaneously improved properties of hardness, ductility and magnetism. In the experiments, the core-shell structured iron nitrogen compounds were prepared by nitriding the iron powders of about 250 μm with ammonia at 600 °C, and the effects of nitriding time, ammonia pressure and cooling method on the product were investigated. The composition, morphology, magnetic properties and mechanical properties of the product were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), magnetometer and nanoindenter, respectively. Under experimental conditions of ammonia pressure of 0.2 Mpa, nitriding time of 3 h and water quenching, the abrasive was obtained with the external grinding phase of ε-Fe3N and γ′-Fe4N in a thickness of 35.10 μm and the internal ferromagnetic phase of α-Fe. Its magnetic saturation intensity and hardness were 148.5 A m2 kg−1 and 8.15 GPa, respectively. Grinding with this abrasive, the surface roughness of Ti-6Al-4V alloy plate was effectively reduced from 0.305 μm to 0.077 μm.