Thermodynamic quantitative analysis and formation mechanism on novel multilayered Fe-Si core-shell magnetic abrasives

Abstract

Based on the direct combination of traditional abrasive hard phase particles and ferromagnetic phase matrix, this study introduces a multilayer self-sharpening structure aimed at improving the durability of abrasives. The effects of holding temperature and holding time on the microstructure of the gradient grinding layer on the surface of ferromagnetic phase during the pack cementation process are analyzed. The phase transition mechanism of the abrasive layer, transitioning from a bilayer structure in the pre-insulation phase to a trilayer structure in the post-insulation phase explained by diffusion thermodynamics. A model is established between the diffusion driving force (F) and the thickness (H) of each layer in the gradient coating through ∆G. Finally, the finishing performance and durability of the new abrasive is tested. The results show that the microstructure of abrasive formed at 725 °C for 3 h, consisting of 3 μm FeSi₂ outer layer, 14 μm FeSi intermediate layer and 5 μm Fe₃Si inner layer, exhibits uniform and dense structure, without obvious cracking and spalling at the coating-substrate interface, and forms a strong metallurgical bonding interface. Quantitative calculations from the diffusion model show that the diffusion driving force is directly related to the thickness of each layer within the gradient diffusion layer. The greater the driving force of the compound, the greater the thickness. The surface roughness (Ra) of the zirconium tube decreases from 0.2008 μm to 0.1170 μm after 3 passes of finishing. The gradient self-sharpening structure of the new abrasive makes its finishing life reach 150 min, demonstrating excellent durability.