Study Of Preparation And Properties Of Al₂O₃-Tic-Fe Magnetic Abrasive Grain

In this thesis, the relationship among composition, manufacturing process, phase constituent,microstructure mechanical properties and abrasive properties of Al₂O₃-TiC-Fe magnetic abrasive hasbeen systematically investigated by thermal analysis, X-ray diffraction （XRD）, scanning electronmicroscope （SEM）, energy dispersive X-ray analysis （EDS）. Finally, the characteristic of magneticabrasive finishing of TiC/Fe magnetic abrasive was studied.At first, the processing mechanism, stress analysis and influence factors on magnetic abrasivefinishing of magnetic abrasives have been summaried. Then the problems on the preparationtechnologies were proposed. At last, the purpose and significance of this paper have been pointed out.The main physical and chemical changes of the Al₂O₃-TiC-Fe magnetic abrasive during thevacuum sintering process were studied. Some conclusions were drawn as follows: at the temperaturebelow900℃, a part of Mo and C generated the Mo2C, Cr dissolved in the Fe matrix by through thesolid state diffusion. The final phase constituents of Al₂O₃-TiC-Fe magnetic abrasives were Fe-Cr,Al₂O₃and TiC.The influences of the sintering process on the phase composition, microstructures, mechanicalproperties and polishing properties of Al₂O₃-TiC-Fe magnetic abrasives were studied. Duringsintering process, appropriate liquid-state sintering improved the polishing performance and servicelife of magnetic abrasives. The Al₂O₃-TiC-Fe magnetic abrasives sintered at1220℃for2h displayedhigher density and mechanical properties. The surface roughness of workpiece made of45steelachieved Ra0.314μm, and the service life of the magnetic abrasives achieved36min.The influences of the Al₂O₃content on the phase composition, microstructures, mechanicalproperties and polishing properties of Al₂O₃-TiC-Fe magnetic abrasives were studied. Someconclusions were drawn as follows: when the content of Al₂O₃was15%, Al₂O₃and TiC particalsuniformly distributed in the Fe matrix and had appropriate particle size. The samples had highermechanical properties, polishing properties and longer service life. The linear shrinkage rate, relativedensity, microhardness, transverse rupture strength and single particle compressive strength were1.7%,63.6%,525.1HV,105.9MPa,45.8MPa, respectively.The influences of Si and Ni contents on the phase composition, microstructures, mechanicalproperties, polishing properties of Al₂O₃-TiC-Fe magnetic abrasives were studied. Si reduced thetemperature of liquidus. When Si content was5wt%, complete liquid sintering made the distribution uniformity of abrasive paticles increase, and improved the density and mechanical properties. Thesurface roughness of workpiece achieved0.275μm and the service life achieved36min when itfinished the workpiece made of45steel. When Ni content was10%, the wettability between Fematrix and Al₂O₃, TiC was improved significantly, the surface roughness of workpiece achieved Ra0.301μm and the service life achieved36min when it finished the workpiece made of45steel.However, when the content of Ni was15%, the magnetic properties would be significantly reducedand the magnetic abrasives could not be arranged along the direction of magnetic field lines. Thus, itcouldn’t effectively polish the workpiece.