Study On The Preparation And Properties Of TiC/Fe Magnetic Abrasive Grain

In this thesis, TiC/Fe magnetic abrasives were prepared by vacuum sintering. Then, the relationship among composition, manufacturing process, microstructure and mechanical properties of TiC/Fe magnetic abrasive has been systematically investigated by thermal analysis, X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive X-ray analysis (EDS). Finally, the characteristic of magnetic abrasive finishing of TiC/Fe magnetic abrasive was studied.In the first part, the development and present research situation of magnetic abrasive finishing were critically overviewed, which includes the principle, mechanism of magnetic abrasive finishing. Then, the present research situation of the magnetic abrasive was summarized, such as the composition, microstructure, and performance requirement of magnetic abrasive and the preparation techniques of magnetic abrasive. Based on above work, the purpose and significance of the dissertation have been pointed out.The main physical and chemical changes of the Fe/TiC magnetic abrasive added with Mo, Cr, during the sintering process were studied. Some conclusions were drawn as follows: when the sintering temperature was below 1150℃, Cr was completely dissolved in the Fe matrix, and a thin Mo-rich rim phase was formed at the surface of TiC particle. When the sintering temperature was between 1150℃and 1200℃, the incomplete Mo-rich rim phase was formed obviously at the surface of TiC particle by the dissolution-precipitation mechanism.The effects of main technical parameters during sintering on the microstructure and mechanical properties of TiC/Fe magnetic abrasive were studied. The results showed that the grinding performance and service life of the TiC/Fe magnetic abrasive were improved by liquid phase sintering. The samples sintered at 1180℃for 2h had higher density and more homogeneous uniform microstructure. In addition, the samples were easily crushed to manufacture magnetic abrasive. The surface roughnesses of the workpiecees made of 45 steel and SUS304 after finishing were Ra0.30μm and Ra0.35μm respectively, and the service life of the magnetic abrasive achieved 33min when it finished the workpiece made of 45 steel.The effects of the individual chemical composition C, Mo and B₄C on the microstructure and mechanical properties of TiC/Fe magnetic abrasive were studied. The conclusions were obtained as follows: when the content of C was 0.6wt%, the better grinding performance, longer service life and higher fragility of the magnetic abrasive was obtained. The wettability between the Fe binder phase and TiC hard phase was improved by the addition of the Mo, making the microstructure more homogeneous. When the content of Mo was 4.2wt%, the sample had the higher mechanical properties, relatively modest magnetic properties, better grinding performance and longer service life. The addition of B₄C reacted with Fe during sintering, which resulted in the reduction of magnetic properties, serious agglomeration of hard phase and poor interface bonding. Consequently the grinding performance and service life were reduced.The effects of the main factors on the machining effect of magnetic abrasive finishing were studied. The conclusions were obtained as follows: the descending order of the magnetic abrasive processing parameters, which affected the grinding efficiency and surface roughness was magnetic field strength, work space and pole speed. The surface roughness Ra of the workpiece made of 45 steel was 0.19μm under the optimum magnetic abrasive process parameters which were magnetic field strength of 1.4T, machining gap of 1.5mm and pole speed of 2500r/min respectively. When the different types of magnetic abrasive were used to grind the same workpieces, the grinding performance and service life of TiC/Fe magnetic abrasive were better than that of other magnetic abrasives. In addition, the grinding performance of TiC/Fe magnetic abrasive apparently was decreased with the increasing of TiC/Fe and TiC particle size.