Study On Preparation Of Magnetic Abrasives By Gas Atomization With Rapid Solidification And Their Finishing Performance

Magnetic abrasive finishing (MAF), as an advanced finishing method, can be widely used inmany field, such as aeronautics, astronautics, medical apparatus and instruments etc. And magneticabrasives play a very important role in MAF, further more directly determines the surface quality ofparts finished. However, the irregular shape, low processing efficiency, short service life, complexprocess, high cost exist in the commercial magnetic abrasives which are prepared by traditionalmethods, so the preparation of magnetic abrasives becomes a bottleneck problem urgently to besolved in MAF.Therefore, a new method, that combines gas atomization and rapid solidification, is proposed toprepare spherical composite magnetic abrasive in this paper. Depending on improving the system ofpreparation powder, the high-pressure atomizing gas and ceramic hard abrasive powder werebeforehand mixed uniformly, it makes the molten ferromagnetic alloy matrix atomize into tinydroplets, and the tiny droplets were rapidly cooled down and solidified, and then the sphericalcomposite magnetic abrasive powder was obtained. Subsequently this spherical composite magneticabrasive was used in MAF to process non-conductive magnetic material and conductive magneticmaterial.The main work and the results obtained in this dissertation are as follows:(1) The system equipment which fabricates powder of metal or its alloy by gas atomization andrapid solidification was studied and analyzed firstly. And a special equipment to prepare sphericalcomposite magnetic abrasive through a process that combines gas atomization and rapid solidificationwas developed based on performance requirement of magnetic abrasives. This equipment can solvethe technical conundrum for the system of ceramic/Fe-based composite in which the compatibility ofFe-based phase and ceramics phase is very bad, and make the preparation process simple, cost low,productivity high. And this method can realize the large-scale industrial manufacturing of magneticabrasives.(2) The study was carried out on composite materials preparation theory of ceramic/Fe-basedsystem, magnetic property of ferromagnetic alloys and process characteristics of gas atomization andrapid solidification. The composition of spherical composite magnetic abrasive under the condition ofgas atomization and rapid solidification was investigated according to ideal micro-morphology andperformance requirement of magnetic abrasive. Al2O3/Fe-based and SiC/Fe-based sphericalcomposite magnetic abrasive, which conform to the ideal structural model and requirements of mechanical and soft magnetic properties of the magnetic abrasive, were successfully obtained.(3) The formation mechanism, interfacial microstructure and influencing factors of sphericalcomposite magnetic abrasive under different conditions of gas atomization and rapid solidificationwere detected by means of scanning electron microscope(SEM), energy dispersion spectrometer(EDS)and X-ray diffraction(XRD). The results demonstrate that three factors, i.e. process parameters for gasatomization and rapid solidification, alloying of the ferromagnetic matrix and the hydrodynamic effectare effectively controlled at the same time, the magnetic abrasive which conforms to the idealstructural model and requirements of mechanical and soft magnetic properties of the magneticabrasive can be obtained. The interfacial microstructure of Al2O3/Fe-based is joining mixed withmechanical, dissolved and wetted combined; the interfacial microstructure of SiC/Fe-based ismetallurgy reaction wetting joining.(4) The MAF system of open magnetic field of Nd-Fe-B rare earth permanent magnetic poleswas developed according to the magnetic flux continuous principle and Amp loop theorem based onMAF theory. The investigation were carried out on the processing performance of magnetic abrasivefor316L stainless steel and S136mold steel based on this MAF system developed. During machining,not only Al2O3/Fe-based and SiC/Fe-based spherical composite magnetic abrasive under differentconditions could realize high efficiency and nanometer level surface roughness finishing, but also thesurface quality of the machined parts could be observably improved.(5) The tests were carried out on wearing characteristics and service life of the magneticabrasives. During tests, the abrasion wear is the dominating wear behavior for the Al2O3/Fe-based andSiC/Fe-based spherical composite magnetic abrasive. The disadvantageous phenomenon of the fallout of Al2O3and SiC grains have never happened, their service life reaches to more than140minutesin the tests. This indicates that between the ferromagnetic matrix phase and abrasive phase of thismagnetic abrasive had been realized strong joining through gas atomization and rapid solidification inthis special equipment developed. And this process can make the service life of magnetic abrasiveimprove significantly.This work can provide basis and guidance for the large-scale industrial manufacturing ofspherical composite magnetic abrasives.