Development Of Composite Lubricants For Powder Warm Compaction And Its Application In The Fabrication Of Soft Magnetic Fe-Si Materials

Warm compaction is a new powder forming technique to obtain ferrous P/Mparts with high density at relatively low cost. Research on the basic theory andapplications of warm compaction has great academic and practical significance toexplore its potential and promote the development of the technology, and muchattention has been paid on this new technique since1990’s. It has been shown thatthe choice the lubricants is one of the key in warm compaction technology.Therefore, much work has been done in the development of novel lubricants forwarm compaction of metal powders. Fe-6.5Si is a soft magnetic material with goodproperties. Because of the high content of Si in this alloy, this alloy shows poormachinability, and the conventional methods for preparing Fe-Si alloys have somedisadvantages such as complicated procedure and high energy consumption.Furthermore, this alloy is difficult to prepare by the conventional powdercompaction method. Therefore, in this dissertation, new lubricants for warmcompaction of different ferrous powders were developed, and warm compactionwas used to prepare Fe-6.5Si soft magnetic materials with the new compositelubricants.In the development of new lubricants for warm compaction, several organicmaterials were blended at different weight ratio to obtain composite lubricants.Then, these composite lubricants were blended with reduced iron powders andatomized steel alloy powders, respectively, to obtain powder mixes. Apparentdensity and flowability of the powder mixes were tested. Then the powder mixedwith different contents of the lubricants were warm compacted, and effects of theprocess parameters, such as compaction pressure and temperature, on the density ofthe warm compacts were investigated, the compacted samples were sintered and thedensity, microstructure, and mechanical properties of the sintered samples weretested. It have shown that both the composition and the amount of the compositelubricants have obvious effects on the density and other properties andmicrostructure of the obtained green compacts and the sintered samples. Amaximum apparent density of3.33g/cm~3and a minimum flowability of26.30s/50gwere obtained for reduced iron powders with0.6%lubricant of (1B+1D). Meanwhile, a maximum apparent density of3.52g/cm~3and a minimum flowabilityof25.03s/50g were obtained for ferrous alloyed powders with0.5%lubricants of(3A+2D). After compaction at pressure of500MPa-700MPa, a maximum greendensity of7.37g/cm~3was obtained for iron powders added0.5%of (1C+1D), at acompaction pressure of700MPa and temperature of130℃.After sintering at1200℃, maximum density of7.38g/cm~3and7.32g/cm~3were obtained for samplesadded0.5%of (1C+1D) and0.6%of (1C+1D), respectively. The hardness andtensile strength of the sintered samples increase as the density increases. Maximumhardness and tensile strength for the reduced and alloyed iron powder samples are51.6HRB,218MPa and57.8HRB,235MPa, respectively, at density level of7.32g/cm~3and7.38g/cm~3. Microstructure observation shows that the samplessintered have homogeneously microstructure of ferrite, and the powders andprocess parameters also have effects on the microstructure.In this dissertation, Fe-6.5Si alloyed powders were also warm compacted withthe composite lubricants developed in the work.The alloyed powders were mixedwith the lubricants(1C+1D) and proper nanosized alumina and silica powders toobtain powder mixes. The powder mixes were then warm compacted at differentpressure and temperature. The green compacts were sintered at different sinteringconditions in H2. The effects of compacting pressure, temperature and sinteringconditions on the properties of green and sintered Fe-Si samples were investigated.Microstructures of the green and the sintered samples were also observed. It wasshown that the properties of Fe-Si samples were influenced greatly by thecompaction, temperature and sintering conditions. The maximum density of greensamples compacted at800MPa and150℃is6.29g/cm~3.After sintering at1275℃,amaximum density of7.22g/cm~3, a radial crushing strength of436MPa andsaturation magnetization of1.28T, and coercivity of0.16kA·m-1were achieved.Itwas also shown that sintering shrinkage of the Fe-Si samples increases obviouslywith sintering time. The sintered samples have a microstructure of ferrite.The EDSresult showed that the sintered samples are carbon free,which is beneficial toimprove the coercivity.