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1、Pressless process for isotropic magnets and its applicationManlong Xia27 November 2015 DTU Energy s annual PhD symposiumDTU Energy, Technical University of DenmarkOutline Introduction The application of magnet The Press-less Process (PLP) Experimental work The Pressless and compact magnets from stri

2、p cast material Discussion about PLP method using for recycling magnets ConclusionDTU Energy, Technical University of DenmarkCritical elements for clean energy technology-U.S. strategyU.S. Department Of Energy, Critical Materials Strategy, December 2011DTU Energy, Technical University of DenmarkAlte

3、rnative supplies of RE to Danish industryRFeBmagnetsApplicationsR metalRare earth oxidesMineralRockRFeB PowderToyota Prius Motor1 kg PM / carDirect drive wind turbine SWT-3.0-1012 tons PM / 3 MW turbineWaste ! Recycling? DTU Energy, Technical University of DenmarkR2Fe14B magnetic alloyNedko Drebov e

4、t al, Ab initio screening methodology applied to the search for new permanent magnetic materials. New Journal of Physics 15 (2013) 125023N48M commercial magnetDTU Energy, Technical University of DenmarkVacuumschmelzePatent: EP 0 680 054 B2 (2004)T1: Nd2Fe14BT2: Nd1+Fe4B4Sagawa et. al., “NdFeB Perman

5、ent Magnet Materials,” Jpn. J. Appl. Phys., vol. 26, pp. 785-800, 1987.P. Bjse, PhD thesis 1990.Phase diagramDTU Energy, Technical University of DenmarkPress Less method Sagawa (2012)Patent: EP 2 472 535 A1 (2012)Jet MillGraphite mouldCompactingAlignment magnetHeating coils (250 oC)Vacuum furnaceMou

6、ld stackingM.Sagawa prepared 0.3m powder by HDDR+HD+He jet millDTU Energy, Technical University of DenmarkThe principle for Pressless processcompactPLPPLP process can produce low oxygen content of sample by enclose the whole system in argon. K. Hono and H. Sepehri-Amin. Scripta Materialia 67 (2012)

7、530535DTU Energy, Technical University of DenmarkMethodsAdvantageDisadvantageCompact methodEasy to get dense and a higher magnetic properties.Successful in the industrial production.Big press machine is needed.The oxygen content cant go down any more.Pressless methodSave the press machine and relate

8、d costs.Can integrate the whole system to get lower oxygen content.Can acquire high coercivity NdFeB magnets without Dy.Porosity: hard to get denseRemanence and (BH)max: No report about using PLP method to prepare N52 magnets.DTU Energy, Technical University of DenmarkPressless process and tradition

9、al compact method in experiment Two kinds of strip-cast NdFeB alloys were used in our experiment: Dy = 0 wt% (BL8214) Dy = 4 wt% (48508) The strip cast alloys were subjected to hydrogen in 2 hours for rough grinding. Dry high energy ball milling in DTU and jet milling in Tallinn Technology Universit

10、y were used to produce fine powder. For Pressless method, tap the fine powder into graphite crucibles to a density of 3 g/cm3.To make a comparison with samples prepared by Pressless method, we also compact the sample with axial press (445MPa pressure). The samples were transport into furnace tube to

11、 do pump and prepare for sintering. The sintering program is shown below. The sintering time will be 2 h and we sintered samples at 1090, 1110 and 1130, and then cool down. DTU Energy, Technical University of DenmarkSintering profile25/4-2012 timeTemp oC2 oC/min250 oC*1h 2 oC/minTsinter*2h 5 oC/min5

12、70 oC*1hcoolingDTU Energy, Technical University of DenmarkSuccessful magnets microstructure: thin grain boundary The microstructure of 48508 (4 wt % Dy) 1130 PLP sample.Backscattered electrons(BSE)Secondary electrons(SE)2 m 2 mGrain boundaryGrain boundaryDTU Energy, Technical University of Denmark0

13、wt% Dy (BL8214) PLP samples 1090*2h1110*2h1130*2hDTU Energy, Technical University of Denmark4 wt% Dy (48508) PLP samples1110*2h1090*2h1130*2hDTU Energy, Technical University of DenmarkPLP vs compact magnets25/4-2012DTU Energy, Technical University of DenmarkThe interesting fact about Pressless Proce

14、ssOxygen content 4 wt% Dy PLP sample was sintered at 1110 for 2h, the samples oxygen content is 6101 ppm, however, the coercivity of the sample is still 368 kA/m.Initial powder sizeUsing high energy ball milling to dry mill 4 wt% Dy sample, we got powder whose mean size is 46.18 m (laser). Using the

15、se to do pressless process and sintered at 1110 for 2h, we got sintered samples whose magnetic properties are: Hci = 1022 kA/m, Br = 0.69 T. DTU Energy, Technical University of DenmarkConclusion We successfully prepared high density samples by Press-Less process by jet milling powder and high energy dry ball milling powder. The key issue for thi