As a novel functional material ,magnetostrictive material has risen comprehensive attention by the experts in the high-tech fields and got momentum in the past few years.Much work has done on the preparation ,composition ,phase structure ,magnetic-structure and properties in U.S.A ,Japan and so on ,which make the technology mature gradually .But as a ferromagnetic electric conductor, when the magnetic field changes,eddy that makes material heat will produce. And when the reversal frequency of magnetic field is higher, the eddy is violent,those defects limit its application in ultrasonic technology. The appearance of polymer-bonded giant magnetostrictive composite(GMPC) solved this bottle-neck.The effective frequency of GMPC can reach to 100KHz ,which greatly extended the application of magnetostrictive materials in ultrasonic technology .GMPC has great developmental prospects .
The main aims are:(1)a mould which applied to the fabrication of GMPC was designed and produced,the magnetic field was also considered;(2) excellent GMPC was fabricated with the technique of manual milling,mould,and powder felting, properties of magnetostriction,resistance and so on was also tested;(3)the magnetic properties which were influenced by the processing in the magnetic field were researched,the optimum technics was also explored.
The properties of GMM and GMPC were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), standard resistance strain gauge technique , VSM and so on in this paper.
The GMPC in this experiment was cured with GMM powder and resin under stress .We got optimum particle size of 112.5μm ,compaction pressure of 0.5GPa ,phenol content of 3.1~4wt%,and the direction of applied magnetic field according to the data essayes provided.The material was formed in that optimum condition.The results show as follows:(1)the GMM was fabricated by the technique of arc-melting-casting after controlling the direction of heat,result shows that the phase of the alloy was REFe2,struture was uniform and had some preferiation ,the maximum magnetostriction in the magnetic field provided in this experiment(λm) was 780×10-6 and turned to be ideal alloy;(2)the excellent GMPC was fabricated with the technique of manual milling,mould,and powder felting.λm was 491.3×10-6 which loses only 30% with respect to the magnetostriction of GMM(705.6×10-6 more or less);(3)the composites pressing in the magnetic field has the λm of 491.3×10-6 and those without 402.6×10-6,the composites pressing in the magnetic field have better property;(4)The gained composites are of uniform microstruture ,few air hole and high density,what's more,resistance of the sample is about 32×10-2Ω·m which is four orders of magnitude larger than GMM reported.
The mushrooms that appeared in the processing of Ho dopping alloy were analysed ,which shows:(1)The alloy rods have the structure of obvious MgCu2 Laves cubic structure while mushrooms are phase of rare-earth oxidation ,RE(Tb,Dy)5Si3 and also Laves cubic;(2)the separating out of the mushroom(the seprating of excessive rare-earth elements) makes the component of Tb0.2234Dy0.678Ho0.354Fe2 which leads to good magnetostriction properties;in theory ,the appearing of the mushroom is the minimization of energy;(3)the magnetostriction of the alloy decreases with the increasing amount of Ho dopping,minimum occurs at x(ratio of Ho atom)=0.20 and increases gradually until x=0.25 with the magnetostriction of 538.8×10-6.