Effect Of Phase Structure Difference On Internal Friction And Corrosion Properties Of Fe-27Ga Alloy And Its Mechanism

Fe-Ga alloy(Gaffeol alloy)is a new type of high performance ferromagnetic material reported by Clark in 2000,which has excellent magnetostrictive and mechanical properties,low cost and so on.Fe-Ga alloy maks up for the brittleness for the traditional rare earth magnetostrictive materials and high cost and low magnetostrictive coefficient represented by Ni and Fe-Al alloy,so it has high application value in sensors,actuators,micro-motors and other industries.In ferromagnetic alloys,magneto-mechanical hysteresis loss(internal friction)is usually proportional to the saturation magnetostriction coefficient of the alloy,which is closely related to the phase structure.Therefore,as a magnetostrictive alloy with multiple phase structures,the internal friction behavior corresponding to different phase structures in Fe-Ga alloy is necessarily different.In particular,the zero magnetostrictive internal friction behavior caused by the superposition of positive and negative magnetostrictive phases is worth studying,which has important guiding significance for understanding the energy dissipation mechanism of this kind of material and expanding its application in engineering.Therefore,this paper mainly takes Fe-27Ga alloy(all alloys in this article are atomic percentages)as the research object,combined with arc melting and differential heat treatment process,successfully prepared Fe-27Ga and rare earth element Dy doped alloy samples with different L12 phase content.The effects of phase composition and Dy content on internal friction,magnetostriction and corrosion properties of Fe-27Ga alloy were studied systematically.The main achievements of the paper are as follows:(1)Fe-27Ga alloys with different L12 phase contents(0%,1.3%,28.4%,53.9%,74.1%,88.2%)were designed and prepared,and their internal friction behavior and magnetostriction property were systematically studied.The results indicated that the peak height and peak temperature of Snoek relaxation peak(Pi)and Zener relaxation peak(P2)were closely related to the content of L1 2 phase.When the applied magnetic field intensity is greater than 4000 Oe and the high strain amplitude mode(10-3),the magnitude of magnetostriction coefficient and internal friction value showed the same evolution trend.The internal friction test under applied magnetic field revealed that the magnetic domain walls of D03 phase can move easily under a low stress,while those of L12 phase can be driven only when the stress is high enough.This was consistent with the results that the domain walls of D03 phase could move at low magnetic field intensity,while the domain walls of L12 phase could only be driven at high magnetic field intensity.The related results provide a reference for the design of high performance damping alloys based on the domain wall dissipating mechanism.(2)Based on the results of L12 phase proportional control,the range of L12 phase content(34.4%,39.8%,44.8%,51.7%)was modulated by reducing and regulating the heat treatment temperature range,and the sample of Fe-27Ga alloy with near zero magnetostrictive coefficient was successfully prepared.The phase composition,microstructure,internal friction behavior and magnetostriction property were systematically studied.The results indicated that L12/D03 biphase(L12:～44.8%)Fe27Ga alloy with near zero magnetostrictive coefficient(～-4 ppm)was prepared when annealing at 480℃ for 1 h,and its specific damping capacity(SDC)was about 0.04.In terms of damping mechanism,for Fe-27Ga alloy with L12/D03 biphase structure,the damping at low strain amplitude is mainly derived from D03 phase with high magnetomechanical damping,while at high strain amplitude,it is related to L12 phase with high non-magnetic damping,which is caused by the non-magnetic damping contribution of the twin boundary movement in L12 phase.The above research results can provide scientific data and reference for the design of Fe-Ga alloys suitable for different application fields such as micro-vibration field,strong vibration field,magnetic field or non-magnetic field.(3)The effect and mechanism of rare earth element Dy doping on the internal friction behavior and magnetostrictive coefficient of Fe-27Ga alloy were analysed systematically.The results indicated that the doping of Dy element has little effect on the Snoek peak in Fe-27Ga alloy,but the peak temperature and peak height of Zener peak are closely related to the content of Dy.At the same time,doping of Dy first promoted and then inhibited the phase transition of D03→L12.Trace rare earth elements in terms of damping and magnetic,Dy doping can be synchronized to a certain extent improve the damping performance(SDC:～0.06→～0.07)and magneto can scale(～78→～92 ppm),which provided a scientific basis for the design of Fe-Ga-based alloy with good magnetostriction and internal friction properties.(4)Considering the applicability of Fe-Ga alloy devices in corrosive environment(marine environment,wet environment,etc.),the effects of different phase structures on the corrosion properties of Fe-27Ga were studied by using 3.5 wt.%NaCl solution to simulate seawater condition.The stability and corrosion resistance of D03 and L12 phases are analyzed from the first principles.The results showed that the L12 phase has higher electrochemical corrosion resistance and stability than the A2/D03 phase.Samples with high L12 phase content can form stable and dense layers of corrosion products,and thus exhibit optimal corrosion resistance.Relevant research results provide a reference for the design of Fe-Ga alloys with corrosion resistance.