Study On The Internal Friction Mechanism And Performance Optimization Of Ferromagnetic Fe-Ga Based High Damping Alloys

Since the ferromagnetic high damping alloy(FHDA)has temperature insensitivity(-200?380?),high damping stability,wide applicable amplitude range(especially in the low amplitude range),it is expected to be widely used in transportation,ship,aerospace,and other fields,especially in extreme conditions,such as the high-temperature environment in a nuclear reactor,submarine motor,and space environment(-100?100?)in which man-made satellites work.The application of FHDA in these vibration environments can not only effectively reduce the structural complexity of the damper,but also save the raw materials and costs of preparation.However,the damping value of ferromagnetic damping alloy is relatively low(Q-1?0.01)compared with high damping alloy based on grain boundary sliding mechanism(Q-1?0.05).So it is necessary to explore a new high damping ferromagnetic alloy and investigate the influence and mechanism of element composition and preparation process on damping capacity.Fe-Ga alloy is a new generation of magnetostrictive material.Due to its good mechanical properties and magnetostrictive properties,it makes up for the shortage between the traditional magnetostrictive material with a low magnetostrictive coefficient represented by Fe-Al and Ni-based and the giant magnetostrictive material with low mechanical properties represented by Tb-Dy-Fe alloy.Therefore,it has been widely studied since it was found by the National Laboratory of the United States Navy in the early 21st-century.Since the hysteresis loss of magneto-mechanical is closely related to the magnetostrictive coefficient,the hysteresis damping of magneto-mechanical is positively related to the magnetostrictive coefficient without considering the stress distribution.Therefore,Fe-Ga alloy with a high magnetostrictive coefficient is expected to become a new generation of ferromagnetic high damping material.In this paper,the internal friction behaviors of Fe-18Ga alloy in different heat treatment states were studied systematically,and a new internal friction peak related to the ordering transformation of Ga atom was found.The formation mechanism of the internal friction peak at high-temperature was explained from different standpoints.Through the systematic study of the influence of plastic deformation and rare earth doping on the damping and mechanical properties of Fe-18Ga alloy,a heat treatment process to improve the damping property of Fe-18Ga alloy is developed,which provides a new idea for the study of high performance and wide temperature range damping alloy.The main innovative research achievements of this paper include:In the study of the characteristic internal friction spectrum of Fe-18Ga alloy,a phase transition peak with no change of frequency was found for the first time in the temperature range of 530?680?,and the peak consists of two secondary internal friction peaks,which correspond to different transformation processes respectively.Further,through the study of high-temperature quenching,furnace cooling,and thermal cycle,it was found that the peak type and peak temperature evolution is closely related to the heat treatment.Through rolling,doping,adjusting the Ga content in the matrix,magnetostriction,resistance experiment,in-situ synchrotron radiation XRD and so on,the transition mechanism of the order-disorder phase transition has been clarified from the atomic scale,which is related to the phase transition from the ordered D03 phase in the low temperature to the B2 intermediate phase and then to the disordered A2 phase in the high temperature.The temperature range of the order-disorder phase transition has been measured accurately.The results of the study are instructive to improve the damping and magnetostrictive properties of Fe-Ga alloys based on the thermal history of the material.A continuous heat treatment process of high-temperature hot rolling(1000?),quenching and medium temperature annealing has been developed.The damping and mechanical properties of Fe-18Ga alloy plates have been effectively optimized by adjusting the grain size and the second phase distribution.Through this process,the tensile strength of Fe-18Ga binary alloy can be greatly increased to?791 MPa,the fracture elongation can reach?5.7%,and the damping property can reach?2.5 �10-2.According to the microstructure analysis,the good mechanical properties come from a large number of pinned dislocations and dispersed precipitated the second phase,and the good damping properties come from the increase of 90� domain formed during annealing.The damping of the material can be effectively improved by La addition in the binary Fe-18Ga alloy.When 0.2at.%La doping,the damping property reaches?3.4 �10-2.On the one hand,the solution of La into the matrix results in the increase of the internal stress,on the other hand,it forms the Laves structure in the material opposing the movement of domain walls.With the increase of La content,the interaction between the domain and the second phase gradually changes from bypassing the reverse nucleation to pinning between the main domain and the additional domain,even bending the flux direction of the main domain.For La-doped Fe-18Ga alloy,the improvement of damping performance mainly comes from the appropriate 90� domain and the second phase.When the resistance to block the movement of the domain and the movable distance of the domain wall are moderate,the energy consumption of the irreversible movement of domain wall can reach the maximum.This suggests that when we consider how to improve the damping performance of ferromagnetic materials in the future,we need to take into account both the distribution of the resistance of the domain wall and the mobility.