Physical And Magnetostrictive Properties Of Fe-Ga And Fe-Ga-Co Alloys

As a new magnetostrictive material,Fe-Ga alloy has been researched for many years since it was discovered by Clark et al.in 2000.With both good magnetostrictive properties and mechanical properties it can be used to many fields and can be welded into different shapes and configurations,which makes it become more popular and be different from the materials that we are using.In addition,the magnetostriction of Fe-Ga alloy doesn't depend on its temperature,which means that it can be used over a wide temperature range with little changes of its performance.Different form conventional magnetostrictive materials,such as PZT,Terfenol-D et al.,it has more advantages and can be applied to more fields.At the beginning of this thesis,I briefly introduce the theoretical progress of Fe-Ga alloy and its applications.This thesis mainly focus on the magnetosriction of binary(Fe_100-xGa_x,?x=20?25?30?35?40?45?50?)and ternary(Fe₇5Ga_25-xCo_x,?x=5?10?15?and Fe75-xGa25Cox,?x=5?10?15?)Galfenol.And many measurements has been made so that we can find the underlying physical mechanism producing the magnetostriction.In order to study the magnetostrictive properties of Fe-Ga alloys and improve their mechanical properties and magnetostriction,we produce 7 Fe-Ga alloys with different Ga content by vacuum arc furnace.All of these samples are analyzed by X-ray diffraction and PPMS which is used to measure the variation of their magnetization when we change the magnetic field.In addition,we make a measurement of their positron lifetime spectrum and Vickers-hardness.For the binary Fe-Ga alloys,the results of XRD and microscopic structure show that Fe-Ga alloy has the disordered bcc structure and it will shift to ordered structure and have a smaller factor of magnetostriction when the content of Ga atoms get to 35 at%.With the increase of Ga content,Ga atoms begin to full in?110?directions,resulting that the increase of lattice constant.And when the content of Ga atoms is more than 30 at%,more Ga atoms will be fulled in?200?direction.From themeasurements of X-Ray Diffraction,what can we see is that the internal structure of our samples become more complex,resulting the appearance of ordered DO₃.According to the results of XRD,it is found that the saturation magnetization of the sample is affected by the structure of the sample.When the phase structure is consistent,the more content of Ga,the lower the saturation magnetization.The results of Vickers-hardness measurements show us that a harder sample will result in a greater magnetostrictive coefficient.Which means that the higher the hardness,the greater the magnetostrictive coefficient.It has been showed that the addition of the third elements is a reasonable method to improve the magnetostriction of samples.In the previous studies,it has been studied that the addition of the elements with valence electrons less than pure Fe,such as V,Cr,Mn,Mo,will affect the performance of Fe-Ga alloy,which is similar to the addition of valence electrons above Fe,such as Co,Ni,Rh.In order to discuss the influence of ternary substitutions for Ga on magnetostriction of Fe-Ga alloy,we select Co as a ternary addition added into the Fe-Ga alloy samples,found that the addition of Co has a significant effect to the saturation magnetization of the samples and can significantly improve the magnetic properties of the samples.And the saturation magnetization of the samples increases with the increase of Co content.When we improve the content of Co,the vacancy cluster increases,but the samples with more Ga has less vacancy.The addition of Co does cause a decrease in the magnetostriction coefficient of Fe-Ga alloy samples,the reason is that the addition of Co leads to the stabilization of the ordered DO₃ phase in the samples.What's more,the hardness of ternary alloys is also analyzed.The results show that Ga has a greater influence on the hardness of the samples in a certain range,and the more the content of Ga,the greater the hardness of the alloy.