| The martensitic transformation and the magnetic properties of Ni-Mn-Sn ferromagnetic shape memory alloys have a strong composition dependence,which can be modified through composition tuning or alloying.In the present work,the master Ni50Mn39Sn11 alloy was alloyed through Fe,Cu,Co substitution for Ni,respectively.Three group polycrystalline alloys with the nominal composition of Ni50-xFexMn39Sn11(x=0,1,2,3,4,5,6,7),Ni50-xCuxMn39Sn11(x=1,2,3,4,5,6,7)and Ni50-xCoxMn39Sn11(x=1,2,3,4,5,6,7)were prepared by arc-melting under an argon atmosphere.Based on differential scanning calorimetry(DSC),X-ray diffraction(XRD),magnetic property measurement system(MPMS),vibrating sample magnetometer(VSM),scanning electron microscope(SEM)and material testing system,the influence of Fe,Cu,Co substitution on the martensitic transformation behaviors,magnetic properties,crystal structures,microstructures and mechanical properties was studied systemically.Based on the results of EDS,it was shown that the compositions of the ingots were almost the identical with the nominal compositons,where Mn content in the ingots was generally lower than that of the nominal one.According to DSC measurement,it was found that martensitic transformation temperatures of Ni50-xFexMn39Sn11 alloys decreased with the increase of Fe content The entropy change of the Ni50-xFexMn39Sn11 alloys firstly increased,and reached the maximum value when the Fe content was at 2%.Then the entropy change decreased with the increase of Fe content.With the increase of Cu content the martensitic transformation temperatures of Ni50-xCuxMn39Sn11 alloys decreased.And the entropy change also decreased with the increasing of Cu content.The martensitic transformation temperatures of Ni50-xCoxMn39Sn11 alloys decreased with the increase of Co content.However,the entropy change had no regular tendency.XRD measurement results showed that the room temperature phase of Ni50-xFexMn39Sn11 alloys was four layered martensite(40)as x changed from 0 to 4.When x was between 5 and 7,the room temperature phase is austenite with precipitated phase on the base.When x is between 0 and 5,the room temperature phase of Ni50-xCuxMn39Sn11 alloys were also four layered martensite.When x is between 6 and 7,the room temperature phase of the alloy turned to be austenite with cubic L21 structure.For Ni50-xCoxMn39Sn11 alloys,the room temperature phase was four layered martensite,as x changed from 0 to 4.When x is between 5 and 7,martensite and austenite co-exist at room temperature.According to SEM observations,we found that the microstructure of Ni50-xFexMn39Sn11 alloys was characterized with the broad plates,when x was between 0 and 4.Moreover,much thinner plates were found inside the broad plates.On the other hand,when x changed from 5 to 7,the microstructure of Ni50-xFexMn39Sn11 alloys was austensite with the emergence of precipitation.The microstructure of Ni50-xCuxMn39Sn11 alloys were filled with broad plates which were consist of much thinner plates,when x changed from 0 to 5.However when x was between 6 and 7,the microstructure of Ni50-xCuxMn39Sn11 was austenite at room temperature.When x was less than 5,the microstructure of Ni50-xCoxMn39Sn11 alloys were characterized with thin plates.The micro structure of Ni50-xCoxMn39Sn11 alloys were consisted of martensite and austensite,when x changed from 5 to 7.According to VSM measurements,when x was in 0-3,Ni50-xFexn39Sn11 alloys were in paramagnetic state at room temperature.While Ni50-xFexMn39Sn11 alloys were in ferromagnetic state at room temperature when x changes from 4 to 7.When x was between 0 and 5,Ni50-xCuxMn39Sn11 alloys were in paramagnetic state at room temperature.When x is between 6 and 7,the alloy was in ferromagnetic state at room temperature.When x changed from 0 to 4,Ni50-xCoxMn39Sn11 alloys were in paramagnetic state at room temperature.Ni50-xCoxMn39Sn11 alloys were in ferromagnetic state at room temperature,when x was between 5 and 7.From the results of MPMS measurement,we fond that the reverse martensitic transformation starting temperature(As)of Ni45Fe5Mn39Sn11 alloy in the 50000G magnetic field was 6 K lower than that of 50 G magnetic field.Thus,the magnetic-field-induced reverse transformation could occur in this alloy.However,the high-field had little influence on the martensitic transformation temperatures of Ni45Cu5Mn39Sn11 and Ni44Cu6Mn39Sn11 alloys.The reverse martensitic transformation starting temperature(As)of Ni43Cu7Mn39Sn11 alloy in the 50000G magnetic field was 2 K lower than that of 50 G magnetic field.Thus,the magnetic-field-induced reverse transformation also could occur in this alloy.Compression experiment showed that the fracture strength of the Ni50-xFexMn39Sn11 alloys decreased in the beginning,and reached the minimum at 4%.Then the fracture strength rised,and reached the maximum at 7%.The fracture strength of the Ni50-xCuxMn39Sn11 alloys increased in the beginning and reached the mixmum at 1%.Then fracture strength decreased with the increase of Cu composition.The fracture strength of the Ni50-xCoxMn39Sn11 alloys firstly increased and reached the mixmum at 4%.Then the fracture strength decreased. |
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