A Study On Martensitic Transformation And Magnetic Properties Of Si Doping NiCoMnIn Ribbons

The martensitic transformation and the magnetic properties of Ni-Co-Mn-In magnetic shape memory alloys exhibit strong compostitional dependence,which can be modified through alloying.In this work,polycrystalline ribbons with the nominal compostition of Ni45Co5Mn37In13-xSix(x=0,1,3,5,7)were fabricated by means of melt-spinning.Based on differential scanning calorimetry(DSC)?X-ray diffraction(XRD)?scanning electron microscope(SEM)?Energy Disperse Spectroscopy(EDS)?vibrating sample magnetometer(VSM)?magnetic property measurement system(MPMS),the influence of Si substitution on the martensitic transformation behaviour?crystal structure?microstructure and magnetic properties of quenched and annealed ribbons were investigated systemically.According to the DSC measurement,the martensitic transformation temperatures of Ni45Co5Mn37In13-xSix(x=0,1,3,5,7)melt-spun ribbons gradually decreased with the increase of Si content.After annealing,the phase transformation temperature of the ribbons increased because of the decrease of segregation,the release of internal stress,and the increase of atomic order.XRD results showed that the room temperature phase of the melt-spun ribbons changed from 6M to austenite as the Si content increased.The lattice constant and unit cell volume of the austenite phase decreased with the increase of Si content because the Si atom radius was smaller than the In atom radius.Moreover,the unit cell volume decreased after annealing which was due to the elimination of a large number of lattice defects in the ribbons.In addition,XRD measurements indicated that a second phase appeared in the annealed ribbons when the Si content was 7%.SEM results showed that with the increase of the Si content,the microstructures of the melt-spun ribbons at room temperature changed from single martensite to the mixture of martensite and austenite,and then to single austenite grains.The origianl austenite grain size and martensite plate width significantly inceased after annealing.In addition,in the annealed ribbons with x=5 and x=7,the second phase was indentified inside the martensite plates.The thermalmagnetic measurements showed that the replacement of In with Si could not only decrease the martensitic transformation temperature of the ribbons,but also the Curie transiton temperature.When 0?x?3,the magnetic field could induce the reverse martensitic transformation both for melt-spun and annealed ribbons.It was noted that with the increase of Si content,the phase hysteresis of both melt-spun and annealed ribbons significantly reduced.Moreover,the phase hysteresis of annealed ribbons was lower than that of melt-spun ribbons.At the field change of 5T,for the annealed ribbons with the Si content of 1%,the magnetic entropy was 16.2 J kg-1 K-1 and the effective cooling capacity was 151.14 J kg-1,which was much higher than the magnetic entropy(10.1 J kg-1 K-1)and the effective cooling capacity(135.61 J kg-1)of the annealed ribbon without Si.Therefore,an appropriate amount of Si addition could not only reduce the phase hysteresis,but also improve the magnetocaloric properties of the Ni-Co-Mn-In based ribbons.