Effect Of B On Phase Transformation And Magnetic Properties Of Ni-Co-Mn-Sn Magnetic Shape Memory Alloys

In this paper, Ni40Co10Mn4iSn9-xBx(x=0.5,1, 2, 3, 4) and Ni40Co10-xMn41Sn9Bx(x=0.5, 1,2, 3) magnetic shape memory alloys were prepared by substituting Sn and Co in Ni40Co10Mn41Sn9, respectively by B element. By means of optical microscopy, scanning electron microscopy (SEM), X-ray diffraction (XRD), differential scanning calorimetry(DSC), mechanical testing machine and physical properties measurement system (PPMS), the influences of the content of B on martensitic transformation, microstructure, magnetic properties and mechanical properties of the above alloys were systematically studied.It is found that, the volume fraction of tetragonal martensite phases decreases with increasing B content in Ni40Co10Mn41Sn9-xBx(x=0.5,1, 2, 3, 4)? Ni40Co10-xMn41Sn9Bx(x=0.5,1,2, 3) alloys, while the amount of second phases increase. Furthermore, the second phases consist of Mn2B resulting from the addition of B and cubic y-phases originally existing in the master alloy, Ni40Co10Mn41Sn9.DSC results show that, both B-free and B-doped Ni40Mn41Co10Sn9 alloys undergo only single-step martensitic transformation and reverse phase transition, which means that B addition does not change the transformation sequence. With increasing the content of B, the transformation temperatures of Ni40Co10Mn41Sn9-xBx(x=0.5,1, 2, 3, 4) gradually increase,while the transition temperatures of Ni40Co10-xMn4iSn9Bx (x = 0.5, 1,2, 3) gradually decline.Thermal cycling stability of Ni40Co10Mn41Sn9-xBx (x=0.5, 1, 2, 3,4) and Ni40Co10-xMn41Sn9Bx (x=0.5, 1, 2, 3) are almost not affected by the addition of B. All these alloys exhibit high stability even after 10 thermal cycles.Adding the appropriate amount of B can significantly improves the mechanical properties of the alloy. A small amount of B increases slightly the compression fracture strain and fracture strength of Ni40Co10Mn41Sn9-xBx (x=0.5,1, 2, 3, 4) and Ni40Co10-xMn41Sn9Bx(x=0.5, 1, 2, 3). More addition of B leads to a significant improvement on the mechanical properties. As a result, the compression fracture strain and fracture strength increase greatly.Opposite tendency for the change of magnetic properties caused by the addition of B was found in Ni40Co10Mn41Sn9-xBx(x=0.5,1,2,3,4) and Ni40Co10-xMn41Sn9Bx(x=0.5,1,2,3). The replacement of B for Sn gradually weakens the magnetic properties, while the substitution of B for Co strengthens the magnetic properties by a small scale.