Preparation And Properties Of Ni50Mn50-xSnx Magnetic Shape Memory Alloys (MSMA)Ribbon And Powder

Ni50Mn50-xSnx(x=7,9,11,13,15; at.%) magnetic shape memory alloys (MSMA) were prepared by mechanical alloying and melt-spinning. The effect of alloy compositions and heat treatment on micro structure、martensitic transformation、 magnetic properties of alloys was investigated by X-ray diffraction (XRD), Differential Scanning Calorimetry (DSC)、 Vibrating Sample Magnetometer (VSM) and Scanning Electron Microscope(SEM). The major results as follows:In Ni50Mn50-xSnx alloy, mechanical alloying are influenced greatly by atomic ratio of Mn/Sn. In Ni5oMn43Sn7, it could be observed that Ni2MnSn phase is gradually formed such intermediate phases as Mn1.77Sn, MnSn2, Ni3Sn2and Ni4Sn etc. When Ni50Mn41Sn9mixed powder was milled30h, mechanical alloying has been completed and Ni2MnSn phase forms, without unknown phase with36°peak. It suggested the process of mechanical alloying is different from that of Ni50Mn43Sn7. In milling process, the particle size decreases and agglomeration occures obviously. After90h milling, the particle size tended to be stable, granules existed in agglomeration form. After mechanical alloying completed, the Ni2MnSn phase is formed in two alloys, so they has similar saturation magnetization Ms. It suggested the effect of atomic ratio of Mn/Sn on magnetic properties of alloy is no obvious.In hot pressing, Ni2MnSn phase in Ni50Mn41Sn9alloy partly decomposited to form the Mn1.77Sn, Ni3Sn2and unknown phase with36°peak in XRD pattern. In Ni50Mn43Sn7samples, Ni2MnSn phase completely decomposites to form intermediate phases, such as Mn1.77Sn、 MnSn2、 Mn3Sn、Ni3Sn2、NiSn and Ni4Sn. This showed that composition has more influence on phase structure of the sintering samples. In the same sintering temperature, with increasing of hot pressing pressure, the saturation magnetization (Ms) of sintering samples decreased; in the same hot pressing pressure, with increasing of sintering temperature, Ms of sintering samples increased.With the increase of the Sn content, the Ni50Mn50-xSnx(x=7,9,11,13,15; at.%) melt-spun ribbons changes gradually from martensite phase to parent phase. The structure of martensite was orthorhombic. and the austenitic was body-centered cubic body L21structure. The microstructure of Ni50Mn50-xSnx (x=7,9,11,13,15; at.%) melt-spun ribbons is related with atomic ratio of Mn/Sn. The Ni50Mn50-xSnx(x=7,9,11; at.%) ribbons are in martensite state at room temperature, with Sn content increased gradually, the size of grain decreased. The Ni50Mn50-xSnx(x=13,15; at.%) ribbons were in parent phase, with the similar flowers structure. In the parent phase state, saturation magnetization (Ms) is changed greatly with the content of Sn increase. In martensite structure, the Ms is no obvious related with Sn content. Inverse martensite transformation temperature is very sensitive to composition, with the increase of the Sn content, As (start temperature of austenitic transformation) and Af (finish temperature of austenitic transformation) were reduced gradually. Inverse martensitic transformation temperature of Ni50Mn50-xSnx(x=7,9,11; at.%) was close to room temperature. Inverse martensitic transformation temperature of Ni50Mn50-xSnx(x=13,15;at.%) is far lower than room temperature. After annealing in873K for2h, no obvious microstructure change occurs in Ni50Mn35Sn15alloy. In Ni50Mn37Sn13alloy, orthorhombic martensite transforms into body-centered cubic austenitic structure. In Ni50Mn50-xSnx(x=7,9,11; at.%) alloy, a small part of martensite transforms into parent phase structure. After annealing, the sample has higher Ms, lower As and higher Af.