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报道了课题组在国际上率先开展利用同步辐射高能X射线衍射和中子衍射技术,成功地实现了多场(温度场,磁场,应力场)耦合作用下,铁磁性记忆合金微结构、晶粒取向、磁结构、母相与变体取向及其与功能行为耦合的原位研究。利用原位飞行时间中子衍射技术,跟踪了铁磁性形状记忆合金Ni-Mn-Ga在单轴压力下马氏体变体的转变行为,这是目前其它方法(如EBSD)仍无法实现的。测试了M_s点为393K的Ni_(47)Mn_(25)Ga_(22)Co_4合金在不同的单轴压力(0,-60MPa,-110MPa,-140MPa,-7MPa)下从523～298K之间的中子衍射花样,并利用GSAS软件获得了不同单轴压力下马氏体相的反极图(IPFs)。利用高能球磨及后续热处理的方法制备出了Ni_(51)Mn_(27)Ga_(22)纳米颗粒。铁磁性Ni_2MnGa纳米颗粒功能行为受晶粒尺寸,原子有序度及固有磁结构交互作用的影响,经历了各种不同的结构转变序,这与它们相应的块体材料是完全不同的。通过高能球磨法制备出尺寸分布均匀约10 nm左右的Ni_(51)Mn_(27)Ga_(22)颗粒,其室温晶体结构由原始的体心四方结构转变为一种无序面心立方结构。高能球磨后的纳米颗粒经过623K,4h退火后,又完全转变为Heusler母相结构。利用高能X射线研究了该纳米颗粒在退火过程中结构的原位转变,证明转变动力学由一种具有非晶结构的中间相控制。高能球磨及后续热处理之后的纳米粒子,在约274K下转变为调制马氏体(14M)结构,并且该结构可以稳定到4K。
It is reported that the research group is the first in the world to make use of synchrotron radiation high energy X-ray diffraction and neutron diffraction technology to successfully realize the multi-field (temperature field, magnetic field and stress field) coupling effect. The microstructure of ferromagnetic memory alloy, Orientation, magnetic structure, parent phase and variant orientation and their coupling with functional behavior in situ. The in-situ time-of-flight neutron diffraction technique is used to track the transformation behavior of martensitic variants of ferromagnetic shape memory alloy Ni-Mn-Ga under uniaxial pressure, which is still not achieved by other methods such as EBSD. The Ni_ (47) Mn_ (25) Ga_ (22) Co_4 alloys with M_s point of 393K were tested at different uniaxial pressures (0, -60MPa, -110MPa, -140MPa and -7MPa) Neutron diffraction pattern, and obtained the inverse polarograms (IPFs) of martensite under different uniaxial pressures by using GSAS software. Ni_ (51) Mn_ (27) Ga_ (22) nanoparticles were prepared by high energy ball milling and subsequent heat treatment. The functional behavior of ferromagnetic Ni_2MnGaN nanoparticles, under the influence of the grain size, the degree of atomic ordering and the interaction of intrinsic magnetic structure, has undergone various structural transition sequences, which are completely different from their corresponding bulk materials. The Ni 51 Mn 27 Ga 22 particles with a size distribution of about 10 nm were prepared by high energy ball milling. The room-temperature crystal structure changed from the original body-centered tetragonal structure to a disordered face-centered cubic structure. After high-energy ball milling nanoparticles after 623K, 4h annealing, and completely transformed into Heusler matrix structure. The in-situ transition of the structure during the annealing process was investigated by high-energy X-ray. It was demonstrated that the transition kinetics was controlled by a mesophase with an amorphous structure. The high-energy ball milling and subsequent thermal treatment of the nanoparticles transforms to a modulated martensitic (14M) structure at about 274K, and the structure can stabilize to 4K.