Phase Transformation Behaviors and Effects of Terbium in Polycrystalline Ni-Mn-Ga Magnetic Shape Memory Alloys

The phase transformation behaviors of two kinds of magnetic shape memory alloys NisoMn25 x Ga25-x and Ni50 Mn29Ga21-x Tbx were studied. When the composition of Ni in these alloys was constant, increasing Mn and reducing Ga contents make martensitic transformation temperatures rise obviously. Simultaneously, thermal hysteresis of phase transformation reduce but Curie temperature una|ters. When terbium was added, phase transformation temperature went up further and Curie temperature kept constant. The alloys still show strong ferromagnetism and properties of thermoelastic martensite phase transformation.     

Ni-Mn-Ga磁控形状记忆合金中的马氏体相变

文章采用电弧熔炼法熔炼Ni48Mn31Ga21和Ni2MnGa两种合金,并对这两种合金进行了热处理,借助交流磁化率测定、金相显微镜观察、X射线以及磁化曲线等手段研究了Ni-Mn-Ga磁控形状记忆合金中的马氏体相变。结果表明：（1）Ni48Mn3lGa21合金在室温下发生了马氏体转变,而Ni2MnGa合金在室温下则未发生马氏体转变;（2）室温下Ni2MnGa合金的饱和磁化强度比Ni48Mn3lGa21合金高;对于Ni48Mn31Ga2l合金,其马氏体态的饱和磁化强度要高于奥氏体态。     

Phase Transition and Texture Evolution in the Ni-Mn-Ga Ferromagnetic Shape-Memory Alloys Studied by a Neutron Diffraction Technique

The phase transition and influence of the applied stress on the texture evolution in the as-cast Ni-Mn-Ga ferromagnetic shape-memory alloys were studied by the time-of-flight (TOF) neutron diffraction technique. The neutron diffraction experiments were performed on the General Purpose Powder Diffractometer (Argonne National Laboratory). Inverse pole figures were determined from the neutron data for characterizing the orientation distributions and variant selections of polycrystalline Ni-Mn-Ga alloys subjected to different uniaxial compression deformations. Texture analyses reveal that the initial texture for the parent phase in the as-cast specimen was composed of , , , and , which was weakened after the compression deformation. Moreover, a strong preferred selection of martensitic-twin variants (and ) was observed in the transformed martensite after a compression stress applied on the parent phase along the cyclindrical axis of the specimens. The preferred selection of variants can be well explained by considering the grain/variant-orientation-dependent Bain-distortion energy. This article is based on a presentation given in the symposium entitled “Neutron and X-Ray Studies for Probing Materials Behavior,” which occurred during the TMS Spring Meeting in New Orleans, LA, March 9–13, 2008, under the auspices of the National Science Foundation, TMS, the TMS Structural Materials Division, and the TMS Advanced Characterization, Testing, and Simulation Committee.     

Martensite Transformation in Ni-Mn-Ga Ferromagnetic Shape-Memory Alloys

The crystal structure of Ni-Mn-Ga ferromagnetic shape-memory alloys is extremely sensitive to composition. Several martensitic structures including tetragonal (five-layered), orthorhombic (seven-layered), and nonmodulated tetragonal have been observed. Temperature-dependent X-ray diffraction measurements and calorimetry have revealed markedly different transformation behavior in the tetragonal and orthorhombic materials. The orthorhombic material shows a much larger difference between the martensite start and finish temperatures as compared to tetragonal martensite. The difference in transformation character can be explained from a thermodynamic standpoint by including the difference in the strain energy contribution for the two different martensite phases. This article is based on a presentation made in the symposium entitled “Phase Transformations in Magnetic Materials," which occurred during the TMS Annual Meeting, March 12–16, 2006, in San Antonio, Texas, under the auspices of the Joint TMS-MPMD and ASMI-MSCTS Phase Transformations Committee.     

稀土多晶Ni-Mn-Ga铁磁记忆合金的马氏体孪晶与磁感生应变

铁磁性形状记忆合金Ni-Mn-Ga是一种新型功能材料,它在磁场作用下能产生大的应变.研究了Ni50Mn29Ga21Tb1.2室温下的晶体结构和磁感生应变,并用O'Handley的解析模型分析合金产生大磁感生应变的原因是马氏体孪晶在磁场下的迁动.     

稀土铽对Ni-Mn-Ga磁性记忆合金力学性能的影响

研究了稀土Tb对Ni50Mn29Ga21磁性记忆合金抗弯强度和断裂行为的影响。结果表明:稀土Tb可以显著提高材料的抗弯强度,改变断口形貌。不含稀土试样弯曲断裂后其断口主要是晶界断裂。添加稀土后,随着稀土加入量的增多,断裂方式由以晶界断裂为主转为以解理断裂为主。此外,Tb的加入,明显细化了晶粒,同时使材料的含氧量降低。     

Ni-Ti形状记忆合金中的相变

根据作者的工作、并结合新近文献,对近等原子Ni-Ti合金中的相变作了系统的综述,包括:相变的顺序,无公度相变,R相变,马氏体相变,合金成分及热循环对相变临界温度的影响,逆相变及沉淀。     

Ti-Ni-Ce合金的相变行为及其形状记忆效应

通过示差扫描量热仪(DSC)等试验手段,系统分析了添加稀土元素Ce后所形成的Ti-Ni-Cex(x＝2 at%、3 at%、4 at%)系合金的相变行为和形状记忆效应,以及相变温度和相变潜热与稀土含量之间的关系.研究结果表明,相变温度(Ms,Mf,As,Af)受稀土含量的影响较大,总的趋势是先升高后下降,然后有稍微升高;而对相变潜热(马氏体相变潜热ΔHB2M、逆马氏体相变潜热ΔHMB2)的影响,则是随着稀土元素Ce含量的升高呈现上升的趋势;稀土的添加使Ti-Ni二元合金的相变滞后明显变窄,但与稀土的含量没有明显关系.研究发现,添加稀土后Ti-Ni形状记忆合金优良的形状记忆效应没有改变,而相变温度却有明显的提高.     

Effects of Sm on Phase Transformation in Ni-Mn-Ga Alloys

The effects of small amount additions of Sm on the martensitic transition and magnetic phase transition of polycrystalline Ni-Mn-Ga alloys were investigated. The experimental results show that the Sm doped alloys also undergo a thermal-elastic martensitic transformation and reverse transformation during cooling and heating process and the addition of Sm decreases the martensitic transformation temperature and Curie temperature in different degree respectively. Ni-Mn-Ga alloys of adding Sm still possess Heusler structure, but their crystal lattice parameters are modified slightly. The addition of a proper amount of Sm does not basically decrease Tc of the alloy when avoiding the appearance of second phase. In addition, the doped alloys have favorable toughness because of grain refinement of Sm.     

The Effects of Composition and Aging on the Martensite and Magnetic Transformations in Ni-Fe-Ga Ferromagnetic Shape Memory Alloys

The martensite and magnetic transformations in Ni-Fe-Ga ferromagnetic shape memory alloys are very sensitive to both alloy chemistry and thermal history. A series of Ni-Fe-Ga alloys near the prototype Heusler composition (X₂YZ) were used to investigate how the martensite and magnetic transitions change with alloy composition and isothermal aging above and below the B2/L2₁ ordering temperature. Calorimetry and magnetometry were employed to measure the martensite transformation temperatures and Curie temperatures. Compositional variations of only a few atomic percent result in martensite start temperatures and Curie temperatures that differ by about 230 and 35 K, respectively. Aging a Ni₅₃Fe₁₉Ga₂₈ alloy for 3600 seconds at various temperatures shifts the martensite start temperature and the Curie temperature by almost 70 K. Transmission electron microscopy investigations were conducted on the aged Ni₅₃Fe₁₉Ga₂₈ alloy. The considerable variations in the martensite and magnetic transformations in these alloys are discussed in terms of microstructural differences resulting from alloy chemistry and aging treatments. This article is based on a presentation made in the symposium “Phase Transformations in Magnetic Materials: Magnetic Shape Memory Alloys which occurred March 14, 2006, during the TMS Spring Meeting in San Antonio, TX, under the auspices of the ASMI/MPMD-Phase Transformations, EMPMD/SMD-Chemistry & Physics of Materials, and EMPMDNanomaterials Committees."     

Microstructure and Magnetic Property Variation with Addition of Rare Earth Element Dy in Co-Ni-Al Ferromagnetic Shape Memory Alloy

The influence of rare earth element Dy on martensitic transformation and magnetic properties of Co-Ni-Al alloy was studied.The results showed that the microstructure of the sample has a dual-phase structure(γ-phase and martensite).The rare earth element Dy was segregated in Co-richγ-phase and took the place of Co after its addition into the Co-Ni-Al alloy.As Dy content increased to over 0.5at.%,the grain was refined and the rare earth intermetallic compounds Co5 Dy were precipitated inγ-phase.Meanwhile,one-step thermo-elastic martensitic transformation occurred in the sample,wherein the phase transformation temperature significantly increased with rising Dy content.The martensite had a tetragonal L10 structure with a(111)twinning plane.Furthermore,the sample exhibited obvious hysteresis behaviors in the magnetic hysteresis loops.In addition,the saturation magnetization,coercivity,retentivity and magnetocrystalline anisotropy were significantly enhanced owing to the bigger radius of Dy which took the place of Co in the alloy.     

预变形和时效对NiTi合金相变的影响

对Ti-50．8at％Ni形状记忆合金丝施加不同的预变形，随后在不同的温度时效，研究了预变形、时效温度与NiTi形状记忆合金的相变特性之间的关系。结果表明，预变形和时效对NiTi形状记忆舍金的相变特性有着显著的影响，可促使NiTi合金发生R相变，使NiTi形状记忆合金在较窄的温度区间内发生B2-R-B19’三种相变，为进一步研究NiTi形状记忆合金的性能提供了方便。     

加工TiNi形状记忆丝材的新工艺

概述了用包套－碎屑挤压法加工ＴｉＮｉ形状记忆丝材的新工艺。     

Phase Transformation and Shape Memory Effect of Ti(Pt, Ir)

The martensitic transformation and shape memory effect of Ti₅₀(Pt, Ir)₅₀ with 5?C37.5 at. pct Ir were investigated using differential thermal analysis (DTA), high-temperature X-ray diffraction (HT-XRD), and compression tests. The austenite finish temperature, A _f, increased with increasing Ir content from 1331?K (1058?°C) in Ti-50 at. pct Pt to 1491?K (1218?°C) in Ti-12.5Pt-37.5Ir. The structure of the parent and martensite phases was identified as B2 and B19 in all tested alloys. A large strain recovery rate was obtained in Ti₅₀(Pt, Ir)₅₀ with 10 to 30 at. pct Ir. The highest shape recovery ratio was 57?pct in Ti-25Pt-25Ir after deformation at 1123?K (850?°C), followed by heating to above A _f. Using HT-XRD, the dependence of lattice parameter change on Ir content and temperature was investigated. The volume change during phase transformation from B2 to B19 was estimated using the lattice parameter of the B2 and B19 phases. Strain recovery is discussed along with volume change and lattice parameter change.     

Additive Manufacturing of Co-Ni-Ga High-Temperature Shape Memory Alloy: Processability and Phase Transformation Behavior

Metallurgical and Materials Transactions A - Co-Ni-Ga high-temperature shape memory alloy is additively processed by selective laser melting for the first time. Reversible martensitic...     

Effect of Co-Doping on the Microstructure,Martensitic Transformation Behavior,and Magnetocaloric Effect of Ni-Mn-Sb-Si Ferromagnetic Shape Memory Alloys

Metallurgical and Materials Transactions A - We have studied the effect of Co-doping on the microstructure, martensitic transformation, and magnetocaloric effect (MCE) of a Ni50Mn38Sb9Si3 alloy....     

Cu-Zn合金的形状记忆效应

通过扭转法和电阻测量法对Cu-Zn合金的形状记忆效应进行了实验研究。发现在M_s点以上,不存在热弹性马氏体的情况下,由应力诱发马氏体可以引起形状记忆效应。另外,在M_s点以下有热弹性马氏体的情况下,根据实验结果可以证明,应力诱发马氏体在形状记忆效应中仍然起主要作用。     

An Investigation on Phase Formations and Microstructures of Ni-rich Ni-Ti Shape Memory Alloy Thin Films

Ni-rich Ni-Ti alloy thin films were fabricated by radio frequency (RF)-direct-current (DC) magnetron sputtering using elemental Ni and Ti as sputter targets. Si (100) was chosen as a substrate that was either held at room temperature or at 573 K (300 °C) during the depositions. The 380-nm-thick films were characterized by field emission scanning electron microscopy, energy dispersive spectroscopy, grazing incidence X-ray diffraction, atomic force microscopy, high-resolution transmission electron microscopy, and Vickers microhardness tester. The results suggests that because of the lack of surface mobility of the adatoms at the room temperature, the deposited films were smooth and amorphous, with a crystallite size of 15 nm accompanied with a porous morphology. At higher substrate temperatures, an increase in the surface diffusion leads to the formation of partially crystalline, rougher films with a denser, compact, fibrous grain microstructure. The formation of Ni-rich precipitates such as Ni₄Ti₃, Ni₂Ti, and Ni₃Ti along with small amount of the NiTi phase were attributed to the localized heating and cooling within the grains. Few grains exhibited band structures that are believed to be a result of <110> type II twins.