Critical evaluation of the Fe–Ni,Fe–Ti and Fe–Ni–Ti alloy systems

The Fe–Ni–Ti alloy system has been evaluated, together with Fe–Ni and Fe–Ti binary subsystems, to provide reliable information for applications and in view of a thermodynamic modelling of the system. Available literature has been critically evaluated, mainly considering phase constitution and phase equilibria, thermochemical and diffusion data, as well as ab initio atomistic calculations. A discussion of the presently available CALPHAD-type thermodynamic assessments is also presented. Finally, new experimental investigations needed to solve uncertain and contradictory data are suggested.     

Ti50Ni47Fe3合金的铸态及均匀化热处理显微组织

采用真空感应法熔炼制备了Ti50 Ni47 Fe3合金铸锭,对合金铸锭进行了均匀化热处理,运用金相显微镜,XRD,带有EDS的SEM等手段进行显微组织分析.结果表明,Ti50 Ni47 Fe3合金的铸态显微组织由内到外依次呈不规则胞状、柱状和细长等轴状,主要原因为冷却速度不同导致合金的晶粒形核和长大存在差异.均匀化热处理一定程度上能消除枝晶偏析,1000℃下均匀化12 h后,合金枝晶偏析和析出相显著减少.     

Phase transformations in a Ti50Ni47.5Fe2.5 shape memory alloy

An optical metallographic study involving surface relief was made of the phase transformations in a Ti₅₀Ni_47.5Fe_2.5 alloy. The formation and reversion of two different kinds of surface relief associated with R-phase and martensitic transformations were observed upon thermal cycling. The nature of the R-phase transition and its microstructural changes during deformation were also observed; these are described.     

退火温度对Ni47Ti44Nb9合金冷轧板组织与性能的影响

采用金相显微镜、电子背散射衍射（EBSD）、维氏硬度计、差示扫描量热仪（DSC）和电阻-温度测量仪,研究了不同温度（300~900 ℃）退火1 h对Ni₄₇Ti₄₄Nb₉合金冷轧板的微观组织、力学性能及相变行为的影响。结果表明,当热处理温度低于400 ℃时,材料硬度值变化不明显,合金未发生马氏体相变;当退火温度为400 ℃时,硬度值显著下降,合金开始发生再结晶;当退火温度在500~800 ℃时,随着温度升高,再结晶越充分,马氏体相变温度越高,相变焓增加。800 ℃退火1 h后,合金基本完成再结晶,晶粒尺寸约11 μm;当退火温度升高至900 ℃,晶粒出现长大现象,晶粒尺寸增加至20 μm。     

Ti（50）Ni（47）Fe3形状记忆合金冷轧变形后的组织与性能

采用拉伸测试、维氏硬度测试、电阻率-温度曲线测试及扫描电镜和透射电镜观察显微组织的方法研究冷轧变形量为25%的Ti50Ni47Fe3合金经450-750°C下1 h退火后的显微组织和性能。结果表明,冷轧变形增强了合金的抗拉强度和屈服强度,冷轧变形后形成的应力场有助于R相变的发生。随着退火温度的升高,合金的抗拉强度和屈服强度下降,伸长率增大;当退火温度高于650°C时,强度和伸长率趋于稳定。电阻-温度曲线表明,在升、降温过程中发生两阶段相变B2-R-B19′。随着退火温度的升高,合金的相变温度降低;当退火温度高于650°C时,相变温度趋于稳定。随着退火温度的升高,合金依次发生回复、再结晶和晶粒长大。     

Ti49.2Ni50.8合金在等径角挤压过程中Ti3Ni4析出相的演化规律

采用透射电子显微镜研究Ti49.2Ni50.8合金中Ti3Ni4析出相在等径角挤压及中间退火过程中的演化规律.固溶态Ti49.2Ni50.8合金在450℃时效处理10～60 min以获得尺寸为37～75 nm的Ti3Ni4析出相.在450℃等径角挤压处理1道次后,时效处理10 min和30 min试样中Ti3Ni4析出...     

Transformation behaviors of Ti48.5Ni48Fe2Nb1.5 dependence of annealing and thermomechanical cycling

The effect of annealing treatments and thermomechanical cycling on the transformation behaviors and shape memory effect of Ti48.5Ni48Fe2Nb1.5 shape memory alloys were investigated using electrical resistivity measurement and tensile testing. It is found that the transformation behaviors are influenced considerably by the annealing treatments. Both Ms and As increase with increasing annealing temperature and cooling rate. Martensite stabilization occurs during thermomechanical cycles, thus resulting in lower...     

Phase transformation behaviors and mechanical properties of Ti50Ni49Fe1 alloy with severe plastic deformation

In this work, transformation behaviors and mechanical properties of cold-rolled shape memory alloy TisoNia9Fel by severe plastic deformation （SPD） were intensively investigated. The phase transformation behaviors, phase analysis, and microstructures were characterized by differential scanning calorimetry （DSC）, X-ray diffraction （XRD）, and transmission electron microscopy （TEM）, respectively. Tensile testing was performed to analyze the effect of SPD on the mechanical properties and shape memory of TisoNi49Fel alloy. When the thickness reduction is beyond 30 %, the martensitic transformation is suppressed. After cold-rolling, the alloy is mainly com- posed of B2 parent phases with some stress-induced martensitic B 19t phases, and high density of dislocations are generated and the grains are obviously refined. The yield stress ab significantly raises from 618 MPa of 0 % cold rolling to 1,338 MPa of 50 % SPD. Shape-memory effect increases from 6.5 % without cold rolling to 8.5 % after 30 % SPD, ascribed to the induced defects in cold rolling. Those results indicate that TisoNi49Fel alloy has improved mechanical properties and potential commercial applications after SPD.     

Further investigation on phase relation and microstructures in Ni3Si–Ni3Ti–Ni3Nb pseudo-ternary alloy system

The isothermal phase diagram at 1323 K in the Ni₃Si–Ni₃Ti–Ni₃Nb pseudo-ternary alloy system was re-investigated by scanning electron microscopy (attached with a wavelength dispersive spectroscope), X-ray diffraction and transmission electron microscopy (TEM), focusing on the phase relation among possible geometrically-close-packed (GCP) Ni₃X phases. The prepared alloys exhibited widely different microstructures, depending on alloy compositions whether they exist in a single phase, a two- or a three-phase region, and also on the constituent GCP Ni₃X phases. The L1₂(Ni₃Si), D0₂₄(Ni₃Ti) and D0_a(Ni₃Nb) phases were directly equilibrated one another or each other when keeping Ni content 79.5 at.%. On the other hand, the D0₁₉(Ni₃Ti_0.7Nb_0.3) phase was identified to exist when keeping Ni content 75 at.%. The phase stability and existing region of each GCP Ni₃X phase identified in the Ni₃Si–Ni₃Ti–Ni₃Nb pseudo-ternary alloy system were discussed, based on the electron concentration (e/a) and the atomic size factor (R_x/R_Ni) of the constituent atoms.     

Evolution and stability of phases in a high temperature shape memory alloy Ni49.4Ti38.6Hf12

Ni_49.4Ti_38.6Hf₁₂ shape memory alloy has been characterized for structure, microstructure and transformation temperatures. The microstructure of the as-cast sample consists of B19′ and R-phases, and (Ti,Hf)₂Ni precipitate phase along the grain boundaries in the form of dendrites. The microstructure of the solution treated sample contains only B19′ martensite phase, whereas a second heat treatment after solutionizing results in reappearance of the R-phase and the (Ti,Hf)₂Ni grain boundary precipitate phase in the microstructure. A detailed microstructural examination shows the presence of precipitates having both coherent and incoherent interface with the matrix, the type of interface being dictated by the crystallographic orientation of the matrix phase. The present study shows that the (Ti,Hf)₂Ni precipitates having coherent interface with the matrix, drive the formation of the R-phase in the microstructure.     

Phase transformation behavior of Ti49Ni49.5Fe1V0.5 and Ti48Ni48.5Fe1V2.5 alloys after different heat treatments简

The effects of heat treatments on the phase transformation behavior of Ti49 Ni49.5 Fe1 V0.5 and Ti48 Ni48.5 Fe1 V2.5 alloys were investigated. The results indicate that the alloys subjected to different heat treatments have B2 structure at room temperature. All the specimens exhibit a twostage B2→R→B190martensitic transformation on cooling, but a B190→B2 one-stage reverse martensitic transformation on heating except aged A1 alloy, which undergoes an abnormal two-stage transformation upon heating. The phase transformation temperatures are affected by heat treatments and V content, which can be attributed to the variation of the second-phase particles content in the matrix.     

Freeform fabrication of Ti–Ni and Ti–Fe intermetallic alloys by 3D Micro Welding

A novel freeform fabrication method for refractory metals named 3D Micro Welding (3DMW) has been proposed, which is a rapid prototyping combined with TIG (Tungsten Inert Gas) welding. Formation of beads and small pin objects composed of the Ti–Ni and Ti–Fe intermetallic alloy phases was attempted. Morphological changes of their beads in diameter, height, and contact angle were investigated as a function of the pulsed-arc peak current. As the arc peak current increased from 5 A to 30 A, the height and the contact angle decreased, while the bead diameter increased in Ti–Ni and Ti–Fe systems. Ti, Ti₂Ni and TiNi phases were formed in the Ti–Ni system, while Ti, TiFe and TiFe₂ phases in the Ti–Fe system. Small pin objects of these two systems were made by stacking molten beads on a fixed z-axis and their microstructures were observed. There were micro-cracks in beads of both system, but no crack appeared in these small pin objects.     

Mechanical and functional behavior of a Ni-rich Ni50.3Ti29.7Hf20 high temperature shape memory alloy

The mechanical and functional behaviors of a Ni-rich Ni_50.3Ti_29.7Hf₂₀ high temperature shape memory alloy were investigated through combined ex situ macroscopic experiments and in situ synchrotron X-ray diffraction. Isothermal tension and compression tests were conducted between room temperature and 260 °C, while isobaric thermomechanical cycling experiments were conducted at selected stresses up to 700 MPa. Isothermal testing of the martensite phase revealed no plastic strain up to the test limit of 1 GPa and near-perfect superelastic behavior up to 3% applied strain at temperatures above the austenite finish. Excellent dimensional stability with greater than 2.5% actuation strain without accumulation of noticeable residual strains (at stresses less than or equal to −400 MPa) were observed during isobaric thermal cycling experiments. The absence of residual strain accumulation during thermomechanical cycling was confirmed by the lattice strains, determined from X-ray spectra. Even in the untrained condition, the material exhibited little or no history or path dependence in behavior, consistent with measurements of the bulk texture after thermomechanical cycling using synchrotron X-ray diffraction. Post deformation cycling revealed the limited conditions under which a slight two-way shape memory effect (TWSME) was obtained, with a maximum of 0.34% two-way shape memory strain after thermomechanical cycling under −700 MPa.     

Microstructural changes observed in a rapidly solidified Ni3Al alloy during isothermal treatments

A series of metastable conditions arises in Ni₃Al alloys out of their rapid solidification, the most important one being the formation of a bimodal distribution of ordered domain sizes. The fine ordered domains are surrounded by elongated ones. Another characteristic is that the number of vacancies traps is higher than the equilibrium one. In this study, several tapes obtained by melt-spinning a Ni₃Al alloy with 76.5 at% Ni were annealed at 500°C for several periods from 0.5 to 120 h. These tapes were studied by means of transmission electron microscopy and X-ray diffraction. The latter technique allowed us to detect that the degree of ordering decreases in the first stages of the treatment; this occurs due to the formation of prismatic dislocation loops as a result of vacancy precipitation, this behavior is also due to the initial high long range order. Thus, the beginning of atomic movement causes the “right” sub-lattice atoms to occupy “wrong” sub-lattice positions. The structure recovers at the end of the process, followed by an increase in the degree of ordering. The vacancy precipitation was found to be heterogeneous; the region with higher density of fine ordered domains provides more sites to prismatic defects than the one with coarse domains.     

Mechanical spectroscopy and twin boundary properties in a Ni50.8Ti49.2 alloy

The internal friction (IF), Young's modulus (E) and heat flow (DSC) have been measured in a Ni_50.8Ti_49.2 alloy as a function of temperature after both ageing and solubilization followed by water quenching. The IF of aged material measured at kilohertz frequencies, besides hardly detectable peaks associated with the A↔R and R↔M transitions, displays two additional non-thermally activated peaks P_TWM and P_TWR, which appear to be due to stress-induced hysteretic motions of twin boundaries within the martensite and the R-phase, respectively. In the solubilized state a large peak corresponding to the A↔M transition is observed together with a thermally activated relaxation P_d occurring at around 100 K (for f=1.2 kHz). The activation energy and limit time of this peak are 0.11 eV and 10⁻¹⁰ s, respectively. Peak P_TWM was not observed in the solubilized state. Peak P_d, which is found to increase with the number of thermal cycles through the transition region undergone by the sample, is attributed to stress-induced motions of dislocations around their equilibrium positions within the B19′ structure of the martensite. The absence of a twin boundary peak in the martensite formed from the solubilized austenite, as well as the large difference in the strength of the transformation relaxations in the aged and solubilized states of the material are accounted for in terms of the different nature of the predominant twin boundaries in the two different states of the material.     

Hydrogen storage properties of a Ni,Fe and Ti-added Mg-based alloy

Mg-5wt%Ni-2.5wt%Fe-2.5wt%Ti (referred to as Mg-5Ni-2.5Fe-2.5Ti) hydrogen storage material was prepared by reactive mechanical grinding, after which the hydrogen absorption and desorption kinetics were investigated using a Sievert-type volumetric apparatus. A nanocrystalline Mg-5Ni-2.5Fe-2.5Ti sample was prepared by reactive mechanical grinding and hydriding-dehydriding cycling. Analysis by the Williamson-Hall method from an XRD pattern of this sample after 10 hydriding-dehydriding cycles showed that the crystallite size of Mg was 37.0 nm and that its strain was 0.0407%. The activation of Mg-5Ni-2.5Fe-2.5Ti was completed after three hydriding-dehydriding cycles. The prepared Mg-5Ni-2.5Fe-2.5Ti sample had an effective hydrogen-storage capacity near 5 wt% H. The activated Mg-5Ni-2.5Fe-2.5Ti sample absorbed 4.37 and 4.90 wt% H for 5 and 60 min, respectively, at 593K under 12 bar H₂, and desorbed 1.69, 3.81, and 4.85 wt% H for 5, 10 and 60 min, respectively, at 593K under 1.0 bar H₂.     

Low temperature heat capacity and electrical resistivity of the Ti40Zr25Cu12Ni3Be20 glass forming alloy

Gaining knowledge of electronic structure provides useful information for understanding unique properties of metallic glasses. In this study, low temperature heat capacity and electrical resistivity of the glass forming Ti₄₀Zr₂₅Cu₁₂Ni₃Be₂₀ alloy with glassy, quasicrystalline, or crystalline states below 300 K were investigated. The precipitation of the I-phase was revealed in the initial crystallization process of the Ti₄₀Zr₂₅Cu₁₂Ni₃Be₂₀ BMG. The glassy state has higher state density at Fermi level than its quasicrystalline or crystalline counterparts, which could be interpreted by the electron localization in glassy state as well as a pseudo-Brillouin zone formed nearby Fermi surface in the quasicrystalline state. None of the three states showed superconductivity phenomenon down to 1.9 K. Temperature dependence of resistivity for both the glassy state and the quasicrystalline state exhibited negative temperature coefficient and was less sensitive to temperature than the crystalline state. The electrical resistivity showed a smaller value for the I-phase than that for the glass due to lower structural integrity of I-phase. Electrical resistivity as well as heat capacity measurements indicated that the electronic structure of the quasicrystalline state is quite similar to glassy state but far from crystalline state.     

不完全再结晶Fe40Mn10Cr25Ni25高熵合金的室温及低温力学性能

采用冷轧和退火热处理工艺制备了不完全再结晶结构的Fe40Mn10Cr25Ni25高熵合金,分析了合金的室温(298 K)及低温(77 K)拉伸时的力学性能.结果表明,合金具有优良的室温及低温力学性能,合金在低温拉伸时强度和塑性均得到了提高,其室温强度和断后伸长率分别为880 MPa和18％,低温强度和断后伸长率分别为1...