高熵形状记忆合金的研究进展

TiNi形状记忆合金具有优异的形状记忆效应和超弹性,使其广泛应用于航空航天、生物医疗等领域。然而,面对日益增长的在更苛刻环境下服役的需求,传统二元TiNi合金存在着相变温度低、高温环境下功能特性丧失和强度不足等问题,还需要不断优化合金成分和热处理工艺以提升其性能,从而发展出高性能形状记忆合金。TiNi合金的力学性能和功能特性受多种因素的影响,本文主要从合金成分的角度重点概述了各合金化元素对合金微观组织、马氏体相变行为、形状记忆效应和超弹性的影响,并结合高熵合金化思想,综述了近年来在TiNi基高熵形状记忆合金领域取得的进展。最后展望了TiNi基形状记忆合金未来的发展方向及应用前景。     

高熵形状记忆合金的研究进展

高熵形状记忆合金是在等原子比NiTi合金的基础上,结合高熵合金的概念,逐渐发展起来的一种新型高温形状记忆合金.近年来,已开发出了综合性能优异的(TiZrHf)50(NiCoCu)50系和(TiZrHf)50(NiCuPd)50系高熵形状记忆合金,引起了广泛的关注和研究兴趣.本文从物相组成、微观组织、马氏体相变行为、形状...     

Ti-49.8Ni形状记忆合金的氧化、相变和形变特性

用热重分析仪、X射线衍射仪、示差扫描热分析仪及拉伸试验机研究了Ti-49.8Ni形状记忆合金(SMA)的氧化、相变和形变特性.结果表明,退火温度超过600℃时Ti-49.8Ni合金的氧化加剧;400～600℃退火态Ti-49.8Ni合金冷却/加热时的相变类型为A→R→M/M→A(A-母相,R-R相,M-马氏体相),随退火温度升高,合金的马氏体相变温度升高,R相变温度基本不变,马氏体相变热滞先减小后升高,马氏体再取向应力先降低后升高,合金的塑性提高.Ti-49.8Ni合金室温相组成为M和TiO2,呈形状记忆效应;形变温度超过110℃后合金呈超弹性.400～550℃退火态合金的SME特性良好,退火温度高于600℃后合金特性变差;随循环次数增加,Ti-49.8Ni合金弹簧的应变恢复率减小,循环次数超过100次后恢复率衰减变缓.     

热处理对CuAlBe形状记忆合金组织和相变行为的影响

采用DSC法和电阻法测定了CuAlBe形状记忆合金的相变点,并通过组织观察和性能(硬度)测定等方法,综合分析研究了热处理工艺对其组织和相变行为的影响。结果表明,热处理对合金的晶粒大小和相变点影响较大,加热温度高和保温时间长都会使晶粒长大、相变点升高。热循环使相变行为的稳定性提高。低温时效会使相变点降低;而高温时效会使马氏体部分分解,造成马氏体逆转变困难。     

50Ti-50Pd高温形状记忆合金研究

研究了50Ti-50Pd合金的马氏体相变、显微组织和形状记忆效应。结果表明：实验合金马氏体相变热滞小,呈热弹性,室温相为B19斜方结构;固溶处理50Ti-50Pd合金试样的记忆效应随起始恢复温度的升高而增大,弯曲循环可改善合金的记忆效应。     

Ni-Mn-Ga-V高温形状记忆合金研究

本文采用光学显微镜、X射线衍射仪、扫描电子显微镜、透射电子显微镜以及压缩力学试验机系统的研究了钒元素对(Ni56Mn25Ga19)100-xVx (x = 0, 1, 3) (at.%)高温形状记忆合金性能的影响。结果表明,由于钒取代方法的不同,我们所研究合金的组织结构和某些性能与已报到的Ni56Mn25Ga19-xVx合金差异较大。未掺杂钒元素时,试验合金由单相非调制四方结构马氏体构成,当钒含量为1at.%和3at.%时,合金由四方结构马氏体和竹叶状γ相构成。随着钒含量的增加,γ相的数量增多,但其尺寸和形状保持不变。钒掺杂改善合金的力学性能和形状记忆效应。 (Ni56Mn25Ga19)99V1合金变形10%后加热,可以得到6.7%的可逆应变。     

铁基形状记忆合金及其相变特性

通过对铁基形状记忆合金从微米到亚纳米尺度的显微观察,讨论了铁基合金形状记忆效应的机制和特性。大多数有应用前景的铁基形状记忆合金与面心立方到体心四方（ｆｃｃ／ｂｃｔ）和面心立方到密排六方（ｆｃｃ／ｈｃｐ）相变有关。在这些相变体系中,对直接与形状记忆效应有关的应力诱发马氏体相变及其逆相变的模型进行了详细的研究。为取得良好的形状记忆效应,必须满足以下一些条件：（１）对ｆｃｃ／ｂｃｔ相变,ｂｃｔ马氏体的正     

NiAlMnFe高温形状记忆合金的马氏体相变行为

用示差扫描量热仪、X射线衍射仪、扫描电镜及能谱仪、光学显微镜和显微硬度计等研究了固溶、时效工艺及热循环对Ni60Al19Mn16Fe5高温形状记忆合金马氏体(M)相变行为的影响。固溶淬火态以及固溶淬火加时效态Ni60Al19Mn16Fe5合金冷却、加热时发生可逆热弹性M相变。M相变温度、热滞和相变热随固溶温度的升高而增加，时效对M相变行为亦有较大影响，1100℃固溶处理和400℃时效处理后该合金具有良好的M相变行为。热循环几乎不影响正M相变，但第1次热循环时，M显示稳定性效应，使逆M相变推迟。第1次热循环后，逆M相变不再受热循环影响。该合金的固溶淬火组织为β(M) γ，其中γ相约占20％，M的硬度高于γ相。     

形状记忆合金的研究与应用

本文综述了形状记忆合金的发现历史、相变晶体学和热力学特性及当前的应用与研究的若干热点。     

磁性形状记忆合金Ni2MnGa的研究现状及发展

本文系统地阐述了Ni2MnGa合金的晶体结构、马氏体相变行为、相变应变、磁诱导应变及其形状记忆效应机理的研究现状，分析了影响Ni2MnGa合金马氏体相变、应力应变及各物理量的主要因素，介绍了Ni2MnGa合金的制备工艺现状及发展趋势，并提出了Ni2MnGa合金需深入研究的问题。     

NiTi基高温记忆合金相变行为与组织性能研究

本文总结了近年来国内外Ni-Ti-Pd和Ni-Ti-Pt高温镍钛形状记忆合金研究进展,分析了化学成分、热机械处理和训练工艺等对高温记忆合金的马氏体相变行为、高温单程和双程记忆性能和循环使用性能稳定性等方面的影响。研究结果表明,Ni-Ti-Pd和Ni-Ti-Pt高温镍钛形状记忆合金的相变温度、滞后宽度、高温马氏体变形与蠕变行为、高温循环特性等受显微组织影响显著。通过采取Sc、B、Cu等元素合金化、固溶和时效、冷轧退火处理,有利于细化晶粒,在基体析出细小弥散沉淀相,如Ti₂Ni 和Ti₂(Ni,Pd)等,起到固溶强化和沉淀强化作用,改善高温记忆合金高温记忆性能。在一定应力条件下训练处理在基体形成具有特定应力场位错组态易于诱发择优取向的马氏体变体形核,从而提高高温单程和双程记忆性能和功能尺寸稳定性。     

Martensitic transition and shape memory effect of Ti-Zr-Mo series alloys

Development of shape memory alloys is always one of the most important directions for functional Ti alloys. The Ti-Zr-Mo series alloys with various Mo contents were prepared. The main aim of the current work is to investigate the effects of Mo on martensitic transition and shape memory effect of Ti-Zr alloy. The X-ray diffraction and transmission electron microscope results indicate that the phase constitution of the examined alloys is greatly dependent on Mo content. The Ti-Zr-Mo alloy with 2 wt% Mo is composed mainly of α′ martensite and a few β phase. As the Mo content increased to 4 wt%, the Ti-50Zr-4Mo alloy consists of α″ martensite and β phase. As the Mo content further increased to 8 wt%, the alloy consists mainly β phase and a barely detectable amount of α″ martensite. Thermal analysis shows that the reverse martensitic transition temperature of the examined alloys decreases with the increasing of Mo. The reverse martensitic transition start, A_s, temperature is approximately 584 °C for Ti-50Zr-2Mo alloy and 519 °C for Ti-50Zr-4Mo, respectively. And the martensitic transition start, M_s, temperature is approximately 553 °C and 501 °C for that two alloys, respectively. But no obvious exothermic and/or endothermic peak can be observed in DSC curve of Ti-50Zr-8Mo alloy. Furthermore, the effect of Mo content on shape memory recovery ratio, η, of the examined alloys was also investigated. Results show that the η first increases and then decreases with the increasing of Mo. The alloy with 4 wt% Mo has the maximum η approximately 13.8%. The influencing mechanism of Mo content on shape memory effect of the examined alloys was also discussed. This findings not only supplied a series of shape memory TiZr-based alloys, but also enriched and deepened the theory of shape memory effect.     

Microstructure and martensitic transformation of cast TiNiSi shape memory alloys

The martensitic transformation behavior, second phases and hardness of Ti₅₁Ni_49−xSi_x shape memory alloys (SMAs) with x = 0, 1 and 2 at.% are investigated. The transformation temperature of one stage martensitic reaction B2 ↔ B19′ is associated with the forward (M_s) and reverse (A_s) martensitic transformations, respectively. All experimental DSC results such as martensitic transformation peaks (M*) and reverse martensitic transformation peaks (A*) are increased and became sharper with increasing Si-content. The microstructure investigation of the studied SMAs (Ti₅₁Ni_49−xSi_x) showed that there are two types of precipitated second phase particles. The first one is Ti₂Ni which mainly located at grain boundaries and intermetallic compound of Ti₂(Ni + Si) phase distributed inside the matrix. The volume fraction of these two phases is increased with Si content. Additionally, a small amount of Si remained in solid solution of the matrix of Ti₅₁Ni_49−xSi_x SMAs. Moreover, hardness of Ti₅₁Ni_49−xSi_x SMAs is increased as the Si-content increases.     

Microstructure and martensitic transformation of TiNiNbB shape memory alloys

In present work, microstructure, martensitic transformation and mechanical properties of Ti₄₄Ni_47−xNb₉B_x (x = 0, 0.5, 1, 5 at.%) alloys were investigated as a function of B content. The results show that the addition of B significantly influences the microstructure of the alloys. The microstructure of Ti₄₄Ni₄₇Nb₉ alloy consists of B2 parent phase matrix and β-Nb phase. When the B content is 0.5 at.%, Nb₃B₂ phase presents. With further increasing B content to above 1 at.%, TiB and NbB phases present instead of Nb₃B₂ phase. With increasing B content, the transformation temperatures increase due to the reduced Ni/Ti ratio and Nb content in the matrix. The mechanical properties can be optimized by the addition of 1 at.% B.     

Shape memory behavior and tension-compression asymmetry of a FeNiCoAlTa single-crystalline shape memory alloy

A 〈1 0 0〉 textured polycrystalline FeNiCoAlTa shape memory alloy was recently shown to possess large superelastic strain and stress levels. In this study, the shape memory behavior of a Fe-28Ni-17Co-11.5Al-2.5Ta (at.%) single-crystalline material oriented along the 〈1 0 0〉 direction was studied, for the first time, by thermal cycling under constant stress levels in both tension and compression. When γ′ precipitates with an average size of 5 nm are introduced by an aging heat treatment, the single crystals show fully recoverable transformation strains up to 3.75% in tension and 2% in compression. The change in transformation temperatures for a unit change in applied stress level was higher in compression than in tension, in accord with the lower transformation strains in compression obtained both from theoretical calculations and experimental observations. However, in all specimens, the observed transformation strain levels were lower than theoretically predicted, possibly owing to significant volume fraction of non-transforming precipitates, incomplete martensite reorientation due to martensite variant interactions, and a slightly higher-than-expected martensite c/a ratio in the samples used in this study. The ramifications of relevant structural parameters and microstructural features on reaching theoretical transformation strain and high strength levels are also discussed.     

Differences of transformation behavior between Ni-rich TiNi shape memory films and alloys

The differences of transformation behavior between Ni-rich TiNi shape memory film (SMF) and shape memory alloy (SMA) age-treated at 773K after solution-treatment at 973K have been investigated, using Ti-51.5Ni thin film and Ti-51.5Ni bulk alloy as examples, by differential scanning calorimetry (DSC), SEM and EDX. It is found that the age-treated Ni-rich TiNi SMF and SMA are of the same types of transformation, i.e., A→R→M (during cooling), and M→A (during heating) (A: parent phase; R: R-phase; M: martensite); the transformation temperature of the TiNi SMF is lower than that of the SMA, but the SMFs hysteresis is larger. The transformation heat of the TiNi SMF and SMA is nearly the same. The reason that TiNi SMFs strain is sensitive to temperature is not hysteresis, but its thickness is thinner, and the temperature is easy to distribute homogeneously.     

Martensitic transformation and magnetic properties of Ti-doped NiCoMnSn shape memory alloy

Martensitic transformation, microstructure, and magnetic properties of Ti-doped Ni43-xTixCo7Mn43Sn7（at%）（x = 0, 0.5, 1.0, 2.0, and 4.0） shape memory alloys were investigated. The results show that transformation temperatures of Ni43Co7Mn43Sn7 can be efficiently adjusted by the substitution of Ti for Ni. For example, the martensitic transformation starting temperature（Ms） is reduced by about 278 K with 4 at% addition of Ti. Room temperature microstructure evolves from single tetragonal martensite for the Ti-free alloy to dual phases（tetragonal martensite ＋ second phase） with 0.5 at%, 1.0 at%, and2.0 at% addition of Ti to dual phases（cubic austenite ＋ second phase） for 4.0 at% Ti-doped alloy. The mechanical properties can be obviously improved by adding an appropriate amount of Ti. A noteworthy point is that magnetic-field-induced reverse transformation is observed in Ni39Ti4Co7Mn43Sn7 alloy.