Phase transformation behaviours of Ti-Ni-Cu shape memory alloy powders fabricated by mechanical alloying

In our research, Ti-Ni and Ti-Ni-Cu alloy powders were fabricated by mechanical alloying, and then phase transformation behaviours were investigated by means of X-ray diffraction, scanning electron microscopy, energy dispersive X-ray analysis and transmission electron microscopy. The size of the Ti-Ni-Cu alloy powders decreased as Cu-content increased. The powders of as-milled Ti-Ni and Ti-Ni-Cu alloys with Cucontents less than 5at.% were amorphous, whereas those of as-milled Ti-Ni-Cu alloys with Cu-content more than 10at.% were crystalline. These characteristics indicate that Cu addition tends to suppress amorphization of Ti-Ni based alloy powders. The monoclinic B19’ martensite is formed in the Ti-Ni-Cu alloy powders with Cu-content less than 10 at.%, whereas the orthorhombic B19 martensite is formed in the Yi-Ni-Cu alloy powders Cu-content more than 10 at.%. The Fe contamination is reduced by decreasing rotation speed from 350 rpm to 250 rpm.     

Ti-Ni-Cu形状记忆合金的温度记忆效应

采用差示扫描量热仪研究了Ti50Ni35Cu15以及Ti50Ni45Cu5(摩尔分数,%)形状记忆合金的温度记忆效应.结果表明:温度记忆效应仅在Ti-Ni-Cu合金的逆转变加热过程出现,在单斜结构马氏体与母相逆相变(B19'→B2)及正交结构马氏体与母相逆相变(B19→B2)过程中均能发生温度记忆效应;在随后的完全循环过程中,温度记忆记忆效应不再出现,DSC相变曲线又"恢复"到其原始形态;而在马氏体相变冷却过程中未发现温度记忆效应.分析表明,不完全相变过程中的弹性能再分布是可能的温度记忆效应机制.     

Microstructures and transformation behavior of Ti-Ni-Cu shape memory alloy powders fabricated by ball milling method

Ti-Ni and Ti-Ni-Cu alloy powders have been fabricated by ball milling after which their microstructures and transformation behaviors were investigated by means of scanning electron microscopy, X-ray diffraction, energy dispersive X-ray analysis, transmission electron microscopy and differential scanning calorimetry. The powders of as-milled Ti-Ni-Cu alloys whose Cu-content is less than 5 at.% were mixtures of crystal and amorphous, whereas those alloy powders whose Cu-content is more than 10 at.% were crystalline. The B19’ martensite is formed in the Ti-Ni-Cu alloy powders whose Cu-content is less than 10 at.%, whereas the B19 and B19’ martensites coexist in those whose Cu-content is more than 10 at.%. The martensitic transformation range became wider with increasing rotating speed, and so endothermic and exothermic peaks obtained from differential scanning calorimetry were indiscernible.     

T6态AlMgCu铝合金激冷甩带的反常析出行为(英文)

利用高分辨透射电镜和硬度测试表征时效态AlMgCu铝合金激冷甩带的析出相组成。铸态合金甩带的冷却速率通过经验公式计算为1.60×105 K/s。T6态热处理是试样经固溶处理后再进行200°C保温16 h的时效处理。结果表明,T6态AlMgCu铝合金激冷甩带含有Al2CuMg相和反常非晶SiO2两种析出相。Al2CuMg析出相的晶体结构和成分配比与文献[Wang et al.(2007;2005)]结果一致。综合实验结果分析表明,反常非晶SiO2相的析出可能与激冷甩带具有高的冷却速率有关,它的析出对其硬度的影响不大。     

热处理对Ti-Ni合金显微组织和力学性能的影响

研究了冷加工变形量为48%的Ti-Ni合金经中温退火(350～600 ℃)处理后退火温度对合金显微组织及室温力学性能的影响.结果表明,变形后获得部分非晶的纳米组织,400 ℃退火后合金发生再结晶;500 ℃退火后完成再结晶,晶粒开始长大;600 ℃退火后合金组织完全粗化,室温下为粗大的自协调马氏体.退火温度升高,合金的抗拉强度大大下降,当退火温度高于500 ℃时,伸长率大大增加,伸长率大于50%.室温下合金拉伸变形时应力诱发马氏体相变的临界应力值σs受退火温度和相变温度的制约.     

Ti-Ni形状记忆合金多阶段可逆相变的类型及其演化过程

用示差扫描量热仪(DSC)和部分热循环分析法研究了350-800℃退火态和300-500℃时效态Ti-(50.2-50.8)Ni(原子分数,%)形状记忆合金多阶段可逆相变的类型及其演化过程.结果表明,这些合金发生R和马氏体两种可逆相变,相变可以一阶段完成,也可以多阶段完成.时效态合金的相变比退火态复杂,时效温度越低相变越复杂.若用DSC曲线上冷却相变峰数/加热相变峰数表示相变类型,则退火态和时效态合金冷却/加热时可以发生1/1,2/1,2/2,3/2和3/3等类型的相变.给出了各类相变发生的热处理工艺.多阶段可逆相变是一个渐变过程,在冷却相变峰的温度区间进行部分热循环时,随冷却停止(加热开始)温度降低,逆相变峰温度降低.     

退火对Ni47Ti44Nb9合金激光焊接接头力学性能与形状记忆效应的影响

为了降低镍钛铌(NiTiNb)宽滞后记忆合金紧固环的制备成本,研究了退火对激光焊接接头力学性能和记忆效应的影响。焊接接头在850℃进行了退火处理。结果表明:焊接接头的组织粗大且不均匀,抗拉强度与延伸率均显著低于母材。经过退火后,再结晶导致焊接接头组织更加均匀;母材与焊接接头抗拉强度均大幅度下降,但延伸率均得到较大提高,尤其是焊接接头的延伸率可以提升到28.57%。退火态焊接接头在-40℃变形13%时表现出接近于母材的形状恢复率。     

Microstructure, phase transformation and mechanical properties of Ni-Mn-Ga-Y magnetic shape memory alloys

Influence of rare earth Y addition on the microstructure and phase transitions and mechanical properties of polycrystalline Ni₅₀Mn₂₉Ga₂₁ ferromagnetic-shape memory alloy (FSMA) are investigated. It is shown that microstructure of the Ni-Mn-Ga-Y alloys consists of the matrix and the Y-rich phase. The Y-rich phase firstly disperses homogeneously in the matrix with small amounts and then tends to segregate at the grain boundaries with increasing Y substitution for Ga. The Y-rich phase is indexed to Y(Ni,Mn)₄Ga phase with a hexagonal CaCu₅ type structure. The structural transition from 5 M to 7 M, and then to non-modulated T martensite appears with the increase of Y content. The martensitic transformation temperature increases remarkably with increasing Y content, whereas the Curie temperature almost keeps unchanged. It is revealed that the appropriate addition of Y significantly enhances the yield strength and improves the ductility of the alloys. The mechanism on the influence of Y content on the improved mechanical properties and martensitic transformation temperature is also discussed.     

激冷Ti-46Ni合金薄带的组织、相变和形状记忆效应

用激冷甩带法制备了Ti-46Ni合金薄带,用扫描电子显微镜、X射线衍射仪、示差扫描热分析仪和弯曲试验研究了合金薄带的组织特征、相变行为和形状记忆效应。结果表明,铸态及400~600℃退火态Ti-46Ni合金薄带的显微组织形态呈树枝状,晶粒细小,由B19?马氏体和B2母相组成;在冷却、加热过程中,该合金薄带发生一阶段马氏体相变;铸态和退火态Ti-46Ni合金薄带均具有良好的形状记忆效应。     

Martensitic transformation of Ti50Ni30Cu20 alloy prepared by powder metallurgy

Phase transformation behavior of Ti50Ni30Cu20 shape memory alloys prepared by powder metallurgy is analyzed with respect to the duration of mechanical alloying. The processed blends were studied by differential scanning calorimetry and room temperature X-ray diffraction. The martensitic transformations evidenced by thermal scans are discussed in correlation with the relative phase content obtained from the refinement of the X-ray diffraction patterns.     

NiTi-W原位复合材料的马氏体相变与性能

为获得高性能NiTi基记忆合金复合材料,通过熔炼、锻造、拔丝等手段获得一种NiTi-W原位复合材料。利用SEM扫描电镜观察材料显微组织;DSC测试材料的马氏体相变行为;利用WDT II-20万能拉伸试验机测试材料的力学性能。SEM分析结果显示,拔丝加工使W纤维直径细化至几微米,甚至亚微米级别,在NiTi基体中沿拔丝方向一致排布。DSC测试结果显示,材料经不同温度退火后展现出复杂的可逆马氏体相变行为,在某些升、降温曲线上出现多个吸放热峰现象。拉伸测试结果显示,600 ℃退火样品经适当的预拉伸变形后,屈服强度会大大增加,由~200 MPa提升到~800 MPa,断裂应力超过1 GPa,断裂应变高达40%,材料展现出优秀的线性超弹性,是一种集高强度、高塑性、高线性超弹性于一身的高性能材料。     

Microstructures and mechanical properties of laser-welded TiNi shape memory alloy and stainless steel wires

The Nd:YAG laser welding was used to join the TiNi shape memory alloy and AISI304 stainless steel wires. The microstructural features of the dissimilar material joint were analyzed. The tensile and hardness tests were carried out to examine the mechanical properties and microhardness distribution of the welded joint. The results show that the joint has the non-homogeneous microstructure and element distribution. The brittle phases such as Fe2Ti, FeTi, Cr2Ti, Ti3Ni4, Fe0.2Ni4.8Ti5 and TiN mainly segregate in rich Ti region of fusion zone. The laser-welded joint has the tensile strength of 298 MPa with the elongation of 3.72% and exhibits the brittle fracture features on the fracture surfaces. The reasons for low joint strength were discussed in this investigation.     

时效对TiNiCr形状记忆合金马氏体相变与超弹性的影响(英文)

通过X射线衍射分析(XRD)、透射电子显微观察(TEM)、差式扫描量热分析(DSC)与拉伸实验研究时效处理对Ti48.4Ni51.1Cr0.5合金显微组织、马氏体相变与超弹性的影响规律与机制。经400°C时效处理30 min后,合金中形成Ti3Ni4析出相。当时效温度介于400°C和500°C之间时,合金表现出两步马氏体相变。经时效处理的Ti48.4Ni51.1Cr0.5合金在室温下表现出优异的超弹性。随时效温度自300°C升高到450°C,超弹性恢复率增加。继续升高时效温度,恢复率下降。超弹性应力滞后表现出相反的变化趋势。通过分析Ti3Ni4析出相随时效处理的演化规律解释了时效处理与马氏体相变和超弹性之间的关系。     

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。     

烧结温度对快速凝固TiAl合金组织及力学性能的影响(英文)

将快速凝固Ti-46Al-2Cr-4Nb-0.3Y(摩尔分数,%)合金薄带破碎成粉末,然后通过等离子烧结(SPS)制备成块体。研究烧结温度对烧结块体的组织和力学性能的影响。在1200℃烧结时得到完全致密的块体。进一步升高烧结温度对合金密度的影响不大,但是对烧结块体的显微组织及相结构有显著影响。烧结块体主要由γ和α2相组成,随着烧结温度的升高,α2相的体积分数降低,块体合金由近γ组织演变为近层片组织,且组织逐渐粗化,但是长大不明显。1260℃烧结得到的块体组织细小、均匀,没有明显微偏析,具有良好的综合力学性能,室温压缩断裂强度和压缩率分别为2984MPa和41.5%,高温(800℃)拉伸断裂强度和伸长率分别为527.5MPa和5.9%。     

热处理对NiTi形状记忆合金力学性能的影响

研究了热处理工艺对50.8at%NiTi形状记忆合金力学性能的影响。通过对NiTi合金试样在不同温度下进行固溶处理和时效处理并进行单向拉伸试验,得到试样的屈服强度、抗拉强度、弹性模量和泊松比等力学性能参数。通过光学显微镜对热处理前后试样的显微组织进行观察,估算其晶粒尺寸,并利用Hall-Petch理论分析了试样的晶粒尺寸对屈服强度的影响。研究发现将NiTi合金先进行固溶处理,再进行时效处理,其力学性能改善较为明显。为NiTi 形状记忆合金的工程应用提供了试验依据,有利于扩大该合金的工程应用范围。     

Superelastic properties of nanocrystalline NiTi shape memory alloy produced by thermomechanical processing

Effects of thermomechanical treatment of cold rolling followed by annealing on microstructure and superelastic behavior of the Ni₅₀Ti₅₀ shape memory alloy were studied. Several specimens were produced by copper boat vacuum induction melting. The homogenized specimens were hot rolled and annealed at 900 °C. Thereafter, annealed specimens were subjected to cold rolling with different thickness reductions up to 70%. Transmission electron microscopy revealed that the severe cold rolling led to the formation of a mixed microstructure consisting of nanocrystalline and amorphous phases in Ni₅₀Ti₅₀ alloy. After annealing at 400 °C for 1 h, the amorphous phase formed in the cold-rolled specimens was crystallized and a nanocrystalline structure formed. Results showed that with increasing thickness reduction during cold rolling, the recoverable strain of Ni₅₀Ti₅₀ alloy was increased during superelastic experiments such that the 70% cold rolled–annealed specimen exhibited about 12% of recoverable strain. Moreover, with increasing thickness reduction, the critical stress for stress-induced martensitic transformation was increased. It is noteworthy that in the 70% cold rolled–annealed specimen, the damping capacity was measured to be 28 J/cm³ that is significantly higher than that of commercial NiTi alloys.     

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.     

Comparison of shape memory effect between casting and forged alloys of Fe14Mn6Si9Cr5Ni

The effect of different manufacturing techniques on the shape memory effect (SME) of the Fe14Mn6Si9Cr5Ni alloy has been studied. The SMEs of casting and forged alloys are similar. At ambient temperature, creep and stress-relaxation experiments of the casting alloy show that the casting alloy presents a good creep rupture strength. The manufactured pipe joints of the casting alloys keep jointing under a tensile force of 20 kN and keep sealing under a pressure of 5 MPa. Those excellent mechanical properties satisfy the requirements for pipe jointing in general industrial applications.     

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。