Analysis of the internal friction spectrum of TiNiCu alloy

The internal friction spectra of TiNiCu shape memory alloy (SMA), which involves thermoelastic martensitic transformation, can be divided into three different terms: intrinsic, transitory and phase transition. In this paper, the damping behavior during the reverse martensitic transformation in Ti₅₀Ni₂₇Cu₂₃ SMA has been investigated using dynamic mechanical analyzer instrument. The internal friction spectra of Ti₅₀Ni₂₇Cu₂₃ SMA have been analyzed quantitatively and divided into intrinsic and transitory contributions using an iterative method. The internal friction spectra with different oscillation frequency have been predicted based on the quantitative analysis.     

Effect of heat treatment on the transformation behavior and temperature memory effect in TiNiCu wires

The effect of heat treatment on the phase transformation behavior of TiNiCu shape memory alloy wires and the temperature memory effect in this alloy were investigated by the resistance method. These results showed that with increasing annealing temperature and annealing time, the phase transformation temperatures of TiNiCu wires were shifted to higher temperatures in the heating and cooling process. It was also found that incomplete thermal cycles, upon heating the TiNiCu wires, which were arrested at a temperature between the start and finish tem-peratures of the reverse martensite transformation, could induce a kinetic stop in the next complete thermal cycle. The kinetic stop tempera-ture was closely related to the previous arrested temperature. This phenomenon was defined as the temperature memory effect. The result of this study was consistent with the previous report on the phenomenon obtained using the differential scanning calorimetry method, indicating that temperature memory effect was a common phenomenon in shape memory alloys.     

Microstructure of martensitic phase in the Co39Ni33Al28 shape memory alloys revealed by transmission electron microscopy

In the Co₃₉Ni₃₃Al₂₈ alloy, the ferromagnetic shape memory effect was investigated. A martensitic transformation (MT) occurred in the Co₃₉Ni₃₃Al₂₈ alloy when the temperature was lower than the martensitic start transformation temperature, M_S = 233 K. The morphologies and microstructures of the martensitic phase characterized by transmission electron microscope (TEM) showed a new 28-layered (28M) modulated martensite consisting of pinstripes and co-existing with the non-modulated martensite. Anomalies in magnetic properties and strain emerging around the MT have been briefly discussed.     

Microstructure and shape memory behavior of a Ti–30Nb–3Pd alloy

High temperature shape memory behavior has been found in a Ti30Nb3Pd (wt%) ternary alloy. The alloy has a M_s  561 K, M_f  446 K, A_s  678 K and A_f  772 K after being deformed and solution treated at 973–1173 K, followed by water-quenching. A strain limit for 100% recovery was measured around 2% after aging at 873 K for 20 min. A detailed microstructural investigation related to the shape memory effect is reported.     

Ta1/Ta8Ni30Cr20Cu42/0Cr18Ni9储能焊接头组织与性能

针对钽与钢之间因物化性能差异大,储能焊接头易产生脆性金属间化合物等问题,依据熔核金属高熵化技术思路,以等摩尔比的Ta₂₀Fe₂₀Ni₂₀Cr₂₀Cu₂₀合金为熔核目标成分,依据焊接过程两种母材熔合比折合得到Ta₈Ni₃₀Cr₂₀Cu₄₂中间层合金,将其用于Ta1/0Cr18Ni9的储能焊连接. 结果表明,熔核金属的高熵合金化可有效地抑制熔核中脆性金属间化合物的形成,Ta1/Ta₈Ni₃₀Cr₂₀Cu₄₂/0Cr18Ni9储能焊接头形貌完整,熔核呈规则的杯形,长径约0.6 mm,整体向钢侧发生了偏移. 熔核组织以简单FCC固溶体为主相,兼有少量BCC固溶体. 熔核中心凝固组织以细小的等轴晶为特征,熔核与两侧母材熔合区则形成了平行生长的柱状晶,熔核区与母材结合良好. 在焊接电压1 000 V,电容500 μF,电极力30 N工艺条件下,接头平均抗剪强度372 MPa.     

Temperature memory effect of Ni47Ti44Nb9 wide hysteresis shape memory alloy

The temperature memory effect (TME) phenomenon of Ni₄₇Ti₄₄Nb₉ wide hysteresis shape memory alloy was studied. It was found that TME occurred during the reverse transformation for the thermally-induced martensite (TIM) but not for the stress-induced martensite after incomplete transformation cycling. The reverse transformation temperature interval of TIM can be doubly broadened after 10 incomplete transformation cycles.     

Effect of Pd additions on phase stability and hydrogen-induced internal friction of Ti34Zr11Cu47Ni8 glassy alloys

The effects of additions of Pd below 10 at.% on the stability and hydrogen-induced internal friction behavior of Ti₃₄Zr₁₁Cu₄₇Ni₈ glassy alloys have been investigated. Thermal analyses indicate that the supercooled liquid region decreases distinctly with increasing Pd content. It was found that internal friction peak temperatures of Ti₃₄Zr₁₁Cu₄₇Ni₈–Pd hydrogenated glassy alloys (HGAs) in the hydrogen content range below approximately 30 at.% H were higher than those of the original Ti₃₄Zr₁₁Cu₄₇Ni₈ HGAs, especially at hydrogen contents below 10 at.% H. It was also found that the internal friction peaks of Ti₃₄Zr₁₁Cu₄₇Ni₈–Pd HGAs increased with increasing hydrogen content below 15 at.% H, after which they tended to saturate. These results are in contrast to the effects of Si addition as previously reported. The effects of Pd are discussed from the viewpoint of the interstitial site distribution for hydrogen and local atomic structure of the glassy alloy.     

Grain size effect on multiple-stage transformations of a cold-rolled and annealed equiatomic TiNi alloy

Ti₅₀Ni₅₀ shape memory alloy cold-rolled and annealed at specific conditions can exhibit a four-stage martensitic transformation. There are two small and two large peaks which are associated with the B2 → R → B19′ transformations of large grains in the specimen center and that of small grains near the rolling surface, respectively.     

Effect of amorphous–crystalline interfaces on the martensitic transformation in Ti50Ni25Cu25

A partially crystallized amorphous Ti₅₀Ni₂₅Cu₂₅ melt-spun ribbon showing spherical particles in martensite has been investigated. Microstructural observations support the hindering of the martensitic transformation as well as the production of additional autoaccommodated structures nearby the interface compared with the ones used inwards.     

Hydrogen-caused phase transformations, relaxation and hysteretic phenomena in fcc alloys Fe55Cr25Ni20 and Fe50Ni50

Hydrogen-induced phases, relaxation and hysteretic phenomena in Fe₅₅Cr₂₅Ni₂₀ and Fe₅₀Ni₅₀ alloys were studied using neutron scattering and internal friction. Substitution of chromium by nickel prevents the hydrogen-induced γ→ transformation, which was used for interpretation of the IF peaks. A new relaxation peak is observed in the hydrogen-charged Fe₅₀Ni₅₀ alloy.     

时效对Ti—50.8Ni—0.3Cr形状记忆合金组织和超弹性的影响

利用TEM和拉伸实验研究了时效工艺对Ti-50.8Ni-0.3Cr（原子分数,%）形状记忆合金（SMA）显微组织和超弹性的影响.随时效时间(t_ag)延长,300℃时效态Ti-50.8Ni-0.3Cr SMA的Ti₃Ni₄析出相呈细小颗粒状,400℃时效态合金的析出相由颗粒状逐渐变为针状,500℃时效态合金的析出相由针状逐渐变为粗片状.时效温度对析出相形态的影响比t_ag显著.随t_ag延长,300和400℃时效态合金的抗拉强度（σ_b）先增大后趋于稳定,σ_b（500℃）先减小后趋于稳定,且σ_b（400℃）>σ_b（300℃）>σ_b（500℃）.300和400℃时效态合金的超弹性优于500℃时效态合金.随t_ag延长,该合金的应力诱发马氏体相变临界应力逐渐减小,300℃时效态合金的超弹性能耗（△W）降低,400℃时效态合金的△W升高,500℃时效态合金的△W先升高后降低.     

Pressure effect on the structural relaxation and glass transition in metallic glasses

Two different enthalpy recovery methods were applied to investigate the effects of pressure on structural relaxation and glass transition temperature (T_g) in two metallic glasses (Pd₄₀Ni₁₀Cu₃₀P₂₀ and Zr₆₅Al_7.5Cu_27.5). The pressure-induced enhancement of T_g (dT_g/dP) was derived to be 6 K/GPa in Pd₄₀Ni₁₀Cu₃₀P₂₀ glass, while an increment of 50 K/5 GPa was observed in Zr₆₅Al_7.5Cu_27.5 glass. Activation (formation and migration) volumes of the flow defect were used to interpret the pressure dependence of the structural relaxation and T_g in terms of the free volume model. According to the measured results, the activation volume of relaxation was derived to be 16.7 ų for Pd₄₀Ni₁₀Cu₃₀P₂₀, which is much smaller than that of the polymers.     

Microstructure studies of Zr65Cu17.5Al7.5Ni10 and Zr65Cu15Al10Ni10 glass forming alloys: Phase morphologies and undercooled melt solidification

Zr₆₅Cu_17.5Al_7.5Ni₁₀ (at.%) and Zr₆₅Cu₁₅Al₁₀Ni₁₀ (at.%) glass forming alloy microstructures have been investigated by means of optical and electron microscopies. They are composed of a fine eutectic matrix with eutectic dendrites (EDs) that have peculiar morphologies. Al and Cu concentrations, in these alloys, favour primary dendrites and determine the ED morphologies and compositions. Their locations within the microstructures suggest a two-step solidification process of the two undercooled melts. The identified crystalline phases indicate the occurrence of solid state phase transformations in agreement with the structural defects observed in the grains. The crystalline phases can be classified into Zr-rich, Cu-rich, Ni-rich and Al-rich compounds resulting from competing diffusion between Cu, Ni, and Al in the melts.     

TA2/ Co13Cr28Cu31Ni28/ Q235脉冲TIG焊接头组织与性能

针对钢与钛之间因物化性能差异大,焊接过程易产生大量金属间化合物而难以实现可靠连接的问题,依据焊缝金属固溶高熵化思路,选用Co₁₃Cr₂₈Cu₃₁Ni₂₈高熵合金作为中间过渡层对TA2钛和Q235钢进行脉冲钨极氩弧焊,并对Co₁₃Cr₂₈Cu₃₁Ni₂₈高熵合金及接头的组织和性能进行分析研究. 结果表明,Co₁₃Cr₂₈Cu₃₁Ni₂₈主要是双相面心立方结构,分别为富Cu的晶间和晶内面心立方结构,强度和塑性良好;焊接接头两部分焊缝均成形良好,无气孔、裂纹等缺陷,焊缝组织均为简单的固溶体结构,Q235侧焊缝主要为面心立方结构相,TA2侧焊缝主要由简单的体心立方结构和面心立方结构相构成,以体心立方结构相为主;焊接接头抗拉强度为224 MPa,在TA2侧靠近高熵合金的熔合线处断裂,主要由于生成了脆性的Cr₃O₈,断口有较多韧窝和一部分解理面,为混合断裂,表现出一定的韧性断裂特征.     

Nb合金化对电弧增材制造NiTi基形状记忆合金的影响

NiTi合金是一种应用广泛的形状记忆合金,其中Ti₄₇Ni₄₄Nb₉成分的合金是一种可靠的航空管接头材料. 采用双丝电弧增材制造(WAAM)的方法制备了Ni₅₂Ti₄₈合金,并以Nb元素进行了原位合金化得到了Ti₄₇Ni₄₄Nb₉合金,研究了其典型组织、压缩性能、相变温度与形状记忆效应,分析了Nb元素的添加对WAAM镍钛合金组织及性能的影响. 结果表明,加入Nb元素后,合金的组织除B2相晶粒外,还在晶界处有细小的β-Nb相析出,使得合金的压缩强度在横向与纵向上分别增加了7.9%与3.1%,形状记忆回复率则下降了4.0%,相变温度滞后从?6.4 ℃提升至40.9 ℃,使得该材料作为记忆合金管接头时更加利于储存与装配.     

HRTEM study of crystallization of Zr–Cu–Ni metallic glass

Employing differential scanning calorimetry (DSC) and high-resolution transmission electron microscopy (HRTEM), the micromechanism for crystallization of Zr₇₀Cu₂₀Ni₁₀ metallic glass under isothermal annealing conditions has been investigated. It is found that the relationship between the annealing temperature and the peak position, incubation time and ending time in the isothermal annealing DSC traces of Zr₇₀Cu₂₀Ni₁₀ metallic glass obeys a first-order exponential function. However, the time–temperature transformation curves of Zr₇₀Cu₂₀Ni₁₀ metallic glass at different crystallized volume fractions can be well fitted by a second-order exponential function. It is observed that at the initial crystallization stage some ordered atomic clusters precipitate first, acting as nucleation sites and facilitating the subsequent crystallization process, and the crystal growth process mainly proceeds through the atomic depositing on the previously formed crystals. This behavior confirms that the new micromechanism for crystallization of amorphous alloys proposed by Lu and Wang can also be applied to the new series of zirconium based amorphous alloys.     

Microstructure evolution in CoNiGa shape memory alloys

Magnetic shape memory CoNiGa alloys hold great promise as new smart materials due to the good ductility and a wide range of martensitic transformation (MT) temperatures as well as magnetic transition points. This paper reports the results of investigations on the equilibrium phase constitution and microstructure evolution in quenched or aged CoNiGa alloys using the optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD) and transmission electron microscopy (TEM) methods. The dendritic γ phase decreases as lowering of Ga content in studied two series of samples (Co₅₀Ni_50 − xGa_x, x = 0–50 and Co_100 − 2yNi_yGa_y, y = 15–35). Some γ′ precipitates with different morphologies were found in given alloys conducted with water quenching (WQ) at 800 °C or long-time ageing at 300 °C. After 800 °C quenching, the γ′ phase has a rod-like shape for the Co₅₀Ni₃₀Ga₂₀ alloy but shows a Widmanstätten morphology as Ga increases to 25 at%, and trends to be block structure in further high Ga content alloy. In the case of 300 °C aged alloys, the γ′ particles prefer to nucleate in interior of γ phase or at the interface of β–γ. We also presented an illustrative vertical section phase diagram keeping 50 at% Co, and isothermal section phase diagram at 1150 and 800 °C of the CoNiGa system. Based on the schematic ternary phase diagram, the composition scope which potentially holds over the magnetic pure martensite phase structure at room temperature (RT) was pointed out. It is believed that this optimized range alloys would play an important role in the functional materials design for application.     

Infrared brazing of Ti50Ni50 shape memory alloy using pure Cu and Ti–15Cu–15Ni foils

Infrared brazing of Ti₅₀Ni₅₀ using two brazing filler metals was investigated in the study. Three phases, including Cu-rich, CuNiTi (Δ) and Ti(Ni,Cu), were observed in the Ti₅₀Ni₅₀/Cu/Ti₅₀Ni₅₀ joint after brazing at 1150 °C. The Cu-rich phase was rapidly consumed in the first 10 s of brazing, and the eutectic mixture of CuNiTi and Ti(Ni,Cu) phases were subsequently observed in the joint. Samples brazed for longer time resulted in less CuNiTi and more Ti(Ni,Cu) phases in the joint. The existence of CuNiTi phase deteriorated the shape memory effect of the joint, but Ti(Ni,Cu) could still preserve shape memory behavior even alloyed with a large number of Cu. Therefore, higher shape recovery ratio was observed for specimens brazed for a longer time period. Extensive presence of Ti₂(Ni,Cu) phase was observed in Ti₅₀Ni₅₀/Ticuni^®/Ti₅₀Ni₅₀ joint upon brazing the specimens up to 1150 °C. The bending test could not be performed due to the inherent brittleness of Ti₂(Ni,Cu) matrix. Moreover, the stable Ti₂(Ni,Cu) phase was difficult to be removed completely by increasing either brazing time and/or temperature.     

Ti-13at.-％Ni-37at.-％Pd记忆合金预形变与高温形状记忆效应SCIEI

本文着重地研究了Ti-13at.-％Ni-37at.-％Pd合金的高温形状记忆效应与预形变温度的关系.该合金A_s温度是620K,具有单程形状记忆效应和双程形状记忆效应。在620—640K温度预形变,可以得到最大的形状记忆应变,这与在此温区产生的最小可逆应变能有关。     

Glass formation ability and isothermal crystallization of melt-spun NdNiCuAl ribbons

On the basis of the previous work on (Nd_62.5Ni_37.5)₈₅Al₁₅ alloy, Cu is selected to partially substitute Ni to form (Nd_62.5Ni_37.5−xCu_x)₈₅Al₁₅ (x = 0, 10, 20, 30) melt-spun alloys. The glass-forming ability (GFA) of the as-prepared alloys is evaluated by the isochronal differential scanning calorimeter (DSC) measurement. The results show that GFA increases with Cu content according to several different criterions. The isothermal crystallization behaviors in the corresponding supercooled liquid region is discussed by both Johnson–Mehl–Avrami (JMA) equation and some nucleation and growth models. The fitting shows that it is reasonable to divide the whole crystallization processes into two stages. And the fittings with the nucleation and growth models infers that with increasing Cu content, the nucleation mechanism of the primary stage changes from the quenched-in and steady-state nucleation for (Nd_62.5Ni_37.5)₈₅Al₁₅, to the steady-state nucleation for (Nd_62.5Ni_27.5Cu₁₀)₈₅Al₁₅ and (Nd_62.5Ni_17.5Cu₂₀)₈₅Al₁₅, then to the time-dependent nucleation for (Nd_62.5Ni_7.5Cu₃₀)₈₅Al₁₅. And the dependence of crystallization mechanisms on Cu substitution agrees well with the change of their GFAs.