Effects of thermal aging on transformation temperatures and some physical parameters of Cu–13.5wt.%Al–4wt.%Ni shape memory alloy

Balo, Ş. Nevin; Sel, Neslihan

doi:10.1016/j.tca.2012.02.007

Cited by 39 publications

(17 citation statements)

References 18 publications

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“…The XRD of the alloys with a monoclinic structure was similar to earlier works. [8,33] Although the XRD results showed similar characteristics, some of the diffraction pattern planes shifted in the location during the addition process. One of the most important factors that has a significant effect on martensitic transformation is the structure ordering.…”

Section: A Microstructural Observationsmentioning

confidence: 88%

“…One of the most important factors that has a significant effect on martensitic transformation is the structure ordering. [33,34] The crystallite size was determined by a Scherrer method, [35,36] with the mean value of the main five peaks of (122), (0018), (128), (1210), and (208) being calculated as per the following equation:…”

Section: A Microstructural Observationsmentioning

confidence: 99%

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Effect of Quarterly Element Addition of Cobalt on Phase Transformation Characteristics of Cu-Al-Ni Shape Memory Alloys

Saud

Bakar

Hamzah

et al. 2015

Metall Mater Trans A

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In the current study, a new type of Cu-based shape memory alloys with the function of shape memory effect was successfully produced with the introduction of high-purity Co precipitates between the phases of Cu-Al-Ni shape memory alloy. The microstructure, transformation characteristics, and mechanical properties were systematically investigated by means of differential scanning calorimetry, field emission scanning electron microscopy, energy dispersive spectroscopy (EDS), transmission electron microscopy, X-ray diffraction (XRD), a tensile test, a hardness test, and a shape memory effect test. The typical microstructures show that a new phase was formed, known as the c 2 phase, and the volume friction and the size of this phase were gradually increased with the increasing Co content. According to the results of the XRD and EDS, it was confirmed that the c 2 phase represents a compound of Al 75 Co 22 Ni 3 . However, the presence of c 2 phase in the modified alloys was found to result in an increase of the transformation temperatures in comparison with the unmodified alloy. Nevertheless, it was found that with 1 wt pct of Co addition, a maximum ductility of 7 pct was achieved, corresponding to an increase in the strain recovery by the shape memory effect to 95 pct with respect to the unmodified alloy of 50 pct.

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Section: A Microstructural Observationsmentioning

confidence: 88%

Section: A Microstructural Observationsmentioning

confidence: 99%

Effect of Quarterly Element Addition of Cobalt on Phase Transformation Characteristics of Cu-Al-Ni Shape Memory Alloys

Saud

Bakar

Hamzah

et al. 2015

Metall Mater Trans A

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“…This material has been the subject of active research during recent years, since associated with the martensitic transition, it displays interesting shape memory and superelastic properties [13]. Problems such as the influence of aging [14,15] and cycling [16] on the transition and martensitic microstructure, and the elastic behavior above and below the transformation [17,18] among others, have been studied in detail due to their relevance in relation to potential technological applications of this material.…”

Section: Introductionmentioning

confidence: 99%

Avalanche criticalities and elastic and calorimetric anomalies of the transition from cubic Cu-Al-Ni to a mixture of18Rand2Hstructures

et al. 2016

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We studied the two-step martensitic transition of a Cu-Al-Ni shape-memory alloy by calorimetry, acoustic emission (AE), and resonant ultrasound spectroscopy (RUS) measurements. The transition occurs under cooling from the cubic (β, F m3m) parent phase near 242 K to a mixture of orthorhombic 2H and monoclinic 18R phases. Heating leads first to the back transformation of small 18R domains to β and/or 2H near 255 K, and then to the transformation 2H to β near 280 K. The total transformation enthalpy is H T = 328 ± 10 J/mol and is observed as one large latent heat peak under cooling. The back-transformation entropy under heating breaks down into a large component 18R to β at 255 K and a smaller, smeared component of the transformation 2H to β near 280 K. The proportions inside the phase mixture depend on the thermal history of the sample. The elastic response of the sample is dominated by large elastic softening during cooling. The weakening of the elastic shear modulus shows a peak at 242 K, which is typical for the formation of complex microstructures. Cooling the sample further leads to additional changes of the microstructure and domain wall freezing, which is seen by gradual elastic hardening and increasing damping of the RUS signal. Heating from 220 K to room temperature leads to elastic anomalies due to the initial transformation, which is now shifted to high temperatures. The transition is smeared over a wider temperature interval and shows strong elastic damping. The shear modulus of the cubic phase is recovered at 280 K. The phase transformation leads to avalanches, which were recorded by AE and by time-resolved calorimetry. The cooling transition shows very extended avalanche signals in calorimetry with power-law distributions. Cooling and heating runs show AE signals over a large temperature interval above 260 K. Splitting the transformation into two martensite phases leads to power-law exponents ε ∼ 2 (β ↔ 18R) and ε ∼ 1.5 (β ↔ 2H ) while the phase mixture shows an effective AE exponent of 1.7.

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“…With nickel addition, while the eutectoid temperature remains at approximately 565°C, the material experiences eutectoid composition variation that affects the martensite microstructure [10]. Many factors are affected on the transition characteristics of the Cu-Al-Ni SMAs, e.g., adding alloying elements, applying aging treatment, and fabrication techniques [11][12][13][14][15]. Among the aforementioned factors, the aging treatment has been found to be the most significant process for enhancing the shape memory characteristics of the ternary Cu-Al-Ni alloys [11].…”

Section: Introductionmentioning

confidence: 99%

X-phase precipitation in aging of Cu–Al–Ni–xTi shape memory alloys and its influence on phase transition behavior

Saud

Hamzah

Abubakar

et al. 2015

J Therm Anal Calorim

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The present work aims to investigate the aging treatment effects on the microstructure, transition characteristics, and mechanical properties of Cu-Al-Ni-xTi shape memory alloys. The aging treatment of the homogenized and modified alloys of Cu-Al-Ni-xTi results in variations of the martensite morphology, volume fraction, and precipitate size. These variations in the features of precipitates have an obvious effect on transition behavior and mechanical properties. The transition temperatures are increased slightly with an increase in the aging time and temperatures; such increase is mainly attributed to changes in the c 0 1 and b 0 1 morphology and distribution, along with the precipitates. The thermodynamic parameters (DH and DS) tend to decrease with an increase in the aging time and temperatures. Moreover, the brittleness, low strength, and poor processability of Cu-Al-Ni alloys greatly limit their application. We attempted to improve the mechanical properties without losing the thermoelastic properties through the additions of Ti and appropriate aging treatments. The highest tensile strength and strain of 640 MPa and 4.3 % were obtained in alloy of Cu-Al-Ni-0.7 mass% Ti aged at 250°C for 24 h and 100°C for 48 h, respectively. The shape memory behavior of the alloys was studied using a specially designed machine. The strain recovery by shape memory effect of the alloys increases with an increase in the aging tomes and temperature, where the highest recovery (100 %) is obtained with the alloy of Cu-Al-Ni-0.7 mass% Ti after being aged at 250°C for 24 h.

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Effects of thermal aging on transformation temperatures and some physical parameters of Cu–13.5wt.%Al–4wt.%Ni shape memory alloy

Cited by 39 publications

References 18 publications

Effect of Quarterly Element Addition of Cobalt on Phase Transformation Characteristics of Cu-Al-Ni Shape Memory Alloys

Effect of Quarterly Element Addition of Cobalt on Phase Transformation Characteristics of Cu-Al-Ni Shape Memory Alloys

Avalanche criticalities and elastic and calorimetric anomalies of the transition from cubic Cu-Al-Ni to a mixture of18Rand2Hstructures

X-phase precipitation in aging of Cu–Al–Ni–xTi shape memory alloys and its influence on phase transition behavior

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