Phase transformation and microstructure behaviour of Cu-Al-Ni shape memory alloys incorporated with cobalt addition

The effect of Co addition on phase transformation temperatures and microstructures of Cu-Al-Ni SMA were investigated via differential scanning calorimetry, field emission scanning electron microscopy corresponding with energy dispersive spectroscopy and x-ray diffraction. The results revealed that the β1’ and γ1’ phases’ morphology and orientation were varied after the addition of Co along with the presence of intermetallic compounds known as γ2. This phase was indicated using the EDS and XRD is related to the intermetallic compound of Al75Co22Ni3. In addition, the phase transformation temperatures tend to increase with the addition of Co and this enhancement is mainly attributed to the variation of phase morphology and the existence of γ2 precipitates

Modeling the Physical Properties of Gamma Alumina Catalyst Carrier Based on an Artificial Neural Network

Porous γ-alumina is widely used as a catalyst carrier due to its chemical properties. These properties are strongly correlated with the physical properties of the material, such as porosity, density, shrinkage, and surface area. This study presents a technique that is less time consuming than other techniques to predict the values of the above-mentioned physical properties of porous γ-alumina via an artificial neural network (ANN) numerical model. The experimental data that was implemented was determined based on 30 samples that varied in terms of sintering temperature, yeast concentration, and socking time. Of the 30 experimental samples, 25 samples were used for training purposes, while the other five samples were used for the execution of the experimental procedure. The results showed that the prediction and experimental data were in good agreement, and it was concluded that the proposed model is proficient at providing high accuracy estimation data derived from any complex analytical equation

Microstructure, mechanical properties, and shape memory effect of annealed Cu-Al-Ni-xCo shape memory alloys

In order to develop the main applications of Cu-based shape memory alloys (SMAs), the effect of annealing time and temperature on the microstructure, mechanical properties, and shape memory characteristics of Cu-Al-Ni-xCo SMAs (x is 0.38, 0.6, and 1.2 wt.%) were studied. A distinct consideration is lent to the microstructural changes, phase transformation, and mechanical properties, which might take place in accordance with the changes in the alloying element/composition and/or heat treatment implementation. Because of this, the microstructural changes were portrayed using a variable-pressure scanning electron microscope, energy-dispersive spectrometer, and x-ray diffraction. The strength and hardness were determined using a universal Instron testing machine and Vickers hardness testing machine, respectively. The shape memory test was carried out using specially designed with an insulated system. The results indicated that the phase transformation of Cu-Al-Ni-xCo SMAs can be changed by varying the annealing temperature and time, and subsequent annealing can cause an effective impact on the shape memory effect. Moreover, it was also realized that the annealing treatment is involved in controlling the presence of γ2 phase precipitate, thereby, improving the mechanical properties. The highest fracture stress and strain of 860.94 MPa and 9.43%, respectively, were determined in the Cu-Al-Ni-0.6 wt.% Co SMAs after being annealed at 500 °C for 3 h. In particular, the Cu-Al-Ni-1.2 wt.% Co SMAs obtained 84.08% recovery, which is the highest strain recovery after being annealed at 500 °C for 3 h

Effect of a fourth alloying element on the microstructure and mechanical properties of Cu-Al-Ni shape memory alloys

The present investigation aims to enhance the mechanical properties and shape memory characteristics of Cu–Ni–Al shape memory alloys (SMAs) by alloying additional elements. These additions were found to control the phase morphology and grain size, along with the formation of different volume fractions, sizes, and distributions of precipitates. The features of the precipitates were mainly dependent on the type of alloying element. It was found that a Co (1.14 wt%) alloy gave the best overall improvement in terms of the transformation temperatures, ductility, and shape memory recovery. These improvements were mainly due to the exceptionally high presence of the γ2 phase in the microstructures of the modified alloy. The results of the current investigation were analyzed and compared to those of previous studies related to Cu–Al–Ni

Effect of Ta Additions on the Microstructure, Damping, and Shape Memory Behaviour of Prealloyed Cu-Al-Ni Shape Memory Alloys

The influence of Ta additions on the microstructure and properties of Cu-Al-Ni shape memory alloys was investigated in this paper. The addition of Ta significantly affects the green and porosity densities; the minimum percentage of porosity was observed with the modified prealloyed Cu-Al-Ni-2.0 wt.% Ta. The phase transformation temperatures were shifted towards the highest values after Ta was added. Based on the damping capacity results, the alloy of Cu-Al-Ni-3.0 wt.% Ta has very high internal friction with the maximum equivalent internal friction value twice as high as that of the prealloyed Cu-Al-Ni SMA. Moreover, the prealloyed Cu-Al-Ni SMAs with the addition of 2.0 wt.% Ta exhibited the highest shape recovery ratio in the first cycle (i.e., 100% recovery), and when the number of cycles is increased, this ratio tends to decrease. On the other hand, the modified alloys with 1.0 and 3.0 wt.% Ta implied a linear increment in the shape recovery ratio with increasing number of cycles. Polarization tests in NaCl solution showed that the corrosion resistance of Cu-Al-Ni-Ta SMA improved with escalating Ta concentration as shown by lower corrosion current densities, higher corrosion potential, and formation of stable passive film

Shape memory characteristics of microwave sintered porous Ti–30 at.%Ta alloy for biomedical applications

In this work, the influence of microwave sintering time and temperature on the microstructure characterisation, and thermal and mechanical behaviours of Ti–30Ta were investigated. The relative densities of Ti–30Ta samples were in the range of 65–72% and as the sintering times/temperatures increased, the relative density decreased. The pore size averages were in the range of 6–17 µm with different sintering parameters, for instance the smallest pore size of 6.8 µm was observed after being sintered at 900 ℃ for 30 min (Ta2). Two morphologies of plate-like (P) and needle-like (N) structures were observed, as well as two regions – dark region (Ti-rich region) and bright region (Ta-rich region), also two phases – β and α. The DSC results revealed that the Ms to Mf transformation range was 98.86 to 80.5 ℃, respectively, while the range of As to Af transformation was about −22.35 to 92 ℃, respectively. The maximum fracture strength and its strain were acquired in the sintered sample of 900 ℃ for 30 min. The total strain recovery (ɛT) was improved linearly as the sintering temperature increased, correspondingly, the best ɛT was implied in Ti–Ta shape memory alloys after being sintered at 1000 ℃ for 30 min (Ta4)

The influence of γ-irradiation on the structure and properties of the Cu-11.5 wt. % Al-4 wt. % Ni shape memory alloys

This study investigated the influence of 60Co-γ-irradiation on the structure and properties of Cu-Al-Ni shape memory alloys. The phase transformation temperatures were evaluated by differential scanning calorimeter (DSC). It was found that the γ-irradiation had a complex influence on the phase transformation parameters of Cu-Al-Ni SMAs. However, the transformation temperatures were shifted and a new curve was obtained after exposure to different irradiation doses. The thermodynamic parameters such as enthalpy and entropy tended to increase/decrease depending on the amount of the exposure. The structural properties of the exposed samples were studied by using optical microscopy and hardness measurements at room temperature. It was also found that the structural-properties of the Cu-Al-Ni SMAs were completely affected by the amount of the applied γ-irradiation dose

Effects of quenching media on phase transformation characteristics and hardness of Cu-Al-Ni-Co shape memory alloys

This paper presents the investigation on the effects of various thermal treatments and quenching media on the phase transformation behaviour of Cu-Al-Ni-Co shape memory alloys (SMAs). The transformation temperatures were determined using a differential scanning calorimeter. The variation of cooling rates had a consequential effect on the phase transformation characteristics of the Cu-Al-Ni-Co SMAs. Nevertheless, the transformation temperature peaks were varied in terms of location as well as heat flow. The results indicated that there was an improvement in transformation temperatures whenever ice water was used as quenching medium. It was also observed that the forward transformation temperatures were higher than the reverse transformation. It was verified that the required heat for the transformation of martensite into austenite was more than the transformation of austenite into martensite. Moreover, thermodynamic parameters, such as enthalpy and entropy, tended to decrease and increase as a result of the changes in the cooling rates of each medium. To clarify the variations of the structures and properties of Cu-Al-Ni-Co SMA quenched samples, x-ray diffraction, atomic force microscopy, field emission scanning electron microscopy, energy dispersive spectroscopy, and Vickers hardness were used

Effect of Sn additions on the microstructure, mechanical properties, corrosion and bioactivity behaviour of biomedical Ti–Ta shape memory alloys

Ti–Ta and Ti–Ta–xSn shape memory alloys (SMAs) were produced successfully by microwave sintering. Tin element was added to Ti–Ta SMA with three different atomic percentages (0.37, 0.745 and 2.26 at.%). The influences of Sn addition on microstructure, transformation temperatures, mechanical properties, shape memory behaviours, corrosion resistance and bioactivity were investigated. It was found that the morphologies of the modified and unmodified Ti–Ta alloys contain a plate-like and needle-like structure, where the former structure is related to the β phase and the latter related to the α phase. The transformation temperatures of Ms to Mf with and without Sn additions were observed to be in the range of 389.65 to 355 K, while the transformation temperatures of As to Af were found to be in the range of 250.42 to 365.8 K. By increasing the proportion of Sn, the compressive fracture strength and shape memory behaviour were enhanced; however, the corrosion resistance tended to be decreased. Based on the bioactivity results, antibacterial activity was improved with the addition of Sn. In conclusion, the existent results indicate that Ti–30 at.% Ta SMAs may be a convenient alternative to Ni–Ti for certain biomedical applications