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Porous Ti-Nb-xSn shape memory alloys (SMAs) are fabricated by microwave sintering technology. The microstructures exhibit needle-like morphologies, β(N) (normal straight and crossed needles along with needle-like morphology that resembles spaghetti or irregular lines with α-phases in between) as well as plate-like morphologies [normal straight plate-like morphology, α′′ and dendritic plate-like morphology, β(D)]. Increases in Sn addition significantly induce an increase in the density of the α-phase. XRD patterns exhibited three phases, namely the β-main phase with smaller intensities of α′′ and α. Further, the addition of 0.25% Sn led to more effective improvement in the intensity of the α′′-phase compared with 0.5% and 1.5% Sn addition. Additions of Sn also enhanced the fracture strength and its corresponding strain along with the shape memory effect (SME), where the best enhancement was achieved at 0.25% Sn. The corrosion rate (Ri) was reduced by rising Sn content, while both corrosion resistance and antibacterial zones were increased. The lower elastic modulus, as well as the robust mechanical properties and bioactivity, made these SMAs rather suitable for biomedical application purposes, where the low elastic modulus had value in terms of avoiding the problem of "stress shielding." [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The influence of defocusing distance of the fiber laser welding on Ti-51at%Ni, Ti-28%atNb and Ti-30at%Ta shape memory alloys (SMAs) was investigated. These alloys were produced by powder metallurgy (P/M) and sintered by furnace and microwave processes. The experimental results showed that the furnace-sintered Ti-Ni welds have the maximum porosity density and the lowest weld quality. While, the microwave sintered alloys of Ti-Nb and Ti-Ta SMAs presented better weldability, even though porosities were still observed. Ti-Ta SMA showed the best welding quality compared with the other welded joints. It can be concluded that porosities play important role in the welding of powder metallurgy alloys and in order to achieve high-quality welds, the porosities should be minimized. [ABSTRACT FROM AUTHOR]

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 γ 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 γ phase represents a compound of AlCoNi. However, the presence of γ 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. [ABSTRACT FROM AUTHOR]

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 SMAs. [ABSTRACT FROM PUBLISHER]

Extensive research on the effect of spark-plasma sintering and free forging on the microstructure, transformation temperature, and superelasticity of Ti-23 at% Nb shape-memory alloys (SMAs) was undertaken. Based on the obtained results, it was found that the specimen showed significant results after deformation than the homogenization step, from which it can be concluded that the deformation has considerable effects on the mechanical properties and shape-memory characteristics of Ti-based SMAs. The microstructure of homogenized and deformed Ti-23 at% Nb SMAs consists of β, α, α′ and ω phases, while the sintered sample shows only β and α phases. Endothermic and exothermic peaks of the austenite ↔ martensite transformation are seen in the homogenized sample, then after being deformed, the exothermic peak disappeared. The highest austenite start and finish temperatures were observed with the deformed sample due to disappearance of TiNb 4 intermetallic compounds and a high percentage of β phase. The ductility of the deformed sample shows the highest value compared with the homogenized sample due the elimination of coarse α precipitates and brittle intermetallic compounds of TiNb 4 , along with the suppression of the brittle ω phase and retaining β matrix. [ABSTRACT FROM AUTHOR]