Cu-Al-based high temperature shape memory alloys are preferred commonly due to their cheap costs and shape memory properties. In recent years, studies have been conducted on developing and producing a new type of Cu-Al based shape memory alloy. In this study, the CuAl-Cr alloy system, which has never been produced before, is investigated. After production, the SEMEDX measurements were made in order to determine the phases in the Cu84–xAl12Crx+4 (x = 0, 4, 6) (weight %) alloy system; and precipitate phases together with martensite phases were detected in the alloys. The confirmations of these phases were made via x-ray measurements. The same phases were observed by XRD diffractogram of the alloys as well. The values of transformation temperature of alloys were determined with Differential Scanning Calorimetry (DSC) at 20°C/min heating rate. According to the DSC results, the transformation temperature of the alloys varies between 320°C and 350°C. This reveals that the alloys show high temperature shape memory characteristics.

The article presents a constitutive model for Shape Memory Alloys (SMA) along with result of dynamic simulations of SMA model. The applications of devices incorporating SMA in civil engineering focus mostly on mitigation of the seismic hazard effects in new-build and historical buildings or improvement of fatigue resilience. The unique properties of SMA, such as shape memory effect and superelasticity give promising results for such applications. The presented model includes additional phenomenon of SMA – internal loops. The paper shows the method of formulation of physical relations of SMA based on special rheological structure, which includes modified Kepes’s model. This rheological element, introduced as dual-phase plasticity body, is given in the context of martensite phase transformation. One of the advantages of such an approach is a possibility of formulation of constitutive relationships as a set of explicit differential equations. The application of the model is demonstrated on example of dynamic simulations of three dimensional finite element subjected to dynamic excitation.

In this work, vacuum hot pressed Ni-Mn-Sn-In Heusler alloys with different concentration of In (0, 2 and 4 at.%), were investigated. The magneto-structural behaviour and microstructure dependencies on chemical composition and on heat treatment were examined. It was found that the martensite start transformation temperature increases with growing In content and to a lesser extent with increasing temperature of heat treatment. The high energy X-ray synchrotron radiation results, demonstrated that both chemical composition as well as temperature of heat treatment slightly modified the crystal structures of the studied alloys. Microstructural investigation performed by transmission electron microscopy confirmed chemical composition and crystal structure changes in the alloys.

In the present study, the corrosion behaviors of amorphous-nanocrystalline Ni50Ti50 shape memory alloy with different crystallite sizes were investigated. The Ni50Ti50 homogenized specimens were hot rolled and annealed at 950°C. Thereafter, the nanocrystalline Ni50Ti50 specimens with different crystalline sizes in the range of 40-350 nm were prepared by cold rolling and annealing at temperature range of 400 to 900oC. The corrosion resistance of Ni50Ti50 specimen with coarse grain size has significantly increased after cold rolling as a result of the formation of amorphous-nanocrystalline structure. The amorphous and nanocrystalline (with the crystallite size of about 40 nm) Ni50Ti50 samples exhibited the best corrosion resistance in the 5% HCl electrolyte with the corrosion potential and corrosion current density of about –197 mV and 2.34×10–6 A/cm2, respectively. This effect can be attributed to the higher density of crystalline defects in amorphous and nanocrystalline structures to quickly form protective films on the surface.

Samples prepared using various additive manufacturing methods were compared in terms of structure, texture, transformation temperature and superelastic properties. Samples manufactured using laser engineered net shaping (LENS) method showed texture several degrees deviated from the <001> build direction, however with composition near to the initial powder composition, enabling superelastic effect. The electron beam additive manufacturing (EBAM) samples showed martensitic structure at room temperature due to a shift of transformation temperatures to the higher range. This shift occurs due to a lower Ni content resulting from different processing conditions. However, EBAM method produced sharper <001> texture in the build direction and made it possible to obtain a good superelastic effect above room temperature. Intermetallic particles of size 0.5-2 mm were identified as Ti2Ni phase using EDS and electron diffraction analyses. This phase was often formed at the grain boundaries. Contrary to the LENS method, the EBAM prepared samples showed Ni-rich primary particles resulted from different processing conditions that reduce the Ni content in the solid solution thus increase the martensitic transformation temperature. Ageing at 500°C allowed for shifting the martensitic transformation temperatures to the higher range in both, LENS and EBAM, samples. It resulted from the formation of Ni rich coherent precipitates. In samples prepared by both methods and aged at 500°C, the presence of martensite B19’ twins was observed mainly on {011} B19’ planes.

Two single crystals with compositions Fe-Ni-Co-Al-Ta and Fe-Ni-Co-Al-Ta-B were selected and fabricated by Bridgman method. Subsequently, ingots were homogenized, oriented and subjected to a two-step heat treatment process in order to obtain fine and coherent γ' precipitates. Subsequently, superelastic cycling experiments were performed at 77 K. The next step included detailed microstructural characterization using transmission electron microscopy and high-energy synchrotron X-ray diffraction measurements together with Rietveld refinement. The results show that the number of fully reversible superelastic strains is very sensitive to the size of γ' precipitates. The smaller (3 nm) γ' precipitates ensured more superelastic response compared to material with larger γ' particles size (5 nm), in which the material did not receive its original shape after 10 cycles even after being heated.

In this study, a simple and effective way to fabricate highly porous scaffolds with controlled porosity and pore size is demonstrated. Ti-7Zr-6Sn-3Mo shape memory alloy fibers were prepared through a melt overflow process. The scaffolds with porosity of 65-85% and large pores of 100-700 μm in size were fabricated by sintering the as-solidified fibers. Microstructures and transformation behaviors of the porous scaffolds were investigated by means of SEM, DSC and XRD. The scaffolds were composed of β phase at room temperature. Superelasticity with the superelastic recovery strain of 7.4% was achieved by β↔α” phase transformation. An effect of porosity on mechanical properties of porous scaffolds was investigated by using compressive test. As the porosity increased from 65% to 85%, elastic modulus and compressive strength decreased from 0.95 to 0.06 GPa and from 27 to 2 MPa, respectively.

FeMnSiCrNi alloys represent a promising class of FeMnSi-based shape memory alloys (SMAs) characterized by excellent characteristics of formability and corrosion resistance. The present paper is focused on a 68Fe-18Mn-3Si-7Cr-4Ni (mass. %) SMA, produced by powder metallurgy routine, which was tested to creep, using a dual cantilever specimen holder, and analyzed by means of the dedicated software of a dynamic mechanical analyzer. The specimens were tested at five temperatures by applying, at each of them, four bending force values, during 2000 s. The variation of bending creep deflection with time, temperature and force was discussed both from the point of instant value and 1000 s-value. These results enabled plotting a space diagram of stabilized creep rate variation with both applied force and test temperature. In such context, a theoretical model in a multifractal paradigm of motion was built, considering that FeMnSiCrNi shape memory alloy can be assimilated, both structurally and functionally, with a multifractal object. Finally, this model was validated by means of experimental data.