Papers by Keyword: Shape Memory Properties

Abstract: Due to their properties, potential for demonstrating shape memory behavior, and cheaper cost, copper-based SMA materials hold great promise for use in a variety of industrial and medical applications. This work used powder metallurgy to create Cu-based SMA using Cu-25Zn-4Al as the master alloy. The master alloy having Beryllium additions of (0.4, 0.8, and 1.2%wt.) was studied. After combining the powders, all samples were compacted using compaction stresses of (800 MPa). Then, the process of sintering in a tube furnace using argon gas has been accomplished in three stages, the first stage lasting two hours at 350°C, the second lasting two hours at 550°C, and the third lasting three hours at 900°C. All samples are treated with a solution heat treatment that involves heating them to 850 °C for an hour, quenching them quickly in saline ice water, and then aging them at 450 °C for 180 minutes. According to linear polarization tests the adding 1.2 weight percent of the Be to the base alloy (Cu-25Zn-4Al alloy) decreased corrosion rate by (95%) as compared to the base sample in a 3.5 weight percent NaCl solution. Keywords-Cu-Zn-Al shape memory alloys, corrosion behavior, shape memory properties, Beryllium, microstructure

Abstract: Additive manufacturing (AM) is a prominent technology in the industrial fields such as aerospace, medical, automotive and so on. Especially, selective laser melting (SLM) process is available to create three-dimensional complicated structures of various alloys such as stainless steel, titanium alloy, aluminium alloy, nickel-based superalloy and so on. And also, copper and copper alloys are used as a material for products with complicated shape, electrical components, and a heat exchanger because of having the high electrical conductivity and the high thermal conductivity. It is known that copper alloys show a good shape memory behaviour by adding Al, Ni and Zn. Especially, Cu-Al-Ni alloy shows a good shape memory properties at high temperature. However, it is difficult to fabricate high-density Cu-Al-Ni alloy by the SLM process. This is mainly because Cu-Al-Ni alloy has high elastic anisotropy and brittleness in polycrystalline state. In this research, the optimum fabrication condition of Cu-Al-Ni alloy by SLM process was investigated. The optimum laser power and scan speed were able to be found by evaluating the surface morphology, density and microstructure of the as-build specimens.The maximum density of the as-built specimen was 99.47%.

Abstract: Shape memory composites and structures were produced by using carbon fiber reinforced prepregs and a shape memory epoxy resin. The matrix of the prepregs was an epoxy resin as well but without remarkable shape memory properties. This way, two different technical solutions were adopted. Shape memory composite tubes and plates were made by adding a shape memory layer between two carbon fiber reinforced skins. An optimal adhesion between the different layers was achieved thanks to the compatibility of the prepreg matrix and the shape memory material. Shape memory composite structures were also produced by joining composite shells with shape memory foams. Mechanical, dynamic mechanical and shape recovery tests were carried out to show the properties of the composite materials and structures. Results confirm the ability of this class of materials to easily change their shape without affecting the mechanical stiffness of the recovered structures.

Abstract: In order to increase critical stress for slip in Ti-Nb base shape memory alloys, strengthening by carbon additions (0.2 and 0.5mass%C) to Ti-27mol%Nb was investigated. It was found that all the alloys were  (bcc) phase at room temperature, and TiC existed in C-added alloys. The grain size was decreased with carbon content due to grain boundary pinning. Texture measurement revealed that strong {112}<110> recrystallization texture was formed in C-free alloy and that weak {001}<110> texture in C-added alloys. Tensile tests revealed that clear superelasticity appeared in C-free alloy but that stress-induced martensitic transformation seems to be suppressed by TiC in C-added alloys. The critical stress for slip was linearly increased by carbon content. Then, carbon addition affects the shape memory properties of TiNb alloys, and is effective to enhance the critical stress for slip.

Abstract: Crystal structures and shape memory properties of Ti-rich Ti52Ni23Cu25 (at.%) ribbon annealed at 450°C for 10 min and 1 h were investigated by X-ray diffraction and dynamic mechanical analyzer. As-spun ribbon was full amorphous and its crystalline peak temperature is 455.4°C. The annealed ribbon is crystallized with strong preferential (110)-B2 orientation. It shows a well-defined shape memory effect and the transformation hysteresis for the annealed ribbon under an external load in the range of 3-9 N is about 38.5°C. With annealing time increasing from 10 min to 1 h, the maximum of transformation strain under the external stress decreases from 1.93% to 1.7%. The temperature dependence of the external stress increases from 0.3 N/°C to 0.43 N/°C. The residual plastic strain is up to about 0.4% at a load of 9 N.

Abstract: Biodegradable novel poly(D,L-lactide)-based shape memory polymers (SMPs) were prepared from poly(D,L-lactide) (PDLLA) Diols, hexamethylene diisocyanate(HDI) and butanediamine(BDA) via two steps polymerization reaction. Its thermal, mechanical properties and shape-memory behaviors were investigated by means of differential scanning calorimetry, stress-strain measurements and bending test. The glass transition temperature of the SMPs changes with composition from 38 to 45°C which close to body temperature in a predictable manner. These type SMPs can achieve the high modulus and tensile strength, and their elongation at break can be greater than 500% at lower hard segment content. All SMPs display excellent shape-memory properties. When a deformation temperature 20°C above Tg was chosen, the ratio of the shape-memory fixation approximately 100%, and the recovery ratio was 95-100%. Meanwhile, the recovery time is relevant to the recovery temperature, the recovery time decrease with increasing the recovery temperature. By adjusting the composition of SMPs, the recovery temperature could be adjusted to the neighborhood of the body temperature and it can be designed as potential biomaterials for use in biomedical fields.