A review on shape memory metallic alloys and their critical stress for twinning

Abstract

Shape Memory Alloys (SMAs) is a class of smart materials with the ability to remember the original shape. SMAs exhibit stress-induced martensitic transformation through twinning which is an important deformation mechanism that renders strength and ductility. Tailoring the capability of alloys for deformation twinning enables to optimize their mechanical performance. This paper presents a comprehensive review on the effect of internal and external parameters on the twinning propensity. Among these parameters, the effect of the composition, grain size, temperature and strain rate will be explored. In addition the use of shape memory phase as a strategy to improve the ductility of metallic use memory behaviour is of great importance to develop SMAs for multiple applications including mechanical, automotive, aerospace, civil and biomedical industries. A tentative outlook about the challenges and proposed solutions will be also discussed.

Shape Memory Corrosion-Resistant Polymeric Materials

“…However, shape recovery for alloys can be more easily tested for and determined via bending tests where the alloy is bent to a certain angle under a certain maximum strain and then recovery may then be induced by heating to a temperature specific to the alloy and subsequently letting cool to room temperature, which allows for the shape memory ratio to be calculated based on the returning angle of the sample [7]. Nickel-titanium, copper, and iron form the basis for some of the more common shape memory alloys [10,11]; a brief overview can be found in Table 1.…”

“…Additionally, the performance of shape memory alloys may be enhanced through the addition of tertiary or quaternary elements [9,11]. Typically, these shape memory alloys are reinforced with chromium, aluminum, nickel, manganese, copper, silicon, nitrogen, or rhenium, but the addition and quantity of these elements in the alloy may risk sacrificing the superelasticity of the alloy, especially at room temperature conditions [9].…”

“…As mentioned previously, transformations are induced in a shape memory alloy through heating; this is a cause for concern for the application of shape memory polymers as a means of corrosion protection as they may have differing temperatures to induce transformation. This concern may be alleviated by the limitation that most current shape memory alloys have transition temperatures below 100°C; thus, it is possible for polymers to act as a means of corrosion inhibition [11]. For instance, most DA adducts form at temperatures of around or below 90°C and dissociate at temperatures ranging from 110 to 130°C.…”

“…Markets are pushing towards developing hightemperature shape memory alloys capable of transformation temperatures much higher than 100°C. However, any attempts at forming stable materials higher than 100°C are frustrated by the issue that exposure to large amounts of thermal energy affects the rate-dependent processes that occur within the material and therefore affects the microstructural stability, its resistance to deformation, the recovery, and the environmental resistance [11]. Matching the developments has been the development of high-temperature shape memory polymers; one such example would be that of a selfhealing high-temperature polyimide which has an operational temperature of 243°C if polystyrene is incorporated into the polymer [37].…”

Self-Healing in Titanium Alloys: A Materials Science Perspective

“…Shape Memory Alloys (SMAs) are special materials with great potential in various engineering applications since they possess a number of unique characteristics, including superior energy dissipation capacity compared to normal metallic materials [39]. Other beneficial properties, apart from SMEs, including superelasticity, favorable damping ability and other important characteristics of shape memory alloys, allow it to be applied in a wide range of fields, including electronic, chemical, medical devices, electricity, aerospace, etc.…”