Twinning-Induced Elasticity in NiTi Shape Memory Alloys

Abstract

Pseudoelasticity (PE) in shape memory alloys relies on the formation of stress-induced martensite during loading and on the reverse transformation during unloading. PE yields reversible strains of up to 8 % and is applied in applications such as medical implants, flexible eye glass frames, damping elements, and others. Unfortunately, PE shows a strong temperature dependence and thus can only be exploited within a relatively narrow temperature window. The present work focuses on a related process, which we refer to as twinning-induced elasticity (TIE). It involves the growth and shrinkage of martensite variants which are stabilized by dislocations, which are introduced by appropriate cold work. TIE yields reversible strains of the order of 3 %. The TIE effect does not suffer from the strong temperature dependence of PE. The weak temperature dependence of mechanical TIE properties makes TIE attractive for applications where temperature fluctuations are large. In the present work, we study the TIE effect focusing on Ni 50 Ti 50 shape memory alloy wires. The degree of plastic pre-deformation of the initial material represents a key parameter of the ingot metallurgy processing route. It governs the exploitable recoverable strain, the apparent Young's modulus, and the widths of the mechanical hysteresis. Dynamic mechanical analysis is used to study the effects of pre-deformation on elementary microstructural processes which govern TIE.

Fabrication of Thermal Plasma Sprayed NiTi Coatings Possessing Functional Properties

“…This corresponds with the typical response of a martensite-phase NiTi shape memory alloy at room temperature observed from the bending and tensile response of samples [33]. The hysteresis response is more prominent towards lower temperatures (≤50 • C) with the unrecovered strain that correlates to the twinned martensite phase [34]. On loading, the twinned martensite NiTi shape memory alloy deforms to a detwinned martensite with the unrecovered strain upon unloading.…”

Microstructure and Mechanical Property Correlation Between Rotary Friction Welded Nitinol–Nitinol Joints

“…Martensite formation from austenite would result in slip and dislocation network formation to facilitate the volumetric change of the martensite. Also, martensite is formed preferentially during a cold deformation process to release the local stress fields (Fernandes et al, 2011;Birk et al, 2016). Figure 2C shows the EDS spectrum of the nitinol base metal.…”

Влияние Пластической Деформации В Мартенситном Состоянии На Развитие Эффектов Сверхэластичности И Памяти Формы В Сплавах На Основе Никелида Титана

“…Это сверхупругость второго типа, не связанная с протеканием МП. По классификации [4], twinning-pseudoelasticity, а в последнее время используется формулировка twinninginduced elasticity [6]. Ранее передвойникование мартенситной фазы наблюдалось в сплавах на основе меди, например Cu−Al−Ni [7].…”