Papers by Keyword: Super Elasticity

Abstract: Smart materials are a class of materials characterized by having a different behavior due to external stimulation, which can be mechanic, thermal, electric, or magnetic. This chapter approaches the different types of smart materials and their classification according to the material’s nature (fluid, ceramic, polymeric and metallic). Emphasis is given to the theoretical study of the metallic materials with shape memory, presenting the fundamentals, crystallographic study and the mathematical methods of phase transformation. Due to these metallic material’s unique features, shape memory effect and super elasticity, the usage in the production of composite structures has gained space. Such materials present several advantages if compared to traditional composites being subject of research for several industrial applications

Abstract: In the paper is shown the study of super elasticity of Ni-Ti shape memory alloys from the point of view of stored energy, strain dependencies and martensitic transformations that influence superelasticity of Ni-Ti shape memory alloys [1]. We also present the influence of temperature and alloy composition on the properties of Ni-Ti alloys after plastic deformation and heat treating [2].

Abstract: Shape memory thin films deposited by sputtering are attractive candidates for micro-electro-mechanical-system (MEMS) because of their large deformation and strong recovery force. In the present study Ni-Ti thin films have been deposited on NaCl substrates by DC magnetron sputtering source fitted with an 80mm diameter alloy target. In order to obtain a variety of film compositions, several discs of alloy target, which prepared in vacuum arc remelting (VAR), were used. Three types of thin films have been deposited; Ti and Ni-rich thin films were separately deposited on NaCl substrate and also a composite layer of Ni45Ti50Cu5 and Ni-rich. The as deposited Ni-Ti thin films were crystallized to change the amorphous structure to a nanostructured material to characterize shape memory and superelastic behaviors. The effect of composition on film structure and mechanical behavior was studied by using X-ray diffraction (XRD) and nanoindentation. The results of thin films behavior were used to calculate the thickness ratio of be-layer composite NiTi to obtain enhanced shape memory behavior.

Abstract: A Ni-rich Ti-50.7.at%Ni alloy was processed by Equal Channel Angular Extrusion (ECAE) at 500°C. After 8 passes ECAE, microstructure was refined to sub-micron scale, approximately 0.2 μm～0.3 μm. TEM observation reveals that Ti3Ni4 phase precipitated in Ni-rich Ti-50.7.at%Ni alloy during the preheating treatment before each ECAE pass, but re-dissolved during sequent ECAE processes. After ECAE treatment, the B2R transformation occurred within a larger temperature range. Comparing with the solution-treated TiNi specimen, the martensitic transformations start (Ms) and peak temperatures (Mp) of TiNi specimens ECAEed were dramatically lowered. Super-elasticity characteristics of TiNi alloy were tested by tensile loading and unloading cycles. The results reveal that at a tensile strain of 4% or smaller, ultrafine-grained (UFG) TiNi alloy processed by 4 passes ECAE shows better super-elasticity than solution-treated sample. Microstructure evolution and its effect on phase transformations and super-elasticity characteristics have been discussed.

Abstract: In order to investigate the performance of shape memory alloy wire, two types of alloy wire were studied. The results showed that the phase transition temperature of the superelastic wire were: Ms and Mf were 21.18 °C and 7.08 °C; As and Af were 12.32 °C and 25.13 °C. The phase transition temperature of memory effect alloy wire were that Ms =- 11.85 °C, Mf =- 29.37 °C, As = 36.77 °C, Af = 43.35 °C. By the tensile test of the SMA wire, the stress - strain curves of the two kinds of alloy wire were obtained.

Abstract: In this paper, single crystal of CuAlNiBe shape memory alloy (SMA) was prepared in a high temperature gradient directional solidification furnace with a selective growing crystallizer. And its performance characters were systematically studied. The results show that the mechanical and shape memory properties of the single crystal of CuAlNiBe SMA alloy has much better than that of the polycrystalline material. This may be explained that the stress concentration at grain boundary caused by the difference of bilateral strains is the dominant reason of deterioration of fatigue properties; therefore single crystal alloy possesses the excellent properties duo to its elimination of grain boundary.