Abstract
Successful one-step manufacturing of micro-foils of NiTi shape memory compound by pulsed-current sintering of nickel and titanium is reported. Sandwich-like starting configurations of Ni/Ti/Ni (ST1, ST4), Ti/Ni/Ti (ST3), and a simple Ni/Ti (ST2) one, were used. XRD and differential scanning calorimetry (DSC) measurements revealed multistep martensitic transformation, much more pronounced for ST1 than for ST2 and ST3. SEM/energy dispersive X-ray spectrometer (EDS) measurements showed the predominant NiTi phase in ST1, ST4, and other intermetallic compounds in addition to it, for ST2 and ST3. The temperature dependence of the electrical resistance for ST4 shows a peak corresponding to the R-phase and a high residual resistivity. The shape memory effect of 100% was obtained for ST1 and ST4, with the temperature range of its recovery dependent on the initial strain. The ST2 and ST3 materials revealed brittleness and a lack of plasticity due to the dominancy of the austenite phase and/or the intermetallic compound content.
Highlights
Ni-Ti alloys have been a subject of interest to many scientists and engineers in the world.Their extraordinary properties (e.g., super-elasticity and shape memory effect (SME) of the NiTi compound) have found applications in many areas of industry [1,2,3]
The present paper focuses on the possibility of one-step fabrication of NiTi shape memory micro-foils by pulse-current pressure sintering from elemental micro-foils of their lowest number
The appropriate sets of elemental foils were placed into graphite dies of the pulse-current pressure sintering machine (PLASMAN, S S Alloy Co., Ltd., Hiroshima Prefecture, Japan) between two 1 mm thick tantalum foils, with a protective thin layer of boron nitride sprayed on their outer surfaces
Summary
Ni-Ti alloys have been a subject of interest to many scientists and engineers in the world. Their extraordinary properties (e.g., super-elasticity and shape memory effect (SME) of the NiTi compound) have found applications in many areas of industry [1,2,3]. SME originates in them from the martensitic and the reverse martensitic transformations due to external stress and thermal treatment (martensite, B19’ monoclinic phase ↔ austenite, B2 cubic phase) [4]. Vacuum melting methods are mainly used, and deposition methods are applied in the case of thin films [8], e.g., magnetron sputtering, pulsed laser deposition (PLD) [9,10], or biased target ion beam deposition (BTIBD) [11].
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