Tensile Failure of 55-Nitinol Wire

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100113858 ◽

1975 ◽

Vol 33 ◽

pp. 46-47

Author(s):

F. I. Grace

Keyword(s):

Shape Memory ◽

Shape Memory Effect ◽

Memory Effect ◽

Stoichiometric Composition ◽

Tensile Failure ◽

Initial State ◽

Initial Shape ◽

Nitinol Wire ◽

Cscl Type ◽

Shear Transformation

An interest in NiTi alloys with near stoichiometric composition (55 NiTi) has intensified since they were found to exhibit a unique mechanical shape memory effect at the Naval Ordnance Laboratory some twelve years ago (thus refered to as NITINOL alloys). Since then, the microstructural mechanisms associated with the shape memory effect have been investigated and several interesting engineering applications have appeared.The shape memory effect implies that the alloy deformed from an initial shape will spontaneously return to that initial state upon heating. This behavior is reported to be related to a diffusionless shear transformation which takes place between similar but slightly different CsCl type structures.

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High performance shape memory effect in nitinol wire for actuators with increased operating temperature range

Functional Materials Letters ◽

10.1142/s1793604714500635 ◽

2014 ◽

Vol 07 (05) ◽

pp. 1450063 ◽

Cited By ~ 10

Author(s):

Riccardo Casati ◽

Carlo Alberto Biffi ◽

Maurizio Vedani ◽

Ausonio Tuissi

Keyword(s):

Shape Memory ◽

Shape Memory Effect ◽

Memory Effect ◽

High Performance ◽

Room Temperature ◽

Operating Temperature ◽

Niti Wire ◽

Shape Memory Actuators ◽

Nitinol Wire ◽

Operating Temperature Range

In this research, the high performance shape memory effect (HP-SME) is experimented on a shape memory NiTi wire, with austenite finish temperature higher than room temperature. The HP-SME consists in the thermal cycling of stress induced martensite and it allows achieving mechanical work higher than that produced by conventional shape memory actuators based on the heating/cooling of detwinned martensite. The Nitinol wire was able to recover about 5.5% of deformation under a stress of 600 MPa and to withstand about 5000 cycles before failure. HP-SME path increased the operating temperature of the shape memory actuator wire. Functioning temperatures higher than 100°C was reached.

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Thermoelastic Martensitic Transformations and the Nature of the Shape Memory Effect

MRS Proceedings ◽

10.1557/proc-21-657 ◽

1983 ◽

Vol 21 ◽

Cited By ~ 6

Author(s):

C. M. Wayman

Keyword(s):

Single Crystal ◽

Shape Memory ◽

Crystal Structures ◽

Shape Memory Effect ◽

Memory Effect ◽

Shape Change ◽

Parent Phase ◽

Shape Deformation ◽

Initial Shape ◽

Plate Group

ABSTRACTInvestigations of the shape memory effect in alloys forming thermoelastic martensites with various crystal structures (2H, 3R, 9R and 18R) reveal that universal behavior exists. A unified explanation of the martensite deformation processes and subsequent shape recovery is now in hand, even though the various martensites are both internally twinned and internally faulted and, in addition, have different crystal structures. In cases studied to date, an initial parent phase single crystal transforms into self-accommodating arrangements of martensite variants (plates) which are characterized by “plate groups.” Each group consists of four variants. The average shape deformation in a plate group is essentially zero.Upon stressing below the Mf temperature the martensite undergoes deformation by detwinning (2H and 3R only), variant-variant coalescence and twinning processes, and further group-to-group coalescence. The deformed specimen eventually becomes a single crystal of martensite consisting of that particular habit plane variant whose shape deformation permits maximum extension in the direction of the applied stress. The deformed martensite persists after unloading has occurred; reverse rearrangements of twins and variants do not occur. Specimens deformed below Mf regain their initial shape characteristic of the initial parent phase upon heating from As to Af, during which the single crystal of martensite obtained by stressing the 24-variant configuration transforms back to the original parent phase single crystal in a unique manner, which is basically a simple “unshearing” process. The unshearing is the essence of the memory.The two-way shape memory effect results after the initial martensitic transformation upon cooling is preprogrammed by the introduction of stresses which preferentially bias the transformation so that only a single variant of martensite forms upon cooling. The shape change of this single variant causes the characteristic spontaneous “bending” upon cooling. The characteristic “unbending upon heating is as with the conventional “one-way” shape memory effect.

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Shape memory effect of laser welded NiTi plates

Functional Materials Letters ◽

10.1142/s1793604715500691 ◽

2015 ◽

Vol 08 (06) ◽

pp. 1550069 ◽

Cited By ~ 20

Author(s):

J. P. Oliveira ◽

F. M. Braz Fernandes ◽

N. Schell ◽

R. M. Miranda

Keyword(s):

Laser Welding ◽

Shape Memory ◽

Shape Memory Effect ◽

Memory Effect ◽

Microstructural Analysis ◽

Industrial Applications ◽

X Ray Diffraction ◽

Initial Shape ◽

Bending Tests ◽

Remarkable Result

Laser welding is a suitable joining technique for shape memory alloys (SMAs). This paper reports the existence of shape memory effect (SME) on laser welded NiTi joints, subjected to bending tests, and correlates this effect with the microstructural analysis performed with X-ray diffraction (XRD). All welded samples were able to recover their initial shape after bending to 180°, which is a remarkable result for industrial applications of NiTi involving laser welding.

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