CRITICAL EXPONENTS OF THE TRANSPORT PROPERTIES AT THE B2⇔IC⇔C(R) TRANSITIONS IN Ti-Ni-Me SHAPE MEMORY ALLOYS

2000 ◽  
Vol 14 (17) ◽  
pp. 1729-1742 ◽  
Author(s):  
V. KOLOMYTSEV ◽  
V. NEVDACHA ◽  
L. BATAILLARD ◽  
R. GOTTHARDT
Keyword(s):  
Shape Memory Alloys ◽  
Shape Memory ◽  
Energy Gap ◽  
Density Wave ◽  
Normal Pressure ◽  
Gap Formation ◽  
Resistance Change ◽  
Total Enthalpy ◽  
Β Phase ◽  
Gap Opening

Critical behaviour of the physical properties at the B2⇔IC ⇔C(R) phase transitions in TiNi-based shape memory alloys has been analyzed in the frame of the charge density wave (CDW) model. Variation of total resistance at the Peierls-type B2⇔IC ⇔C(R) transition in TiNiMe (Me=Cr, Fe, Al, Ge) alloys has been found to be a sum of the β-phase normal contribution, fluctuating CDW resistance ρ f (T) in the incommensurate state and resistance change due to the energy gap formation ρc(T) in the commensurate state. The fitting parameters such as the energy gap at saturation Δ(0) and the number of electrons involved in the process of the CDW's formation ψ(0) have been determined as a function of the alloy chemical composition and thermal treatment at moderate temperature. The critical resistive fluctuations in the incommensurate phase follow a power law dρ f /dt*~t*m with critical exponent m=-1. In the frame of the CDW model this means that the process of electron scattering from periodic distortion is strongly limited to a definite plane of the crystal and system is two-dimensional. The change of ρ c with temperature is controlled by the activation energy law corresponding to electron single excitations through the gap Δ(T), with a varying ψ(T) effective number of the electrons involved in the process. The total enthalpy measured during cooling is compared with the heat calculated for the energy gap opening at the Fermi level during the IC⇒C(R) transition in the frame of the Shottky anomaly approximation. Both values are of the same order. When hydrostatic pressure is applied to the material, a small drop in the conductivity is observed around P~2 GPa and interpreted as CDW pinning by commensurability locking at a temperature higher than the transition temperature at normal pressure.

Reordering in the β-Phase of Cu-Zn-Al Shape Memory Alloys

1991 ◽  
Vol 56-58 ◽  
pp. 481-485 ◽  
Author(s):  
T. Suzuki ◽  
Y. Fujii ◽  
A. Nagasawa
Keyword(s):  
Shape Memory Alloys ◽  
Shape Memory ◽  
Β Phase

scholarly journals Evidence for a vestigial nematic state in the cuprate pseudogap phase

2019 ◽  
Vol 116 (27) ◽  
pp. 13249-13254 ◽  
Author(s):  
Sourin Mukhopadhyay ◽  
Rahul Sharma ◽  
Chung Koo Kim ◽  
Stephen D. Edkins ◽  
Mohammad H. Hamidian ◽  
...  
Keyword(s):  
Fermi Surface ◽  
Energy Gap ◽  
Density Wave ◽  
Broken Symmetry ◽  
Hole Doping ◽  
Thermal Transitions ◽  
Electronic Density ◽  
Pseudogap Phase ◽  
Nematic State ◽  
Gap Opening

The CuO2 antiferromagnetic insulator is transformed by hole-doping into an exotic quantum fluid usually referred to as the pseudogap (PG) phase. Its defining characteristic is a strong suppression of the electronic density-of-states D(E) for energies |E| < Δ*, where Δ* is the PG energy. Unanticipated broken-symmetry phases have been detected by a wide variety of techniques in the PG regime, most significantly a finite-Q density-wave (DW) state and a Q = 0 nematic (NE) state. Sublattice-phase-resolved imaging of electronic structure allows the doping and energy dependence of these distinct broken-symmetry states to be visualized simultaneously. Using this approach, we show that even though their reported ordering temperatures TDW and TNE are unrelated to each other, both the DW and NE states always exhibit their maximum spectral intensity at the same energy, and using independent measurements that this is the PG energy Δ*. Moreover, no new energy-gap opening coincides with the appearance of the DW state (which should theoretically open an energy gap on the Fermi surface), while the observed PG opening coincides with the appearance of the NE state (which should theoretically be incapable of opening a Fermi-surface gap). We demonstrate how this perplexing phenomenology of thermal transitions and energy-gap opening at the breaking of two highly distinct symmetries may be understood as the natural consequence of a vestigial nematic state within the pseudogap phase of Bi2Sr2CaCu2O8.

Study of the stability and decomposition process of the β phase in Cu–Al–Ni shape memory alloys

2006 ◽  
Vol 438-440 ◽  
pp. 734-737 ◽  
Author(s):  
J.I. Pérez-Landazábal ◽  
V. Recarte ◽  
V. Sánchez-Alarcos ◽  
M.L. Nó ◽  
J. San Juan
Keyword(s):  
Shape Memory Alloys ◽  
Shape Memory ◽  
Decomposition Process ◽  
Β Phase ◽  
The Stability

Implementation and Investigation of a Compact, Powerful System for Diagnosis and Control of Shape Memory Alloys in Technical Applications

2019 ◽  
Author(s):  
Max Kaiser ◽  
Nils Neblung ◽  
Martin Gurka
Keyword(s):  
Phase Transformation ◽  
Shape Memory Alloys ◽  
Shape Memory ◽  
Electrical Resistance ◽  
Control Strategies ◽  
Memory Systems ◽  
Constant Load ◽  
Resistance Change ◽  
Model Based ◽  
And Control

Abstract In this paper we present the development, implementation and testing of a compact system for diagnosis and control of actuators based on metallic shape memory alloys (SMA). Using NiTi-SMA, very compact, cost-effective and lightweight actuation systems can be realized. In applications where the SMA is activated by internal Joule heating or its condition is diagnosed by the self-sensing of its electrical resistance, an electrical system capable of reliably measuring very small resistance changes (&lt; 1 ohm) without affecting the phase-state of the SMA is required. In addition, the system must offer the possibility to evaluate the nonlinear, hysteresis-afflicted behavior of the SMA and to handle this difficulty, e.g. utilizing a model-based control. This paper presents a simple compact and adaptive system based on a microcontroller that meets these requirements. Detailed functional tests were carried out with the system to establish a correlation between the change in electrical resistance in the range &lt; 200 mOhm and the current strain state of the actuator. For this purpose, a first series of tests was performed, with the SMA wires working against a constant load. In a second tests series, the SMA wires worked against springs of different stiffness. The use of a microcontroller enables simple implementation of different control strategies. The control system for the non-linear resistance change utilizes a fuzzy logic which divides the control algorithm into three regimes. In the regime of the martensitic phase transformation a PI-controller is used. The state of actuators with an absolute electrical resistance &lt; 1 Ohm and a resistance change &lt; 200 mohm associated with the phase transformation can be precisely measured and controlled with an accuracy &lt; 10 mohm. The system can be configured with little effort for different tasks and shape memory systems of different sizes. Furthermore, it is possible to implement more complex control algorithms up to model-based controllers.

SEM study of diffusion bonded interfaces in Cu-Al(11,46)-Mn(6,62) and Cu-Al(6,94)- Zn(18,86) copper-based shape memory alloys

1990 ◽  
Vol 48 (4) ◽  
pp. 1004-1005
Author(s):  
F.A. Calvo ◽  
J.M. Gómez de Salazar ◽  
A. Ureña ◽  
F.J. Méndez ◽  
J.M. Guilemany
Keyword(s):  
Martensitic Transformation ◽  
Shape Memory Alloys ◽  
Shape Memory ◽  
Shape Memory Effect ◽  
Diffusion Bonding ◽  
Diffusion Processes ◽  
Experimental Unit ◽  
Β Phase ◽  
Sem Study ◽  
Temperature Time

The copper-based alloys studied belong to the group of those materials showing Shape Memory Effect (SME). Diffusion Bonding (DB) procedure is an alternative joining method of welding copper-based Shape Memory Alloys, traditionally welded by techniques like electron bean welding (EBW). However EBW provides embrittlement to the joint. This situation has been corrected by DB as confirm the SEM-EDS study presented here.A material shows SME when once has been thermomechanically deformed, it is able to recover its original (as fabricated) shape by means of a simple heat-up. This pheno menom is possible only for those materials which have β phase prone to undergo martensitic transformation. DB technique estimulates diffusion processes betwen materials by the combination of pressure, temperature, time, surface materials roughness and atmosphere condition in the experimental unit with the aid, sometimes, of a third material, in foil or plated form, which is known by the name of interlayer. The parameter set and details of attaing diffusion bonding joints procedure are under a patent developed recently by the authors .

Vibrational behavior of the β phase near martensitic transformation in Cu–Al–Ni shape memory alloys

2004 ◽  
Vol 378 (1-2) ◽  
pp. 243-247 ◽  
Author(s):  
J.I. Pérez-Landazábal ◽  
V. Recarte ◽  
J.M. Ezpeleta ◽  
P.P. Rodrı́guez ◽  
J. San Juan ◽  
...  
Keyword(s):  
Martensitic Transformation ◽  
Shape Memory Alloys ◽  
Shape Memory ◽  
Vibrational Behavior ◽  
Β Phase

Determination of the next-nearest neighbor order in β phase in Cu-Al-Ni shape memory alloys

2002 ◽  
Vol 81 (10) ◽  
pp. 1794-1796 ◽  
Author(s):  
J. I. Pérez-Landazábal ◽  
V. Recarte ◽  
R. B. Pérez-Sáez ◽  
M. L. Nó ◽  
J. Campo ◽  
...  
Keyword(s):  
Shape Memory Alloys ◽  
Shape Memory ◽  
Nearest Neighbor ◽  
Β Phase

Self-Accommodating Nature of Martensite Formation in Shape Memory Alloys

2014 ◽  
Vol 213 ◽  
pp. 114-118
Author(s):  
Osman Adiguzel
Keyword(s):  
Martensitic Transformation ◽  
Shape Memory Alloys ◽  
Shape Memory ◽  
Parent Phase ◽  
Alloy System ◽  
Phase Region ◽  
Martensite Formation ◽  
Martensite Variant ◽  
Β Phase ◽  
Phase Condition

Shape memory effect is a peculiar property exhibited by certain alloy system. This behavior is facilitated by martensitic transformation, and shape memory properties are intimately related to the microstructures of alloys; in particular, the morphology and orientation relationship between the various martensite variants. Martensitic transformation occurs in thermal manner, on cooling the materials from high temperature parent phase region. Thermal induced martensite called self-accommodated martensite or multivariant martensite occurs as multivariant martensite in self-accommodating manner and consists of lattice twins. Shape memory alloys are deformed in low temperature martensitic phase condition, and deformation proceeds through a martensite variant reorientation. Copper based alloys exhibit this property in metastable β - phase region.

Phase Transitions and Elementary Processes in Shape Memory Alloys

2015 ◽  
Vol 1101 ◽  
pp. 124-128
Author(s):  
Osman Adiguzel
Keyword(s):  
Martensitic Transformation ◽  
Shape Memory Alloys ◽  
Shape Memory ◽  
Shape Memory Effect ◽  
Memory Effect ◽  
Smart Materials ◽  
Structural Changes ◽  
Elementary Processes ◽  
Cooperative Movement ◽  
Β Phase

Shape memory effect is a peculiar property exhibited by certain alloy systems, and shape memory alloys are recognized to be smart materials. These alloys have important ability to recover the original shape of material after deformation, and they are used as shape memory elements in devices due to this property. The shape memory effect is facilitated by a displacive transformation known as martensitic transformation. Shape memory effect refers to the shape recovery of materials resulting from martensite to austenite transformation when heated above reverse transformation temperature after deforming in the martensitic phase. These alloys also cycle between two certain shapes with changing temperature.Martensitic transformations occur with cooperative movement of atoms by means of lattice invariant shears on a {110} - type plane of austenite matrix which is basal plane of martensite.Copper based alloys exhibit this property in metastable β-phase field. High temperature β-phase bcc-structures martensiticaly undergo the non-conventional structures following two ordered reactions on cooling, and structural changes in nanoscale level govern this transition cooling. Atomic movements are also confined to interatomic lengths due to the diffusionless character of martensitic transformation.

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