Results are reported about the pseudoelastic cycles β-martensite obtained by compression of β Cu-Zn-Al single crystals with electronic concentration 1.52. Stress-strain curves at different temperatures and in situ observations were carried out. The results are compared with those obtained from tension test.

The lattice relaxation at the type I faults in the 18R martensite was studied by high resolution TEM. Local atomic plane rotations and small changes of the interplanar distances were observed over a distance of 1.5 nm. It is shown that this distorted region can be rationalized as an intermediate structure between the martensite and the second variant of the parent phase.

Thin films of near-equiatomic titanium-nickel are capable of thermally induced shape-strains and have recently been applied to silicon-based micromachined reversible actuators in force-production devices requiring energy-density levels substantially exceeding those available from piezoelectric, electromagnetic, electrostatic, or bimetal systems. Reversible actuation requires the presence of a resetting agent, or ‘bias’ force, capable of deforming the martensite phase during the exothermic transformation on cooling. Here, we show that both the initial martensite ‘programming’ force, and the bias force for subsequent reversible actuation, can readily be provided by manipulating intrinsic and extrinsic stresses developed during low-pressure sputter deposition of TiNi, and subsequent cooldown from either the deposition process temperature or from the crystallization annealing temperature. The stability of both intrinsic and extrinsic stresses at temperatures below the deposition temperature allows considerable flexibility in the design of the force-producing system, and reversible stress-production to levels beyond 0.7 GPa are shown to be readily achieved, corresponding to energy-density levels approaching 10 MJ-m−2. The present paper will review recent results from our group on the development of residual stresses in TiNi sputtered on (100) Si, using the wafer-curvature method applied during isochronal and isothermal vacuum annealing of both amorphous and crystalline thin films, with an emphasis on the combined influence of deposition temperature and annealing temperature on stress-relaxation rates, and on the response of the system to temperature cycling in the displacive transformation range.

Shape memory alloys are known for their ability to build up large deformations under an applied stress, either in martensitic phase or in the pseudoelastic region.

The electrical resistance of shape memory alloys, traditionally used to define the transformation temperatures, shows interesting features when considering its modification as a function of strain. The electrical resistance in NiTiCu ribbons, obtained by melt spinning, is here examined, either in martensite or in the pseudoelastic range or under a constant applied stress across the transformation range. In each examined case, the results obtained show that the electrical resistance follows a linear relationship as a function of the imprinted strain.

Free-standing shape memory thin films of the system Ti-Ni-Pd-Cu exhibiting the two-way-effect have been fabricated by d.c. magnetron sputtering onto unheated substrates followed by annealing and training processes. Their transformation temperatures were investigated by differential scanning calorimetry and electrical resistivity measurements. By the Ni-Pd substitution the transformation temperatures (austenite/martinsite finish temperature; Af/Mf) could be varied between 32°C/-38°C for the binary TiNi films to 570°C/498°C for the binary TiPd films. By the Ni-Cu substitution the transformation hysteresis (Af/Mf) could be reduced from 70°C for the binary film to 20°C for films with 10 at % Cu. A similar behavior was observed for TiNiPdCu films.

The evolution of the stress-strain behavior of a superelastic NiTi alloy over a range of cyclic frequencies up to 10 Hz is presented. Due to the stress-strain hysteresis typical of these alloys work is dissipated as heat during every cycle. Also, the heat release and absorption induced by the cyclic phase transformation responsible for the superelastic effect causes the material to undergo a cyclic temperature history which is superimposed on the average temperature resulting from the dissipative nature of the stress-strain cycle. As the cyclic frequency is increased the imposed strain rate is also necessarily increased. The stress-strain loops at very low frequencies are under isothermal conditions. As the cyclic rate is increased nearly adiabatic conditions are achieved at the higher frequencies. This affects the hysteretic cyclic behavior and the damping capacity of the material.

NiTi shape memory alloy presents interesting mechanical properties as surgical implants. However, due to its high amount of Ni which may dissolve and release toxic ions in human fluids, the medical use of this material is a great concern. We have developed a laser treatment which modifies the oxide layer and enhances uniform and localised corrosion resistance of NiTi alloy.

In this paper we further analysed the effect of this treatment with potentiostatic and AC impedance measurements in physiological Hank's solution. We conclude that the laser treatment creates a stable passive film which results in improved corrosion resistance of this alloy.

We have fabricated granular Cu95Co5 thin films by laser ablation-deposition. Within a regime of annealing temperatures, these samples exhibit Giant Magneto Resistance (GMR), typically 5% in 0.5 Tesla at 5 K. The magnetic hysteresis loops are found to show finite coercive fields in the whole temperature range 2 K - 300 K. Below 9 K, the field dependence of the MR shows a split maximum. We interpret the data in terms of coercivity arising from blocking phenomenon of single domain superparamagnetic Co clusters. A quantitative determination of the upper limit for the cluster moment contributing to GMR is estimated to be 17000 μB (a cluster size of 5 nm).

Electrolytic cylindrical amorphous CoP multilayers, grown on copper wires, with controlled continuos variation of the magnetic anisotropy, in both, direction and magnitude, have been produced. The inner zone of the samples has been grown to exhibit radial anisotropy and the overlayer has been obtained with planar longitudinal anisotropy. Our studies have revealed that the magnetization at the surface of the samples is strongly coupled with the bulk anisotropy for thickness of the overlayer of ≈ 1.5 μm. Furthermore, it has been found that an angular deformation applied to the samples, when the copper wire is subjected to a torsion, modifies the direction of the longitudinal anisotropy to the helical direction. Also, a large spontaneous Matteucci effect is induced by means of this angular deformation.

Quantitative micro-macro combined experimental research on the deformation field of single crystal CuAINi shape memory alloy (SMA) is performed by using high sensitivity Moiré technique. The study is focused on the micro-macro correspondence of the deformation behavior of single crystal uniaxial tensile specimen during stress induced forward and reverse transformations. The aim of the experiment is to quantitatively relate the macroscopic applied stress with the deformation field in the mesoscale. The large deformation due to the lattice distortion during transformation was first successfully recorded by Moiré interferometry. Some important microstructure-related deformation features of single crystal SMA under uniaxial tension are first reported.

Biosensors are a special class of chemical sensors that take advantage of the high selectivity and sensitivity of biologically active material. We are currently investigating the characteristics of various deposited electrode coatings (Au and Pt) on 10 MHz quartz crystals using the sputtering method. We are also investigating the effect of magnetic behavior (by intermixing Fe and Ni with electrodes) on the binding nature of antigen with the substrate. A change in mass occurs due to the binding of antigens and antibodies on the surface of the thin film coating. The frequency change as a result of a change in mass makes it possible to use these crystals as biological sensor devices. This paper describes the construction of antibody-based piezoelectric crystals capable of detecting mycobacterial antigens in diluted cultures of attenuated M. tuberculosis. The microstructural features of these crystals have been studied using scanning electron microscopy (SEM) and atomic force microscopy (AFM) techniques. The crystallographic properties have been characterized using the X-ray diffraction (XRD) method. The long term objective of this research is to develop a rapid quantitative method of analysis for the diagnosis of tuberculosis (TB) and other infections caused by mycobacteria, using biosensor technology.

Recent NUWC research efforts in the field of high power sonar transducers designed to produce high acoustic outputs over significant bandwidths while being of minimal size and weight have been aided by advances in the continuing development of several new high energy density transducer drive materials. Both Terfenol-D, a rare earth magnetostrictive material, and lead magnesium niobate, a relaxor ferroelectric, have demonstrated a tenfold increase in field-limited energy density over a typical very hard lead zirconate titanate (i.e., Clevite PZT-8) piezoelectric ceramic. The Center's focus is to double the demonstrated performance of each material and to address such issues as hysteresis reduction in the magnetostrictive material and coupling coefficient improvements in the electrostrictive materials. Poly (vinylidene fluoride-trifluoroethylene) can also be considered a high energy density material because of its excellent energy density and its broad bandwidth possibilities. The application of these material technologies, either separately or as hybrid composites, to smart material design will be detailed.

Traditionally, control algorithms for Terfenol-D® magnetostrictive actuators have modelled the strain as a linear function of magnetic field and stress, but nonlinearity becomes important for strains of more than a few hundred parts per million (ppm), and for many applications even the maximum strain, about 1500 ppm, is inadequate. Larger strokes can be obtained by various types of stroke amplifiers, by resonant operation, or by inchworming. Previously, SatCon successfully used a 10:1 lever arm stroke amplifier in a helicopter flap actuator [1]. Current projects include a water pump using a hydraulic stroke amplifier, which potentially could be more compact and efficient than a lever arm amplifier, and linear and rotary inchworm motors for robotics. In all these designs, satisfactory performance requires careful attention to machining tolerances and to making the mechanisms and housing stiff enough or compliant enough. A model for inchworm motors has been developed, including finite load and resonant effects. Nonlinear control algorithms will be discussed, applicable to arbitrarily large Terfenol-D® strains, stresses, and magnetic fields.

Experimental and theoretical results are presented for a composite magnetostrictive material system. This material system contains Terfenol-D particles blended with a binder resin and cured in the presence of a magnetic field to form a 1–3 composite. Test data indicates that the magnetostrictive material can be preloaded in-situ with the binder matrix resulting in orientation of domains that facilitate strain responses comparable to monolithic Terfenol-D. Two constitutive equations for the monolithic material are described and a concentric cylinders model is used to predict the response of the composite structure. Experimental data obtained from the composite systems coincide with the analytical models within 10%. Particle size, resin system, and volume fraction are shown to significantly influence the response of the fabricated composite system.

The recognition of chaos as a new type of behavior for complex systems initially spurred efforts to avoid it and, later, to control it. Yet in many cases chaos may be beneficial. We present a method for maintaining chaos in physical systems and implement the method on a simple magnetomechanical system. Application to other systems is discussed briefly.

Material structures having an electromagnetic or magnetomechanical resonance can be excited or detected remotely using an antenna. Incorporating smart materials into such structures provides new opportunities to encode ID and sensor information in the electromagnetic signature of the “tag.” In this way, it is possible to create tags which not only have a unique ID but which can also respond to local changes in their environment (e. g. force, temperature, light, etc.). This principle forms the basis for a low-cost wireless ID and wireless sensor technology which has many potential applications in manufacturing, inventory control, security, surveillance, and new human-computer interfaces. As a means of illustrating this concept, two simple examples are given: a force sensor incorporating a piezoelectric polymer and a relative position sensor which incorporates a magnetoelastic amorphous metal ribbon.

Magnetostrictive multilayer films which combine exchange coupled giant magnetostrictive materials (amorphous Tb0.4Fe0.6) and materials with large polarizations (Fe or Fe0.5Co0.5) were prepared by dc or rf magnetron sputtering using a rotary turn-table technique in a stop-and-go mode. The magnetic properties of TbFe/Fe and TbFe/FeCo multilayers were investigated in relation to the layer thicknesses and the annealing temperatures. Giant magnetoelastic coupling coefficients (or magnetostrictions) are achieved at low fields, due to the magnetic polarization enhancement in such multilayers. Saturation magnetoelastic coupling coefficients of 20 MPa at 20 mT in the case of TbFe/Fe and of 28 MPa at 20 mT in the case of TbFe/FeCo were achieved. These high low-field magnetoelastic coupling coeffients and the possibility to engineer the material's properties by layer thickness variation are considered to be important features for applications of these films as thin film transducers in microsystems.

There is a need for powerful active materials in microsystem actuators. Research on thin film magnetostrictive materials has concentrated on optimising the magnetostrictive response notably by reducing the required driving magnetic field. Here we present a novel type of multilayer, where 2 alloys having different properties are coupled together. The resulting composite system represents a new material with novel characteristics, which can not be fulfilled by simple alloys. In particular here we have investigated magnetostrictive multilayers, with remarkable low field performances (i.e. very large ∂λ / ∂H).

Most magnetostrictive microactuators are based on a bimorph structure. However, these simple structures are prone to thermal drift. We present here also some results on a torsion based magnetostrictive microactuator prototype being insensitive to thermal drift.

The TiNi shape memory alloy wires were plasma coated by α-Al2O3 ceramics and afterwards they were cast into Ti6Al4V or Ti6Al1.5V2.5Nb (Ti-alloy) matrix. The wire fibers melt and the alumina ceramics reacts with both TiNi and Ti-alloy if cooling rate is small. The interphases which are formed are Ti2(Al, Ni) and Ti3AL-type phases, respectively. The structure of TiNi wires changes to dendritic one, Ti-alloys contain 10 to 15% of primary α and transformed β phase. The optimal conditions for rolling are 900°C with reductions of 5%. At this conditions all the constituents of composite material can be deformed plastically. The adhesive strength of TiNi/Al2O3 is 60 MPa.