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An extended investigation of the pseudoelastic properties of Ni45Ti50Cu5 alloy suggested the presence of a two-stage transformation behavior. This behavior was brought to evidence performing stress strain measurement on ternary alloy specimens submitted to different thermal treatments and pulled slightly overbehind the maximum pseudoelastic transformation strain. The concurrent measurement of Electric Resistance(ER) and of the temperature of the specimen proved clear modifications of these physical properties at the end of the pseudoelastic plateau both during the loading and unloading process. Investigation of the stress strain curve at different temperatures above the Af (austenite finish) values together with a systematic comparison of ER measurements on differently thermally treated specimens suggest the presence of an another transformation in competition with the usually accepted cubic to monoclinic. Results obtained are here presented and discussed at the light of this working hypothesis. Analysis of the ER(ε) curves allows to relate directly this physical property to the transformation strain of the pseudoelastic curve. Both at the end of the loading and unloading plateau there is evidence of a marked change of the ER(ε) , only slightly modified by the thermal treatment procedure. In more detail measurements were performed at different temperatures taking into account the modification in Af temperature induced by the thermal treatment.

Stress Assisted Two Way Memory Effect (SATWME) and Electrical Resistance (ER) have been investigated on a Ni45Ti50Cu5alloy preliminarily prestrained in martensite to modify the critical stress for slip. Different prestrain levels have been applied. ER vs ε during SATWME follows an almost linear relationship across the transformation range : the plastic deformation accumulated during cycling generally increases, but the figure of εplowers with increasing the preliminary prestrain. Even the highest applied prestrain (≈ 15%) does not allow to eliminate the build up of plastic strain in each cycle. Different procedures to modify the critical stress for slip must be envisaged.

The influence of thermal cycling driven by electrical current under a small and constant applied stress of 50 MPa on martensitic transformation, microstructure and electrical resistance of crystallized melt-spun ribbons of a Ti50Ni25Cu25(at.%) shape memory alloy is investigated. Cycled specimens and uncycled ones as a reference are characterized by various methods like differential scanning calorimetry, X-ray diffraction, transmission electron microscopy, and electrical resistance. After thermal cycling DSC curves during cooling exhibit two transformation peaks whereas the reverse transformation proceeds in only one step. The separation of the two peaks and also their maximum remains stable during cycling but the peak shapes become broader. The reason for the two-stage transformation is found in a crystalline surface layer already present in the as-spun state. A heat treatment between 700°C and 800°C for 600s is able to recrystallize the surface layer. Only minor changes of the microstructure due to current-driven thermal cycling could be observed. The average grain size is about 500 nm in both cycled and uncycled specimens. A few plate-like precipitates are present created during the crystallization process. Twins are frequently observed. Dislocations, however, are never observed not even in the cycled specimens.

The use of shape memory alloys for sensing/actuating strictly relies on the possibility to easily relate the Electrical Resistance (ER) to strain (E). Previous measurements of ER vs ε on Ni25Ti50Cu25ribbons detected during thermal cycling under a stress state have clearly shown that a linear relationship between ER and ε can be obtained for an applied stress lower than 50 MPa. ER and ε have been here investigated during repeated electrically driven thermal cycles under an applied stress either 50 or 100 MPa on Ni25Ti50Cu25melt spun ribbons up to 8000 electrically-driven cycles. Small plastic deformation, with a typical figure of εp≈ 5.10-4for 50 MPa and εp≈ 1.10-3for 100 MPa, is built in during cycling and levels after few thousand cycles. Under a stress of 100 MPa specimens break after 2000-4000 cycles. No broken specimen has been found even after 8000 cycles under 50 MPa applied stress. The hysteresis width of the ER-ε curves modifies with cycling for both applied stresses.

The investigations till now performed on the Step-wise Martensite to Austenite Reversible Transformation (SMART) have identified the relevant key features both of the transformation itself and of the Incomplete Cycling on Heating (ICH), procedure required to induce the SMART. The SMART phenomenology, proved in several shape memory alloys, appears quite general, despite of the differences both in the kinetic and in the crystallographic characters of the thermoelastic martensitic transformations involved. The microstructural mechanism underlying SMART has however not yet been clarified. A working hypothesis, already advanced, is based on the idea that the ICH procedure is effective in inducing kinetic barriers, related to local assemblies of defects localized in the martensite phase ; that, however, contrasts, at least in TiNi, with X-ray diffraction (XRD) and Electrical Resistance (ER) measurements which support an increasing structural order as a consequence of the ICH procedure. With the aim to gain further insight into the microstructural modifications in martensite, induced by the ICH procedure, ER measurements have been here undertaken both on a Ti49.8Ni50.2(at%) and on a Ti50Ni45Cu5(at%) alloys. The experimental findings are discussed and contrasted with the ones already obtained on TiNi alloys.

It is well known that applications of NiTi alloys in orthodontics rely on the pseudoelastic properties developed at temperatures higher than Af. That implies as a necessary condition that the body temperature (Tb) be higher than Af; the level of reversion stress, σrdepends moreover upon the difference between Tband Af. Nowadays the interest is directed to obtain an archwire with distinct σrin different segments : that means to modify locally the properties of the wire by local thermal treatments. Current methodologies exploit either the joule effect or a hot air thermal treatment : both have been here used on NiTi archwires to modify (Tb- Af) and, as a consequence, the expected σr. The properties detected along the archwires by means of Differential Scanning Calorimetry, have been found quite disuniform when the active procedure of the resistive heat treatment was used, whilst good uniformity has been found when adopting the passive hot air heat treatment method. At the light of the present results, the hot air treatment method, allowing a better local temperature control, appears more reliable than the resistive heat treatment method.

In recent years, the electric transport properties of NiTi and NiTiCu alloys under applied stress have been investigated either in the martensitic phase or in the austenitic one. Moreover, with the aim to use the electrical resistance (ER) as a state control variable of a shape memory actuator, the ER has been investigated either in the recovery process under stress or in the two way memory effect (TWME). In relation to the recovery process and the TWME, the ER vs ε shows, in the transformation region (i.e. the "operating" temperature range), a linear trend, which appears appealing for the control of the shape memory actuator. While the interest in microactuators is steadily growing, results on ER vs. ε in thin wires are still lacking. In the present paper, the ER vs. ε has been investigated in thin NiTi wires (ф=25Oμm), where the strong drawing is expected to induce textures and the surface-to-volume ratio is higher than in the previous investigations. The results here obtained are compared and contrasted in the light of the previous results detected on NiTi alloys.

The superelasticity of NiTi shape memory alloys is exploited in orthodontics to provide a constant force in the correction of malocclusions, allowing both to nillfill the requirements of the "opumaTorthodontic force and to considerably shorten the therapy. Though some little drawbacks (superelasticity prevents formability, few choices of the force are available), which can however be overcome by the so-called "Shape & Force user Programmable Orthodontics", the great benefits offered by superelasticity have dictated the success of NiTi wires in orthodontics. Since superelasticity follows the Clausius-Clapeyron like equation, changes in the superelastic force can be expected as a consequence of a temperature change, induced by oral environment temperature modifications. In order to investigate the change in the superelastic force at body temperature (Tb) as a consequence of temperature loops, 3-point bending measurements have been here undertaken on NiTi orthodontic wires. The results have shown that, at a fixed deflection on the reversion plateau, simulating a state in the orthodontic therapy, the superelastic force is generally increased as a consequence of a temperature loop. However, as the unloading proceeds, at T=37°C, the superelastic force, expected at Tb , is nearly recovered. In order to enlighten these results, tensile tests have also been performed. The 3-point bending results have been discussed at the light both of the tensile tests results and of the inhomogeneous stress-strain fields which set in along the bent wire.

The "Step-wise stimulated Martensite to Austenite Reversible Transformation" (SMART) in NiTi alloys is here examined by means of X ray diffraction spectra detected: 1) before the procedure required to activate SMART; 2) after each step of the procedure; 3) after SMART. Results obtained prove that some specific reflections are affected by the procedure, notably the ones which correspond to the orientations apt to store the highest transformation strains.

Mechanical properties of shape memory NiTi alloys have been widely investigated : though a reasonable understanding of the micromechanisms underlying macroscopic behaviour is known, these sometimes can hardly be inferred from macroscopic stress-strain curves. Electrical Resistance (ER) measurements, extensively used to investigate thermal martensite, are here performed on NiTi alloys under stress state. Attention is here focused on the mechanical and electrical behaviour of a NiTi alloy in one start single phase : -in martensitic phase, at [MATH] or within the hysteresis cycle ; -in parent phase, at [MATH] or within the hysteresis cycle. ER, sensitively affected by electronic structure modifications, lattice structure defects, residual impurities, can profitably be exploited to enlighten similar macroscopic stress-strain behaviour. ER results here obtained allow to discriminate different active micromechanisms, specifically at a same temperature within the hysteresis cycle where similar stress-strain curves are obtained.

The R-phase in a polycrystalline 50Ti48Ni2Fe shape memory alloy has been here investigated by X-Ray Powder counter Diffractometry (XRPD). With the aim to determine the R-phase lattice parameters accurately, an original XRPD calibration method, specifically apt for shape memory alloys, has been developed. The intrinsic aberrations that affect the XRPD have been taken into account by evaluating the XRPD spectrum of the high temperature b.c.c. phase. The correction function Δ(2θ) has been calculated and applied to the R-phase diffraction peaks. A full indexing of the X-ray spectrum of the R-phase, not achievable by raw experimental data, has thus been obtained and the lattice parameters calculated on a set of reflections in un-aberrated angular positions with an accuracy of ≈part in 10000. The calibration method here developed can be used also in the XRPD study of crystalline materials that undergo a first solid-solid phase transition.

The Step-wise Martensite to Austenite Reversible Transformation (SMART) has been widely investigated in polycrystalline shape memory alloys and its key features are, on the whole, well established. Though some working hypothesis have been put in advance, the full understanding of this “micromemory” phenomenon is still open. Specifically, the most probable origin of the SMART, relies on a local relaxation of the elastic energy. In order to clarify the advanced hypothesis, a CuZnAl single crystal alloy, where the elastic energy contribution to the thermoelastic balance is typically smaller than in the case of polycrystalline specimens, has been examined. All the investigated specimens have shown, though at different extent the SMART: results have shown that the larger the elastic energy involved, the more evident the SMART phenomenology is. Thus, the present findings further support the role of the elastic energy in the SMART.

The axonal forms of Charcot-Marie-Tooth (CMT2) disease are a clinically and genetically heterogeneous group of disorders. Mitofusin 2 gene (MFN2) mutations are the most common cause of CMT2. Complex phenotypes have been described in association with MFN2gene mutations, including CMT2 with pyramidal features (hereditary motor and sensory neuropathy HSMN V) and CMT2 with optic atrophy (HMSN VI).

The step-wise martensite to austenite reversible transformation (SMART) in shape memory alloys (SMA) is a martensitic thermoelastic transformation where a step-wise kinetics is induced by a partial cycling procedure within the hysteresis cycle (incomplete cycle on heating (ICH) procedure). The ICH procedure has been proved effective in inducing a reversible microstructural modification of the martensitic phase. Results till now obtained both on the SMART behaviour and on the effects of the ICH procedure are reviewed here: the hypotheses advanced till now are discussed to explain experimental evidences.

To evaluate the efficacy of acebutolol, 400–600 mg/day in elderly hypertensive patients, and to compare it with hydrochlorothiazide 25–50 mg/day, 45 patients with mild-moderate uncomplicated hypertension were treated for 6 weeks in a multicentre, single-blind, randomized, crossover trial. Acebutolol decreased supine systolic blood pressure from 186.5 to 162.7 mmHg and diastolic blood pressure from 107.4 to 92.4 mmHg. Hydrochlorothiazide decreased systolic blood pressure from 185.0 to 166.4 and diastolic blood pressure from 107.2 to 96.4. There was no difference between the effects of acebutolol and hydrochlorothiazide on blood pressure during the trial. Both drugs proved to be safe and effective antihypertensive agents, provided the major contraindications for their use were taken into account. Beta-blockade by acebutolol was highly effective in treating mild-moderate arterial hypertension in the elderly.

Abstract: The unusual mechanical properties (i.e. shape memory effect and superelasticity) of shape memory alloys (SMA) rely on the thermoelastic martensitic transformation (TMT) which is a first-order solid-solid, non-diffusive phase transition, athermal in character. Differential scanning calorimetry (DSC) is often used as a convenient method of investigating the thermal properties ofSMAs. The common practice of standard temperature calibration, required for a correct instrument performance, is here critically discussed in relation to the study of both the direct exothermic transformation on cooling, and the reverse endothermic transformation on heating in a NiTiSMA. The DSC results show that, with the standard temperature calibration, the instrument is calibrated on heating but un-calibrated on cooling. A general method is advanced to overcome this problem, intrinsically related to the dynamic character of DSC.

Since ten years the NiTi alloys have gained an ever increasing place in orthodontic practice: that is due to their peculiar mechanical properties ascribed to a martensitic thermoelastic transformation which can be thermally or, in a proper temperature range, stress-induced. In the last case, when martensite is stress-induced at body temperature, the stress-strain behaviour is pseudoelastic with large deformations gained or recovered at constant stress, respectively in direct/reverse transformation: this behaviour exploited in orthodontics allowed to overcome the drawbacks intrinsic to the use of conventional alloys as stainless steel or Co-Mo alloys, where small displacements can be achieved at decreasing loads.From the phase state diagram of NiTi alloys it appears that at body temperature they are stable, but out of equilibrium: thermal treatments at intermediate temperatures can therefore modify the equilibrium state and as a consequence the transformation temperatures respect to body temperature. That allows to modify the recovery stress level according to the requirements of practice and thus disclosing new roads: the capability to foresee NiTi archwires pre-programmed in different sections, with a personalized scheme.Attention has not currently been paid to the modifications in the recovery stress induced by a temperature change inside the oral cavity. Recent results have shown that the thermal changes in the oral cavity induced by cold/hot liquid intake can considerably modify the stress level to which the dentition is exposed: though confined to the time extent connected with drinking, similar effects can be expected also for meals intake and should be taken into account for a correct procedure.

The use of NiTi shape memory alloys, introduced into orthodontics because of their ability to develop light continuous forces that prove more effective than heavy intermittent forces in the teeth movement, requires the mastering of the functional properties of NiTi wires. More specifically, the recovery force acting on the teeth is a sensitive function of temperature: knowledge of oral temperature modifications is therefore required to understand the stress state modification felt during orthodontic therapy. The temperature modifications induced by cold or hot drink intake in the oral cavity were investigated by using arch wires, fixed to removable Hawley retainers, similar to those currently used in orthodontic practice, by means of six temperature sensors placed in correspondence with specific teeth. Similarly, the temperature changes were detected on a metallic frame, fixed onto the palatal zone to a Hawley retainer, where a palatal expander was placed to correct unilateral or bilateral crossbites in deciduous or in early mixed dentition. The maximum temperature change was observed in the interincisor area: The temperature modification on other teeth depends on the modality of drink intake, with the highest temperature variations being detected in the palatal zone. Hence modifications in the stress state during orthodontic therapy with NiTi wires are to be expected. (Am J Orthod Dentofac Orthop 1997;112:58-63.)

The mechanical properties of A 533B C11 steel in uniaxial tension have been investigated as a function of specimen orientation throughout the temperature range 24–288°C. Simultaneously, measurements of the acoustic emission output have been made and this has been shown to be a sensitive function of the metallurgical microstructure. Attention has been focused on the relationship between yield stress and strain ‘energy’ released as acoustic emission at general yielding. The results demonstrate two distinct trends, one for longitudinal and transverse specimens, the other for short-transverse specimens. Signal amplitude analysis did not discriminate between different specimen orientations, but it proved to be useful in the detection of load instabilities the microstructural origin of which has been explored by examinations of the fracture surfaces using a scanning electron microscope.

Tensile data for A508 steel in the temperature range 24°C ≤ T≤ 288°C are examined using acoustic emission and compared to similar data previously obtained for A533B steel. The ‘energy’ rate at yielding shows a well defined yield stress dependence and a Boltzmann law dependence upon temperature. Strain aging is found at 200°C for A508 but at 288°C for A533B, connected with a Portevin–Le Chatelier effect.

The thermoelectric power variation with alloying ΔS and the residual resistivity Δp of Cu3Au alloy doped with 3d transition metals are reported as a function both of T and of the atomic number of the impurity. The different state of order of the alloy affects the absolute values of ΔS and Δp but does not drastically modify the general trend of the curves, which suggests a resonance mechanism between the conduction electrons and the d states of the impurities.

Static magnetic susceptibility measurements were performed on Cu3Au alloy for 20°C < T < 1100°C. Its behaviour in the disordered state is quite similar to that shown by pure Cu and Au, but it changes abruptly when order sets in. Such modification is discussed in connection with the new Fermi surface, typical of order.The influence of 3d transition metal impurities was also investigated as a function of order.

The experimentally observed presence in NaCl and KC1 crystals of comparable concentrations of complexes between divalent impurity cations and positive-ion vacancies in the ground and first excited states, is shown to be in agreement with the results yielded by the Born-Mayer theory of ionic crystals. Theoretical estimates for the binding energy of the first excited state of the Sr2+impurity complex and of the vacancy pair in NaCl and KC1 crystals are presented and discussed. Si mostra che la presenza in oristalli di NaCl e KC1 di concentrazioni confrontabili di complessi fra cationi d’impurità bivalenti e posti vaoanti da ione positivo negli stati fondamentale e primo eccitato, osservata sperimentalmentei è in accordo con i risultati forniti dalla teoria di Born-Mayer dei oristalli ionioi. Sono presentati e discussi risultati teorici per l’energia di legame del primo stato eccitato del oomplesso di impurità per ioni Sr2+e della coppia di posti vaoanti in cristalli di NaCl e KCl.

On étudie le pouvoir thermoélectrique de l’alliage Cu3Au en fonction de l’ordre avec l’hypothèse des électrons libres et en supposant que la forme des zones de Brillouin ne varie pas au point critique.

The thermoelectric power of the alloy Cu3Au has been measured in the range of temperature 180°K < T < 1000°K both for samples at equilibrium and for samples disordered by quenching.The thermoelectric power depends remarkably upon the degree of order: the disordered samples present a behaviour quite similar to that of Cu and Au, whilst the samples at equilibrium show a drastic change near the critical temperature Tc and a different behaviour as a function of temperature for T < Tc.A comparison is made with the theoretical curves previously obtained and the results are discussed in connection with the modifications of the Brillouin zones consequent to the order-disorder transition.