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A smart composite material constituted of a magnetic hybrid film and a NiTi shape memory alloy (SMA) ribbon was obtained and characterized. The magnetic hybrid film was joined to the NiTi ribbon in order to combine the properties of both materials. This new composite material combines magnetic properties of the hybrid film, (Fe2O3-CMC)/(polyvinyl butyral), and the shape memory properties of the NiTi ribbon, which has a chemical composition of Ti-50.13 at. % Ni. This smart composite material has a mass of 18.3% NiTi ribbon and 81.7% magnetic hybrid film. Results obtained by DSC show that the smart composite material presents a small delay of transformation during warming and cooling because the magnetic hybrid film acts like a thermal insulator. Thermomechanical results indicate that the hybrid material also acts as a mechanical reinforcement, since it is observed that the Stress-Assisted Two-Way Memory Effect (SATWME) of the smart composite is lower than the SATWME of the SMA ribbon. The density current values of phase transformations were clearly identified with a thermomechanical apparatus developed in our laboratory. Finally, displacements of the smart composite material in cantilever configuration are obtained by applying an external magnetic field. All these results demonstrate that the smart composite material can be

Abstract. Shape Memory Alloys are susceptible to annealing heat treatments, which are capable of partially or fully recover atomic mobility and, therefore, affect the overall thermomechanical response of the material. In this work, NiTi SMA orthodontic minicoil springs in superelastic state, widely commercialized, were submitted to annealing treatments as a way to modify their thermomechanical response and adapt it to the use in mechanical systems in other fields besides orthodontics. The main objective is to study the influence of temperature and time of annealing on the thermomechanical behaviour of the coil springs, originally superelastic at room temperature. Using a factorial design, three mechanical properties of interest were studied: spring constant, shear modulus and energy dissipation capacity. It was demonstrated that annealing in the range of 500°C-600°C is capable of converting superelastic springs to an apparently actuator state, as residual strain after loading/unloading at room temperature was observed, when a maximum 7% shear strain was attained in the cross section of the spring's wire.

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High transformation temperature shape-memory alloys (HTSMA) usually present a martensitic transformation temperature (Ms) starting at 100 ºC. That is the case of high nickel Ni-Ti-Hf alloys. This article presents experimental results obtained from arc melting of Ni 50 Ti 50-X Hf X .at% (X = 8, 11, 14, 17 and 20 .at%) alloys. This process homogenized every composition with similar relative crystallinity. Results confirm that transformation temperatures (TT) increase with increasing the amount of Hf. A martensitic matrix is formed by two metastable phases: R and B19'. From all the alloys studied, the B19' phase presented the highest percent fraction. Gradually adding Hf 3 .at% promoted a slow increase of crystalline fraction of R phase and a slow reduction of phase (Ti, Hf) 2 Ni, located at grain boundaries. Coherent/semi-coherent interface between (Ti, Hf) 2 Ni phase and the matrix may intensify the driving force for the formation of R phase, present on X-ray diffractograms.

Melt undercooling opens new solidification pathways for non-equilibrium phases and non-conventional microstructures. Several techniques, including the fluxing technique, have been developed in order to reduce nucleation sites and to produce high undercoolings for metals and alloys. In this work the fluxing technique was applied to Pb-25wt%Sn (hypoeutectic), Pb-61.9wt%Sn (eutectic) and Pb-90wt%Sn (hypereutectic) alloys to investigate the influence of the undercooling on the microstructure of these alloys. For the hypoeutectic alloy, an increasing of the undercooling (∆Te) from 7 to 13 K resulted in interdendritic eutectic refinement. For the hypereutectic alloy, an increasing of undercooling from 8 to 16 K resulted in a reduction of the β-Sn primary dendrites arm spacing from 50 m to 30 m. For the both hypoeutectic and eutectic alloys, an increasing of the undercooling resulted in an interdendritic eutectic with anomalous morphology. The results indicated that the critical eutectic undercooling, ∆Te * , that causes a transition from lamellar eutectic to anomalous eutectic in the Pb-Sn alloys, is around 6 K.

Thin films of titanium were deposited onto Al 2 O 3 substrate by hollow cathode discharge method for the formation of a ceramic-ceramic joint using indirect brazing method. An advantage of using this technique is that a relatively small amount of titanium is required for the metallization of the ceramic surface when compared with other conventional methods. Rapidly solidified brazing filler of Cu 49 Ag 45 Ce 6 in the form of ribbons was used. The thickness of deposited titanium layer and the brazing temperature/time were varied. The quality of the brazed joint was evaluated through the three point bending flexural tests. The brazed joints presented high flexural resistance values up to 176 MPa showing the efficiency of the technique.

The usual process to produce NiTi shape memory alloys is vacuum induction melting (VIM). Currently a new alternative process to produce NiTi shape memory alloys by rapid solidification structures called Melt Spinning has been studied. In this work, results of ribbons with a chemical composition Ti-55.2 Ni (wt %) alloy prepared by this method are presented. The ribbons are prepared at two different linear velocities: 30 m/s and 50 m/s. After that, samples are heat treated at 350 °C during 1 hour. The alloys are characterized by Scanning Electron Microscopy (SEM), Differential Scanning Calorimetry (DSC) and X-Ray Diffraction. According to the cycled DSC test, transformation peaks are associated with the B2→R→B19´ transformation during cooling and B19´→R→B2 during heating, showing transformation in multi-peaks. The martensite B19´ start (M s ) is varying from 35 to 39°C and the martensite finish (M f ) from 15 to 21°C, 42-47°C for austenite B2 start (A s ) and 65-69°C for austenite finish (A f ) approximately. All analyzed ribbons show very similar values of transformation hysteresis temperatures at 50% of transformation of around 28°C. In order to change solidification rate, linear velocity is varied during the melt spinning process. Results indicate that linear velocity affects directly the temperature of transformation. When the linear velocity is increasing, crystallographic Ti-rich precipitates are developed, but dendritic growth disappears, changing the microstructure and decreasing these transformation temperatures. Then changes in linear velocity can dramatically affect shape memory properties, and in this case a velocity of 50 m/s produces a more homogenous alloy.