Abstract 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 Ni50Ti50-XHfX .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 Hf3 .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.

To obtain high temperature shape memory alloys of the lower cost Ni-Ti-X system, elements such as Hf and Zr are introduced to modify the thermal and mechanical properties of these alloys. This work studied the production and characterization of Ti50 Ni50-x Zrx alloys (x = 0, 5, 10 at.%) with the aim of improving their thermal, mechanical and corrosion resistance properties. In the resulting alloys, transformation of phase B2 into phase B19' occurred in a single stage. The addition of zirconium led to an increase of transformation temperatures, as well as the appearance of second phase particles in the grain boundaries of the matrix. The increase in zirconium percentage favored the increase of corrosion resistance from 520.23KΩ to 1007.30KΩ and of microhardness from 346HV to 543HV for the N0 and N10 alloys, respectively.

In this paper are presented theoretical analysis and experimental results concerning the performance of toroidal cores used in current transformers. For most problems concerning transformers design, analytical methods are useful, but numerical methods provide a better understanding of the transformers electromagnetic behaviour. Numerical field solutions may be used to determine the electrical equivalent circuit parameters of toroidal core current transformers. Since the exciting current of current transformers alters the ratio and phase angle of primary and secondary currents, it is made as small as possible though the use of high permeability and low loss magnetic material in the construction of the core. According to experimental results presented in this work, in comparison with others soft magnetic materials, nanocrystalline alloys appear as the best material to be used in toroidal core for current transformers.

Este trabalho teve como objetivo determinar os melhores parâmetros para brasagem de juntas cerâmicas de Al2O3 pré-metalizadas com Ti por processo a plasma utilizando fitas amorfas de ligas Cu49Ag45Cx e como metal de adição. As ligas foram preparadas em forno a arco, e, posteriormente processadas por melt-spinning, variando conteúdo Ce de 4-6. %. A brasagem foi realizada em forno à vácuo e as seguintes variáveis analisadas: tempo de deposição do filme de Ti e temperatura e tempo de brasagem , que foram relacionados com a resistência à flexão em 3 pontos da junta brazada. A equação de regressão linear foi obtida, e verificou-se a interação entre estes fatores. As superfícies cerâmicas metalizadas apresentaram excelente uniformidade e as juntas brasadas muito boa adesão atingindo valores de resistência à flexão de até 176,8 MPa.

This work had as objective to establish de best brazing parameter to joint Al2O3 pre-metalized with Ti by plasma process using amorphous ribbons of Cu49g45Ce x alloys as filler metals. The alloys were prepared in arc furnace and processed by melt-spinning process varying the Ce percentiles from 4 to 6. % . The brazing was accomplished in vacuum furnace and the following variables analyzed: deposition time of Ti film, brazing temperature and brazing times which were related to the brazed joint 3-point bending resistance. The interaction between those factors was obtained by linear regression equation. The metalized ceramic surfaces presented an good uniformity and the joint a very good adhesion reaching bending resistance up to 176,8 MPa.

Based on electrical and magnetic properties, such as saturation magnetization, initial permeability, and coercivity, in this work are presented some considerations about the possibilities of applications of nanocrystalline alloys in toroidal cores for current transformers. It is discussed how the magnetic characteristics of the core material affect the performance of the current transformer. From the magnetic characterization and the computational simulations, using the finite element method (FEM), it has been verified that, at the typical CT operation value of flux density, the nanocrystalline alloys properties reinforce the hypothesis that the use of these materials in measurement CT cores can reduce the ratio and phase errors and can also improve its accuracy class.

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 (deltaTe) 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 beta-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, deltaTe*, that causes a transition from lamellar eutectic to anomalous eutectic in the Pb-Sn alloys, is around 6 K.