Danieli Aparecida Pereira Reis

AVALIAÇÃO DAS TEMPERATURAS DE TRANSFORMAÇÃO NO DSC EM LIGA NiTi APÓS O ENVELHECIMENTO COM E SEM CARGA

In this work were machined CDP alloy with composition 50.9 at% Ni, and then the samples were aged at temperatures between 350-550°C, 60 MPa applied voltages and times of 45 and 180 minutes. In addition, aging was also performed without application of load under the same conditions of temperature and time for comparison of properties, but adding a solubilized sample at 850C for 1 hour. Subsequently DSC to determine the phase transformation temperatures characterized the samples. It is observed in this paper that the DSC some samples presented both in heating and in cooling two peaks of transformation that could be related to the onset of phase R. Also, may have been the formation of Ni3Ti4 stage as alloys with levels above at 50.6%at. Ni are characterized by the formation of Nirich precipitates, which may entail a decrease in the concentration of Ni in the matrix and increase the transformation temperature. This work is important because there are few studies related to the effect of aging load the memory effect of shape properties and superelasticity of NiTi alloy.

Image characterization after SEM analysis for equimolar samples of Nb2O5-YTZP

The turbines are usually recovered by ceramic coatings to guarantee higher temperatures as well lower degradation through hostile environments. These primary systems are composed by yttria-stabilized zirconia (YSZ), but new researches have found that the presence of rare-earth oxides, like Ta2O5/ Nb2O5 can increase the efficiency of mechanical properties for coatings. The lack of knowledge in this system leads this study with niobia, because of high production of them in Brazil. Samples made of 16% mol of Y2O3 and Nb2O5 were done with zirconia, that composition was used because there are traces of tetragonal phase stabilization, which is related to the best properties of the TBC. SEM images were obtained and by using a ImageJ software were done a microstructural analysis. It was possible to reveal the format of the grains, which appear to be equiaxials, their size, to be around 3μm, and the phases presented were revealed after thermal attack.