Avaliação comparativa de propriedades geradas pelos processos de soldagem TIG e brasagem em uma liga odontológica à base de Ni-Cr / Comparative assessment of properties generated by the process of TIG welding and brazing in a Ni-Cr dental alloy

AUTOR(ES)
DATA DE PUBLICAÇÃO

2009

RESUMO

The purpose of this study was to compare, by means of microhardness testing and metallurgical characterization techniques as metallography, optical microscopy, scanning electron microscopy (SEM) and energy dispersion spectroscopy (EDS), mechanical and metallurgical properties of welded joints by TIG and brazing methods in a dental alloy based on Ni-Cr (FIT-CAST SB). The studied regions in each sample were the base metal (MB), the heat affected zone (ZTA) and the fusion zone (ZF). Forty cylindrical bodies-of-proof, stick-shaped, with 2.5mm diameter and 18.0mm in length were made from dental casting by centrifugation (lost wax technique). Twenty cylinders were used for each technique, which formed, after the welding, groups of ten samples for each procedure. The microstructure of the MB is presented as a matrix of a solid solution based on Ni-Cr with a typical dendritic arrangement of eutectic structure. The alloy presented metallic precipitates in the interdendritic region of the eutectic structure. The semiquantitative chemical analysis obtained by EDS technique showed results consistent with the quantitative chemical composition provided by the alloy manufacturer. In the brazing method, the MB and ZF showed different microstructures. The ZF showed a rough dendritic morphology with the presence of precipitates and porosities. The semiquantitative chemical analysis by EDS of the ZF had very similar results to those obtained for the MB. In the bodies-of-proof joined by the brazing process, the average Vickers microhardness for the MB, ZTA and ZF were respectively 83.501, 87.782 and 127.520. The t-Student statistical analysis revealed significant differences between the MB and ZF regions. In the TIG process, the microstructure of ZF presented similar aspect to the MB, but with a more refined dendritic arrangement. The semiquantitative chemical analysis by EDS of ZF presented similar results to those obtained for the MB. The bodies-of-proof had an average Vickers microhardness of the MB, ZTA and ZF respectively: 74.607, 71.649 and 75.409. The t-Student statistical analysis revealed no significant differences between the studied regions. According to the methodology applied in this study and from the statistical analysis of the obtained data, we can conclude that the process of union by brazing created microstructural and Vickers microhardness differences between the ZF and MB; in welded joints by the TIG method, the Vickers microhardness tests showed uniformity in the mechanical behavior among the ZF, ZTA and MB; the TIG welding process generated a very similar microstructure between the ZF and MB and made on that just a dendritic arrangement of more refined eutectic structure; the EDS chemical analysis revealed that there was no significant change in the chemical composition between the MB and ZF of welded joints by both methods.

ASSUNTO(S)

brasagem tig dental welding soldagem odontológica dental soldering tig brazing nickel-chromium alloys odontologia metalurgia odontológica soldagem (odontologia) ligas níquel-cromo

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