RESUMEN
Introduction: There is a growing concern on the development of adequate materials to interact with the human body. Several researches have been conducted on the development of biomaterials for dental applications. Objective: This study aimed to determine the microstructural and mechanical properties of a nickel- based alloy, after the casting process. Material and methods: The alloy was melted through lost wax technique and centrifugation, by using blowtorch with liquefied petroleum gas. To evaluate the mechanical properties, tensile bond strength and microhardness tests were performed. The microstructural characterization was performed using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). Statistical analyses were performed on microhardness results, through Student t test. A program for digital image processing was used to determine the percentage of the existing phases. Results and Conclusion: The tensile strength was higher than that reported by the manufacturer, 559.39±25.63MPa versus 306 MPa, respectively. However, the yield strength was slightly lower, 218.71±29.75 MPa versus 258 MPa, reported by the manufacturer. The microhardness tests showed about 70 HV, far above the value informed by the manufacturer (21 HV). It can be affirmed with 95% confidence interval that the casting process did not alter the material's hardness. The alloy's microstructure is formed by a matrix with dendritic aspect and gray color and a second white interdendritic phase with equally distributed precipitates as well as porosities. EDS tests showed that the matrix is rich in nickel and chromium, the interdendritic second phase is rich in molybdenum and the precipitates in titanium or silicon. The matrix represents 86% of the area and the second phase 12%.
RESUMEN
Introdução: Durante a fabricação de reconstruções dentárias, que utilizam sistemas metalocerâmicos, é utilizado um tratamento térmico para promover a adesão da porcelana ao metal. Entretanto, sabe-se que tratamentos térmicos podem alterar a microestrutura do material metálico, modificando suas propriedades. Objetivo: Este trabalho objetivou avaliar as possíveis modificações causadas na microestrutura de liga à base de níquel-cromo utilizada para reconstruções metalocerâmicas, quando a mesma é submetida ao tratamento térmico para adesão da porcelana.Material e método: O material pesquisado foi dividido nos grupos CR, F e TT, que representam, respectivamente, o material como recebido do fabricante, o material apenas submetido ao processo de fundição e o material após fundição e tratamento térmico. Os grupos CR e F foram submetidos à análise química quantitativa. A caracterizaçãomicroestrutural dos três grupos foi realizada através da técnica de microscopia eletrônica de varredura, com um sistema de Energy Dispersive Spectroscopy. Técnicas de análise e processamento digital de imagens foram aplicadas às micrografias dos grupos F e TT, para determinação de possíveis modificações quantitativas nas fases presentes. Resultado: A microestrutura da liga era formada por uma matriz de estrutura dendrítica de coloração cinza, rica em níquel; uma segunda fase interdendrítica de coloração branca e aspecto rendilhado, rica em molibidênio, e precipitados de coloração preta, podendo ser ricos em silício ou titânio. Também foram identificadas porosidades.Conclusão: A microestrutura após o processo de fundição apresentou um tamanho da fase interdendrítica menor. Não foram identificadas mudanças na microestrutura e na composição química das fases após o tratamento térmico.
Introduction: Manufacturing process of metal-ceramic dental reconstructions systems includes heat treatment to promote adhesion of the porcelain in the metal. However, it is known that heat treatment can promote changes in the microstructure of metallic materials, thereby affecting their properties. Objective: This work evaluated themicrostructure stability of dental quality nickel base alloy submitted to the heat treatment aiming at achieving porcelain adhesion. Material and method: The samples divided into three sets, CR, F and TT, representing,respectively, the material received from the manufacturer, the material just before the casting process and the material after casting end heat treatment. The CR and F sample sets were submitted to quantitative chemical analysis. The samples of CR, F and TT sets was submitted to the microstructural characterization by scanning electron microscopy and energy dispersive spectroscopy. Digital images processing techniques were applied to micrographics of F and TT sets to determine the changes in the material microstructure before and after heat treatment. Result: The alloy microstructure exhibits a gray dendritic structure in a clear matrix, rich in nickel, and a white inter-dendritic second phase, rich in molybdenum, with scattered precipitates, rich in titanium or silicon,and porosity. Conclusion: The microstructure has an average size of the interdendritic phase less than the alloy after casting. Changes in the microestructure and in the chemical composition of each phase were not identified, whether before nor after thermal treatment.