Influência do modo de sinterização nas propriedades superficiais e limite de fadiga de uma nova cerâmica de zircônia.
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Data
2020-03-06
Autores
Domingues, Camila Ferreira Leite Madruga
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Editor
Universidade Estadual Paulista (Unesp)
Resumo
O presente estudo tem como objetivo avaliar a influência do modo de sinterização nas propriedades superficiais e no limite de fadiga de uma nova cerâmica de zircônia (Y-TZP). 50 discos de cerâmica à base de óxido de zircônio (IPS e.max ZirCAD LT) para CAD/CAM (Computer Aided Design/Computer Aided Manufacture) foram confeccionados de acordo com a norma ISO 6872:2015. Os discos foram divididos em dois grupos, de acordo com o modo de sinterização do material: MP (modo padrão) e MR (modo rápido). Os discos do grupo MP foram sinterizados conforme o programa padrão (n=25), enquanto os discos do grupo MR foram sinterizados utilizando o programa rápido (n=25). Por se tratar de um novo material, previamente ao ensaio de fadiga, cinco amostras de cada grupo foram confeccionadas de forma semelhante e utilizadas para as seguintes avaliações: rugosidade superficial, perfilometria, microscopia eletrônica de varredura (MEV), sistema de energia dispersiva (EDS), difração de raios-X e mensuração da cor e translucidez. Cinco discos de cada grupo foram submetidos ao teste monotônico de flexão biaxial com célula carga de 50 kgf e velocidade de 0,5 mm/min até o momento da fratura para determinação da carga a ser utilizada no teste de fadiga staircase. Setenta por cento do valor médio da carga máxima (MPa) registrada na fratura de cada espécime foi utilizado como carga inicial para o teste de fadiga. A carga foi aplicada sobre o espécime por 20.000 ciclos, a uma frequência de 20 Hz. As análises fractográficas dos espécimes foi realizada e amostras representativas foram submetidas à MEV para avaliação da origem da fratura. Comprovada a normalidade dos dados, os resultados de rugosidade superficial, limite de fadiga e leituras de cor foram avaliados através de ANOVA – 1 fator seguido pelo teste de Tukey, ambos com significância de 5%. O limite médio da fadiga em flexão biaxial foi calculado de acordo com o método de Collins (1993). As imagens de MEV e perfilometria foram avaliadas qualitativamente. ANOVA revelou não haver diferença para Ra, Rz e RSm (p>0.05) entre MP (0,13±0,02; 1.21±0,26; 24,91±2,19) e MR (0,14±0,03; 1,32±0,25; 24,68±2,26). As microscopias confirmaram similaridade na morfologia superficial dos grupos. DRX apresentou semelhantes fases. A resistência à fadiga foi semelhante entre MP (512 MPa; 464.39 – 560.06) e MR (542 MPa; 472.49 - 611.51) e a fractografia apresentou a origem das falhas no lado de tração, independentemente do modo de sinterização dos discos. Os valores de coordenadas L* (p = 0,000) e a* (p = 0,001) foram superiores para o grupo MR enquanto a coordenada b* (p = 0,977) foi semelhante entre os modos de sinterização. E, um valor de ΔE = 2 foi observado. Já a translucidez foi semelhante entre os grupos (p = 0,788).
The present study aims to evaluate the influence of sintering mode on surface properties and fatigue limit of a new zirconia ceramic (Y-TZP). 50 zirconium oxide (IPS e.max ZirCAD LT) ceramic discs for CAD/CAM (Computer Aided Design/Computer Aided Manufacture) were prepared based on ISO 6872:2015. The discs were divided into two groups according to the material sintering mode: MP (standard mode) and MR (fast mode). MP group discs were sintered according to the standard program (n = 25), while MR group discs were sintered using the fast program (n = 25). As it is a new material, before the fatigue test, five samples from each group were similarly made and used for the following evaluations: surface roughness, profilometry, scanning electron microscopy (SEM), dispersive energy system (EDS), X-ray diffraction and color and translucency measurements. Five discs from each group were submitted to the monotonic biaxial flexion test with a load cell of 50 kgf and 0.5 mm/min speed until the fracture moment to determine the load to be used in the staircase fatigue test. Seventy percent of the mean maximum strength (MPa) recorded during fracture of each specimen was used as the initial load for the fatigue test. The load was applied to the specimen for 20,000 cycles at a frequency of 20 Hz. Fractographic analyzes of the specimens were performed and representative samples were submitted to SEM to assess the origin of the fracture. Once the data normality was verified, the results of surface roughness, fatigue limit and color readings were evaluated by one-way ANOVA followed by Tukey 's test, both with 5% significance. The mean limit of biaxial flexion fatigue was calculated according to the Collins method (1993). SEM and profilometry images were qualitatively evaluated. ANOVA revealed no difference for Ra, Rz and RSm (p> 0.05) between MP (0.13 ± 0.02; 1.21 ± 0.26; 24.91 ± 2.19) and MR (0.14 ± 0, 03, 1.32 ± 0.25; 24.68 ± 2.26). The microscopies confirmed similarity in the superficial morphology of the groups. XRD presented similar phases. Fatigue strength was similar among MP (512 MPa; 464.39 - 560.06) and MR (542 MPa; 472.49 - 611.51) and fractography showed the failure origin on the tensile side, regardless of the sintering mode of the discs. The L * (p = 0.000) and a * (p = 0.001) coordinate values were higher for the MR group while the b * coordinate (p = 0.977) was similar within the sintering modes and a value of ΔE = 2 was observed. Translucency was similar between groups (p = 0.788).
The present study aims to evaluate the influence of sintering mode on surface properties and fatigue limit of a new zirconia ceramic (Y-TZP). 50 zirconium oxide (IPS e.max ZirCAD LT) ceramic discs for CAD/CAM (Computer Aided Design/Computer Aided Manufacture) were prepared based on ISO 6872:2015. The discs were divided into two groups according to the material sintering mode: MP (standard mode) and MR (fast mode). MP group discs were sintered according to the standard program (n = 25), while MR group discs were sintered using the fast program (n = 25). As it is a new material, before the fatigue test, five samples from each group were similarly made and used for the following evaluations: surface roughness, profilometry, scanning electron microscopy (SEM), dispersive energy system (EDS), X-ray diffraction and color and translucency measurements. Five discs from each group were submitted to the monotonic biaxial flexion test with a load cell of 50 kgf and 0.5 mm/min speed until the fracture moment to determine the load to be used in the staircase fatigue test. Seventy percent of the mean maximum strength (MPa) recorded during fracture of each specimen was used as the initial load for the fatigue test. The load was applied to the specimen for 20,000 cycles at a frequency of 20 Hz. Fractographic analyzes of the specimens were performed and representative samples were submitted to SEM to assess the origin of the fracture. Once the data normality was verified, the results of surface roughness, fatigue limit and color readings were evaluated by one-way ANOVA followed by Tukey 's test, both with 5% significance. The mean limit of biaxial flexion fatigue was calculated according to the Collins method (1993). SEM and profilometry images were qualitatively evaluated. ANOVA revealed no difference for Ra, Rz and RSm (p> 0.05) between MP (0.13 ± 0.02; 1.21 ± 0.26; 24.91 ± 2.19) and MR (0.14 ± 0, 03, 1.32 ± 0.25; 24.68 ± 2.26). The microscopies confirmed similarity in the superficial morphology of the groups. XRD presented similar phases. Fatigue strength was similar among MP (512 MPa; 464.39 - 560.06) and MR (542 MPa; 472.49 - 611.51) and fractography showed the failure origin on the tensile side, regardless of the sintering mode of the discs. The L * (p = 0.000) and a * (p = 0.001) coordinate values were higher for the MR group while the b * coordinate (p = 0.977) was similar within the sintering modes and a value of ΔE = 2 was observed. Translucency was similar between groups (p = 0.788).
Descrição
Palavras-chave
Zircônia translúcida, Fadiga, Sinterização, Fractografia, Translucent zirconia, Fatigue, Sintering, Fractography