RESUMO
The presented study investigates the effects of weight percentages of boron carbide reinforcement on the wear properties of aluminum alloy composites. Composites were fabricated via ball milling and the hot extrusion process. During the fabrication of composites, B4C content was varied (0, 5, and 10 wt.%), as well as milling time (0, 10, and 20 h). Microstructural observations with SEM microscopy showed that with an increase in milling time, the distribution of B4C particles is more homogeneous without agglomerates, and that an increase in wt.% of B4C results in a more uniform distribution with distinct grain boundaries. Taguchi and ANOVA analyses are applied in order to investigate how parameters like particle content of B4C, normal load, and milling time affect the wear properties of AA2024-based composites. The ANOVA results showed that the most influential parameters on wear loss and coefficient of friction were the content of B4C with 51.35% and the normal load with 45.54%, respectively. An artificial neural network was applied for the prediction of wear loss and the coefficient of friction. Two separate networks were developed, both having an architecture of 3-10-1 and a tansig activation function. By comparing the predicted values with the experimental data, it was demonstrated that the well-trained feed-forward-back propagation ANN model is a powerful tool for predicting the wear behavior of Al2024-B4C composites. The developed models can be used for predicting the properties of Al2024-B4C composite powders produced with different reinforcement ratios and milling times.
RESUMO
The aim of the present study was to evaluate the effects of different remineralization agents associated with erbium, chromium:yttrium-scandium-gallium-garnet (Er,Cr:YSGG) (0.5 W power, 20 Hz frequency, 60% water, 40% air, 25 mJ pulse energy, 8.84 J/cm2 fluence, 60 µs pulse duration, 600 µm tip diameter, and an approximate 1-1.5 mm distance to the target) laser irradiation on erosion induced by the consumption of carbonated drinks in human primary enamel. There were 8 groups and 10 primary teeth in each g0roup. The distribution was as follows: group 1, casein phosphopeptide-amorphous calcium phosphate with fluoride (CPP-ACPF); group 2, Er,Cr:YSGG laser+CPP-ACPF; group 3, fluor varnish; group 4, Er,Cr:YSGG Laser+fluoride varnish; group 5, ROCS® medical mineral gel; group 6, Er,Cr:YSGG laser + ROCS® medical mineral gel; group 7, Er,Cr:YSGG laser; and group 8, artificial saliva. The samples in the groups were submerged in artificial saliva and acid twice a day for 6 s at 6-h intervals and were then exposed to an erosion cycle 15 times. In the groups in which the Er,Cr:YSGG laser was applied in combination with the remineralization agents, the laser application was made first, and then the remineralization agents were applied for 4 min in each group. The Friedman and Wilcoxon signed-rank tests and the Bonferroni correction were used in statistical analyses, and the significance level was taken as p < 0.05. According to the results, all agents had a statistically significant difference (groups 1, 2, 3, 4, and 6: p = 0.005, p < 0.017; groups 5 and 7: p = 0.007, p < 0.017) between BL-RM periods. However, all agents had a statistically significant remineralization effect on primary teeth enamel (groups 1, 2, 3, 6, and 7: p = 0.005, p < 0.017; group 4: p = 0.011, p < 0.017) except that group 5 (p = 0.074, p < 0.017) between DM-RM periods. The coadministration of an agent with the laser did not make any difference at a statistical level (p = 0.804, p > 0.05). The results were supported by scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis. As a result of this study, CPP-ACPF had a notable impact in terms of the remineralization effect on eroded enamel, and the Er,Cr:YSGG laser alone may be an alternative method, which may be related to the modified hydroxyapatite structure, 38.5% H0.56Ca4.56O13P3Y0.44, that was determined in XRD analysis.