Composition and microhardness of Si–Ge solid solution precipitates in Al–Si–Ge alloys solidified during centrifugation
Abstract The chemical composition of precipitates, the Knoop microhardness of the precipitates and of the matrix of Al–Si–Ge alloys solidified during centrifugation at 7 ×  g were investigated. The initial content of (Si + Ge) was (10 + 10), (20 + 20) or (25 + 25) at.%. The Knoop microhardness of the ingots varied with height in the ingot. This variation is attributed to sedimentation of Si–Ge during solidification. Chemical analysis showed that the maximum Si:Ge ratio in the precipitates for Al–10 at.% Si–10 at.% Ge alloy was about 92:8, and decreased with increasing Si and Ge content in ingots. The Si:Ge ratio and Knoop micro hardness also varied throughout each precipitate. The composition was constant along precipitates of alloy solidified without centrifugation. A variation in Knoop microhardness along the precipitates was attributed to this composition variation. The variation of the maximum Si:Ge ratio in the precipitates in ingots of different composition solidified with centrifugation is attributed to nonequilibrium conditions of solidification induced by decreased mass transport in the melt adjacent to the growing precipitates. The variation of Si and Ge along the Si –Ge precipitates is created by convection of the melt during solidification with centrifugation.
Influence of Ge content on the microstructure, phase formation and microhardness of hypereutectic Al–Si alloys
Abstract In this study, composition of the phases in ternary Al–18Si– x Ge alloys was investigated. It was found that except α-Al, there may form primary Si, primary Ge, eutectic Si and eutectic Ge, depending on different composition of the alloys. The influence of Ge content on the microstructure, phase formation and microhardness in Al–18Si alloy was investigated. Experimental results show that the introduction of Ge in Al–18Si alloy can modify the microstructures, and Ge and Si can replace with each other to some extent in both primary and eutectic phases. The increase of Ge addition level in Al–18Si– x Ge alloys leads to an increase of Ge content in primary Si. There also exist continuous composition transition zones for Si and Ge in eutectic structure. Combining with the microstructures, the solidification process of the Al–18Si– x Ge alloys was analyzed by differential scanning calorimeter (DSC). Besides, with the increase of Ge content in the alloys, the microhardness of primary Si decreases first and then increases, while the microhardness of the eutectics and macrohardness of the bulk alloys exhibit monotone increase.
Efficacy of Biodentine as an Apical Plug in Nonvital Permanent Teeth with Open Apices: An In Vitro Study
The aim of this study was to evaluate the apical microleakage of Biodentine and MTA orthograde apical plugs and to compare the effect of thickness of these biomaterials on their sealing ability. A total of eighty maxillary anterior teeth were used. The apices were removed by cutting with a diamond disc (Jota, Germany) 2 mm from the apical root end in an attempt to standardize the working length of all specimens to 15 ± 1 mm. Both materials were placed in 1–4 mm thickness as apical plugs root canal. Root canal leakage was evaluated by the fluid filtration technique. One-way ANOVA was used in order to determine normality of dispersal distribution of parameters; thereafter, results were analyzed by Kolmogorov-Smirnov test. Overall, between microleakage values of MTA and Biodentine regardless of apical plug thickness, no difference was observed. In terms of plug thickness, a statistically significant difference was observed between the subgroups of MTA and Biodentine (p < 0.05). The apical sealing ability of Biodentine was comparable to MTA at any apical plug thickness.