Search Results (4)

The potential of glass ceramics as applicable materials in various fields including fillers for dental restorations is our guide to present a new procedure for improvements of the mechanical properties of dental composites. This work aims to use Zn₂SiO₄ and SiO₂–ZnO nano-materials as fillers to improve the mechanical properties of Bis-GMA/TEGDMA mixed dental resins. Zn₂SiO₄ and SiO₂–ZnO samples were prepared and characterized by using XRD, FE-SEM, EDX, and FT-IR techniques. The XRD pattern of the SiO₂–ZnO sample shows that ZnO crystallized in a hexagonal phase, while the SiO₂ phase was amorphous. Similarly, the Zn₂SiO₄ sample crystallized in a rhombohedral crystal system. The prepared samples were used as fillers for the improvement of the mechanical properties of Bis-GMA/TEGDMA mixed dental resins. Five samples of dental composites composed of Bis-GMA/TEGDMA mixed resins were filled with 2, 5, 8, 10, and 15 wt% of SiO₂–ZnO, and similarly, five samples were filled with Zn₂SiO₄ samples (2, 5, 8, 10, and 15 wt%). All of the 10 samples (A₁–A₁₀) were characterized by using different techniques including FT-IR, FE-SEM, EDX, and TGA analyses. According to the TGA analysis, all samples were thermally stable up to 200 °C, and the thermal stability increased with the filler percent. Next, the mechanical properties of the samples including the flexural strength (FS), flexural modulus (FM), diameter tensile strength (DTS), and compressive strength (CS) were investigated. The obtained results revealed that the samples filled with 8 wt% of SiO₂–ZnO and 10 wt% of Zn₂SiO₄ had higher FS values of 123.4 and 136.6 MPa, respectively. Moreover, 8 wt% of both fillers displayed higher values of the FM, DTS, and CS parameters. These values were 8.6 GPa, 34.2 MPa, and 183.8 MPa for SiO₂–ZnO and 11.3 GPa, 41.2 MPa, and 190.5 MPa for the Zn₂SiO₄ filler. Inexpensive silica-based materials enhance polymeric mechanics. Silica–metal oxide nanocomposites improve dental composite properties effectively. Full article

Hard-facing as a type of the coating depositing is increasingly used today. Physical-chemical-metallurgical characteristics of contact layers in tribo-mechanical systems depend on the operating conditions and the conditions under which the work surfaces were created. That is the reason the influence of the processing procedures and regime, used in the contact surfaces formation, on development of the wear process of contact elements, is being considered ever more. To determine the influence of the hard-facing technology on characteristics of the gears’ working surfaces, the experimental investigations were performed on samples hard-faced on the steel for cementation, by varying the filler metals (FM) and the hard-facing regimes. The samples tested were hard-faced by five “hard” and three “soft” filler metals. Experimental investigations included measuring the hard-faced layers’ hardness and determination of their microstructure, as well as the wear resistance in the laboratory conditions, on tribometer and on a specially designed device for tests in the real operating conditions of gears. The wear intensity was monitored by the wear trace’s width in the laboratory conditions and by the share of the teeth surfaces affected by the destructive pitting in the operating conditions. The results obtained were compared to results of the base metal (BM) tests, which provided the certain conclusions on which filler metal and which welding procedure are the optimal ones for regeneration of the worn teeth surfaces. Full article

Ni₅₈Cr₃₂Fe₁₀-based alloys, such as Alloy 690 and filler metal 52 (FM-52), suffer from ductility dip cracking (DDC). It is reported that decreasing the stacking fault energy (SFE) of these materials could improve the DDC resistance of Alloy 690. In this work, the effects of alloying elements on the stacking fault energies (SFEs) of Ni₅₈Cr₃₂Fe₁₀ alloys were studied using first-principle calculations. In our simulations, 2 at.% of Ni is replaced by alloy element X (X=Al, Co, Cu, Hf, Mn, Nb, Ta, Ti, V, and W). At a finite temperature, the SFEs were divided into the magnetic entropy (SFE^mag) and 0 K (SFE⁰) contributions. Potentially, the calculated results could be used in the design of high-performance Ni₅₈Cr₃₂Fe₁₀-based alloys or filler materials. Full article

The microsegregation behavior of alloy filler metal 52 (FM 52) was studied using microprobe analysis on two different solidification processes. First, microsegregation was characterized in samples manufactured by directional solidification, and then by gas tungsten arc welding (GTAW). The experimental results were compared with Thermo-Calc calculations to verify their accuracy. It was confirmed that the thermodynamic database predicts most alloying elements well. Once this data had been determined, several tip undercooling calculations were carried out for different solidification conditions in terms of fluid flow and thermal gradient values. These calculations allowed the authors to develop a parametrization card for the constants of the microsegregation model, according to the process parameters (e.g., convection in melt pool, thermal gradient, and growth velocity). A new model of microsegregation, including convection and tip undercooling, is also proposed. The Tong–Beckermann microsegregation model was used individually and coupled with a modified Kurz-Giovanola-Trivedi (KGT) tip undercooling model, in order to take into account the convection in the fluid flow at the dendrite tip. Model predictions were compared to experimental results and showed the microsegregation evolution accurately. Full article