A conventionally cast CoNiFeMn_0.5Cr_1.5 alloy and two versions with 0.25 C & 3.7 Ta or 0.25 C & 3.7 Hf were tested in oxidation at 1000 °C for 50 h with thermogravimetric recording of the oxidation kinetic. In all cases, the obtained mass gain curve is parabolic. The parabolic constants are much lower than the Kp previously determined for the original alloys with an equimolar base (CoNiFeMnCr). However, the post-mortem exploitation of the oxidized samples revealed analogous oxidation features on the surface and the subsurface, also with external oxide strata on the surface with different Mn and Cr contents, and rather great Mn depletion, in addition to a moderate Cr depletion, in the subsurface. Globally, the oxidation behavior is significantly better than was earlier observed for the equimolar version of these alloys.

Objectives: The aim of this study was to compare the hardness, chemical composition, and microstructure of various self-ligating ceramic orthodontic brackets and enamel. Methods: Sixty ceramic brackets (0.022″ × 0.028″) from six different orthodontic firms (Damon^® Clear 2, Genius^® Crystal, Empower^® 2 Clear, Clarity^® Ultra, Alpine SL^® Clear, and Experience Ceramic^®) were tested using a microhardness tester and a scanning electron microscope (SEM) equipped with energy-dispersive spectroscopy (EDS). Results: The hardness of the ceramic brackets ranged from 1969.8 to 2567.3 VH. The statistical analysis using the Kruskal–Wallis and Mann–Whitney tests revealed significant differences in microhardness between most of the ceramic brackets. Additionally, this study found that passive self-ligating brackets exhibited a significantly higher hardness than that of active self-ligating brackets (p = 0.01). The SEM analysis showed that the variations in the oxygen and alumina composition between the six bracket types were also statistically significant (p = 0.01). Conclusions: Among all of the ceramic brackets tested, Alpine^® brackets displayed the lowest hardness values, making them a potential choice for minimizing enamel damage. Notably, the hardness of self-ligating ceramic brackets was found to be at least six times greater than that of enamel, raising concerns about their potential to cause trauma to the enamel of antagonistic teeth. Consequently, the researchers recommend avoiding bonding ceramic brackets to the mandibular teeth or elevating occlusion with turbo-bites to prevent traumatic contact during treatment.

A conventionally cast CoNiFeMn0.5Cr1.5 alloy and two versions with 0.25C&3.7Ta or 0.25C&3.7Hf were tested in oxidation at 1000°C for 50h with thermogravimetric recording of the oxidation kinetic. In all cases the obtained mass gain curves are parabolic. Their parabolic constants are much lower than the Kp previously determined for the original alloys with an equimolar base (CoNiFeMnCr). However, the post–mortem exploitation of the oxidized samples revealed analogous oxidation features on surface and subsurface, with here too external oxide strata on surface with different Mn and Cr contents, and rather great Mn–depletion in addition to a moderate Cr–depletion, in subsurface. Globally, the oxidation behavior is significantly better than earlier observed for the equimolar version of these alloys.

This study investigates the effects of Ti addition on the microstructures, melting temperature ranges, thermal expansion behavior, high-temperature creep and oxidation resistances of an equimolar CoNiFeCr alloy of a foundry origin. The addition of 1.5 wt.% Ti does not really change the single-phase state of the reference quaternary alloy but induces a significant decrease in the melting start and melting end temperatures. The thermal expansion coefficient is slightly lowered. The creep resistance at 1100 °C is significantly enhanced. The oxidation at 1200 °C is controlled by species diffusion through a continuous chromia layer. The parabolic constant is higher than for the quaternary alloy, due to external and internal Ti oxidation. The presence of a thin layer of titanium oxide covering the chromia scale is suspected to limit chromia volatilization and the scale spallation at cooling. Globally, Ti demonstrated the beneficial influence of the high-temperature properties of the alloy.