Indentation onto Stishovite (SiO2), MgO, and a Covered Superalloy: “Pop-In” Repair, Phase-Transition Onsets, Polymorph Energies, and Transition-Energies: A Recent Study

In order to determine the phase-transition onset forces, indentation energies, and transition energies, the Berkovich indentation loading curves of the initially only extraterrestrial available polymorphs of SiO2 are physically analysed using the now well-established FN versus h3/2 plots for conical/pyramidal indentations. These features are described for two phase-transitions of synthesised Stishovite that result in two polymorphs, one of which being Seifertite. For increasing load indentation, a third post-Stishovite polymorph is obviously projected. The anticipated third of them is waiting, and the two of them are currently available for further examination on Earth at room temperature. The force-depth curve had to be self-evidently repaired in order to eliminate the published "pop-ins." It appears to be the first time that the significance of published "pop-ins" has been clarified. There are numerous causes for bothering them and for the avoidance of them. They are mechanical artefacts rather than features of the materials. Although theoretical considerations suggest that the beginning of "pop-ins" involves an elastic-plastic conversion, published pop-ins has absolutely nothing to do with phase transitions. Spherical indentation analyses before them are obsolete and dangerous. Final support is inter alia that one of the two new MgO twinning transitions is within a published “pop-in excursion”. The putting of a pop-in arrow at smooth loading curve without discontinuities in the FN versus h3/2 plot is criticized, as the transfer between chemically different phases is neither phase transition nor “pop-in”. The onset forces, energies, and endothermic or exothermic phase-transition energies of the polymorph are described. Mechanochemical analysis is done on the formation of the Stishovite, post-Stishovite, and MgO polymorphs. For the safe use of technical materials like MgO for building or coated superalloys in things like aeroplanes, turbines, and other large machinery, high pressure polymorph energetic characteristics are crucial also for the earth's sub mantel investigations. The onset and transition energies need to be higher than the maximum permissible mechanical and thermal stress for them to be safe since breakage and catastrophic cracks are more easily initiated at polymorph interfaces.