Investigation on Six Polymorphs of Sodium Chloride upon Depth-Sensing Macroindentation with Unusual Long-Range Cracks Requiring 30 N Load

A sodium chloride single crystal is depth-sensing indented with a Vickers indenter at a Zwick/Roell ZHV Zwicky Z2.5 macro region instrument, together with Stephanie Rosner from Zwick GmbH & Co KG, Ulm, Germany. In order to experimentally secure the onsets of both known and unknown phase-transitions and to locate them with direct linear regression analyses while eliminating iterations. Normal forces up to 50 N load and 120 m m depth are applied. Four sharp phase-transition onsets could thus be identified experimentally, uncovering four new NaCl polymorphs in addition to the long-known fcc and bcc polymorphs. It is unclear how they relate to the three theoretically anticipated higher pressure crystal forms in Reference. The projected metallic character is not clear because the author did not see any colour development or metallic reflection up to 50 N loads. At the indenter tip, there is no cracking of any kind, but at the 30 N ranges, there was a new sort of long-range cracking, and its highly resolved microscopy revealed two-step nucleation at a polymorphs' interface exit. Unloading observed with an inverted 3D microscope that a macroscopic crack had developed along the created interface direction and exited apon slightly higher force, far apart at the crystal edge. Seven powers of ten are covered by the calculated phase-transition energies. These data cast doubt on the accuracy of non-depth-sensing ISO/ASTM Standards for industrial Vickers, Brinell, and Rockwell hardness parameters because they cannot account for multiple phase-changes that are ineluctable under very high loads, do not define pristine as opposed to phase-transformed industrial materials (including super-alloys), and fail to recognise the allowable pressure stress for delaying phase changes, etc. Depth sensing is necessary due to the possibility of failure from crack nucleation at polymorph interfaces. A quick way to identify phase changes is the analysis of the sharp unsteadiness in the FN = k h3/2 plots, as shown by previously reported loading curves. The mathematically required 5/4 ratio of applied work over indentation work is then easily determined (Chapter 2).