Journal of Materials Science

, Volume 29, Issue 12, pp 3295–3308 | Cite as

Measurement and theory of the orientation dependence of Knoop microhardness in single-crystal mercuric iodide

  • J. Marschall
  • F. Milstein


Measurements were made of the orientation dependence of the Knoop microhardness HK on the (001) and (110) faces of single crystals of red (tetragonal) mercuric iodide that were vapour-grown for use in radiation detectors. The (001) faces of the crystals are softest when the major diagonal of the Knoop indentor (called here “the indentor”) is parallel to the [100] crystallographic axis, and HK increases monotonically, by about 25%, as the indentor is rotated from the [100] to the [110] axis. The (110) surfaces are hardest when the indentor is parallel to [001]; HK decreases by about 50% as the indentor is rotated from [001] to [1¯10]; the experimental data indicate an intermediate microhardness minimum that occurs before the [1¯10] orientation is reached. Particularly interesting surface topography, including bands of slip lines, is observed in the vicinity of indentations on the (110) planes, which apparently have not previously been characterized by Knoop microhardness indentation. Theoretically, the size of a microhardness indention is presumed to depend on the volume of material in which appropriate slip systems are stressed sufficiently to cause appreciable slip. To test this concept and determine which particular slip systems dominate the indention process, the “infinite flat punch” model was used to calculate the orientational and volumetric variations of shear stress on various potential slip systems in mercuric iodide. For indention processes controlled by movement (i.e. slip) of material in the [001] direction, over {100} planes, these calculations predict the following (experimentally observed) results: (a) on the (001) plane, HK is smallest at [001] and greatest at [110], with no intermediate extremum; (b) on the (110) plane, HK has its greatest value at [001] and a minimum between [001] and [1¯10]; (c) HK at [110] on the (001) plane is essentially the same as HK at [1¯10] on the (110) plane; and (d) the relative variation of HK is greater on the (110) than on the (001) surface. Finally, the expected orientational variation of HK on the (100) and (101) surfaces was determined theoretically.


Shear Stress Material Processing Surface Topography Slip System Slip Line 
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Copyright information

© Chapman & Hall 1994

Authors and Affiliations

  • J. Marschall
    • 1
  • F. Milstein
    • 1
  1. 1.Departments of Materials and Mechanical EngineeringUniversity of CaliforniaSanta BarbaraUSA

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