High temperature indentation creep tests on anhydrite – a promising first look

Abstract. Indentation creep tests are established in materials engineering, providing information on rheology, deformation mechanisms, and related microstructures of materials. Here we explore the potential of this method on natural, polycrystalline anhydrite. The tests are run at atmospheric pressure, temperatures between 700 and 920 °C, and reference stresses between 7 and 30 MPa. An activation energy Q of 338 kJ mol⁻¹ and a stress exponent n of 3.9 are derived. Deformation is localized into shear zones bounding a less deformed approximately conical plug underneath the indenter. Shear zone microstructures reveal inhomogeneous crystal–plastic deformation, subgrains, and extensive strain-induced grain boundary migration, while mechanical twinning appears not to be activated. Microstructure and mechanical data are consistent with deformation by dislocation creep.