Nanoindentation slip steps and hydrogen embrittlement.

摘要

The usefulness of indentation testing has increased steadily through the past couple decades extending its reach far beyond basic hardness tests. The depth of information available from nanoindentation testing can be extended further through combination with atomic force microscopy (AFM) and orientation imaging microscopy (OIM) as a means to develop a mechanistic understanding of the dislocation reactions taking place around indentations in metallic materials.;Slip steps form on the free surface around indentations in most crystalline materials when dislocations reach the free surface. Analysis of these slip steps provides information about the deformation taking place in the material. Techniques have now been developed to allow for accurate and consistent measurement of slip steps and the effects of crystal orientation and tip geometry are characterized.;It has been shown that these techniques can be applied to study the deformation around grain boundaries and to study the effects of hydrogen on dislocation motion. Hydrogen has been shown to decrease the load at which dislocations nucleate during indentation. Additionally, hydrogen is found to promote the formation of slip steps which see a lower resolved shear stress suggesting that hydrogen increases dislocation mobility, as is suggested by current theories of hydrogen embrittlement.