Effect of the gaseous medium in the process of rolling on the microhardness of aluminum and iron

The load dependence of the microhardness of polycrystalline aluminum and iron specimens produced by rolling in a nitrogen, helium, or air medium has been investigated. It has been found that nitrogen and helium have different effects on the microhardness of these metals in the low-load range. This difference is associated with the specific features in the intensity of dynamic penetration of nitrogen and helium into the surface layer of aluminum and iron, which depends on the initial defect crystal structure of the metals, as well as on the type of bonding of helium atoms and nitrogen molecules with metal atoms. It has been shown that the effect of the gaseous medium of the rolling on the microhardness manifests itself only in a very thin surface layer of metal specimens, where the microhardness exhibits a size effect, and an increase in the microhardness indentation depth remains unchanged with an increase in the load and does not depend on the gaseous medium of the prerolling of the specimens.