Influence of the Structural State of the Mg-1%Ca Magnesium Alloy on Tribological Properties

This paper presents experimental data on the tribological properties of the Mg-1%Ca magnesium alloy with different microstructures (coarse-grained microstructure in the initial state, and ultrafine-grained and nanocrystaline microstructures after severe plastic deformation via two processes – equal-channel angular pressing and high pressure torsion) in contact with an indenter made of the Fe-18W-4Cr-0.8C steel without any coating and with applied hydroxyapatite, which is the main mineral component of bones. An indenter with hydroxyapatite on the surface was used as a bone simulator. As a result of the experiments, it was found that the shear strength of adhesive bonds and the adhesive component of the friction coefficient are structurally sensitive parameters. For all the samples in the considered contact pairs, when using a bone tissue simulator the strength of adhesive bonds was lower than that when using a steel indenter. It is noted that ultrafine-grained and nanocrystalline structures produced as a result of severe plastic deformation via two processes, equal-channel angular pressing and high pressure torsion, contribute to a decrease in the shear strength of adhesive bonds and the adhesive component of the friction coefficient due to strengthening resulting from grain size reduction from originally 100 µm to 1.4–4 µm on average in the investigated Mg-Ca magnesium alloy.