Mechanisms of elastoplastic deformation and their effect on hardness of nanogranular Ni-Fe coatings

Abstract

This article contains the study of correlation between the microstructure, mechanical properties and mechanisms of elastoplastic deformation of Ni-Fe coatings that were grown in five electrodeposition modes and had fundamentally different microstructures. A nonlinear change in hardness was detected using nanoindentation. Explanation of the abnormal change in hardness was found in the nature of the relaxation method of elastoplastic energy under load. It is shown that the deformation of coatings with a grain size of 100 nm or more occurs due to dislocation slip. A decrease in grain size leads to the predominance of deformation due to rotations and sliding of grains, as well as surface and grain boundary diffusion. The effect of deformation mechanisms on the nanoscale hardness of Ni-Fe coatings was established. Full hardening of the coatings (both in the bulk and on the surface) was achieved while maintaining the balance of three mechanisms of elastoplastic deformation in the sample. Unique coatings consisting of two fractions of grains (70% of nano-grains and 30% of their agglomerates) demonstrate high crack resistance and full-depth hardening up to H = 7.4 GPa due to the release of deformation energy for amorphization and agglomeration of nanograins. © 2021