Microstructure and morphology of electrodeposited Ni-P alloys treated by high energy surface mechanical attrition

Fully amorphous Ni-P layer electrodeposited onto a Cu plate was subjected to severe plastic deformation using surface mechanical attrition treatment in a high energy SPEX 8000 shaker mill. Two series of experiments using different milling conditions (series I: 20 6.35-mm balls; series II: 100 1.59-mm balls) were carried out to explore the mechanism of the process and to investigate the structure of the developed coatings. The evolution of the microstructure and mechanical properties of the Ni-P layer after the deformation process was studied by x-ray diffraction, scanning electronmicroscopy and hardness measurements. We demonstrate that the different mechanical treatments controllably influence the mechanical behavior of the Ni-P metallic glass coating. When the vial of the mill is loaded with larger balls, deformation-induced Ni₃P compound particles form in the amorphous matrix resulting in a hard (HV = 17 GPa) but non-uniform coating. In the case of milling with many small balls, the increase in the surface hardness is considerably lower (7 GPa) as a consequence of reduced impact energy.