Effect of energy mechanical pre-treatment on the structural-mechanical properties of (Co – Cr – Mo) alloys obtained by spark plasma sintering

We studied the effect of energy mechanical pre-treatment (EMT) of the initial (Co – Cr – Mo) alloy powders in a vortex layer of ferromagnetic bodies on the structural-mechanical properties of products obtained by spark plasma sintering (SPS). To study the properties of powder and compact samples, the methods of scanning electron microscopy (SEM), optical microscopy, determining the bending strength and microhardness on the Vickers scale were used. It was shown that the EMT of powders for a short time (1 – 3 min) leads to intense plastic deformation of a large part of the initial rounded particles, forming irregular- and plate-shaped particles with high surface roughness. As a result, EMT has a positive effect on spark plasma sintering process of powder, makes it possible to obtain a densely sintered material with a low-porous structure. It was found that the sample pre-treated under EMT for 3 min is compacted during sintering process to a high level (relative density reached 98.3 %) and its mechanical properties has greatly improved (microhardness and bending strength are 16 % and 14 % respectively higher than the sample without pre-treatment). The improvement of structural and mechanical properties of sintered specimens pre-treated under EMT is a result of intensification of diffusion mass transfer processes during sintering due to the plastic deformation of material, change in the shape, surface state of the powder particles and an increase in the total contact area between them. High surface roughness and deviation of particles from the round form lead to a decrease in the radii of curvature of their contact surfaces and, consequently, to an increase in the Laplace forces value, which play a dominant role in the diffusion mass transfer processes during sintering.