Influence of Energy-Mechanical Treatment on Structure-Mechanical Properties of Co–Cr–Mo Alloys Obtained by Spark Plasma Sintering

We investigate the influence of preliminary energy-mechanical treatment (EMT) of the initial Co–Cr–Mo-based powders in the vortex layer of ferromagnetic bodies on the structure-mechanical properties of products obtained by the spark plasma sintering (SPS). To study the properties of the powder and the sintered samples, we employed the scanning electron microscopy (SEM), the optical microscopy, the value determination of the flexural strength and the microhardness on the Vickers scale. We show that the short-time EMT of the powders (1–3 min) in the vortex layer of ferromagnetic bodies results in severe plastic deformation of the majority of the rounded particles of the original powder: they form particles of irregular shape including plates with increased surface roughness. As a result, this treatment influences positively their spark plasma sintering process and makes it possible to produce densely compact sintered material with a low-porosity structure. We discover that the sample preliminarily passing the 3-min EMT compacts densely during sintering (the relative density being 98.3%) and obtains improved mechanical properties (the microhardness and the flexural strength values being by 16% and 14%, respectively, higher than those for the sample without treatment). This improvement of structure-mechanical properties of the EMT-passed sintered samples results from intensification of the diffuse mass transfer during sintering due to the plastic deformation of the material, modification of the shape, the surface condition of the powder particles, and the increase of the total contact area between them. The increased surface roughness and the particle shape deviation from that regular lead to a decrease in the radii of curvature of their contact surfaces and thus an increase in the Laplace force magnitudes, playing the dominant role in the diffusion mass transfer during sintering.