Hollow Corundum Microspheres in Plasma Spraying

When hollow corundum microspheres (hereinafter, HCM) are used in plasma spraying, it
demonstrates the following enhanced characteristics as compared to conventional powders
of aluminium oxide, i.e. electrocorundum and grade GOO (in Cyrillic characters, ‘ГОО’)
aluminium oxide:
  • High materials utilization ratio;
  • Ability to obtain high-density or highly-porous coatings;
  • Excellent mobility (without arching) in the feed pocket;
  • High microhardness of coatings.
The walls of hollow corundum microspheres are relatively thin, and when they get into the plasma jet,
they warm-up to the molten state much faster compared to electrocorundum. Furthermore, we can
obtain various coating porosity degrees depending on velocity of particles flow in plasma jet.
At relatively low plasma spraying velocity (thermal spraying), we can achieve the following
characteristics:
  • Materials utilization ratio for HCM: 34% (analogue: 18%);
  • Total porosity of the coating: 36% (analogue: 19%);
  • HV microhardness of HCM coating: 800-1000 kgf/mm2 (analogue: 1100-1400 kgf/mm2).
At high spraying velocity, e.g. high-velocity oxygen fuel (HVOF) or detonation spraying, we can obtain low-porous coatings due to complete
collapsing of hollow corundum microsphere walls and a highmaterials utilization ratio for HCM, i.e. 40-49% (analogue, electrocorundum: 25-30%).

Detonation spraying
Electrocorundum
Hollow corundum microspheres
3.9% porosity of alumina detonation coating layer 0.3% porosity of HCM detonation coating layer
Total porosity - 3,9%
Total porosity - 0,3%
Microhardness, HV
1500 ± 300
1660 ± 250