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The work investigates the effect of nitrogen ion implantation (NII) of CoCrWC and
hardfacings on the improvement of resistance to cavitation erosion (CE). Two types
of cobalt-based hardfacing were deposited via the tungsten inert gas method on
a structural steel substrate. The CE resistance of stellites ion-implanted by 120 keV
N+ ions, two fluences: 5×1016 cm−2 and 1×1017 cm−2, were comparatively analysed with
the unimplanted stellite and AISI 304 stainless steel. CE tests were conducted according
to ASTM G32 with stationary specimen method. Erosion rate curves and mean depth
of erosion confirm that the nitrogen-implanted hardfacings, two times, exceed the
resistance to CE than unimplanted stellite, and have almost ten times higher CE
reference than stainless steel. The profilometric surface analysis confirms the erosion
stages identified by SEM. The X-ray diffraction (XRD) confirms that NII of cobalt-
based hardfacing favours transformation of the ε(hcp) to γ(fcc) structure. Unimplanted
stellite ε-rich matrix is less prone to plastic deformation than γ, and consequently,
an increase of γ phase effectively holds carbide eutectics. This phenomenon elongates
the CE incubation stage three times, slows the erosion rate and mitigates the material
loss. Metastable γ structure formed by ion implantation consumes the cavitation load
for work-hardening and γ → ε martensitic transformation. In further CE stages, phases
transform as for unimplanted alloy, namely, the cavitation-inducted recovery process,
removal of strain, dislocations resulting in an increase of γ phase.
