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From the wide range of engineering materials traditional Stellite6 (cobalt alloy)exhibits excellentresistance to cavitation erosion (CE). Nonetheless,the influence of ion implantation of cobalt alloys on the CE behaviour has not been completely clarified by the literature.Thus,this workinvestigates the effect of nitrogen ion implantation(NII)of HIPed Stellite 6 on the improvement of resistance to CE. Finally, thecobalt-rich matrix phase transformationsdue to both NIIand cavitationloadwere studied. The CEresistanceofstellites ion-implantedby120 keV N+ions twofluences:5 × 1016cm−2and 1 × 1017cm−2werecomparatively analysedwith theunimplantedstellite and AISI 304 stainless steel. CEtests were conducted according to ASTM G32 with stationary specimen method. Erosion rate curves and mean depth of erosion confirm that the nitrogen-implanted HIPed Stellite6 twotimesexceedstheresistance to CEthan unimplanted stellite,and has almostten times higher CEreferencethanstainless steel.The X-ray diffraction (XRD) confirms that NII of HIPed Stellite 6 favours transformation of the ɛ(hcp) to γ(fcc) structure. Unimplanted stellite ɛ-richmatrixis less prone to plastic deformation than γand consequently, increase of γphaseeffectively holds carbides in cobalt matrix and prevents Cr7C3debonding. This phenomenonelongatesthree times the CE incubation stage, slowserosion rate and mitigates the material loss.Metastable γstructure formed by ion implantation consumes the cavitation load for work-hardening and γ→ɛmartensitic transformation. In further CE stages,phases transform as for unimplanted alloynamely, the cavitation-inducted recovery process, removal of strain, dislocations resulting in increase of γphase. The CEmechanism was investigated using a surface profilometer, atomic force microscopy, SEM-EDS and XRD. HIPed Stellite 6 wear behaviourrelies on the plastic deformation of cobalt matrix,starting at Cr7C3/matrixinterfaces. Oncethe Cr7C3particles lose from the matrix restrain, they debond from matrix and are removed from the material. Carbidesdetachment creates cavitation pits which initiate cracks propagation through cobalt matrix, that leads to loss of matrix phase and as a resulttheCE proceedswitha detachment of massive chunk of materials.
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