Enhancement of Mechanical Properties and Corrosion Resistance of HVOF-Sprayed NiCrBSi Coatings Through Mechanical Attrition Treatment (SMAT)

This study aims at evaluating the effects of surface mechanical attrition treatment (SMAT) on mechanical properties and corrosion resistance of NiCrBSi coatings deposited by high-velocity oxygen-fuel (HVOF) spraying. The as-deposited coating has a typical HVOF-sprayed morphology with unmelted and deformed particles, associated with voids and porosities, whereas after SMAT, the affected zone morphology is more compact, without porosity or crack. The thickness of the affected zone varies from about 30 to 100 mu m according to the SMAT parameters. The surface roughness is much lower for SMAT-treated coatings (from Ra = 6.8 mu m to a Ra approximate to 2.3 mu m). Whatever the SMAT parameters used in this work, the treated materials are harder compared to the as-deposited coating (from 6.6 to 7.6 GPa). They exhibit compressive residual stresses around - 360 MPa, while tensile stresses with an average value of 180 MPa were evaluated for the as-deposited coating. In addition, the treated coatings show better wear resistance as well as better corrosion resistance in a 3 wt.% NaCl solution. The better compromise in terms of SMAT parameters corresponds to amplitude of vibration of the SMAT sonotrode of 15 mu m and SMAT duration of 810 s.