Effect of Ultrasonic Nanocrystal Surface Modification on the Structure, Mechanical Properties, and Tribological Behavior of Detonation-Sprayed NiCrAl Coatings

The effect of ultrasonic nanocrystal surface modification (UNSM) on the structural-phase state, mechanical properties, and tribological behavior of detonation-sprayed NiCrAl coating was investigated. The UNSM treatment conditions are denoted as AxFy, where x represents the ultrasonic vibration amplitude A in μm and y represents the normal load F in N; for example, A30F10 corresponds to an amplitude of 30 μm and a normal load of 10 N. UNSM significantly reduced the surface roughness from Ra = 3.78 μm in the as-sprayed state to 0.25 μm for A40F10. X-ray diffraction showed that the principal AlNi, Al4Ni3, and AlCr2 phases were retained after treatment, while weak Al3Ni5 reflections appeared under the A40F10 condition. SEM/EDS analysis confirmed preservation of the coating–substrate interface and revealed increased activation of inter-splat and subsurface defects at higher treatment intensity. The mean hardness remained comparable to the as-sprayed value under the moderate A20F10 and A30F10 conditions but decreased markedly under the more severe A40F10 and A10F20 conditions. Despite an increase in the coefficient of friction, wear resistance improved considerably. The minimum wear-track cross-sectional area of 1425 μm2 was obtained for A30F10, representing an approximately 81% reduction compared with the as-sprayed coating. A30F10 provided the most favorable overall combination of surface smoothing, hardness, and wear resistance.