Properties of Al2O3–40 wt.% ZrO2 composite coatings from ultra-fine feedstocks by atmospheric plasma spraying

In the present study, both ultra-fine and coarse Al2O3–40 wt.% ZrO2 grains were used as the starting materials to prepare ultra-fine structured and micro-structured Al2O3–40 wt.% ZrO2 composite coatings (coded as NZTA coating and MZTA coating, respectively) by atmospheric plasma spraying. The ultra-fine Al2O3–40 wt.% ZrO2 feedstocks for spraying were prepared by means of crushing sintered, starting from commercially availed powders of ultra-fine Al2O3 and ZrO2. The microstructures and phase compositions of the crushing sintered powders and the corresponding composites coatings were investigated by means of scanning electron microscopy (SEM) and X-ray diffraction (XRD). The friction and wear behaviors of the composites coatings sliding against stainless-steel under dry friction conditions and at room temperature were investigated using an optimol SRV oscillating friction and wear tester. The wear mechanisms of the coatings were discussed based on the SEM observation of the worn surface morphologies and wear debris, and the elemental composition analysis of the wear debris by energy dispersive X-ray analysis as well. Results showed that aside from the typical splat lamellae, equiaxle grains were also observed in the Al2O3–40 wt.% ZrO2 composite coating made from the corresponding ultra-fine crushing sintered powders. The NZTA coatings had higher microhardness and better wear resistance than that of the MZTA coatings, which could be largely attributed to the better inter-splats bonding of the former. And the stainless-steel counterpart matched with the NZTA coatings had a smaller wear rate as well. Moreover, the two types of composites coatings were dominated by spalling and fracture as sliding against the stainless-steel counterpart, and the MZTA coatings experienced more severe worn surface damage at a larger load than the NZTA coatings tested under the same conditions, well corresponding to the difference in the wear resistance of the two types of composite coatings.