Synthesis And Tribological Properties Of ZrO₂/Al₂O₃ Ceramic Coating Deposited By Plasma Spraying

With the development of modern industry, the higher performance of mechanical parts are requested in actual working conditions. The coatings with special properties were deposited on the surface of mechanical parts, which could not only improves the surface properties of materials to perfect the operational performace and extend the life of the workpiece,but also improves economic efficiency.It was high hardness, good wear-resistance and corrosion-resistance that the coating deposited by plasma spraying has been widely used in surface modification of materials.In this paper, the ZrO₂/Al₂O₃ coatings was deposited by plasma sprayeing on 20steel substrate with a reasonable control spraying process conditions, which the rock-bottom was Ni/Al and the feed powers were Al₂O₃-TiO₂ and ZrO₂ of the size was micro-grade, the coatings as follows: 10wt.%ZrO₂-Al₂O₃-TiO₂(10ZAT), 20wt.%ZrO₂-Al₂O₃-TiO₂(20ZAT), 40wt.%ZrO₂-Al₂O₃-TiO₂(40ZAT). The organizational structure and phase composition of coatings were represented with SEM, EDS, XRD and so on, the physical properties and tribological properties of coatings were tested, and the wear mechanism of coatings were analyzed. In addition, the correlation between physical and tribological properties of coatings were discussed. The results as follows: The SEM observation showed that the coatings were typical of layered structure, which interlaced and superimposed and accumulated as waves, the integration was mechanical bond between splats of coatings, however, there were molten, unmolten, porosity and micro-cracks in the coatings. The EDS analysis showed that ZrO₂ and other elements distributed in coatings evenly. With the XRD analysis, the phase composition of feed powders mainly forα-Al₂O₃, TiO₂ and t-ZrO₂, but the phase compostion changed in as-sprayed coatings, namelyα-Al₂O₃ transformed into unstableγ- Al₂O₃ phase, at the same time, Al₂O₃ and TiO₂ reacted and generated a new phase Al2TiO5. On the other hand, there were t-ZrO₂ and a little ofα-Al₂O₃ phases in the as-sprayed coatings. The porosity of coatings increased when the content of ZrO₂ increased, namely 10ZAT caoting was 5.23% and 20ZAT caoting was 5.21% and 40ZAT coatings was 5.59%. On the other hand, the microhardness of coatings reduced with the content of ZrO₂ increased, there were as follow: 537.8, 534.9 and 529.3HV0.1. In addition, while the content of ZrO₂ increased, the fracture toughness of coatings increased, the fracture toughness of 40ZAT coating improved 10.5% and 13.3% than 10ZAT and 20ZAT coatings, for 8.09J/m². Contrasted component, microhardness, porosity and fracture toughness of coatings, the microhardness of coatings reduced with the content of ZrO₂ increased, on the contray, the porosity and fracture toughness of coatings increased with the content of ZrO₂ increased, however, the fracture toughness of coatings increased when the porosity of coatings increased.While the rotational velocity increased, the friction coefficient and volume wear loss of coatings reduced with the condition of load 500g and overall revolution 5000r, but the friction coefficient and volume wear loss of 40ZAT coating was least in the same rotational velocity. At the same time, the volume wear rate of coatings increased with wear time increased, and the volume wear rate of 40ZAT coating was least in the same wear time. Study suggested that the microhardness and the fraction toughness effected on friction and wear performance of coatings, but the fraction toughness played an important role on wear performance of coatings. In addition, the wear mechanism of 10ZAT and 20ZAT coatings were surface fatigue creatived spalling wear, and the 40ZAT coating was abrasive wear and adhesive wear, but mainly in abrasive wear. On the other hand, the friction coefficient of 40ZAT coating reduced with the loadings increased in high speed friction and wear condition, but the wear rate was increased. The wear mechanisms changed from abrasive wear and light spalling wear to micro-brittle fracture created spalling wear and adhere wear.The diffierent contents of ZrO₂ effected on physical properties and tribological properties of ZrO₂/Al₂O₃ ceramic coatings, and yet it was the best that 40ZAT coating was provided with the fracture toughness and tribological properties as above narrated.