| As an effort to improve the mechanical properties, the Cr₂O₃ coatings formed on SM45C substrates by the plasma spraying were subjected to annealing or hot press treatment. After each treatment, mechanical properties such as microhardness, abrasion and bond strength of annealed or hot pressed coatings were compared with the as-sprayed coatings. In case of annealing treatment, as the annealing temperature increased, the porosity decreased. Microhardness and abrasion characteristics were also improved upon annealing. In particular, abrasion characteristics of Cr₂O₃ coatings annealed at 1100℃ were improved 5 times as high as the as-sprayed coating. In case of hot pressing treatment, the increase of temperature and pressure leaded to the improvement of porosity, microhardness and abrasion characteristics of the coatings. The best experimental results were obtained at 900℃ and 30MPa. Specifically, at this condition, the porosity was as low as 4.1% and abrasion characteristics were improved 8 times as good as the as-sprayed coating. Bond strength which was not improved by only annealing or hot press treatment was improved by incorporating the Functional Gradient Layer(FGL). Annealing after forming FGL produced about 14MPa higher bond strength than annealing without FGL, and hot press treatment with FGL showed even better results. |
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