| The plasma sprayed NiCoCrAlY coatings on Inconel 713C substrates were boronizeci or boronized and aluminized. The mechanical properties and hot corrosion resistance of the NiCoCrAlY coatings were studied. Mechanical properties were measured by the microhardness and abrasion tests, and hot corrosion resistance was examined by the cyclic hot corrosion test. The microhardness at the 30㎛ from the surface of the boronized samples was about 1200Hv, which is approximately five times, relative to the as-sprayed NiCoCrAlY coatings probably because of the formation of borides such as Ni₂B and Co₂B within the samples. When the samples were aluminized after boronizing, the samples showed the cross sectional hardness of more than 1200Hv because of the homogeneous distribution of the borides and good hot corrosion resistance, relative to the boronized samples. The heat treated samples after the boronizing and aluminizing contained NiAl phase at the surface. The heat treated samples showed increased cyclic hot corrosion resistance, compared with aluminized after boronizing. Also the heat treatment enhanced abrasion resistance significantly, but did not affect the hot corrosion resistance. It can be, therefore, concluded that the heat treatment after boronizing and subsequent aluminizing for the NiCoCrAlY coatings is necessary to improve the mechanical properties and hot corrosion resistance. |
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