Preparation Of Chrome Carbide Coatings On Carbon Steels By PIRAC Method

Hydraulic metal structures are important parts in the water resources and hydropowerprojects. Corrosion and wear of related parts would seriously affect the safety of waterconservancy and hydropower projects. Frequent reparation and replacement of metal partsand thus induced efficiency decrease of related hydraulic machinery parts also deteriorate theeconomic benefits of water conservancy and hydropower projects. Chromium carbideceramics have been attracting intensive research for coatings due to its high hardness、corrosion resistance and wear resistance. PIRAC (Powder Immersion Reaction AssistedCoating) is a low cost method and can easily obtain smooth good adhesive coatings oncomponents with complex shapes.In the present work, thermodynamic analysis was applied to determine the reactionpowder, temperature range and the powder used in outer container for preparation of chromecarbide coatings by PIRAC. Microstructure, phases composition and oxidation behaviors ofchrome carbide coatings prepared on T/P24by PIRAC under different conditions werestudied. Then, preparation parameters were optimized. Effect of T/P24and Q235substrateson microstructure, phase composition, hardness and friction behavior of the PIRAC chromecarbide coating were studied. The main research results are as follows:1. Thermodynamic analysis was applied to determine the reaction powder, temperaturerange and the powder used in outer container. The preferential reaction powder and thepowder used in outer container were chromium powder and titanium powder, respectively.The temperature range was800oC-1050oC.2. Effects of different treatment temperature and treatment times on chromium carbidecoatings prepared on T/P24by PIRAC. Results show that uniform and dense chromiumcarbide coatings could be prepared on T/P24by PIRAC. Phase composition andmicrostructure of the prepared coatings are differs with PIRAC treatments. Coatings preparedat lower temperature is consists of Cr23C6, Cr7C3and Cr3C2. And the lower the PIRACtemperature is, the more the Cr7C3and Cr3C2are. While, at higher temperatures or longertreatment times, Cr23C6is subtotal phase of the produced coating. 3. Compared the oxidation resistant properties of chromium carbide coatings preparedat different temperatures and different processing time. Optimized preparation parameterswere treatment at900oC for4h.4. Effects of T/P24and Q235two substrates on phase composition, morphology andhardness of coatings were studied. Cr23C6was the only detected carbide for both of thesubstrates after4hours PIRAC treatment, suggesting the two substrates have no effects onphase composition of the formed carbide. Both of the coatings had uniform distributed smallpores or pits. The coating on the T/P24was smooth while that on Q235was coarse composedof granular film. Hardness of coatings prepared on Q235was higher than that of the coatingsprepared on T/P24.5. Friction behavior of coatings prepared T/P24and Q235were comparatively analyzed.Results show that: friction coefficient of coatings prepared on Q235was lower than thatcoatings prepared on T/P24. Wear resistance of coatings prepared on Q235are higher thanthat coatings prepared on T/P24.