| In metallurg, energy, aerospace and chemical industry, many parts often work in the environment of high temperature, the resistance to high temperature oxidation performance of materials proposed higher requirements. Nickel base high temperature composite coating of electrodeposition is to improve the high temperature oxidation behavior of materials is one of the effective methods, the process with multi coating composition, process is simple, low cost advantage has been paid more and more attention. Al and Cr, which are important high temperature oxidation elements, can protect the metal substrate from oxidation by forming a dense layer of oxide film in the material surface. In this paper, the sol-gel method is adopted to the surface coating modification of Al and Cr particles, Ni-Co/Al(Cr) composite coatings were successfully prepared by electrodeposition. Some useful conclusions are obtained for the test of high temperature oxidation resistance of the composite coatings.The sol-gel method is adopted to the surface coating modification of Al and Cr particles, the main evaluation index of the coated particles is its organization structure, size and coating compactness. And after study its process, it is found that the suitable process for Si O2 coated Al(Cr) particles is m Al( Cr): m TEOS:mquadrol:VKH-550: VH2O: Valcohol:Vethanol solution=1:1.5:0.75:0.3:36:20:6, coating temperature 40°C, coating time 5 hours. The surface coating of Al(Cr) powder particles out of sol-gel method is amorphous-structure Si O2. Ultrasonic dispersion treatment can effectively improve particle reunion situation, coated Al powders particle size decreases by 31%, coated Cr powders particle size decreases by 14%. Coating time and coating temperature have remarkable effect on the size distribution of coated powder particles and the compactness of coatings. The particle size increases with the increase of the coating time and temperature, under the suitable coating technology the average particle diameter of coated Al powder is 8.583 um and Cr is 8.161 um. The compactness of the coating increases with the increase of the coating time, if coating temperature increases, the compactness firstly increase and then decrease sharply, under the suitable coating technology the corrosion inhibition rate of Si O2 coated Al particles is 98.3% and of Cr is 97% in 0.1mol/L hydrochloric acid solution, can effectively prevent the dissolution of Al(Cr) particles in acidic solution.The process conditions for preparing Ni-Co/Al(Cr) composite coating by electrodeposition method is 1g/L coated Al powers(2g/L coated Cr powers or 2g/L mixed powder of coated Al powder and coated Cr powder, the mixed powder mass ratio is 1:1),the bath temperature of 45°C, p H 3.2, the intermittent mixing frequency(stirring times per hour) is 3, three kinds of composite coatings Ni-Co-27.82 Al, Ni-Co-33.23 Cr, Ni-Co-12.18Al-16.19Cr(wt%)were prepared by this technique. When coated Al(Cr) powder and Ni-Co matrix metal co-deposite Ni-Co/Al(Cr) composite coating, the 2nd phase particles can change the preferred orientation of grains, the coating is in amorphous transformation tendency. Ni-Co/Al(Cr) composite coating is a kind of Ni based solid solution structure with Al(Cr) particles, which is closely com bined with the matrix. The diffusion of Al particles in the composite coating is more evenly distributed in the coating under 800°C heat treatment, at the same time, the reaction of Al and Ni is composed of the second phase particles to change the Al3Ni2 phase and Ni3 Al phase, Cr particles are diffusing to metal matrix via element diffusion effect, and the coating is crystallized; The composition coatings are uniform and stable after 80 min diffusion heat treatment at 800°C. The hardness of the coating decreases with the prolonging of the diffusion heat treatment time.After 20 h of oxidation at 900°C, weight gain of composite coatings Ni-Co-27.82 Al, Ni-Co-33.23 Cr and Ni-Co-12.18Al-16.19 Cr is 0.99mg·cm-2, 1.14mg·cm-2, 4.39mg·cm-2, after 20 h of oxidation at 1000°C, weight gain of composite coatings Ni-Co-27.82 Al, Ni-Co-33.23 Cr and Ni-Co-12.18Al-16.19 Cr is 1.91mg·cm-2, 5.87mg·cm-2,6.16mg·cm-2, the oxidation kinetics curve of three kinds of composite coatings basically obeys the parabolic growth law.Composite coating at 900°C and 1000°C under constant temperature oxidation of 20 h, the outermost oxide layer of all them is Ni O with small plane. The 2nd outmost oxide layer of Ni-Co-27.82 Al is the composite oxide of Ni O, Al2O3 and Ni Al2O4. The 2nd outmost oxide layer of Ni-Co-33.23 Cr is the composite oxide of Ni O, Cr2O3 and Ni Cr2O4. The 2nd outmost oxide layer of Ni-Co-12.18Al-16.19 C is the composite oxide of Ni O, Al2O3, Cr2O3, Ni Al2O4 and Ni Cr2O4. During the oxidation of 900°C, the oxide layer of both Ni-Co-27.82 Al and Ni-Co-33.23 Cr composite coatings is dense and continuous, the coating has excellent resistance to high temperature oxidation. When up to 1000°C, the oxide layer of Ni-Co-27.82 Al composite coatings is also dense and continuous, and the coating's resistance to high temperature oxidation is also good, however, the Ni-Co-33.23 Cr composite coating decreases the density of the oxide layer, the diffusion performance is enhanced, and the high temperature oxidation resistance of the coating decreases dramatically. At 900°C and 1000°C oxidation, Ni-Co-12.18Al-16.19 Cr composite coating's oxide layer is complete and continuous, but its resistance high temperature oxidation performance is poor. |
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