| Yttria stabilized zirconia (YSZ) coating has excellent thermal barrier properties,good stability and abrasion resistance at high temperature, therefore it has been widelyused in the gas turbine and some components operating in hightemperaturecondition.In this paper, four principal spraying parameters were selected and optimized byorthogonal experimental design, namely, standoffdistance, power input, preheatingtemperature and powder feed rate, and their influences on the ZrO2 coating's bondstrength, porosity and deposition were studied. Furthermore, three different ZrO2powders were selected and three powder injection directions were coMPared, and theirinfluences on the coating's microstructures, properties and deposition were studied.Finally, the thermal shock resistance property was studied for evaluating the coating'sperformance. The failure modes was analysed preliminarily.The results indicated that under the involved conditions, the standoffdistance andpower input played most important role in both the bond strength and the porosity ofthe coating, which showed a reverse trend. When the standoffdistance changed from65mm to 150mm, the bond strength of the coating reduced from 56.7 MPa to 44.4 MPa,porosity increased from 5.53% to 7.57% and deposition efficiency reduced from 30%to 11.3%. When the spraying current changed from 500A to 650A , the bond strengthof the coating incresed from 50.3 MPa to 59.6 MPa, porosity decreased from7.75% to6.9% and deposition efficiency changed from 29.2% to 44.8%. When gasflowratechanged from 40 L?min 1to 80 L?min 1, the deposition efficiency changed from 39.6%to 25%, but it has a complicated influence on the bond strength and porosity of thecoating.The results of thermal shock resistance test indicated that three ZrO2 coatings, whichhave same thickness but different microstructures, have different thermal shock life.The coating which has a proper porosity(6.78%±0.94) exhibited the best performanceon thermal shock resistance test(12 times), the coating which has the highestporosity(10.0%±1.8)has the lowest the????ck life(6 times).With the powder injection directions changed from 75°to 105°, the powder flowhas a shorter residence time at the high temperature plasma flame zone, the porosity ofthe coating changed from 3.98% to 4.14%, the bond strengh of the coating changedfrom 58.1 MPa to 51.6 MPa and the deposition efficiency reduced from 41.6% to16.7%.At the same spraying process, A&S ZrO2 coating has the lowest porosity (4.09%), the highest bond strength (58.2MPa) and deposition efficiency (40%), A&N ZrO2coating has the highest porosity (6.31%), lowest bond strength (50MPa) and depositionefficiency (25%) due to the presence of large armout of unmelt zones in coating.Theresults of thermal shock resistance test indicated that the S&C ZrO2 coating has thehighest thermal shock life(14 times), and A&S ZrO2 coating has the lowest thermalshock life (3 times ), A&N ZrO2 coating did not show a higher thermal shock life thanconventional coatings (only 8 times). |
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