Effects of Additive CeO_2 on Thermal Shock Resistance of Cr_2O_3 Coating
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The influence of additive CeO 2 with different content on the thermal shock resistance of plasma sprayed Cr 2O 3 coating was studied.It is found that the addition of 3.0%CeO 2 to Cr 2O 3 layer reduces the amount and the size of the pores in ceramic layer,and thus increases the resistance to thermal shock.The thermal shock failure of ceramic coating is essentially the fatigue failure induced by cyclic thermal stress during repeated heating and cooling.Keywords:
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Abstract By addition of a Ni-Cr undercoating to a steel substrate, a ZrO2; coating with high thermal shock endurance was produced. This coating resists to an initial quenching temperature gradient of 1000 K. The plasma spray coating material is 7wt%-CaO stabilized ZrO2 powder. The chemical composition and the thermal expansion coefficient of the base steel, and also the Ni-Cr undercoating were evaluated for thermal shock endurance. The thermal shock endurance of the ZrO2 coatings is enhanced by the (Cr+Co) contents in the steels and by applying a Ni-Cr undercoating. The thermal expansivities of the steels have little influence on the thermal shock endurance. The carbon in the steels deteriorates the bonding of the Ni-Cr undercoating, but does not influence the ZrO2 coatings themselves.
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Thermal shock
Temperature cycling
Particle (ecology)
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WT5BZ]The influence of additive CeO 2 and SiO 2 with different content on the thermal shock failure life of Cr 2O 3 coating was studied It is shown that the thermal shock failure mechanism of coating is thermal stress fatigue destruction through thermal shock text The critical temperature range △T C can be greatly enhanced by adding CeO 2 and SiO 2 to Cr 2O 3 layer through reanalysis the results of thermal shock experiment date The addition of proper amount of CeO 2 to Cr 2O 3 layer obviously increase the coefficient of coating's resistance to thermal shock , but proper amount of SiO 2 to Cr 2O 3 layer greatly increase △T C The choosing additive is based on the serve condition of coating When coating works at temperature being lower 300℃,the adding 3 0% CeO 2 to Ce 2O 3 layer is chosen because which has the best complex property But, when coating works between 300℃ and 500℃, the SiO 2 is chosen as additive to Cr 2O 3 layer, which has longer thermal shock lifetime
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The hollow mullite thermal barrier coatings were deposited by Micro-plasma Spraying technique.The bond strength,thermal barrier capability and the anti-thermal shock ability of the coating were tested.The tested results show that the average bond strength of the coating is 5.63 MPa,the fracture begins in the top coating;The thermal barrier of the coatings goes up form 11.5 ℃ to 40 ℃ under the surface temperature going up form 400 ℃ to 900 ℃ conditions in which the steady-state test is employed;the anti-thermal shock times are 165,135,117,81,and 34 when the test temperature is between 400 ℃ and 800 ℃ with interval of 100 ℃;the initial spallation of the mullite coating occurs at the edge of the specimen,and its speed increases at the end of thermal shock life.The main failure reason of the coatings is the thermal residual stress accumulated during the thermal shock test.
Thermal shock
Mullite
Residual strength
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The influence of CeO2 with different content on the thermal shock resistance of plasmasprayed Cr2O3 coating was investigated. The thermal shock failure mechanism of coating was also studied. It is found that the thermal shock failure mechanism of coating is thermal stress fatigue destruction, and the destruction takes place at interface of ceramic and bond coating. The experimental results show that the lifetime of coating fracture and failure increase considerably when 3% CeO2 is added into the plasma-sprayed Cr2O3 coating. The suitable content of CeO2 makes the microcracks exist in network form. The microcrack net can release internal stress in coating, delay the crack forming and expanding and decrease holes in coating. Thus the thermal shock resistance increase largely.
Thermal shock
Failure mechanism
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Thermal shock
Plasma electrolytic oxidation
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The influence of CeO 2 with different content on the thermal shock resistance of plasma sprayed Cr 2O 3 coating was investigated. The thermal shock failure mechanism of coating was also studied. It is found that the thermal shock failure mechanism of coating is thermal stress fatigue destruction, and the destruction takes place at interface of ceramic and bond coating. The experimental results show that the lifetime of coating fracture and failure increase considerably when 3%CeO 2 is added into the plasma sprayed Cr 2O 3 coating. The suitable content of CeO 2 makes the microcracks exist in network form. The microcrack net can release internal stress in coating, delay the crack forming and expanding and decrease holes in coating. Thus the thermal shock resistance increase largely.
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Failure mechanism
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Plasma sprayed Al_2O_3-TiO_2/NiCoCrAlY coatings with a gradient distributed composition or non- gradient distributed compositions were prepared on ZL104 aluminum substrate.In order to study the thermal shock resistance and thermal shock failure mechanism of Al_2O_3-TiO_2/NiCoCrAlY coatings,the samples were heated to 400℃ and hold a certain time then cooled to room temperature by quenching.The results stcow that the thermal shock resistance of gradient coating is much better than that of non-gradient coatings.The main cause of coating flaking-off is due to the thermal stress caused by different thermal expansion coefficients.The gradient distributed composition would release the stress in some extent and it is also of benefit to thermal-shock resistance of the coatings.After heating and cooling,the samples are bent because of the differences of dilation coefficient and heat conductivity between coating materials and substrates,or the plastic deformation of aluminum substrate.The deformation cause a residual strength stress in the coating and reduced its thermal shock resistance.
Thermal shock
Temperature Gradient
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