Research Of Modified NiCrAlY Coating With Nano CeO₂

In this research, rare earth oxides were added in NiCrAIY coatings to modify the coatings properties. Four modified NiCrAIY coatings containing different amount of rare earth oxides were prepared. The coatings were deposited by HVOF spray and plasma spray on to 45 steel and stainless steel. The hardness, thermal shock resistance, high temperature resistance and bond strength of modified and unmodified NiCrAIY coatings were evaluated.Four kinds NiCrAlY feed powders contained 0.5%, 1%, 2% and 4% rare earth oxide were prepared by ball milling. The microhardness was evaluated on the polished cross section of coatings, and the load was 100g. The microhardness of three modified NiCrAlY coatings were improved compared to that of unmodified NiCrAlY coatings. The maximum improvement of microhardness was about 41.1% compared with unmodified coatings. Thermal shock tests were performed by water quenching method in this research. The number of cycles to failure was used to represent thermal shock resistance of coatings. All of modified NiCrAIY coatings exhibited immense improved thermal shock resistance. The thermal shock cycles of unmodified NiCrAlY coatings was 45, however, the thermal shock cycles of modified coatings was increased to 66. The high temperature resistance of coatings was tested by heating persevered samples at 1000℃. After 100 hours high temperature oxidation tests, there were some spherical oxides formed on the surface of unmodified NiCrAlY coatings. However, there was no visible change on the modified NiCrAlY coatings surface. When the high temperature oxidation time was 190 hours, the amount of spherical oxides on unmodified coating surfaces increased and the volume of those oxides enlarged compared to those of at 100 hours. There were about one-third areas of unmodified coating surfaces overlapped by formed spherical oxides. In the same condition, there was still no visible change on the modified NiCrAlY coatings surface. The high temperature oxidation test results showed modified coatings possessed more excellent high temperature resistance than unmodified coatings. The bond strength of coatings was evaluated by drawing process on a universal tensile testing machine. With incensement of added CeO2, the bond strength of modified NiCrAlY coatings firstly increased and then decreased. The maximum bond strength of modified coatings was improved 34.1% compared to that of unmodified coatings. Scanning electron microscope, X-ray diffractometer and optical microscope were used to analyze the microstructure of coatings. Test results showed the modified NiCrAlY coatings possessed improved properties compared to unmodified NiCrAlY coatings. The thermal shock resistance improved 50% and the bond strength improved 34.1% for modified NiCrAlY coatings compared to unmodified NiCrAlY coatings.