Microstructural, mechanical properties and high temperature oxidation of Cr, Al-coated Zr-4 alloy

Cr and Al coating were respectively deposited on Zr-4 alloy by magnetron sputtering and high temperature oxidation (HTO) tests were conducted in air environment at 1200 °C for 3 h for Cr-coated and Al-coated specimens. The morphology and phase composition of the specimens were detected by SEM, EDS and XRD. The adhesion properties were characterized by scratch test. The XRD results revealed that the two coatings were crystalline with preferred orientation. The results of scratch testing showed that critical load of Cr coating was higher than that of Al coating. After HTO test, the Cr-coated specimen was intact without cracking and spalling off, only the outermost layer of Cr coating was oxidized to a Cr2O3 layer of about 4 μm thick with a residual Cr layer of about 4 μm thick, and the internal zirconium alloy was not oxidized. For Al-coated specimen, besides the complete oxidation of the Al coating, there were also about 500 μm Zr-4 alloy oxidized on each side, and there were a lot of voids and cracks in the specimen. The EDS results indicated that a thickness of about 5 μm Cr-Zr diffusion layer developed at the interface between Cr coating and Zr-4 alloy for the Cr-coated Zr-4 specimen. While, for the Al-coated Zr-4 specimen, Al diffused into the specimen to a depth of about 100 μm, and Zr diffused almost to the outermost layer. Moreover, Sn in the Zr-4 alloy is concentrated at the interface between the residual Zr-4 alloy and ZrO2 layer. The obtained results manifested that Cr coating shows better oxidation resistance than Al coating.