Structure And Properties Of Chromium Films Deposited By D.C Magnetron Sputtering On Zircaloy Substrate

Thin film materials have been widely used in industry and high-tech field. Many researches have been taken on various films, but to our knowledge, little work has been done on Chromium (Cr) films deposited on Zircaloy substrate. We try to use Cr thin films to improve Zircaloy's properties on the background of engineering application. In this paper, we deposited Cr films on Zircaloy substrate by D.C magnetron sputtering, and made a preliminary study on the microstructure of these films and the properties of microhardness and adhesion.The Zircaloy substrates were prepared with different pretreatment, then Cr films with the thickness of 0.5μm l.0μm 2.0μm 3.1 μrn and Cr/Nb Nb/Cr binary films were deposited with the same deposition parameters. Some of these samples were annealed separately at 300 ℃% 500 ℃ for one hour and 700 ℃ for 49 hours.The composition of the Cr film was identified by X-ray diffraction (XRD), the interface of Chromium/Zircaloy was studied with scanning electron microscopy (SEM), the morphology of Cr film was observed with atomic force microscopy (AFM). The results showed that the Cr films grew with an inland pattern, and the crystal grains were the type of fiber or conical. With the thickness of Cr film increased from 0.5 μ m to 2 μ m, the grains grew rapidly, the compact fine fiber grains became the ones with conical top. The X-ray diffraction (XRD) analysis indicated that there was a preferred orientation in the Cr films. Annealing at 500 ℃ for an hour could reduce the texture, flaw and compression stress in the films,while Annealing at 750℃ for 49 hours made the films have a recrystallization change, and the recrystal grains were larger then before. The analysis showed that it was a pseudo-diffusion interface between the film and the substrate.The microhardness of all films were tested by microhardness instrument. The results showed that both annealing after the deposition and ion bombardment before the deposition can increase the microhardness. The effect of ion bombardment was more obvious, without ion bombardment the microhardness of Cr film with the thickness of 3.1μ m was1568HK, and ion bombardment made it to 2070HK. When the films were 0.5 μ m and 1.0 μ m, the microhardness was influenced by the substrate in this test.The adhesion of thin film is a critical property for the film to be used in practice. In this study, scratch adhesion tests were performed on a WS-97 Automatic Scratch Tester, we compared the L_cr(Critical Load)of the films with different treatment. We found that the degree of roughness of the substrate's surface had little effect on the adhesion of Cr film; Annealing increased the diffusion of atoms near the interface, and improved the adhesion, and ion bombardment also improved the adhesion of Cr film, the LCT was twice as that of the film without of ion bombardment; When the thickness of Cr film increased from 0.5 μ m to 2.0 μ m, the adhesion decreased about 50%; The Lcr of Nb/Cr binary film was 34 N, which was higher than that of Cr/Nb binary film(14.5N) and that of the pure Cr film with the same thickness(11.5N), indicating the Nb/Cr binary film has a much better adhesion to the Zr substrate.