Low-temperature deposition of Al-rich α-(Al, Cr)2O3 films by sputtering AlxCr95-x(α-Al2O3)5 targets

A newly designed AlxCr95-x(α-Al2O3)5 (x = 60, 70, and 80 at.%) composite target was proposed for depositing a corundum-structured Al-rich α-(Al, Cr)2O3 film at low temperatures. The elemental composition, phase structure, and mechanical properties of the films deposited by sputtering AlxCr95-x(α-Al2O3)5 composite targets with different Cr contents, Al75Cr25 targets, and pure Al targets at low deposition temperatures were examined using electron probe microanalysis (EPMA), grazing incident X-ray diffraction (GIXRD), transmission electron microscopy (TEM) and nanoindentation tests. The results showed that the film deposited at 550 °C by sputtering an Al70Cr25(α-Al2O3)5 target consisted of a single Al-rich α-(Al0.74Cr0.26)2O3 phase with a high nanohardness of 30.2 GPa, a high H/E ratio of 0.12, and a high elastic recovery value of 0.61. Increasing the Al content by sputtering an Al80Cr15(α-Al2O3)5 target led to the formation of mixed phases, including κ, amorphous, and Al-rich α-(Al, Cr)2O3 phases, in the film. When decreasing the Al content by sputtering an Al60Cr35(α-Al2O3)5 target (i.e., x = 60), the phase composition of the film was Cr-rich α-(Al, Cr)2O3 and Al-rich α-(Al, Cr)2O3. The coincorporation of 25 at.% Cr and 5 at.% α-Al2O3 powder in the Al70Cr25(α-Al2O3)5 target not only facilitated the formation of the α-(Al, Cr)2O3 phase but also increased the Al content when the substrate temperature was greater than 550 °C.