Microstructure, Micro-Indentation, and Scratch Behavior of Cr Films Prepared on Al alloys by Using Magnetron Sputtering

In this study, closed-field unbalanced magnetron sputtering (CFUMS) was employed to deposit pure Cr films on soft substrate of 2024 Al alloy. The effects of deposition powers and biases on the microstructures and mechanical performance of Cr films were systematically investigated by using X-ray diffraction (XRD), scanning electron microscope (SEM), micro-indentation and scratch test. Results showed that all the Cr films had a strong (110) preferred orientation and anisotropic surface morphology with columnar structures. The size of Cr particles was in the range of 50-350 nm, increasing with larger target power and higher biases. The hardness of Cr films was between 3.3 and 4.8 GPa, which was much higher than the Al alloy substrate (1.44 GPa). The Young's modulus of Cr film could reach a maximum value of 169 GPa at 2.0 kW/70 V. The critical load increased when increasing the power but decreased with higher bias, achieving a maximum value of 53.83 N at 2.0 kW/10 V. The adhesive failure mechanism of Cr film was mainly attributed to the plastic deformation of softer Al substrate.