Evolution of microstructure and wear properties of aluminum thin films with sputtering substrate temperature

The influence of sputtering substrate temperature on the microstructure and wear properties of aluminum thin films deposited on stainless steel substrates by radio-frequency (RF) magnetron sputtering was studied. The aluminum films were deposited on stainless steel substrates at different temperatures of 70°C, 80°C and 100°C and at a constant power of 300 W. The surfaces of the films were then characterized by field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), surface profiling and wear methods. The wear was undertaken at extremely high sliding load of 50 N. Fine-grained and smooth microstructures exhibiting hillocks were observed at 70°C whereas coarse-grained and rough microstructures consisting of porous structures were obtained at 100°C. Defect-free and well-defined microstructures were obtained at 80°C. All the films obtained within this range of temperatures were crystalline according to the XRD results. Films obtained at 80°C were shown to have the highest coefficient of friction whereas those deposited at 100°C exhibited the lowest wear resistance. The films' failure along the edges of the balls under high sliding load were characterized by thinning, deformation and tearing (cracking).