Ultrafast deposition of ultrahard Cr films in tubes by bipolar-HiPIMS with small target-substrate distance

The PVD deposition of films with excellent surface properties has been a persistent area of research. In this paper, bipolar high power impulse magnetron sputtering with small target-substrate distance is proposed, and ultra-hard Cr films have been deposited with a higher rate in tubes. The microstructure and mechanical properties of the films were characterized using X-ray diffraction, scanning electron microscopy, nanoindentation and scratch test, and compared with films prepared under conventional conditions. With target-substrate distance of 7.5 mm, the ultrafine columnar structure is fabricated due to intensive glow discharge and direct particle-bombardment in high-density plasma. The small grain size of 7.4 ± 0.3 nm is observed although deposition rate as high as 10 μm/hr. The nanohardness of the films reaches 19.94 ± 1.14 GPa, much higher than that reported in the literatures. Meanwhile, the adhesion between film and substrate may be as high as 77 ± 5 N.