Effect of Cu addition on the microstructure and properties of TiB2 films deposited by a hybrid system combining high power impulse magnetron sputtering and pulsed dc magnetron sputtering

TiB2 films with various Cu contents were deposited on the single crystalline Si (100) wafers and SUS 304 stain steel substrates by a hybrid coating system combining high power impulse magnetron sputtering (HiPIMS) and pulsed direct current (PDC) magnetron sputtering. The Cu contents (0-19.2 at.%) in the films were controlled by changing the PDC sputtering power. The composition, microstructure and mechanical properties of TiB2-Cu films were systematically investigated in this work. The results indicated that the pure TiB2 film exhibited columnar structure and strong (0001) preferred orientation, whereas with Cu addition, the (0001) peak became broader and finally disappeared at Cu content of 11.9 at.%, suggesting the formation of nanocrystalline/amorphous tissue phase in films. The existing form of Cu was altered by increasing the Cu content. All the films demonstrated relatively smooth surfaces, confirmed through atomic force microscope (AFM) analysis, with average roughness of about ~3 nm. As the Cu content increased from 0 to 19.2 at.%, the hardness showed a significantly increment initially, due to the solid solution strengthening and formation of a nanocomposite structure, and then dramatically decreased from 32 GPa to 18 GPa, due to the excess softer amorphous Cu phase in the films. In addition, the resistance of the films with various Cu contents to cracking was investigated by exploring the surface morphology after Vickers indentation. The results proved that both hardness and toughness were enhanced by doping proper Cu contents.