Influence of negative bias voltage and deposition temperature on microstructure and properties of superhard TiB2 coatings deposited by high power impulse magnetron sputtering

It is critical to utilize the substrate bias voltage to attract the sputtered ions in high power impulse magnetron sputtering (HIPIMS) plasmas which contain a large amount of target ion species. In this work, superhard titanium diboride (TiB2) coatings were synthesized from TiB2 compound target by a HIPIMS technique at deposition temperatures of 200 °C and 300 °C, respectively. The substrate bias voltage was altered from 0 V to − 200 V. The influence of the bias voltage at 200 °C and 300 °C on the chemical composition, phase structure, microstructure, surface morphology, mechanical and nanowear properties of the TiB2 coatings was investigated. The results indicated that the chemical composition and microstructure were significantly altered by increasing the bias voltage. At 200 °C, the moderate bias voltage of − 50 V to − 100 V lead to enhanced ion energy and surface adatom mobility while the resputtering effect was induced as the bias voltage further increased from − 100 V to − 200 V. The TiB2 coating deposited at − 100 V exhibited the best mechanical and nanowear properties and lowest surface roughness. At 300 °C, the continuous increase of the surface adatom mobility as the bias voltage increased from 0 V to − 200 V acted as the dominant influence factor for the coating properties. The TiB2 coating with the best mechanical and nanowear properties and lowest surface roughness was obtained at − 200 V.