Advanced film/substrate interface engineering for adhesion improvement employing time- and energy-controlled metal ion irradiation

Pre-deposition substrate etching by metal ion bombardment is an efficient and fast cleaning method that ensures improved chemical and topological substrate surface modification. Here, we study the effects of metal ion mass and kinetic energy on etching of industrially-relevant cemented carbide (WC) substrate as well as on adhesion at the Ti0.50Al0.50N/WC interface. Cr+ or W+ ion fluxes are generated by high-power impulse magnetron sputtering (HiPIMS), while their kinetic energy Ekin is tuned by applying negative substrate bias voltage synchronously with the metal ion-rich portion of the flux. The time evolution of ion fluxes at the substrate plane is studied with energy- and time-resolved ion mass spectrometry. The threshold substrate bias voltage required to initiate substrate etching is in the 900–1000 V range for both Cr+ and W+ fluxes. Moreover, we show that the adhesion strength of Ti0.50Al0.50N coatings correlates with Ekin. For Ekin < 900 eV, Cr or W interlayers are grown and no significant improvement in the adhesion strength is observed. Contrary, for Ekin > 900 eV, effective substrate etching with energetic metal ions significantly improves the adhesion strength: we demonstrate an increase of 76–79 % after etching with metal ions as compared to the untreated substrate.