W-ion irradiation promotes dense TiB film growth during magnetron sputtering without substrate heating

Lowering energy consumption during thin film growth by magnetron sputtering techniques is essential for future industry as a step towards reaching the United Nations sustainable development goals. Large potential for energy savings has been demonstrated by employing high-mass metal ion irradiation from targets operated in high impulse magnetron sputtering (HiPIMS) mode. With this approach, tested for transition metal (TM) nitrides, thermally-induced adatom mobility is replaced with that supplied by overlapping collisions cascades of low-energy recoils, resulting in a strong reduction of the necessary external heating. Here, the novel method is tested for TiB x , which is a model system for TM-based diborides, another class of promising materials to be used as protective coatings for cutting tools. We show that such films grown with no external substrate heating develop porosity over a wide range of B/Ti ratios. However, (Ti 1- y W y )B x films grown by the hybrid W 2 B 5 -HiPIMS/Ti-TiB 2 -DCMS co-sputtering with substrate bias synchronized to W + /W 2+ -rich ion fluxes, are dense (without porosity), irrespective of x . Nanoindentation hardness increases from ~20 GPa for TiB x to ~40 GPa for (Ti 1- y W y )B x . The slightly understoichiometric (Ti 0.86 W 0.14 )B 1.91 film exhibits super-hardness and is nearly stress-free. These results prove that selected heavy ion irradiation is beneficial for low-temperature growth of hard diboride films, which demonstrates the versatility of this approach and calls for evaluation in other material systems. • W-ions provide sufficient adatom mobility to grow high-quality films at low T • TiB x films grown by DCMS with no external substrate heating are porous • (Ti 1- y W y )B x films deposited by W 2 B 5 -HiPIMS/Ti-TiB 2 -DCMS co-sputtering are dense • significant increase of hardness is obtained with the addition of W 2 B 5 -HiPIMS • slightly understoichiometric Ti 0.86 W 0.14 B 1.91 films are superhard while stress-free