ADVANCED COATINGS VIA HiGH POWER IMPULSE MAGNETRON SPUTTERING

Introduction Ta-Al-N and TiB2 films were deposited via High Power Impulse Magnetron Sputtering (HiPIMS), which is an advanced PVD technology that combines magnetron sputtering with pulsed power concepts. Applying high power pulses, large fractions of sputtered atoms and gas particles are ionized leading to high-density coatings with enhanced adhesion, often improved toughness and reduced columnar structure. Ta-Al-N is very promising for different technological applications due to its enhanced hardness and thermal stability, noteworthy high temperature oxidation resistance and toughness. TiB2 is a viable alternative material due to its high strength, melting point and conductivity. Moreover, it offers superior hardness, elastic modulus and abrasive wear resistance. Due to its low wettability, TiB2 is suited to coat cutting tools for non-ferrous alloys. Material and Methods Ta-Al-N layers were deposited on Si coupons via HiPIMS from a TaAl target. Working pressure, N2/(Ar+N2) ratio, power, temperature and frequency were kept constant. Conversely, the applied substrate bias voltage was varied from 0 to -100 V and the pulse length was changed over the range 25 - 200 ?s. Then, the authors reduced N2 percentage during sputtering from 50 to 5 % in an effort to improve wear resistance. TiB2 coatings were grown on TiAl6V4 alloy and Si substrates by both DCMS and HiPIMS technologies using a compound target. This study was focused on investigating the influence of frequency (250 - 1500 Hz), substrate temperature (RT - 400 °C) and bias on the resulting microstructure and mechanical properties. Discussion Concerning Ta-Al-N, reducing the N2 amount, a low nitrogen quantity was detected into the coating and also a very small Al at. % was measured. Indeed, the variation in transport behavior and ionization fraction of different species led to a deviation of Ta/Al ratio as compared to the target source. Moreover, microstructure varied and mechanical properties improved (H from ~27 to >30 GPa). HiPIMS stoichiometric TiB2 samples had hexagonal phase, with a marked (001) orientation. The highest hardness values were over 35 GPa. HiPIMS was effective in producing TiB2 specimens with increased toughness, hardness, elastic modulus, elastic strain to failure and resistance to plastic deformation.