STUDY OF TUNGSTEN SPUTTERED FILMS WITH LOW NITROGEN-CONTENT

In this work, tungsten coatings doped with small percentages of nitrogen (%N < 10 at%) were deposited by sputtering and their characterization was focused in view of a possible future application as hard coatings. The films show an alpha-W (bcc) structure, significant changes in the X-ray diffraction peak positions not having been observed for the films containing nitrogen; however, these films have broader peaks than pure W films. All the films present a very dense cross-section morphology. Higher hardness values were found for the tungsten films containing nitrogen (HV = 15 GPa --> HV = [40-50 GPa]). The scratch-test results show that the coatings fail cohesively, firstly by tensile cracking for loads in the range [30-40 N] and after by chipping for loads in the range [50-60 N]. Pure W films present only tensile cracking. The films are structurally stable up to 700 degrees C annealing temperatures, even for a 12 h annealing time, only a narrowing of the diffraction peaks in relation to the as-deposited state being obtained. The hardness does not suffer significant alterations with increasing temperatures and annealing times.