THE CHEMISTRY, STRUCTURE, AND RESULTING WEAR PROPERTIES OF MAGNETRON-SPUTTERED NBN THIN-FILMS

The structural and tribological properties of niobium nitride (NbN) fi lms are investigated because of their potential to improve the wear-li fe and corrosion resistance of bearing components operating in extreme environments such as turbine engines and spacecraft. The films are de posited onto 440C stainless steel substrates by magnetron sputtering. Nitrogen partial pressure (PN,) is varied to change the crystal struct ure of the films. At 4 x 10(-4) torr, the films are cubic: as the part ial pressure of the gas is increasing fraction of hexagonal delta'-NbN phase appears. The substrate bias potential is adjusted to affect the film microsructure. Wear properties and friction coefficients are stu died using a ball-on-flat tribometer with Si(3)h(4) and stainless stee l balls as the counterface materials. Film hardness and adhesion prope rties are measured using a nano indentation tester and a scratch teste r, Chemistry and microstructure: are characterized using X-ray photoel ectron spectroscopy, XRD, SEM and TEM. The films have friction coeffic ients of approximately 0.6 and 0.7 when slid against Si3N4 and stainle ss steel balls. respectively. They have hardness of about 30 GPa. and an adhesion of 2-3 kgf, ns measured by scratch testing. SEM micrograph s indicate the films are smooth and dense. The films are somewhat N de ficient on the basis of XPS,the film chemistry and stoichiometry do no t change significantly with bias or PN2. (C) 1997 Elsevier Science S.A .