CrN-Ag Self-Lubricating Hard Coatings
Abstract
CrN-Ag composite films, 2.5-4 microns thick, were deposited by reactive magnetron sputtering on Si and stainless steel substrates in a 0.4 Pa pure nitrogen atmosphere at 500 deg. C. The layer composition was controlled by the relative power to 7.5-cm-diameter Ag and Cr targets to be 0, 3, 12, and 22 atomic percent Ag. The layers exhibit a dense columnar microstructure where the Ag is homogeneously distributed in the CrN matrix. The coatings were vacuum annealed for t(sub a)=5 - 60 minutes at temperatures ranging from T(sub a) = 600 - 700 deg. C, to study the Ag-lubricant transport to the surface. Ag surface segregation during annealing is negligible for layers with 3 at.% Ag content. However, Ag diffuses to the surface of layers with greater than or equal to 12 at.% Ag and forms particles with diameters ranging, as a function of T(sub a) and t(sub a), from 50 - 1100 nm. Statistical analyses provide average particle sizes of 110 and 375 nm, and surface particle densities of 2 x 10(7) and 1.7 x 10(6) mm-2, for the 12 and 22 % Ag samples, respectively. The Ag diffusive transport occurs 2-3 times faster for the 22% than for the 12%-sample. We attribute the increase in Ag transport as a function of the total Ag concentration to a network of underdense pores that form during deposition due to Ag segregation into nm-size pockets. The pores grow in width and connectivity as the total Ag concentration is increased, leading to a faster Ag-transport at elevated Ag-concentrations. Room temperature micro-scratch tests show that the average friction coefficient decreases from 0.085 to 0.082 to 0.067 to 0.062, while the wear depth decreases from 0.41 to 0.35 to 0.25 to 0.18 microns, for increasing Ag concentrations of 0, 3, 12, and 22 at.%, respectively.
Document Details
- Document Type
- Technical Report
- Publication Date
- Mar 01, 2005
- Accession Number
- ADA587279
Entities
People
- C. P. Mulligan
- D. Gall
Organizations
- United States Army Armament Research, Development and Engineering Center