The Friction and Wear Behavior of Ion Beam Assisted Nitride Coatings
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THE FRICTION AND WEAR BEHAVIOR OF ION BEAM ASSISTED NITRIDE COATINGS Thomas G. Tetreault, J.K. Hirvonen, and G. Parker Spire Corporation, Patriots Park, Bedford, MA 01730 J.P. Hirvonen, University of Helsinki, Helsinki, Finland
ABSTRACT The method of Ion Beam Enhanced Deposition, (IBED), was used to produce hard films of i-BN, i-SixNv and i-TiN . The friction, hardness, adhesion, and wear behavior of these nitride coalings were examined using a ball-ondisc Friction/wear tester. The friction and wear results were sensitive to stoichiometry and the presence of impurities (e.g., hydrogen) in the film as well as the choice of ball material (400C stainless steel or silicon nitride). INTRODUCTION Because of their high hardness and refractory nature, many nitride compounds are excellent candidates for coatings in a variety of high mechanical and/or thermal stress applications [1]. As is often the case with any coating, and in particular with coatings to be used under conditions of high stress, a key limiting factor to optimum performance is its ability to adhere to the substrate upon which it was deposited. Recently, the technique of IBED has become an increasingly studied method of applying highly adherent coatings. The IBED process, shown schematically in Figure 1, consists of an electron beam evaporation of a solid phase (viz., boron, silicon, or titanium) onto a substrate and simultaneous bombardment of the growing layer with energetic (100 - 1000 eV) ions (viz., N2 t and N+). Ion beam bombardment results in a mixed zone interface between substrate and coating, and characteristically gives IBED-grown films superior adhesion as well as higher density and lower porosity, compared to similar films by more conventional techniques, due to the reduction of columnar microstructure growth. EXPERIMENTAL The IBED facility shown schematically in Figure 2, is a two-chambered, differentially pumped, high vacuum system. The lower evaporation chamber contains the electron beam evaporator and is pumped by a four-inch LN 2 trapped diffusion pump. The upper target chamber contains the sample holder and is pumped by an eight-inch cryopumy. The usual working base pressure for the system throughout is 1 x 10- torr (1.3 x 10-5 pa) with water being the predominant component as determined by an in-situ residual gas analyzer. For the coatings in this study, the evaporation rate of the solid phase was set at 2-4 A/sec and was controlled by a quartz crystal rate monitor while the nitrogen ion flux at the substrate was 150-500 microamps/cm2 . The ratio of ion flux to evaporant rate was varied per deposition in order to influence the stoichiometry of the resulting coatings. All coatings were deposited on Si (100) wafers.
Mat. Res. Soc. Symp. Proc. Vol. 128.
1989 Materials Research Society
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