RESIDUAL-STRESS, ATOMIC-STRUCTURE, AND GROWTH-MORPHOLOGY IN B4C SIC MULTILAYER COATINGS/

Engineered multilayer coatings offer a significant potential for impro ved tribological properties. A prime candidate for such a coating is B 4C/SiC multilayers, provided their microstructure and properties can b e quantified and controlled. Residual stress, atomic structure, and mo rphology of sputter-deposited B4C/SiC multilayer coatings on Si substr ates were studied. Double crystal diffraction topography (DCDT) was us ed to measure the average residual stress for a series of coatings of total thicknesses from 60 mm to 1.67 mu m. Residual stress for this se ries is close to a constant value, ranging from 3 to 4 GPa compressive , independent of total film thickness. Films were shown to have an amo rphous atomic structure using asymmetric grazing incidence X-ray scatt ering (GIXS) on a laboratory X-ray source. Surface morphology of the f ilms, as observed using atomic force microscopy (AFM), is found to be strongly affected by the presence of a radio frequency sputter bias on the substrates during growth. Removal of this bias introduced an addi tional short wavelength component to the roughness. Fracture surfaces of cleaved samples were observed in a scanning electron microscope (SE M). Fracture surfaces of biased films were smooth while all unbiased f ilms displayed a crack path which consisted of many deflections.