CHEMICAL VAPOR DEPOSITION OF TANTALUM-CARBIDE/TITANIUM-CARBIDE/ALUMINUM-OXIDE/TITANIUM-NITRIDE MULTI-LAYER COATINGS ON CEMENTED CARBIDE CUTTING TOOLS

Multi-layered TaC-TiC/Al{dollar}sb2{dollar}O{dollar}sb3{dollar}/TiN coatings were deposited onto mixed cemented carbide (WC-Co-TiC-TaC) cutting tools using chemical vapor deposition in a large, commercial reactor. The variability of microstructure, deposition rate, machining performance, phases present, and adherence with position within the deposition reactor were studied for Al{dollar}sb2{dollar}O{dollar}sb3{dollar} deposition temperatures of 915{dollar}spcirc{dollar}C, 1000{dollar}spcirc{dollar}C, and 1035{dollar}spcirc{dollar}C where coating layers were deposited separately in a discontinuous manner. A continuous deposition of TaC-TiC/Al{dollar}sb2{dollar}O{dollar}sb3{dollar} with separate subsequent TiN overlayer deposition was studied, also.; X-ray diffraction of low angle taper sectioned coatings was used to selectively analyze coating and substrate phases present. Phases were similar for all the discontinuously coated inserts with TiN, Al{dollar}sb2{dollar}O{dollar}sb3{dollar}, TiC, and WC phases positively identified.; Auger electron spectroscopy of taper sectioned coatings improved depth resolution by one to two orders of magnitude over conventional SEM/EDS of 90{dollar}spcirc{dollar} sections. The interdiffusion between highly adherent coatings and coating/substrate pairs was low with metallic constituents exhibiting diffusion coefficients of the order of 10{dollar}sp{lcub}-17{rcub}{dollar}cm{dollar}sp2{dollar}/sec.; Al{dollar}sb2{dollar}O{dollar}sb3{dollar} of all depositions was columnar in shape with grains of between 30% to 100% of the Al{dollar}sb2{dollar}O{dollar}sb3{dollar} coating thickness with the major axis perpendicular to the substrate. No significant difference in Al{dollar}sb2{dollar}O{dollar}sb3{dollar} grain size and shape was observed between deposition cycles.; Deposition rate was locally variable for the TiC, Al{dollar}sb2{dollar}O{dollar}sb3{dollar}, and TiN coatings with standard deviations of 10%, 30% and 20% of the mean coating thickness within corners, respectively. The free standing corners had significantly greater Al{dollar}sb2{dollar}O{dollar}sb3{dollar} and TiC deposition rate than other corners in contact with the setter.; Al{dollar}sb3{dollar}O{dollar}sb3{dollar} deposition rate increased with temperature consistent with the increasing formation rate of the oxygen donor, H{dollar}sb2{dollar}O, from CO{dollar}sb2{dollar} and H{dollar}sb2{dollar}. Depletion of reactants was found to increase with increasing temperature causing an eventual decrease in Al{dollar}sb2{dollar}O{dollar}sb3{dollar} deposition rate in the downstream reactor positions.; The continuously deposited coatings had the highest adherence measured by a scratch test and the lowest flank wear. Flaking of coatings followed by crater wear and deformation preceded failure during the accelerated wear tests. (Abstract shortened with permission of author.)...