Structure, mechanical, tribological properties, and high temperature stability of titanium diboride/titanium carbide and titanium oxide/aluminum oxide multilayer coatings synthesized by magnetron sputtering

The focus of this research is the synthesis and characterization of TiB 2/TiC multilayer and TiO2/Al2O3 composite coatings for possible elevated-temperature machining applications. Coatings were synthesized using a dual-cathode, unbalanced magnetron sputtering system. They were characterized as deposited and after annealing, in terms of structure, mechanical, and tribological properties.; TiB2/TiC multilayer coatings are composed of polycrystalline TiB2(001) and amorphous TiC. Coatings synthesized with stationary substrates have high compressive stress (4--7 GPa), and their hardness is slightly enhanced (∼25%) over the rule-of mixture value. Coatings grown with substrate rotation have much lower compressive stress (<2 GPa) and high hardness (>60 GPa). After annealing in an inert environment at 1273 K, these multilayer coatings retain their layer structure. From dry block-on-ring tribotesting, the 3:0.5 multilayer (i.e., the layer thickness is 3.0 nm for TiB2 and 0.5 nm for TiC) provides 4 times improvement in wear resistance over the uncoated M2 steel substrate. Monolithic TiB2 and 3:1 multilayer have flank wear reduction in dry machining by about a factor of ten compared with the uncoated tool after a cutting distance of 600 m. When machining against aluminum, the 3:1 multilayer tool has negligible buildup on the rake face.; TiO2/Al2O3 composite coatings were deposited in the same sputtering chamber with an Ar-O2 (75% argon and 25% oxygen) mixture as the reactive gas. Stoichiometric TiO2/Al 2O3 composites were synthesized in the target-poisoned regime with constant TiO2 volume and decreasing Al2O3 volume. TiO2 has a strong rutile (101) preferred orientation and Al2O3 remains amorphous. Hardness of these TiO 2/Al2O3 coatings approaches 15 GPa, comparing to hardness values of pure TiO2 and Al2O3 of ∼8 GPa and ∼7 GPa, respectively. Films remain intact after annealing in air for 1 hour at 1273 K. Hardness of annealed films remains higher than the monolithic components.