AVS 51st International Symposium
    Advanced Surface Engineering Monday Sessions
       Session SE-MoA

Paper SE-MoA4
Growth and Characterization of New Epitaxial MAX-Phase Thin Films from the Ti@sub n+1@(Si, Ge)C@sub n@ Systems by Magnetron Sputtering

Monday, November 15, 2004, 3:00 pm, Room 303D

Session: Structure Control of Hard Coatings in Sputtering Processes
Presenter: H. Högberg, Linköping University, Sweden
Authors: H. Högberg, Linköping University, Sweden
J. Emmerlich, Linköping University, Sweden
J.-P. Palmquist, Kanthal AB, Sweden
P. Eklund, Linköping University, Sweden
O. Wilhelmssson, Uppsala University, Sweden
L. Hultman, Linköping University, Sweden
U. Jansson, Uppsala University, Sweden
Correspondent: Click to Email
This is a presentation of the state-of-the-art for the materials research on M@sub n+1@AX@sub n@ (n=1 to 3) phase thin films. The MAX-phases are a family of ductile inherently nanolaminated ternary nitrides and carbides with a high potential for industrial applications due to their unique combination of metallic and ceramic properties, as recently reported for the archetype Ti3SiC2. These properties stem from a highly anisotropic hexagonal crystal structure, where early transition metal (M) atoms and C or N (X) atoms form edge-sharing octrahedral MX blocks that are interleaved by layers of group 13-15 elements (A). Using DC magnetron sputtering with elemental sources we deposited epitaxial MAX-phase films from the Ti-Si-C and Ti-Ge-C systems on Al2O3(0001) or MgO(111) substrates at temperatures of 900 oC or 1000 oC, which is 500 oC lower than for conventional bulk processes. Besides demonstrating single-crystal growth of the known phases Ti3SiC2, Ti3GeC2, and Ti2GeC we have discovered two phases Ti4SiC3 and Ti4GeC3 as well as four intergrown structures of stoichiometries Ti5A2C3 and Ti7A2C5. The general trend from synthesis and characterization is that both MAX-phase systems show similarities with respect to phase distribution, mechanical, and electrical properties, reflecting the close chemical relationship between Si and Ge. However, XRD shows that the Ti-Ge-C MAX-phases are restricted to a more narrow deposition window and require slightly higher temperatures due to a more limited diffusivity of the larger Ge atoms. From the nanoindentation analysis we see the characteristic large plastic deformation with extensive pile up for both systems, but measure a slightly lower Youngs modulus of 300 GPa for the Ti-Ge-C films compared to the 320 GPa obtained from Ti3SiC2 films. The four-point probe measurements show a lower conductivity for the Ti3GeC2 films compared to their Si-counterparts with resistivity values of 50 and 25 @micro@@ohm@cm, respectively.