|AVS 58th Annual International Symposium and Exhibition|
|Tribology Focus Topic||Thursday Sessions|
|Session:||Advanced Tribological Materials|
|Presenter:||E. Broitman, Linköping University, Sweden|
|Authors:||E. Broitman, Linköping University, Sweden
H. Högberg, Linköping University, Sweden
L. Hultman, Linköping University, Sweden
|Correspondent:||Click to Email|
The microstructure, nanomechanical and nanotribological properties of ZrB2 thin films grown by DC magnetron sputtering have been studied as a function of Ar pressure, substrate bias, and substrate temperature. Films, ~ 500 nm thick, were deposited onto Si (001) and Al2O3 (0001) substrates from a compound target using an industrial chamber CC-800/9 from CemeCon operated at a fixed target-to-substrate distance of 7 cm.
X-ray diffraction patterns show that 0001-oriented films can be obtained on both substrates at a substrate bias of -80 V without any external heating. Transmission electron microscopy of samples grown at different conditions reveal the presence of an amorphous 100-300 nm thick layer close to the substrate, followed by the nucleation of ZrB2(0001). The same oriented structure appears for samples grown up to 150 oC, but at higher temperatures this orientation is gradually degraded. At 500 oC, cross-sectional scanning electron microscopy shows a columnar microstructure with re-nucleation during the growth. For films grown at 100 °C, little impact on the texture is observed when the substrate bias is changed from floating to -200 V.
Nanomechanical and nanotribological properties measured with a Hysitron TriboindenterTM TI 950 reveal that the films have high hardness and elastic recovery, and low friction. For films grown at low temperature, the hardness, reduced elastic modulus, and elastic recovery decrease from 25 to 19 GPa, 290 to 200 GPa, and 96 to 92%, respectively, when the amorphous interface increases from 100 to 300 nm. Nano-frictional tests were done in a load-controlled feedback mode using a force of 1 mN; a total of 40 reciprocating passes were performed for each test using a diamond 90º probe with a 1 µm tip radius. The friction tests reveal a friction coefficient µ in the range 0.10-0.13 for ZrB2 samples grown at different conditions, in contrast of µ = 0.6 for a pure Zr film.