Abstract
Si-Ti-N coatings with various compositions were deposited on molybdenum substrates using hypersonic plasma particle deposition (HPPD). In this method, vapor phase precursors (TiCl4, SiCl4 and NH3) are dissociated in a DC plasma arc and the hot gas is quenched in a rapid nozzle expansion to nucleate nanoparticles. These nanoparticles are then accelerated in hypersonic flow, causing them to deposit by ballistic impaction on a substrate placed downstream of the nozzle. Films of 10-25 μm thickness were deposited at rates of 2-10 μm/min, depending on reactant flow rates, at substrate temperatures ranging from 200 to 850 °C. When the reactant gases were premixed the coatings consisted of nc-TiN, nc-TiSi2, nc-Ti5 Si3 and amorphous Si3N4. For the unpremixed reactants case, the coatings consisted of free Si, nc-TiN and amorphous Si3N4. Hardness of as-deposited films was evaluated by nanoindentation of polished film cross-sections. Measured hardness values, averaged over 10-15 locations for each film, ranged from 16-24 GPa. In separate experiments with the same conditions, particle size distributions were measured by placing a sampling probe at the same location as the film substrate. The sampled aerosol was rapidly diluted and delivered to a scanning mobility particle sizer (SMPS). In-situ particle size distribution measurements confirmed that the coatings were formed by impaction of nanoparticles in the 5-15 nm range, with higher reactant flow rates producing larger particles. Focused ion beam (FIB) milling was used to observe film cross-section and porosity. For as-deposited films containing pores, in-situ plasma sintering was used to densify the film without grain growth.
Original language | English (US) |
---|---|
Pages (from-to) | 364-370 |
Number of pages | 7 |
Journal | Surface and Coatings Technology |
Volume | 188-189 |
Issue number | 1-3 SPEC.ISS. |
DOIs | |
State | Published - Nov 2004 |
Bibliographical note
Funding Information:This work was supported by NSF Grant # DMI-0103169 and NSF IGERT Grant # DGE-0114372.
Keywords
- Hardness
- Nanostructured
- Plasma synthesis
- Si-Ti-N
- Size distribution