| AVS 66th International Symposium & Exhibition | |
| Advanced Surface Engineering Division | Thursday Sessions |
| Session SE+PS-ThM |
| Session: | Plasma-assisted Surface Modification and Deposition Processes |
| Presenter: | Mehran Golizadeh, Montanuniversität Leoben, Austria |
| Authors: | M. Golizadeh, Montanuniversität Leoben, Austria F. Mendez Martin, Montanuniversität Leoben, Austria B. Rashkova, Montanuniversität Leoben, Austria S. Kolozsvári, Plansee Composite Materials GmbH, Lechbruck am See, Germany R. Franz, Montanuniversität Leoben, Austria |
| Correspondent: | Click to Email |
Cathodic arc deposition (CAD) is a well-established physical vapor deposition technique which is characterized by a highly ionized plasma emitted from the cathode. The energy of the ions in the plasma ranges from 20 to some 100 eV, depending on the cathode material and the discharge conditions. These energetic and highly ionized plasmas significantly influence film growth mechanism and, e.g., high-temperature phases can be stabilized at typically low deposition temperatures in CAD. The plasma properties are influenced by the properties of the converted layer which forms on the surface of composite cathodes due to local consecutive melting-solidification cycles caused by the motion of the cathode spot over the cathode surface. Therefore, a detailed understanding of the formation mechanism and properties of the converted layer is essential to understand and manipulate plasma properties.
Within the current work, composite cathodes with composition of Al0.5Cr0.5 but different grain size, namely 80 and 1200 µm, were eroded in inert Ar gas at a pressure of 1 Pa applying a current of 60 A. A short erosion time of 30 s enabled us to capture single craters left behind by a cathode spot. A cross-section of the crater prepared using focused ion beam (FIB) showed the liquid pool formed by the cathode spot was violently deformed by plasma pressure, pushing the liquid out of the crater to the rim and surrounding space (macroparticles). The leftover liquid was rapidly quenched and there was almost no heat-affected zone below the crater. This finding shows that solid-state diffusion plays a negligible rule in the formation of the converted layer.
Further, cross-sections of the cathodes eroded for 1h were prepared by conventional metallography and FIB. Detailed microstructural and phase analysis using transmission electron microscopy and transmission Kikuchi diffraction together with cross-sectional study of single craters revealed that the converted layer is formed in a way that the rim of a crater fills the neighbouring craters due to step erosion. The splashes ejected from craters by plasma pressure also contribute to forming the converted layer. The later mechanism can be dominating depending on the topography of the cathode surface, which was confirmed by the erosion of the cathodes with 1200 µm grain size.