Nanocomposites and nanomaterials

Influence of vacuum annealing on the dispersion of thin double hafnium-copper films deposited onto oxide ceramic materials
Gab I.I.1, Stetsyuk T.V.1, Fesenko O.M.2, Shakhnin D.B.3
1 Frantsevich Institute for Materials Science Problems of NAS of Ukraine, 
3 Krzhyzhanovskogo st., Kyiv, 03142, Ukraine.
E-mail: gab@ipms.kiev.ua
2 Transfer Technology Department, Institute of Physics of the NAS of Ukraine. Prospect Nauki, 46, Kyiv-03039, Ukraine. 
3 University "Ukraine", 23 L’vivska st., Kyiv, 03115, Ukraine. 

Permanent vacuum-tight precision ceramic joints with an ultra-thin seam can be made by brazing or pressure welding of metallized ceramic parts. This purpose can be achieved by application onto ceramic surfaces of double metal films, one part of which is 100 – 200 nm thickness and consists of an adhesion-active metal (e.g. Hf, Nb etc.), and the other layer is slightly thicker (1–3 microns) and serves as a solder (e.g. Cu, Ni etc.) ensuring joining of metallized ceramic materials during brazing or pressure welding with a fine brazed seam (2–4 microns thickness).
In this work, specimens were used made of leucosapphire, alumina and dioxide-zirconium ceramics and metallized with a 150 nm hafnium nanofilm and then atop, by a 1.5–micron copper film serving as a soldering metal for ceramic samples joining. 
As a result of annealing up to 1000 °C, the films at all oxides’ surfaces remained almost unchanged. The first noticeable changes in them appeared after 5 minutes of annealing at 1050 °C. With the annealing time increase up to 20 minutes, the films began to crack, although they still covered almost 85% of the oxide surface. The rise of the annealing temperature up to 1100 °С led to further swelling and cracking of the double films which now covered only 70–75% of the oxide surface; and the interaction of the molten copper layer with hafnium metallization of oxides becomes already noticeable.
According to our study results kinetic curves of the investigated thin double metallic films decomposition have been built, using which one can determine the basic process parameters (temperature and exposition time at this temperature) for brazing or pressure welding of ceramic materials.
Using the data obtained, process regimes for joining by brazing and pressure welding were selected. According to these regimes, joints’ prototypes with seams up to 2.5 μm thick were made, which strength reached 150 MPa.