Attempts have been made to develop multi-layer ceramic barrier coatings over the reinforcing wire in tungsten wire reinforced nickel-base superalloys suitable for their fabrication by a casting technique. Using the processing of chemical vapor deposition, the wire was first coated with a 1 μm thick layer of TiN, then with a 5 μm thick layer of TiC or TiN or Al2O3, and finally with a 1 μm thick layer of Al2O3. It was found that none of these multi-layer coatings was damaged during the composite fabrication by casting.
The most favorable in terms of the barrier effect was the Al2O3-based coating (TiN-Al2O3/Al2O3), which completely inhibitted the nickel-induced recrystallization of tungsten wire even after 1 000 h exposure at 1 200°C. The TiC-based coating (TiN/TiC/Al2O3) was unfavorable because complicated chemical interactions occured especially between TiC and TiN. While the TiN-based coating (TiN/TiN/Al2O3) was structurally similar to the Al2O3-based coating, results were somewhat different since the constituent layers, TiN and Al2O3, had different thickness. The superiority of the Al2O3-based coating was also confirmed by the composite creep-rupture testing.
