The addition of Pt in cast and diffusion nickel aluminide is known to improve the oxide scale adhesion, but the positive effects of this element remain still imprecise. This present study reports experimental results concerning the diminution of sulfur segregation in the presence of platinum (10% at.) in β-NiAl, at 750°C. However, Pt did not completely prevent sulfur from segregating to a free surface. It was also shown that the addition of Pt in the alloy decreased the formation of voids at the oxide/metal interface after isothermal oxidation at 900°C. The ratio of the oxide thickness to cavity depth strongly decreases in Pt modified nickel aluminide. Lastly, thermogravimetric investigations revealed that Pt increased the oxide growth rate at 1100°C.
The main mechanism of degradation of thermal barrier systems is the spallation of the thermally grown oxide (TGO) formed at the ceramic/metallic sub-layer. Present trends are the use of a platinum modified nickel aluminide layer as metallic sub-layer. But the effect of few p.p.m. or few % at. of zirconium on the oxidation of hipped or cast nickel aluminide was also studied for higher temperature applications. It has been shown that the system ZrO 2 -Y 2 O 3 (8% mass.) EBPVD / cast NiAl(Zr) had at 1200°C a life durability three times longer than the classical system ZrO 2 -Y 2 O 3 (8% mass.) EBPVD /NiAlPt coating/nickel base superalloy. Similar encouraging results were obtained with the system ZrO 2 -Y 2 O 3 (8% mass.) EBPVD / NiAl(Zr) coating deposited by physical vapour deposition/ nickel base superalloy.In this work, a zirconium modified nickel aluminide coating by vapour pack cementation process was developed. The structure of this modified coating is discussed. Cyclic oxidation test results and microscopic investigations are also presented.
The present work, performed on nickel aluminides deposited on a single Ni-based
superalloy AM1, focuses on the effect of the following several parameters on the microstructural
and chemical changes occurring during isothermal heat treatment at 1100°C for 50h :
-oxygen pressure by comparing heat treatment under ambient air (PO2 = 0.2 bar) and under
secondary vacuum (PO2 = 0.2x10-6 bar).
-cooling rate after isothermal heat treatment by comparing furnace cooling (3°C/min) and water
quenching (500°C/min).
-Pt addition in the coating by comparing NiAl and NiPtAl coatings.
Characterizations were performed using SEM, analytical TEM and electron microprobe analyses.
The results show that these parameters have a strong influence on both the microstructural
evolution and the oxidation of the thermal barrier coating (TBC) system. Appropriate heat
treatments are essential to improve interfacial resistance and increase the durability of TBC
systems.
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