材料期刊网

Oxidation of two ternary NiAl-Ag alloys containing 0.5, 1 at.% Ag, denoted as NiAl-0.5Ag and NiAl-1Ag, and Ag-free beta-NiAl was studied at 1173, 1273, and 1373K for 24 h in 10(5)Pa O-2 to study the effect of the presence of silver on the oxidation behavior of beta-NiAl by TGA, XRD, and SEM/EDAX. The NiAl-Ag alloys contain a mixture of a silver-rich phase (a) and a matrix of nickel-aluminide NiAl (beta). Thus, these alloys are ternary two-phase systems containing two reactive elements plus a noble metal. Under the oxygen pressure used, nickel and aluminum can form stable oxides, while silver is noble. An exclusive and adhesive external Al2O3 scale formed on the beta-NiAl, NiAl-0.5Ag, and NiAl-1Ag alloys after 24h oxidation in 10(5)Pa O-2 at 1173 and 1273K. Some voids were observed at the interface of oxide and alloy containing silver and silver free NiAl at 1373K. The oxidation kinetics of the two alloys at 1173K and 1373K is similar to that of beta-NiAl. The initial oxidation rate of NiAl-0.5Ag and NiAl-1Ag at 1373K is similar to that of beta-NiAl. After 4h oxidation at 1373K the alloys containing silver begin to show mass loss. The addition of silver does not affect significantly the oxidation behavior of the NiAl intermetallic compound in all cases, as expected, because silver is essentially present only as a second phase due to its very small solubility in beta-NiAl.