Small amounts of silver have been added to the intermetallic compound NiAl with the purpose of improving its mechanical properties. Four ternary NiAl-Ag alloys containing 0.5, 1, 5 and 10 at. pct Ag, denoted as NiAl-0.5Ag, NiAl-1Ag, NiAI-5Ag and NiAl-10Ag, and the Ag-free NiAl have been oxidized at 1000 degrees C for 24 h in 0.1 MPa O-2 to study the effect of the presence of silver on the oxidation behavior of NiAl. All the NiAI-Ag alloys are composed of a matrix of beta-NiAl containing a dispersion of isolated particles of a second silver-rich phase. A continuous external layer of Al2O3 formed on all the alloys. In addition, the scales formed on NiAI-5Ag contained a thin and discontinuous layer of pure silver located at the alloy/Al2O3 interface, while those formed on NiAI-10Ag contained isolated particles as well as discontinuous layers of silver at various locations in the scale extending up to the gas/scale interface. The kinetic curves of all the alloys were generally composed of two main parabolic stages with smaller parabolic rate constants for the final stage. The addition of silver does not significantly affect 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.
部门归属
chinese acad sci, met res inst, state key lab corros & protect, shenyang 110016, peoples r china. shenyang inst chem technol, shenyang 110142, peoples r china.;niu, y (reprint author), chinese acad sci, met res inst, state key lab corros & protect, shenyang 110016, peoples r china;yniu@imr.ac.cn
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