材料期刊网

The effects of Pt addition (5, 10 and 15 at.%) on the high temperature oxidation behaviour of the intermetallic compound beta-NiAl were studied at 1150 degrees C under both isothermal and thermal cycling conditions. The scale growth mechanism was assessed using two-stage oxidation exposures with (18)O(2) as a tracer in conjunction with high-resolution secondary ion mass spectrometer analysis of isotopic distributions. The scale morphologies were further characterized using secondary electron microscopy, Pt was found to reduce slightly the scale growth rate and improve considerably its resistance to spallation but it did not affect the sequence of scale development. Instead, it slowed the rate at which the scale developed. The alpha-Al(2)O(3) scales that were eventually established were duplex in structure, consisting of a compact inner layer and a thinner outer layer. This outer layer consisted of ridges and grew by the coarsening of these and/or by a dislocation climb mechanism.