The High-Temperature Oxidation of Ductile Cr-Re Alloys

The high-temperature oxidation behavior of ductile Cr-Re alloys contain-ing 32 and 44 a/o (atomic per cent) Re has been investigated using thermo-gravimetric, metallographic, electron microbeam probe, and x-ray analytical techniques. The oxidation reactions taking place include the formation of a Cr203 external scale, a subscale, and volatile Re oxides. The Cr203 scale which forms on the Cr-32 a/o Re alloy is an effective barrier to loss of Re; on the Cr-44 a/o Re alloy, the Cr203 scale is quite porous, and Re loss as volatile oxide ensues, giving rise to l inear kinetics. Air-oxidized samples showed es-sentially the same kinetics as samples exposed to oxygen; Cr2N did not form. Cr-Re alloys with Re concentrations near the bcc a-phase solubility l imit possess good ductil ity and high strength (1-3). Since the use of Cr as a struc-tural material has been limited historically by its lack of ductil ity at low temperature (T<300