THE EFFECTS OF REACTIVE-ELEMENT, ION-IMPLANTATION-INDUCED AMORPHOUS LAYERS ON THE OXIDATION OF CO-12CR AND NI-12CR ALLOYS

Nickel-chromium (Ni-12Cr, wt.%) and cobalt-chromium (Co-12Cr, wt.%) al loys were ion implanted with 150 keV yttrium to fluences that ranged b etween 2 x 10(16) and 1 x 10(17) ions/cm(2). The influence of the impl antation on the microstructure of the alloy was determined The effect of the highest dose implantation on the alloys' oxidation response at 1000 degrees C, 48 hr was measured Both alloys contained an amorphous surface phase as a result of this fluence and one of the effects of ox idation was to recrystallize the amorphized allo in the first few minu tes of oxidation. The lower doses of 2 x 10(16) ions/cm(2) were suffic ient to cause amorphization of both the Ni-12Cr and the Co-12Cr. The i mplantation reduced the isothermal mass gain by a factor of 25% for th e Ni-12Cr, but had a negligible effect on the Co-12Cr alloy. Short-ter m oxidation experiments at 600 degrees C showed via transmission elect ron microscopy that, in the absence of the yttrium implant, the Ni-12C r alloy forms NiO in the first minute of oxidation and the Co-12Cr all oy forms CoO and CoCr2O4. The implanted Ni-12Cr, on the other hand (1 x 10(17) Y+/cm(2)), forms recrystallized Ni-Cr, Y2O3, and NiO in the n ear-surface region, while the implanted Co-12Cr alloy forms CoO, CoCr2 O4, and a recrystallized intermetallic alloy from the amorphized regio n.