A STUDY OF THE EFFECTS OF YTTRIUM ADDITIONS ON THE INITIAL-STAGES OF OXIDATION OF NI-20CR USING GLANCING ANGLE X-RAY TECHNIQUES

Glancing angle X-ray techniques have been used to characterise yttrium-containing Ni-20Cr alloys during the initial stages of oxidation at 700-degrees-C. A direct comparison is made between the oxide dispersoid strengthened alloy MA 754 (Ni-20Cr containing 0.6 Y2O3) and a Ni-20Cr alloy subjected to yttrium ion implantation at a dose of 1 x 10(17) ions cm-2. Depth profiling of samples corroded from 1 to 8 min using glancing angle X-ray diffraction was used to identify the initial phases developed as a function of depth. EXAFS (extended X-ray absorption fine structure) studies at the Cr K-edge complemented the diffraction data and also gave an indication of the degree of disorder in the fcc lattice after implantation with yttrium, and its rearrangement on initial heat treatment.