Low Temperature Gaseous Nitriding of Ni-based Superalloys

In the present work the nitriding response of selected Ni-based superalloys at low temperatures is addressed. The alloys investigated are Nimonic series no. 80, 90, 95 and 100 and Nichrome (Ni:Cr » 80:20). Systematic nitriding experiments at different temperatures were carried out in a thermo balance. The morphology of the “case” developed upon low temperature nitriding of Ni-based superalloys was characterised with reflected light microscopy, scanning electron microscopy and X-ray diffraction analysis. The alloy composition proved to have a major influence on the nitriding response of the different alloys; it is demonstrated that it is possible to obtain expanded austenite in the Nimonic alloys no. 80, 90 and 100 and in Nichrome. Expanded austenite was not identified in Nimonic 95.