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 nos. 80, 90, 95 and 100 and nichrome (Ni/Cr≈80:20). Systematic nitriding experiments at different temperatures were carried out in a thermobalance. 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 nos. 80, 90 and 100 and in nichrome. Expanded austenite was not identified in nimonic 95.