STRUCTURE-ANALYSIS OF PLASMA-NITRIDED PURE IRON

Pure iron, plasma nitrided in low pressure triode ion plating equipment, has been investigated by optical reflection microscopy, scanning transmission electron microscopy and glancing-angle X-ray diffraction, using conventional and synchrotron radiation. The total thickness of the compound layer does not obey the square-root time dependence, as a result of the continuous Ar + N ion bombardment during the nitriding process. The grain size is also reduced in the compound layer. In addition to the variation in thickness of the nitride layers with increasing process time, a change in the nitrogen concentration at the top of the compound zone also is observed. Increasing the nitriding time and/or the N-2 partial pressure in the nitriding apparatus results in a larger nitrogen concentration in the top layer of the epsilon phase. Also, a sin(2) psi method analysis has been carried out to measure the residual macroscopic stresses in the different nitride layers of the compound zone.