Hot corrosion behaviour of Nimonic‐105 in NaCl and Na2SO4

Abstract

AbstractThe hot corrosion behaviour of Nimonic‐105 alloy was investigated in the presence of NaCl and Na2SO4 by employing the crucible test. The experiments were carried out in the temperature range 700°–800°C for periods of 2 to 20 hours. The end reaction products were characterised by the XRD, XRF, SEM, EPMA and chemical analysis techniques. Weight loss plots obtained in pure salts followed a linear rate law. However, the weight loss results obtained in salt mixtures indicated two zones of severe corrosion. The first zone occured in the presence of low concentrations of NaCl (1–5%) when the salt mixture was maintained in the solid + liquid (S + L) state and the other in the molten state, containing higher concentrations of NaCl (15–30%). Blisters and cracks were observed on the immersed surface of the corroded sample in the first zone and on the exposed top surface in the second zone. Both zones were occurred in the temperature range 700°–800°C, i.e., above the eutectic temperature (635°C) of the corrodent mixture and around the m.p. of NaCl (800°C). The heavy corrosion in the second zone was associated predominantly with voluminous formation of nickel coated Ni3S2 globules, and Na2MoO4. Denudation of alloying elements was observed due to preferential removal by the corrodents. The degradation of the alloy in the presence of corrodents is discussed.