Degradation of Fe–Cr–Al–RE and Ni–Cr–Al–RE foils in air and combustion gas atmospheres

Abstract

In the continuing drive to increase gas turbine operating efficiencies (and reduce environmental emissions), it is necessary to consider ways of improving the temperature capabilities of hot gas path sealing materials. One potential route is to investigate the possibility of using alternative materials within the traditional honeycomb structure.This paper presents the results of investigations into the high temperature oxidation performance of a range of commercial Fe–20wt%Cr–5wt%Al–RE and Ni–16wt%Cr–5wt%Al–RE foil materials in air and simulated combusted natural gas environments. The effects of exposures for periods of up to 1500 hours have been studied in the temperature range 950–1300°C. During each series of tests the foils were subjected to regular thermal cycles (to room temperature) with dwell periods at the target exposure temperatures ranging from 20 hours at the higher temperatures to 100 hours at the lower temperatures.The degradation kinetics of each foil sample were monitored using mass change measurements at each thermal cycle. In addition, samples were periodically removed for destructive examinations to enable more meaningful metal loss measurements to be made and degradation mechanisms to be established. In this way the principal parameters governing the oxidation performance were established, as well as times to the onset of breakaway oxidation (when these fell within the exposure periods studied at each temperature). Earlier models for the performance of Fe–Cr–Al–RE materials have been adapted to describe the performances of the foils observed in this study.