Erosion-corrosion in a laboratory-scale coal-firing FBC of various aluminized coatings prepared by low-temperature pack cementation

Using a halide-activated pack-cementation method but at a temperature (600 °C) noticeably lower than normal, an η-Fe₂Al₅ coating and two δ-Ni₂Al₃ coatings with and without dispersions of CeO₂ nanoparticles were developed respectively on a low-carbon steel and the steel pretreated with an electrodeposited film of Ni or Ni-CeO₂. The erosion-corrosion (E-C) performance of the three aluminide coatings during 100 h exposure at ~ 600 °C in a coal-firing laboratory-scale fluidized-bed combustor (FBC) was investigated, by mounting the aluminized samples onto a rig which maintained rotation for accelerating the relative impacting speed of flying solid particles (mainly SiO₂ bed materials). The η-Fe₂Al₅ and the CeO₂-free δ-Ni₂Al₃ coatings experienced an unacceptable recession rate. Compared to the two CeO₂-free aluminide coatings, the CeO₂-dispersed δ-Ni₂Al₃ coating offered profoundly improved E-C resistance, because the latter coating was not only strengthened by the CeO₂ dispersion and grain refinement, it also could grow a more adherent alumina scale.