In situ TEM heating studies on the phase transformation of metastable phases in Fe-Cr-B alloy spray coatings

Abstract

The Fe-Cr-B alloy thermal spray coatings contain a mixture of metastable phases such as nanocrystalline alpha-(Fe,Cr) solid solution phase supersaturated with boron and the remainder of amorphous phase. in order to investigate the thermal stability and phase transformation of these metastable phases, in situ TEM heating experiment has been performed. Upon an exposure to high temperatures, the metastable phases were thermally decomposed in the following sequences: At temperatures above 670 K, the growth of nanocrystalline alpha-(Fe,Cr) crystallites started. At higher temperatures (similar to 820K), Cr:B borides started to precipitate through the matrix. When the annealing temperature was increased further to 960 K, the alpha-(Fe,Cr) grains in the matrix were coarsened rapidly and intragranular precipitation of Cr:B-type borides was consequently triggered. (C) 2001 Published by Elsevier Science B.V.