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

The Fe-Cr-B alloy thermal spray coatings contain a mixture of metastable ph ases such as nanocrystalline alpha-(Fe,Cr) solid solution phase supersatura ted with boron and the remainder of amorphous phase. in order to investigat e the thermal stability and phase transformation of these metastable phases , in situ TEM heating experiment has been performed. Upon an exposure to hi gh temperatures, the metastable phases were thermally decomposed in the fol lowing sequences: At temperatures above 670 K, the growth of nanocrystallin e alpha-(Fe,Cr) crystallites started. At higher temperatures (similar to 82 0K), Cr:B borides started to precipitate through the matrix. When the annea ling temperature was increased further to 960 K, the alpha-(Fe,Cr) grains i n the matrix were coarsened rapidly and intragranular precipitation of Cr:B -type borides was consequently triggered. (C) 2001 Published by Elsevier Sc ience B.V.