Effect of Matrix Substructures on Precipitation of the Laves Phase in Fe-Cr-Nb-Ni System

Abstract

In order to make clear the effect of matrix substructures on the Laves phase precipitation in Fe-Cr-Nb-Ni system, age hardening behavior was examined during isothermal aging up to 1000 h at 873 and 973 K and the precipitation morphology of the Laves phase was investigated by transmission electron microscopy (TEM). The microstructures of Fe-10Cr-1Nb and Fe-15Cr-1Nb (mol%) alloys with ferrite matrix contain high density of rod-shaped Laves phase which precipitates within the ferrite grains during aging. On the other hand, in the Fe-10Cr-1Nb-1Ni alloy with massive ferrite matrix, most of the Laves phase precipitates in subgrain boundaries. Additionally the deformed ferrite matrix has been prepared for examining the effect of dislocation density on morphology of the Laves phase. It is found that the difference of matrix substructures between the ferrite and deformed ferrite provides the different number and distribution of nucleation sites for precipitation of the Laves phase. Mechanical properties were evaluated by tensile tests conducted at room temperature, 873 and 973 K.