The Early Stages of Growth of Second-Phase Particles in an Fe–Ti–Si Alloy

Abstract

The microstructural investigations outlined in this paper represent natural extensions of previous work in investigating precipitation in the Fe–Ti–Si system. The obvious value of the field-ion microscope in enabling pre-peak-hardness microstructures to be defined is established and a correlation between particle size and hardness is given. The observed qualitative changes in microstructure are related to the variation in titanium content of the particles, which are believed to be based on the DO₃Fe₃Si structure. Quantitative size-distribution data are presented that extend the work performed by other authors to shorter ageing times. For ageing times > 1 h at 600° C a linear time-dependence is found for the cube of the mean particle size, in agreement with bulk-diffusion-controlled coarsening theory and previous work. For ageing times < 1 h deviations in such a plot occur, which are shown to arise from an incomplete precipitation reaction.