Abstract
This work addresses a mechanism of columnar microstructure evolution during diffusion bonding in a composite of iron aluminide and CrMo steel focusing on the role of alloying on microstructure. Columnar microstructure develops in the steel side of diffusion couples of iron aluminide and Fe-X (X=Cr, Mo) steel, when the steel composition is in the gamma phase at the bonding temperature. This is consistent with the proposed model for columnar microstructure evolution, which contributes to bonding strength between iron aluminide and steel. Interdiffusion coefficient at the Matano interface decreases with increasing the concentration of alloying elements in steel, and its decrease rate is higher for Mo than for Cr. The columnar grains in the steel side of the couple are longer than expected by chemical composition analysis, and their lengths increase with the interdiffusion coefficient. Microstructure evolution mechanism is discussed in terms of the kinetics of nucleation and subsequent grain growth during diffusion bonding.
