Microstructure evolution in a martensitic 430 stainless steel-Al metallic-intermetallic laminate (MIL) composite

The formation of intermetallic layers in 430-SS/Al MIL composites was investigated for reaction in solid/solid, solid/semi-solid and solid/liquid states. The Fe2Al5 phase was formed as a major phase in the solid-state reaction and co-existed with the τ phase (Al5.5Cr1.95Fe2.55) as precipitates in a uniform layer in the semi-solid and liquid/solid reaction states. The growth of the uniform layer is mainly governed by lattice diffusion except for the grain boundary diffusion controlled mechanism at the early reaction stage. A porous two-phase layer consisting of Fe4Al13 and δ phase (Cr2Al13) was formed in the semi-solid and liquid/solid reaction states and its growth is controlled by interface reaction growth when the liquid phase is present. The growth activation energies of the uniform layer and two-phase layer were calculated as 200 kJ mol−1 and 133 kJ mol−1, respectively. A 430-SS/Al MIL composite with dense intermetallic layers was fabricated in the semi-solid reaction state, which was demonstrated to be the optimized process.