Effect of Sintering Process on Microstructure Characteristics and Mechanical Properties of B2-FeAl Based Metal-Intermetallic Laminate Composites

In this paper, a "multi-thin foil" structure + "two-stage" reaction strategy was employed to prepare B2-FeAl based MIL composite, and the effects of two different processes: conventional low-temperature hot-press sintering (CLT-HP) and fast high-temperature hot-press sintering (FHT-HP) on microstructure and mechanical properties were investigated. The results show that the MIL composites prepared by the two processes both exhibit multi-layer structure consisting of residual stainless steel layer, newly formed intermetallic layer, and intermediate transition layer. The metal layer is composed of both α-Fe and γ-Fe phases for CLT-HP, but only γ-Fe phase for FHT-HP counterpart. The intermetallic layer and transition layer mainly contain B2-FeAl phase for the two processes. Interestingly, multiple-sublayer structure was formed in the intermetallic layer and its thickness is obviously smaller and uniform for CLT-HP than FHT-HP. A kinetics calculation based on one-dimension diffusion equation was conducted to model the growth of B2-FeAl intermetallic layer, which exhibits a good consistency with the experimental results in terms of reaction rate and concentration profiles. CLT-HP MIL composites have better comprehensive mechanical properties than FHT-HP counterpart, especially for the compressive strength in the direction parallel to the layers, which is approximately 1 GPa higher for the former than the latter. This is mainly attributed to a good transitional role in properties through the transition layer and multiple-crack fracture mechanism in the intermetallic layer for CLT-HP MIL composite.