Growth kinetics of interface intermetallic compounds in stainless steel fibre reinforced aluminium matrix composites

Abstract

Growth kinetics of binary intermetallic compounds in the fibre/matrix interface has been studied in stainless steel fibre reinforced aluminium matrix composites fabricated by the P/M hot pressing, squeeze casting, and infiltration techniques. As expected in most binary diffusion couples, more than one intermetallic compound of the type FexAly forms at the interface. However, not all the iron-aluminide intermetallic compounds possible as dictated by the binary phase diagram are present. This is primarily the result of the non-equilibrium conditions at the interphase boundaries as the activation-controlled and diffusion-controlled interfacial reactions progress between the fibre and the matrix. Two equations have been established for the growth kinetics of the interface; one relates to hot pressing, the other to squeeze casting and infiltration. Parabolic rate constants have been determined. A rate constant of about 0.7 × 10−16 m2 sec−1 for hot-pressed composites produces an optimum thickness of the interface of about 3 μm and results in the maximum strength of the composites. In addition to the FeAl and Fe2Al5 that form at the interface, the presence of NiAl3 intermetallic compound is also predicted. Further investigation is suggested for the determination of the rate constants in squeeze-cast and infiltrated composites.