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 Fe_xAl_y 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.