The Role of Deformation Conditions and Mo-Doping on the Evolution of Structure and Mechanical Properties of Powdered Iron Aluminide

Abstract

High-temperature strengthening of iron aluminides is achieved through forging powder technology, utilizing a combination of several structural factors. Milling the initial powder accelerates phase formation during the early stages of heating, contributing to an anisotropic fine-grained microstructure that retains the shape and size of the milled powder particles. Molybdenum micro-additives inhibit diffusion processes during high-temperature deformation, while segregation along boundaries and the distribution of ultra-fine complex oxide particles, formed in situ during mechanical activation and thermomechanical processing, enhance the dispersed strengthening mechanism. Optimizing the thermomechanical processing regimes further strengthens these structural factors. After forging at 1100°C, molybdenum-doped alloys exhibit higher low-temperature strength but show reduced fracture toughness and a tendency to delaminate. Subsequent annealing at 1300°C corrects these defects, though increasing the grain size and second-phase particles. The optimal structure and mechanical properties are achieved by triple forging at 1200°C, under conditions near dynamic recrystallization, and demonstrate a high room-temperature strength of 1600–1900 MPa. Molybdenum-doped alloys show an ultimate strength of 300–330 MPa when stretched at 700°C. The creep rate at 750°C decreases to 8.4 × 10⁻⁷ s⁻¹ for the 2% Mo alloy and 3.7 × 10⁻⁷ s⁻¹ for the 5% Mo alloy, comparable to modern austenitic steels.