Laves phase formation in Fe-based alloys from strengthening particle to self-healing agent: a review

Abstract

In this study, were extensively reviewed the hardening and self-healing properties of Laves-phase in Fe-based alloys. First, the microstructural features of different polytypes of the Laves-phase, focusing on the thermodynamics and kinetics of formation in ferritic and martensitic steels were revised. C14 was identified as the dominant polytype in steels, providing strengthening by precipitation, anchoring of dislocation, and interphase boundaries, thereby increasing the creep resistance. Although the Laves phase is widely known as a reinforcement particle (or even a detrimental phase in some systems) in martensitic/ferritic and ferritic steels, recent findings have uncovered a promising property. Particles with self-healing characteristics provide creep resistance by delaying creep cavities formation. In this regard, different elements such as tungsten and molybdenum are known to provide this feature to binary and tertiary ferrous alloys due to their ability to diffuse into the creep cavities and form Laves-phase Fe(Mo,W)2. To date, self-healing by precipitation has only been reported in commercial stainless steel AISI 312, 347, and 304 modified with boron, nevertheless with a little contribution to creep rupture life. Although, commercial computational tools with thermodynamic and kinetic databases are available for researchers, to tackle the self-healing process with exactitude, genetic algorithms arise as a new tool for computational design. The two properties of Laves phase reported in the literature, precipitation hardening and self-healing agent, is a mix that can bring out a new research field. Therefore, it is not unreasonable to think of tailor-made high chromium creep-resistant steels reinforced by Laves-phase coupled with self-healing properties. However, owing to the characteristic of Laves-phase seems to be a complex challenge, mainly due to the crystallographic features of this phase in comparison with the host matrix, available computational tools, and databases.