Eutectic/eutectoid multi-principle component alloys: A review

Multi-principle component alloys (MPCAs) differ from traditional alloys in that they consist of four or more elements or components each with concentrations of 5–35 at. %. Since the first eutectic multi-principle component alloy (MPCA) was produced in 2008, there has been a growing number of papers on developing eutectic MPCAs as potential structural materials. Eutectic MPCAs can show high ambient temperature yield strengths that increase with decreasing interlamellar spacing, λ, according to either λ−1/2 or λ−1, similar to that observed in pearlitic steels, with a tradeoff between this increased strength and reduced tensile ductility. Ambient temperature tensile ductility has been observed in eutectic MPCAs only when one phase is f.c.c. and when the harder second phase is itself deformable. The yield strength in eutectic MPCAs has been shown to decrease with increasing temperature, and, limited data suggest that, this is related to the softening of the harder phase. Annealing of as-cast eutectic MPCAs, which are not typically at equilibrium, can produce precipitation of fine particles that further increase the strength, and which often reduce the ductility. Both thermo-mechanical processing and nitriding can increase the strengths of eutectic MPCAs by transforming the lamellar eutectic into equi-axed grains and producing fine AlN particles (in aluminum-containing MPCAs), respectively. The properties of eutectic MPCAs can largely be explained by models used for traditional alloys. While a number of different elements have been used to produce eutectic MPCAs, the design of eutectic MPCAs for structural applications should avoid the use of expensive elements like cobalt and niobium, which have often been used. Room temperature yield strengths have been shown to increase with decreasing f.c.c. interlamellar spacing, λ, in lamellar eutectic FeNiMnAl alloys (shown right) according to either λ 1 or λ 1/2, with a resulting trade-off between increased strength and reduced tensile ductility. [Display omitted] •The microstructures and mechanical properties of eutectic/eutectoid multi-principle component alloys (MPCAs) are critically reviewed.•The yield strength and interlamellar spacing, λ, of eutectic/eutectoid MPCAs obey a Hall-Petch-type relationship with either a λ−1 or λ-1/2 relationship.•Thermo-mechanical treatments transform the lamellar eutectic into equi-axed two-phase grain structures, leading to either increases or decreases in strength.•Traditional model