With the application of density-based phase-field modelling we reveal a coupling between grain boundary structure and composition evolution upon segregation of Mn to Fe grain boundaries.
Source: BAM
For the past decades, there has been a continual quest for developing new materials with superior durability, safety, efficiency, and performance. The 3rd generation of advanced high strength steels (AHSS) have emerged into the limelight of novel alloys, meeting these societal and industrial needs through their unique microstructural morphology and excellent performance.
Even though other high-strength steels such as Fe-Ni alloys have established a good name, the pricey Ni diverted focuses to rather cost-efficient Fe-Mn steels, otherwise known as medium Mn steels. Containing 3-10 wt% Mn, these alloys have gained significant recognition as a new generation of steels with a good combination of structural and mechanical properties comparable to Fe-Ni alloys. A major bottleneck of Fe-Mn steels, however, is that these alloys become extremely brittle at low temperatures, severely limiting the performance of these steels in cold environments.
The embrittlement of Fe-Mn steels has been related to irregular Mn segregation into grain boundaries, which hardly can be avoided. In our recent research in the division 5.5, we have revealed that the persistence of the Mn segregation in the grain boundaries is related to a so-called ‘chemo-structural coupling’: Using advanced density-based phase-field modelling, we show that the structural atomistic disorder in the grain boundaries can magnify the interaction with Mn atoms and thus a sudden Mn segregation can occur. Interestingly, we found that this behaviour is centrally driven by magnetic properties of Mn. With this understanding, a new angle is added to the search for tougher, cheaper steels in which researchers need to account for the structure of the grain boundaries in combination to the alloy composition, in order to cure for embrittlement in AHSS ––a chemo-structural microstructure design!
We invite you to further read about our exciting findings here: Grain boundary structural variations amplify segregation transition and stabilize co-existing spinodal interfacial phases
Grain boundary structural variations amplify segregation transition and stabilize co-existing spinodal interfacial phases
Theophilus Wallis, Reza Darvishi Kamachali
published in:
Acta Materialia, Volume 242, Article number 118446 (2022)
BAM Department Materials Engineering
BAM Division Materials Modelling