1 billion tons of nanostructure – segregation engineering enables confined transformation effects at lattice defects in steels

Abstract

Abstract. The microstructure of complex steels can be manipulated by utilising the interaction between the local mechanical distortions associated with lattice defects, such as dislocations and grain boundaries, and solute components that segregate to them. Phenomenologically these phenomena can be interpreted in terms of the classical Gibbs adsorption isotherm, which states that the total system energy can be reduced by removing solute atoms from the bulk and segregating them at lattice defects. Here we show how this principle can be utilised through appropriate heat treatments not only to enrich lattice defects by solute atoms, but also to further change these decorated regions into confined ordered structural states or even to trigger localized decomposition and phase transformations. This principle, which is based on the interplay between the structure and mechanics of lattice defects on the one hand and the chemistry of the alloy's solute components on the other hand, is referred to as segregation engineering. In this concept solute decoration to specific microstructural traps, viz. lattice defects, is not taken as an undesired effect, but instead seen as a tool for manipulating specific lattice defect structures, compositions and properties that lead to beneficial material behavior. Owing to the fairly well established underlying thermodynamic and kinetic principles, such local decoration and transformation effects can be tuned to proceed in a self-organised manner by adjusting (i) the heat treatment temperatures for matching the desired trapping, transformation or reversion regimes, and (ii) the corresponding timescales for sufficient solute diffusion to the targeted defects. Here we show how this segregation engineering principle can be applied to design selforganized nano-and microstructures in complex steels for improving their mechanical properties.

Interfacial Segregation of Sn during the Continuous Annealing and Selective Oxidation of Fe-Mn-Sn Alloys

“…This results in a reduction of the effective concentration of Sn available for segregation to the metal/external oxide interface. Equations ( 5) and (7) show how the interfacial Sn concentration scales approximately linearly with the Sn bulk concentration both at equilibrium and at the early stages of segregation. Thus, the ongoing segregation from the bulk to the metal/external oxide interface is decreased (marked [II] in Figure 14) with the decrease in the effective Sn bulk concentration.…”

“…Models for equilibrium segregation have been developed within the context of temper embrittlement [ 3 , 4 , 5 ], where the enrichment of impurities at GBs is generally seen as undesirable. More recently, “segregation engineering” has become a tool for tailoring the design of interfacial properties [ 6 , 7 ], and deliberate Sn micro-additions to advanced high strength steels (AHSSs) have been suggested to improve the quality of galvanized coatings [ 8 , 9 , 10 , 11 ]. In continuous galvanizing lines (CGLs), commonly employed annealing atmospheres suppress Fe oxidation, while less noble alloying additions—such as Al, Cr, Mn, and Si—undergo selective oxidation.…”

New Applications to Atom Probe Tomography: Insights on Trace Element Diffusion in Naturally Deformed Minerals

“…The links between deformation-induced microstructures and trace element diffusion is an important theme within material sciences and geosciences. In material sciences, investigating the interplay between impurities and crystalline defects has had a significant impact on improving the design of synthetic materials [1,2]. As for geochronology, the reliable use of minerals such as zircon and titanite as U-Th-Pb geochronometers requires minimal radiogenic isotope and trace element mobility [3,4].…”