Linear complexions: Confined chemical and structural states at dislocations

Abstract

For 5000 years, metals have been mankind's most essential materials owing to their ductility and strength. Linear defects called dislocations carry atomic shear steps, enabling their formability. We report chemical and structural states confined at dislocations. In a body-centered cubic Fe-9 atomic percent Mn alloy, we found Mn segregation at dislocation cores during heating, followed by formation of face-centered cubic regions but no further growth. The regions are in equilibrium with the matrix and remain confined to the dislocation cores with coherent interfaces. The phenomenon resembles interface-stabilized structural states called complexions. A cubic meter of strained alloy contains up to a light year of dislocation length, suggesting that linear complexions could provide opportunities to nanostructure alloys via segregation and confined structural states.

Predicting microstructure and strength of maraging steels: Elemental optimisation

“…Mn martensite during ageing [2,[36][37][38], and these features could affect the values of d lath with alloying content. However, small variations in d lath have been observed in a variety of maraging steels with different Ni and Mn content, even for tempered conditions [14,20,25,26,39]; this behaviour can be due to the relatively low lattice distortion and high solubility of substitutional atoms in Fe with respect to C atoms; hence, based on these experimental results, it is considered that d lath = 250 nm remains constant for all steels tested.…”

“…For the case of Fe C steels, w lath was found equal to the length of a Cottrell atmosphere inducing carbon segregation at the lath boundaries [35]; for the case of maraging steels, we consider that w lath equals the thickness of a dislocation distortion field and it has been experimentally estimated in Fe 9Mn (at%) to be w lath ≈ 4 nm [36]. Combining these results, ρ equals: d lath depends on the composition of the steel and it is related to the redistribution of alloying elements into the lath boundaries.…”

Correlative Microscopy—Novel Methods and Their Applications to Explore 3D Chemistry and Structure of Nanoscale Lattice Defects: A Case Study in Superalloys

“…As recently reviewed by Herbig,8 full electron microscopy characterization of specific features can be carried out on needle-shaped specimens prior to APT analysis by utilizing specially designed holders. This approach has, for example, led to a better understanding of diffusional mechanisms resulting in local solute segregation at crystalline imperfections [9][10][11][12][13][14] that critically impact the macroscopic material behavior. APT had previously revealed details of the composition of structural imperfections, 15 the presence of which were confirmed by field ion microscopy 16 or TEM.…”

“…APT had previously revealed details of the composition of structural imperfections, 15 the presence of which were confirmed by field ion microscopy 16 or TEM. 11,17,18 Here, we introduce methodologies to aid target features of interest for correlative TEM/APT investigation by exploiting advanced scanning electron microscopy (SEM) techniques in deformed Ni-and CoNi-based superalloys, one of the most important classes of engineering materials for temperatures above 1000°C. Their high temperature stability is attributed to the uniform distribution of L1 2 -ordered c¢ precipitates coherently embedded in an fcc solid solution c matrix.…”

Atom probe tomography reveals options for microstructural design of steels and titanium alloys by segregation engineering

“…Here, we provide some examples how these different types of segregation phenomena and confined structural states at lattice defects can be used to design complex microstructures in metallic alloys by using simple heat treatments [12][13][14]. We give examples of corresponding segregation effects, complexions and phase transformation phenomena in Fe-Mn steels taken from earlier work [12][13][14][15][16][17][18][19]. Also, we present some related phenomena in the system Ti-Mo.…”