Designing Heusler nanoprecipitates by elastic misfit stabilization in Fe–Mn maraging steels

In this project nanoprecipitates are designed via elastic misfit stabilization in Fe–Mn maraging steels by combining transmission electron microscopy (TEM) correlated atom probe tomography (APT) with ab initio simulations.

Guided by these predictions, the Al content of the alloys is systematically varied, and the influence of the Al concentration on structure stability, size and distribution of precipitates formed during ageing at 450 °C is studied using scanning electron microscopy–electron backscatter diffraction, TEM and APT. Specifically, the Ni2MnAl Heusler nanoprecipitates exhibit the finest sizes and highest dispersion and hence lead to significant strengthening. The formation of the different types of precipitates and their structure, size, dispersion and effect on the mechanical properties of the alloys are discussed.

Fig. 1: (a, b, d, e, g, h) TEM images and APT reconstructions showing size and spatial distribution of the nanosized precipitates in the martensitic matrix after ageing at 450 °C for 65 h: (a, b) MA_L_Al; (d, e) MA_M_Al; (g, h) MA_H_Al alloy. Insets in the TEM micrographs show TEM SADP of [0 0 1]bcc (left) and [0 1 1]bcc (right) orientations showing superlattice reflexes from the precipitates. From the [0 1 1]bcc SADP, it is revealed that the precipitates in MA_L_Al have B2 structure, while the precipitates in MA_M_Al and MA_H_Al are of B2 as well as L21 structure. (c, f, i) Average chemical composition gradients between martensitic matrix and precipitates as derived from the proximity histogram method [1] (alloys aged at 450 °C for 65 h): (c) MA_L_Al; (f) MA_M_Al; (i) MA_H_Al.
[1]
O. Dmitrieva, P. Choi, S.S.A. Gerstl, D. Ponge, D. Raabe
Ultramicroscopy, 111 (2011), p. 623
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