title: Correlative Energy-Dispersive X-Ray Spectroscopic Tomography and Atom Probe Tomography of the Phase Separation in an Alnico 8 Alloy.
abstract: Alnico alloys have long been used as strong permanent magnets because of their ferromagnetism and high coercivity. Understanding their structural details allows for better prediction of the resulting magnetic properties. However, quantitative three-dimensional characterization of the phase separation in these alloys is still challenged by the spatial quantification of nanoscale phases. Herein, we apply a dual tomography approach, where correlative scanning transmission electron microscopy (STEM) energy-dispersive X-ray spectroscopic (EDS) tomography and atom probe tomography (APT) are used to investigate the initial phase separation process of an alnico 8 alloy upon non-magnetic annealing. STEM-EDS tomography provides information on the morphology and volume fractions of Fe-Co-rich and Νi-Al-rich phases after spinodal decomposition in addition to quantitative information of the composition of a nanoscale volume. Subsequent analysis of a portion of the same specimen by APT offers quantitative chemical information of each phase at the sub-nanometer scale. Furthermore, APT reveals small, 2-4 nm Fe-rich α 1 phases that are nucleated in the Ni-rich α 2 matrix. From this information, we show that phase separation of the alnico 8 alloy consists of both spinodal decomposition and nucleation and growth processes. The complementary benefits and challenges associated with correlative STEM-EDS and APT are discussed.
authors.affiliation: 1Oak Ridge National Laboratory,Center for Nanophase Materials Sciences,Oak Ridge,TN 37831,USA.
authors.forename: Wei
authors.initials: W
authors.lastname: Guo
authors.affiliation: 1Oak Ridge National Laboratory,Center for Nanophase Materials Sciences,Oak Ridge,TN 37831,USA.
authors.forename: Brian T
authors.initials: BT
authors.lastname: Sneed
authors.affiliation: 2Ames Laboratory, Division of Materials Science and Engineering,Ames,IA 50011,USA.
authors.forename: Lin
authors.initials: L
authors.lastname: Zhou
authors.affiliation: 2Ames Laboratory, Division of Materials Science and Engineering,Ames,IA 50011,USA.
authors.forename: Wei
authors.initials: W
authors.lastname: Tang
authors.affiliation: 2Ames Laboratory, Division of Materials Science and Engineering,Ames,IA 50011,USA.
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: Kramer
authors.affiliation: 3Oak Ridge National Laboratory,Materials Science and Technology Division,Oak Ridge,TN 37831,USA.
authors.forename: David A
authors.initials: DA
authors.lastname: Cullen
authors.affiliation: 1Oak Ridge National Laboratory,Center for Nanophase Materials Sciences,Oak Ridge,TN 37831,USA.
authors.forename: Jonathan D
authors.initials: JD
authors.lastname: Poplawsky
keywords: alnico alloy; atom probe tomography (APT); correlative tomography; electron tomography; phase separation