Three-dimensional characterisation of the microstructure of an high entropy alloy using STEM/HAADF tomography

Abstract The microstructure of a high entropy alloy with composition of Mo0.5Al1Nb1Ta0.5Ti1Zr1 (the digits refer to molar volumes) has been characterised directly in three dimensions using TEM dark field (DF) imaging and by recording tilt pair micrographs using STEM high angle annular DF (HAADF) imaging. The microstructure contains disordered bcc precipitates that appeared as orthogonal stacks of plate-like features. A tapered needle sample was prepared in a focused ion beam/SEM and was used to acquire a 180° tomographic dataset of STEM/HAADF images in 2° increments. The tilt series images were registered, and the algebraic reconstruction technique was used to reconstruct the three-dimensional microstructure. The bcc precipitates were segmented using a combinative approach involving two threshold techniques. The precipitates were then visualised using commercial software, which revealed surprisingly the existence of both cuboidal and plate-like morphologies. Colouring each precipitate according to its morphology (determined using the omega-2 moment invariant) revealed a precipitate arrangement where plate-like features appeared parallel to each cuboid face.

[1]  Daniel E. Huber,et al.  Development and application of MIPAR™: a novel software package for two- and three-dimensional microstructural characterization , 2014, Integrating Materials and Manufacturing Innovation.

[2]  Michael D. Uchic,et al.  Exploration and Development of High Entropy Alloys for Structural Applications , 2014, Entropy.

[3]  Mark A. Gibson,et al.  Nature of the interfaces between the constituent phases in the high entropy alloy CoCrCuFeNiAl. , 2013, Ultramicroscopy.

[4]  U. Glatzel,et al.  Phase separation in equiatomic AlCoCrFeNi high-entropy alloy. , 2013, Ultramicroscopy.

[5]  X. Yang,et al.  Alloy Design and Properties Optimization of High-Entropy Alloys , 2012 .

[6]  Nikita Stepanov,et al.  Tensile properties of an AlCrCuNiFeCo high-entropy alloy in as-cast and wrought conditions , 2012 .

[7]  P. Liaw,et al.  Refractory high-entropy alloys , 2010 .

[8]  Jeff Simmons,et al.  Three-dimensional analysis of secondary γ′ precipitates in René-88 DT and UMF-20 superalloys , 2009 .

[9]  M. Graef,et al.  On the use of moment invariants for the automated analysis of 3D particle shapes , 2008 .

[10]  Carlos Oscar Sánchez Sorzano,et al.  TomoJ: tomography software for three-dimensional reconstruction in transmission electron microscopy , 2007, BMC Bioinformatics.

[11]  Yong Zhang,et al.  Microstructure and compressive properties of multicomponent Alx(TiVCrMnFeCoNiCu)100−x high-entropy alloys , 2007 .

[12]  Sara Bals,et al.  High-Quality Sample Preparation by Low kV FIB Thinning for Analytical TEM Measurements , 2007, Microscopy and Microanalysis.

[13]  P. Midgley,et al.  3D electron microscopy in the physical sciences: the development of Z-contrast and EFTEM tomography. , 2003, Ultramicroscopy.

[14]  Steve R Brown,et al.  Applications of the FIB lift‐out technique for TEM specimen preparation , 1998, Microscopy research and technique.

[15]  R. Gordon.  A tutorial on art (algebraic reconstruction techniques) , 1974 .

[16]  G. Herman,et al.  Algebraic reconstruction techniques (ART) for three-dimensional electron microscopy and x-ray photography. , 1970, Journal of theoretical biology.

[17]  P. Liaw,et al.  Microstructure and Compressive Properties of NbTiVTaAlx High Entropy Alloys , 2012 .

[18]  M. Radermacher.  Weighted Back-Projection Methods , 2007 .

[19]  J. Frank,et al.  Alignment by Cross-Correlation , 1992 .