ABSTRACT
Poles and zone lines observed within atom probe field evaporation images are useful for a range of atom probe crystallography studies, including calibration of the reconstruction and crystallographic characterisation of microstructural features such as grain boundaries. However, this information is not always readily apparent. Techniques for plotting crystallographically correlated metrics contained within atom probe data to enhance pole and zone line contrast across the detector space are developed. This includes consideration of the electric field, molecular ions, lattice structure retained within the reconstruction, specific elemental species, the number of pulses between detection events, and the lateral distance between sequential detection events. These approaches are then applied to experimental atom probe tomography datasets on technically pure Al, nanocrystalline Al, highly doped Si, and additively manufactured Inconel 738, Haynes 282, and Ti-6Al-4V. The results facilitate the extension of atom probe crystallography studies to a broader range of crystalline datasets where crystallographic information is not readily apparent from existing methods, as well as a deeper understanding of field evaporation behaviour during an atom probe experiment.
ABSTRACT
Recent advancements in data mining methods in atom probe microscopy have enabled new quantitative chemical and microstructural characterization beyond the standard three-dimensional reconstruction. For example, spatial distribution maps have been developed to enable visualisation of the local lattice occupation of a selected region of interest. However, the precision of such studies yet remains unknown as correlation with complementary methods would be required. Therefore, a correlative study of atom probe microscopy, neutron diffraction and microstructural modelling of long-range ordered, nano-scale domains in a well-researched Fe-Co-Mo Maraging-type steel is presented here. Its microstructure consists of Mo-enriched µ-phase (Fe,Co)7Mo6 particles embedded into a body-centred cubic FeCo matrix. Previous research has shown that under slow cooling conditions, this matrix partially decomposes into nano-scale B2 long-range ordered domains surrounded by disordered regions, resulting in reduced toughness in potential cutting applications. Usually, a long-range order parameter S referring to ideal B2 long-range order is assumed within such domains according to neutron diffraction. However, atom probe microscopy and modelling results presented in the current study indicate lattice imperfections with a partial substitution of atoms on the Fe- and Co-sublattices. After considering preferential retention effects during the atom probe experiment, a model unit cell is presented to define the observed imperfect B2 long-range order as pseudo-D03 long-range order, and the potential impact on the materials properties is discussed.
ABSTRACT
It is highly difficult to pinpoint what is going through an animal's mind when it appears to solve a problem by 'insight'. Here, we searched for an information processing error during the emergence of seemingly insightful stone dropping in New Caledonian crows. We presented these birds with the platform apparatus, where a heavy object needs to be dropped down a tube and onto a platform in order to trigger the release of food. Our results show New Caledonian crows exhibit a weight inattention error: they do not attend to the weight of an object when innovating stone dropping. This suggests that these crows do not use an understanding of force when solving the platform task in a seemingly insightful manner. Our findings showcase the power of the signature-testing approach, where experiments search for information processing biases, errors and limits, in order to make strong inferences about the functioning of animal minds.
Subject(s)
Crows/physiology , Animals , Tool Use Behavior/physiologyABSTRACT
Short-range-order (SRO) has been quantitatively evaluated in an Fe-18Al (at%) alloy using atom probe tomography (APT) data and by calculation of the generalised multicomponent short-range order (GM-SRO) parameters, which have been determined by shell-based analysis of the three-dimensional atomic positions. The accuracy of this method with respect to limited detector efficiency and spatial resolution is tested against simulated D03 ordered data. Whilst there is minimal adverse effect from limited atom probe instrument detector efficiency, the combination of this with imperfect spatial resolution has the effect of making the data appear more randomised. The value of lattice rectification of the experimental APT data prior to GM-SRO analysis is demonstrated through improved information sensitivity.
