Guillermo Requena

Non-negative matrix factorization for the near real-time interpretation of absorption effects in elemental distribution images acquired by X-ray fluorescence imaging.

Elemental distribution images acquired by imaging X-ray fluorescence analysis can contain high degrees of redundancy and weakly discernible correlations. In this article near real-time non-negative matrix factorization (NMF) is described for the analysis of a number of data sets acquired from samples of a bi-modal α+β Ti-6Al-6V-2Sn alloy. NMF was used for the first time to reveal absorption artefacts in the elemental distribution images of the samples, where two phases of the alloy, namely α and β, were in superposition. The findings and interpretation of the NMF results were confirmed by Monte Carlo simulation of the layered alloy system. Furthermore, it is shown how the simultaneous factorization of several stacks of elemental distribution images provides uniform basis vectors and consequently simplifies the interpretation of the representation.

Peritectic titanium alloys for 3D printing

Metal-based additive manufacturing (AM) permits layer-by-layer fabrication of near net-shaped metallic components with complex geometries not achievable using the design constraints of traditional manufacturing. Production savings of titanium-based components by AM are estimated up to 50% owing to the current exorbitant loss of material during machining. Nowadays, most of the titanium alloys for AM are based on conventional compositions still tailored to conventional manufacturing not considering the directional thermal gradient that provokes epitaxial growth during AM. This results in severely textured microstructures associated with anisotropic structural properties usually remaining upon post-AM processing. The present investigations reveal a promising solidification and cooling path for α formation not yet exploited, in which α does not inherit the usual crystallographic orientation relationship with the parent β phase. The associated decrease in anisotropy, accompanied by the formation of equiaxed microstructures represents a step forward toward a next generation of titanium alloys for AM.3D printing of titanium alloys today is based on known alloy compositions that result in anisotropic structural properties. Here, the authors add lanthanum to commercially pure titanium and exploit a solidification path that reduces texture and anisotropy.

Determination of Internal Stresses in Lightweight Metal Matrix Composites

Internal stresses are those stresses found in a body when this is stationary and in equilibrium with its surroundings (Withers & Badeshia, 2001). These stresses can arise at different length scales within a microstructure ranging from the size of the analysed body down to the atomic scale. Multiphase materials are prone to develop internal stresses due to the different mechanical and physical properties usually found between the phases that form these materials. This is essential for composites because the distribution and magnitude of the internal stresses may determine their mechanical/physical behaviour. Neutron diffraction has become an essential tool to determine internal stresses nondestructively in metal-based composite materials. The present chapter gives a thorough description of the state of the art of the technique and its use to determine internal stresses developed in lightweight metal matrix composites under mechanical, thermal and thermomechanical loading.

Effect of Mischmetal Additions and Solution Heat Treatments (T4) on the Microstructure and Mechanical Properties of Thixocast ZK60-RE Magnesium Alloys

Solution treatments (T4) at 380 °C for 16 h and 500 °C for 8 h were performed for ZK60 magnesium alloys modified with addition of 0.5, 1.5 and 2.5 wt% of mischmetal (combination of rare-earth (RE) elements). The compression behaviour was investigated at room temperature and at 300 °C correlated with the microstructure and differential scanning calorimetry (DSC) data. The as-cast microstructure is formed by a-Mg matrix with globular grains reinforced by a semi continuous network of Mg-Zn, Mg-Zn-RE and Mg-RE intermetallic particles. Solution-treated alloys show lower yield strengths due to partial dissolution of precipitates. Work hardening was not observed for the alloys compressed at 300°C with the compression speed of 10-3 s-1, whereas it was observed for the compression speed of 10-2 s-1 for the all as-cast, ZK60-1.5RE-T4 at 380 °C and ZK60-1.5RE-T4 at 380 °C.

3D-Characterization of AlCu5Mg0.3Mn0.3 and AlCu7Mn0.4 Alloys

Abstract The three dimensional microstructural evolution of cast B206 (AlCu5Mg0.3Mn0.3) and AlCu7 (AlCu7Mn0.4) alloys is studied as a function of solution treatment time by synchrotron tomography. Both alloys are formed by an α-Al matrix, Al2Cu and Al7Cu2(FeMn). 3D microstructural parameters of the aluminides such as volume fraction and interconnectivity are presented for the alloys in as-cast condition and after 4 h, 8 h and 16 h of solution treatment at 530 °C. Morphological evolution is obtained from the mean and Gauss curvature distribution. Finally, target metallography is combined with energy dispersive x-ray analysis to identify the phases remaining after 16 h of solution treatment.

X-ray refraction distinguishes unprocessed powder from empty pores in selective laser melting Ti-6Al-4V

ABSTRACT For the first time, X-ray refraction techniques are proven for the identification of void formation in Ti-6Al-4V parts produced by selective laser melting. The topology and volume fraction of pores are measured in samples produced with different laser energy density. Unique X-ray refraction methods identify different kinds of defects, characteristic to the regions below and above the optimum laser energy density, namely unprocessed powder (unmolten powder particles, balling effect, and fusion defects) from empty keyhole pores. Furthermore, it is possible to detect small inhomogeneities (voids or cracks) with sizes below the spatial resolution of optical microscopy and X-ray computed tomography. IMPACT STATEMENT For the first time, we show that, unparalleled by high-resolution X-ray-computed tomography or electron microscopy, X-ray refraction can distinguish unprocessed powder from empty pores in additive manufactured materials. GRAPHICAL ABSTRACT

Optimized Segmentation of the 3D Microstructure in Cast Al-Si Piston Alloys

Abstract The thermomechanical behavior of cast Al-Si piston alloys is highly dependent on the condition of the highly interconnected hybrid 3D network which is composed of primary and eutectic silicon and intermetallic phases which are found embedded in the α-Al matrix. The very similar X-ray absorption of silicon and the α-Al matrix is problematic for the local identification of these phases and thus for the accurate segmentation and characterization of all rigid phases in the network when laboratory X-ray tomographs are used. A combination of conventional X-ray computed tomography, synchrotron computed tomography, and chemical deep etching performed on the same alloy and at the same position allows for an automatic segmentation and a more accurate characterization of phases across large representative volumes and thus provides the information necessary for a quantification of the whole 3D microstructure of the alloys.

In-situ monitoring of phase transformation in Ti-6Al-6V-2Sn using laser ultrasonics

Abstract Titanium is of great interest for metal processing industries due to its superior material properties, but it is also quite expensive. Therefore, a detailed knowledge of phase transformation and consequential the distribution of and phase in titanium alloys is crucial for their material properties and as a consequence for further processing steps. Measuring the ultrasonic velocity and attenuation by laser ultrasonics technology (LUS) as a non-destructive and non-contact technique, it is possible to qualitatively monitor in-situ the phase transformation during heating the sample from room temperature up to . We validate LUS methodology against high energy X-ray diffraction as well as against conventional metallurgic measurements and get excellent agreement between the results of these methods.

High energy near- and far-field ptychographic tomography at the ESRF

In high-resolution tomography, one needs high-resolved projections in order to reconstruct a high-quality 3D map of a sample. X-ray ptychography is a robust technique which can provide such high-resolution 2D projections taking advantage of coherent X-rays. This technique was used in the far-field regime for a fair amount of time, but it can now also be implemented in the near-field regime. In both regimes, the technique enables not only high-resolution imaging, but also high sensitivity to the electron density of the sample. The combination with tomography makes 3D imaging possible via ptychographic X-ray computed tomography (PXCT), which can provide a 3D map of the complex-valued refractive index of the sample. The extension of PXCT to X-ray energies above 15 keV is challenging, but it can allow the imaging of object opaque to lower energy. We present here the implementation and developments of high-energy near- and far-field PXCT at the ESRF.