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Nickel–titanium alloys are the most widely used shape memory alloys due to their outstanding shape memory effect and superelasticity. Additive manufacturing has recently emerged in the fabrication of shape memory alloy but despite substantial advances in powder-based techniques, less attention has been focused on wire-based additive manufacturing. This work reports on the preliminary results for the process-related microstructural and phase transformation changes of Ni-rich nickel–titanium alloy additively manufactured by wire-based electron beam freeform fabrication. To study the feasibility of the process, a simple 10-layer stack structure was successfully built and characterized, exhibiting columnar grains and achieving one-step reversible martensitic–austenitic transformation, thus showing the potential of this additive manufacturing technique for processing shape memory alloys.

The Refill Friction Stir Spot Welding is an innovative spot like solid state process befitting of overlap joint configurations of similar and dissimilar materials. This process caught the interest and is rapidly growing in the aerospace sector due to its potential to substitute traditional mechanical fasteners, surpassing their mechanical performance while maintaining the so desired lightweight “rationale.” In the current study, process parameters, namely plunge depth, plunge time and rotational speed, are optimized in order to obtain the highest Ultimate Lap Shear Force (ULSF) of 2024-T3 Aluminum Alloy similar joints. The optimization campaign was carried out using a second order multivariate polynomial regression machine learning (ML) algorithm. The trained ML model was able to generalize and accurately predict the Ultimate Lap Shear Force on the holdout set, having a R2 of 88.0%. Moreover, the model suggested an optimum parameter combination (Rotational Speed = 2,310 rpm, Welding Time = 5.3 s and Plunge Depth = 2.6 mm) from which the predicted maximum ULSF was computed. Confirmation tests were carried out to evaluate the agreement between the predicted and the experimental values.

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Thermal treatments are the main route to achieve improvements in mechanical properties of β-metastable titanium alloys developed for structural applications in automotive and aerospace industries. Therefore, it is of vital importance to determine phase transformation kinetics and mechanisms of nucleation and precipitation during heat treatment of these alloys. In this context, the present paper focuses on the assessment of solid-state transformations in a β-water-quenched Ti-5Al-5Mo-5V-3Cr-1Zr alloy during the early stages of ageing treatment at 500 °C. In situ tracking of transformations was performed using high-energy synchrotron X-ray diffraction. The transformation sequence β + ω → α + α”iso + β is proposed to take place during this stage. Results show that isothermal α” phase precipitates from ω and from spinodal decomposition domains of the β phase, whereas α nucleates from ω, β and also from α” with different morphologies. Isothermal α” is considered to be the regulator of transformation kinetics. Hardness measurements confirm the presence of ω, although this phase was not detected by X-ray diffraction during the in situ treatment.

Estudo in-situ da solubilização e do envelhecimento da liga β-metaestável Ti-5Al-5Mo-5V-3Cr-1Zr usando difração de raio-x com luz síncrotron de alta energia RAFAEL PAIOTTI MARCONDES GUIMARÃES São Carlos RAFAEL PAIOTTI MARCONDES GUIMARÃESEstudo in-situ da solubilização e do envelhecimento da liga β-metaestável Ti-5Al-5Mo-5V-3Cr-1Zr usando difração de raio-x com luz síncrotron de alta energia Recently introduced, the new Ti-55531 titanium based alloy has been developed aiming structural applications such as the automotive and aerospace ones. The present Thesis is focused on the assessment of Ti-55531 alloy in situ solid state transformations during ageing at different temperatures as well as initial conditions. In this sense, the study emphasis will deal with both quantitative and qualitative analysis of the main constitutive phases found in the alloy, namely the body-centered cubic β, both hexagonal α and ω and the martensitic α", this one orthorhombic, by means of Rietveld refinement. Concerning the data, it was obtained by high energy x-ray diffraction (HEXRD) technique in a synchrotron light source facility. All the Debye-Scherrer rings resulting from these in situ experiments were analyzed by both FIT2Dand MAUD software.

A LZSA (Li2O-ZrO2-SiO2-Al2O3) glass-ceramic porous media produced by the replication method has been studied for relatively low temperature applications. Different suspensions have been tested, and appropriated parameters to obtain good impregnation and green strength were determined. The structures after the sintering process (975 °C for 120 min) were evaluated by scanning electron microscopy and showed a good reproducibility for the best tested suspensions (70.0 wt.% LZSA, 3.5 wt.% bentonite as binder and 1.5 wt.% Darvan 821A as dispersant) Strut and geometric densities were determined so that glass-ceramic foams with porosity of about 91% were obtained.