Examinando por Autor "Boccardo, A.D."

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A thermo-metallurgical model for laser surface engineering treatment of nodular cast iron
(Springer Nature, 2021-02-08) Boccardo, A.D.; Catalán, N.; Celentano, D.J.; Ramos-Moore, E.
Heat treatments are frequently used to modify the microstructure of cast irons according to experimental parameters. Among these, laser surface engineering (LSE) has become relevant for being a highly localized treatment with rapid heating and cooling of the irradiated area resulting in minimal distortion of the workpiece. This work presents and experimentally validates a thermo-metallurgical model able to predict the phase transformations occurring during the LSE treatment of nodular cast iron when it is subjected to different laser beam powers and scanning velocities. For this purpose, an experimental characterization of the thermal history and final microstructure is performed for several operating scenarios. In particular, significant changes in the microstructure can be seen at high powers and low scanning velocity where the matrix is transformed into ledeburite and martensite. The final phase volume fractions predicted by the proposed model along the depth of the sample are compared with the corresponding experimental measurements. The results obtained in the simulation are in good agreement with the experimental measurements. This work highlights the use of our model to be systematically applied for the design and optimization of LSE treatments on cast irons.
Beta Titanium Alloys Processed By Laser Powder Bed Fusion: A Review
(Springer Nature, 2021-05-12) Colombo-Pulgarín, J.C.; Biffi, C.A.; Vedani, M.; Celentano, D.; Sánchez-Egea, A.; Boccardo, A.D.; Ponthot, J.-P.
In bTi-alloys, some advances and developments have been reached toward optimizing their mechanical performance and their processability. However, the applications of these alloys via laser powder bed fusion (LPBF) are still under investigation. In this work, the processing of bTi-alloys via LPBF and their properties is reviewed with a focus on six selected metallurgical systems which are expected to be top performance materials in applications in the aeronautical and biomedical contexts. These six systems promise a better mechanical and functional performance considering different in-service environments for medical implants and structural applications. After literature analysis, the applicability of bTi-alloys to be processed via LPBF is then discussed considering the relevant fields of applications.
Martensite decomposition kinetics in additively manufactured Ti-6Al-4V alloy: in-situ characterisation and phase-field modelling
(Elsevier, 2024-04-18) Boccardo, A.D.; Zou, Z.; Simonelli, M.; Tong, M.; Segurado, J.; Leen, S.B.; Tourret, D.
Additive manufacturing of Ti-6Al-4V alloy via laser powder-bed fusion leads to non-equilibrium α′ martensitic microstructures, with high strength but poor ductility and toughness. These properties may be modified by heat treatments, whereby the α′ phase decomposes into equilibrium α+β structures, while possibly conserving microstructural features and length scales of the α′ lath structure. Here, we combine experimental and computational methods to explore the kinetics of martensite decomposition. Experiments rely on in-situ characterisation (electron microscopy and diffraction) during multi-step heat treatment from 400◦C up to the alloy β-transus temperature (995◦C). Computational simulations rely on an experimentally-informed computationally-efficient phase-field model. Experiments confirmed that as-built microstructures were fully composed of martensitic α′ laths. During martensite decomposition, nucleation of the β phase occurs primarily along α′ lath boundaries, with traces of β nucleation along crystalline defects. Phase-field results, using electron backscatter diffraction maps of as-built microstructures as initial conditions, are compared directly with in-situ characterisation data. Experiments and simulations confirmed that, while full decomposition into stable α+β phases may be complete at 650◦C provided sufficient annealing time, visible morphological evolution of the microstructure was only observed for T ≥700◦C, without modification of the prior-β grain structure.
Numerical simulation of austempering heat treatment of a ductile cast iron
(Springer Nature, 2015-11-19) Boccardo, A.D.; Dardati, P.M.; Celentano, D.J.; Godoy, L.A.; Górny, M.; Tyrała, E.
This paper presents a coupled thermo-mechanical-metallurgical formulation to predict the dimensional changes and microstructure of a ductile cast iron part as a consequence of an austempering heat process. To take into account the different complex phenomena which are present in the process, the stress-strain law and plastic evolution equations are defined within the context of the associate rate independent thermo-plasticity theory. The metallurgical model considers the reverse eutectoid, ausferritic, and martensitic transformations using macro and micro models. The resulting model is solved using the finite element method. The performance of this model is evaluated by comparison with experimental results of a dilatometric test. The results indicate that the experimental evolution of deformation and temperature are well represented by the numerical model.