@article{MishurovaCabezaArtztetal.2017, author = {Mishurova, Tatiana and Cabeza, Sandra and Artzt, Katia and Haubrich, Jan and Klaus, Manuela and Genzel, Christoph and Requena, Guillermo and Bruno, Giovanni}, title = {An Assessment of Subsurface Residual Stress Analysis in SLM Ti-6Al-4V}, series = {Materials}, volume = {10}, journal = {Materials}, publisher = {MDPI}, address = {Basel}, issn = {1996-1944}, doi = {10.3390/ma10040348}, pages = {14}, year = {2017}, abstract = {Ti-6Al-4V bridges were additively fabricated by selective laser melting (SLM) under different scanning speed conditions, to compare the effect of process energy density on the residual stress state. Subsurface lattice strain characterization was conducted by means of synchrotron diffraction in energy dispersive mode. High tensile strain gradients were found at the frontal surface for samples in an as-built condition. The geometry of the samples promotes increasing strains towards the pillar of the bridges. We observed that the higher the laser energy density during fabrication, the lower the lattice strains. A relief of lattice strains takes place after heat treatment.}, language = {en} } @article{MishurovaArtztHaubrichetal.2018, author = {Mishurova, Tatiana and Artzt, Katia and Haubrich, Jan and Requena, Guillermo and Bruno, Giovanni}, title = {New aspects about the search for the most relevant parameters optimizing SLM materials}, series = {Additive manufacturing}, volume = {25}, journal = {Additive manufacturing}, publisher = {Elsevier}, address = {Amsterdam}, issn = {2214-8604}, doi = {10.1016/j.addma.2018.11.023}, pages = {325 -- 334}, year = {2018}, abstract = {While the volumetric energy density is commonly used to qualify a process parameter set, and to quantify its influence on the microstructure and performance of additively manufactured (AM) materials and components, it has been already shown that this description is by no means exhaustive. In this work, new aspects of the optimization of the selective laser melting process are investigated for AM Ti-6Al-4V. We focus on the amount of near-surface residual stress (RS), often blamed for the failure of components, and on the porosity characteristics (amount and spatial distribution). First, using synchrotron x-ray diffraction we show that higher RS in the subsurface region is generated if a lower energy density is used. Second, we show that laser de-focusing and sample positioning inside the build chamber also play an eminent role, and we quantify this influence. In parallel, using X-ray Computed Tomography, we observe that porosity is mainly concentrated in the contour region, except in the case where the laser speed is small. The low values of porosity (less than 1\%) do not influence RS.}, language = {en} } @article{MishurovaArtztHaubrichetal.2019, author = {Mishurova, Tatiana and Artzt, Katia and Haubrich, Jan and Requena, Guillermo and Bruno, Giovanni}, title = {Exploring the correlation between subsurface residual stresses and manufacturing parameters in laser powder bed fused Ti-6Al-4V}, series = {Metals}, volume = {9}, journal = {Metals}, number = {2}, publisher = {MDPI}, address = {Basel}, issn = {2075-4701}, doi = {10.3390/met9020261}, pages = {13}, year = {2019}, abstract = {Subsurface residual stresses (RS) were investigated in Ti-6Al-4V cuboid samples by means of X-ray synchrotron diffraction. The samples were manufactured by laser powder bed fusion (LPBF) applying different processing parameters, not commonly considered in open literature, in order to assess their influence on RS state. While investigating the effect of process parameters used for the calculation of volumetric energy density (such as laser velocity, laser power and hatch distance), we observed that an increase of energy density led to a decrease of RS, although not to the same extent for every parameter variation. Additionally, the effect of support structure, sample roughness and LPBF machine effects potentially coming from Ar flow were studied. We observed no influence of support structure on subsurface RS while the orientation with respect to Ar flow showed to have an impact on RS. We conclude recommending monitoring such parameters to improve part reliability and reproducibility.}, language = {en} } @article{MishurovaSydowThiedeetal.2020, author = {Mishurova, Tatiana and Sydow, Benjamin and Thiede, Tobias and Sizova, Irina and Ulbricht, Alexander and Bambach, Markus and Bruno, Giovanni}, title = {Residual stress and microstructure of a Ti-6Al-4V Wire Arc Additive Manufacturing hybrid demonstrator}, series = {Metals}, volume = {10}, journal = {Metals}, number = {6}, publisher = {MDPI}, address = {Basel}, issn = {2075-4701}, doi = {10.3390/met10060701}, pages = {15}, year = {2020}, abstract = {Wire Arc Additive Manufacturing (WAAM) features high deposition rates and, thus, allows production of large components that are relevant for aerospace applications. However, a lot of aerospace parts are currently produced by forging or machining alone to ensure fast production and to obtain good mechanical properties; the use of these conventional process routes causes high tooling and material costs. A hybrid approach (a combination of forging and WAAM) allows making production more efficient. In this fashion, further structural or functional features can be built in any direction without using additional tools for every part. By using a combination of forging basic geometries with one tool set and adding the functional features by means of WAAM, the tool costs and material waste can be reduced compared to either completely forged or machined parts. One of the factors influencing the structural integrity of additively manufactured parts are (high) residual stresses, generated during the build process. In this study, the triaxial residual stress profiles in a hybrid WAAM part are reported, as determined by neutron diffraction. The analysis is complemented by microstructural investigations, showing a gradient of microstructure (shape and size of grains) along the part height. The highest residual stresses were found in the transition zone (between WAAM and forged part). The total stress range showed to be lower than expected for WAAM components. This could be explained by the thermal history of the component.}, language = {en} } @article{PauzonMishurovaEvsevleevetal.2021, author = {Pauzon, Camille and Mishurova, Tatiana and Evsevleev, Sergei and Dubiez-Le Goff, Sophie and Murugesan, Saravanakumar and Bruno, Giovanni and Hryha, Eduard}, title = {Residual stresses and porosity in Ti-6Al-4V produced by laser powder bed fusion as a function of process atmosphere and component design}, series = {Additive manufacturing}, volume = {47}, journal = {Additive manufacturing}, publisher = {Elsevier}, address = {Amsterdam}, issn = {2214-8604}, doi = {10.1016/j.addma.2021.102340}, pages = {10}, year = {2021}, abstract = {The influence of the process gas, laser scan speed, and sample thickness on the build-up of residual stresses and porosity in Ti-6Al-4V produced by laser powder bed fusion was studied. Pure argon and helium, as well as a mixture of those (30\% helium), were employed to establish process atmospheres with a low residual oxygen content of 100 ppm O-2. The results highlight that the subsurface residual stresses measured by X-ray diffraction were significantly lower in the thin samples (220 MPa) than in the cuboid samples (645 MPa). This difference was attributed to the shorter laser vector length, resulting in heat accumulation and thus in-situ stress relief. The addition of helium to the process gas did not introduce additional subsurface residual stresses in the simple geometries, even for the increased scanning speed. Finally, larger deflection was found in the cantilever built under helium (after removal from the baseplate), than in those produced under argon and an argon-helium mixture. This result demonstrates that complex designs involving large scanned areas could be subjected to higher residual stress when manufactured under helium due to the gas's high thermal conductivity, heat capacity, and thermal diffusivity.}, language = {en} }