@article{LaquaiMuellerSchneideretal.2020,
  author    = {Laquai, Rene and M{\"u}ller, Bernd R. and Schneider, Judith Ann and Kupsch, Andreas and Bruno, Giovanni},
  title     = {Using SXRR to probe the nature of discontinuities in SLM additive manufactured inconel 718 specimens},
  series = {Metallurgical and Materials Transactions A},
  volume    = {51},
  journal   = {Metallurgical and Materials Transactions A},
  number    = {8},
  publisher = {Springer},
  address   = {New York},
  issn      = {1073-5623},
  doi       = {10.1007/s11661-020-05847-5},
  pages     = {4146 -- 4157},
  year      = {2020},
  abstract  = {The utilization of additive manufacturing (AM) to fabricate robust structural components relies on understanding the nature of internal anomalies or discontinuities, which can compromise the structural integrity. While some discontinuities in AM microstructures stem from similar mechanisms as observed in more traditional processes such as casting, others are unique to the AM process. Discontinuities in AM are challenging to detect, due to their submicron size and orientation dependency. Toward the goal of improving structural integrity, minimizing discontinuities in an AM build requires an understanding of the mechanisms of formation to mitigate their occurrence. This study utilizes various techniques to evaluate the shape, size, nature and distribution of discontinuities in AM Inconel 718, in a non-hot isostatic pressed (HIPed) as-built, non-HIPed and direct age, and HIPed with two step age samples. Non-destructive synchrotron radiation refraction and transmission radiography (SXRR) provides additional information beyond that obtained with destructive optical microscopy. SXRR was able to distinguish between voids, cracks and lack of melt in, due to its sensitivity to the orientation of the discontinuity.},
  language  = {en}
}
@misc{MuellerKupschLaquaietal.2018,
  author    = {M{\"u}ller, Bernd Randolf and Kupsch, Andreas and Laquai, Rene and Nellesen, Jens and Tillmann, Wolfgang and Kasperovich, Galina and Bruno, Giovanni},
  title     = {Microstructure Characterisation of Advanced Materials via 2D and 3D X-Ray Refraction Techniques},
  series = {Materials Science Forum},
  volume    = {941},
  journal   = {Materials Science Forum},
  publisher = {Trans Tech Publications Ltd},
  address   = {Zurich},
  isbn      = {978-3-0357-1208-7},
  issn      = {0255-5476},
  doi       = {10.4028/www.scientific.net/MSF.941.2401},
  pages     = {2401 -- 2406},
  year      = {2018},
  abstract  = {3D imaging techniques have an enormous potential to understand the microstructure, its evolution, and its link to mechanical, thermal, and transport properties. In this conference paper we report the use of a powerful, yet not so wide-spread, set of X-ray techniques based on refraction effects. X-ray refraction allows determining internal specific surface (surface per unit volume) in a non-destructive fashion, position and orientation sensitive, and with a nanometric detectability. We demonstrate showcases of ceramics and composite materials, where microstructural parameters could be achieved in a way unrivalled even by high-resolution techniques such as electron microscopy or computed tomography. We present in situ analysis of the damage evolution in an Al/Al2O3 metal matrix composite during tensile load and the identification of void formation (different kinds of defects, particularly unsintered powder hidden in pores, and small inhomogeneity's like cracks) in Ti64 parts produced by selective laser melting using synchrotron X-ray refraction radiography and tomography.},
  language  = {en}
}
@article{LaquaiGouraudMuelleretal.2019,
  author    = {Laquai, Rene and Gouraud, Fanny and M{\"u}ller, Bernd Randolf and Huger, Marc and Chotard, Thierry and Antou, Guy and Bruno, Giovanni},
  title     = {Evolution of Thermal Microcracking in Refractory ZrO2-SiO2 after Application of External Loads at High Temperatures},
  series = {Materials},
  volume    = {12},
  journal   = {Materials},
  number    = {7},
  publisher = {MDPI},
  address   = {Basel},
  issn      = {1996-1944},
  doi       = {10.3390/ma12071017},
  pages     = {15},
  year      = {2019},
  abstract  = {Zirconia-based cast refractories are widely used for glass furnace applications. Since they have to withstand harsh chemical as well as thermo-mechanical environments, internal stresses and microcracking are often present in such materials under operating conditions (sometimes in excess of 1700 °C). We studied the evolution of thermal (CTE) and mechanical (Young's modulus) properties as a function of temperature in a fused-cast refractory containing 94 wt.\% of monoclinic ZrO2 and 6 wt.\% of a silicate glassy phase. With the aid of X-ray refraction techniques (yielding the internal specific surface in materials), we also monitored the evolution of microcracking as a function of thermal cycles (crossing the martensitic phase transformation around 1000 °C) under externally applied stress. We found that external compressive stress leads to a strong decrease of the internal surface per unit volume, but a tensile load has a similar (though not so strong) effect. In agreement with existing literature on β-eucryptite microcracked ceramics, we could explain these phenomena by microcrack closure in the load direction in the compression case, and by microcrack propagation (rather than microcrack nucleation) under tensile conditions.},
  language  = {en}
}
@article{MackLaquaiMuelleretal.2019,
  author    = {Mack, Daniel Emil and Laquai, Rene and Mueller, Bernd and Helle, Oliver and Sebold, Doris and Vassen, Robert and Bruno, Giovanni},
  title     = {Evolution of porosity, crack density, and CMAS penetration in thermal barrier coatings subjected to burner rig testing},
  series = {Journal of the American Ceramic Society},
  volume    = {102},
  journal   = {Journal of the American Ceramic Society},
  number    = {10},
  publisher = {Wiley},
  address   = {Hoboken},
  issn      = {0002-7820},
  doi       = {10.1111/jace.16465},
  pages     = {6163 -- 6175},
  year      = {2019},
  abstract  = {Degradation of thermal barrier coatings (TBCs) in gas-turbine engines due to calcium-magnesium-aluminosilicate (CMAS) glassy deposits from various sources has been a persistent issue since many years. In this study, state of the art electron microscopy was correlated with X-ray refraction techniques to elucidate the intrusion of CMAS into the porous structure of atmospheric plasma sprayed (APS) TBCs and the formation and growth of cracks under thermal cycling in a burner rig. Results indicate that the sparse nature of the infiltration as well as kinetics in the burner rig are majorly influenced by the wetting behavior of the CMAS. Despite the obvious attack of CMAS on grain boundaries, the interaction of yttria-stabilized zirconia (YSZ) with intruded CMAS has no immediate impact on structure and density of internal surfaces. At a later stage the formation of horizontal cracks is observed in a wider zone of the TBC layer.},
  language  = {en}
}