Matériaux Ingénierie et Science

This work investigates the effect of ball milling on the microstructure and mechanical properties of Al 0.3 CoCrFeNi high entropy alloy (HEA), starting from two different powders: pre-alloyed powders obtained by gas atomization and a pure elemental mixture. The powders were densified using spark plasma sintering (SPS). For the atomized powders, ball milling leads to the formation of a heterogeneous core–shell structure that remains after sintering, with grain sizes ranging from 1 to 10 μm in the cores and less than 1 μm in the shells. Slight air contamination during the milling stage promoted the formation of nanometric AlN at grain boundaries within the shells, which inhibited grain coarsening during SPS. Additionally, Al₂O₃ precipitates formed at prior particle boundaries (PPBs). Grain size after sintering is refined from 13 μm to 3.3 μm (without and with 28 h milling of atomized powder), resulting in an increase in hardness (from 182 to 280 HV₂), yield strength (from 370 to 615 MPa), and ultimate tensile strength (from 653 to 770 MPa), accompanied by a loss in ductility (from 54 % to 18 %). However, below 28 h of milling, the strengthening is not as high as would be expected from the Hall-Petch effect. PPBs have been identified as crack initiation sites, leading to lower-than-expected tensile properties. This negative effect of PPBs can be decreased by increasing powder particle size through prolonged milling, thereby reducing PPBs density. In contrast, mechanical activation of elemental powder mixture leads to the formation of an ultrafine-grained microstructure with dispersed nanometric B2 and Al₂O₃ phases. This elaboration route allows a higher mechanical strength (1175 MPa) and hardness (512 HV 2 ), but significantly lower ductility (2 %). The random distribution of minor secondary phases does not lead to PPB-related failure. This study demonstrated the strong influence of starting powders on the milling-induced microstructure, phase formation, and the resulting strengthening mechanisms governing the mechanical behavior of Al 0.3 CoCrFeNi HEAs.

Introduction: To report a case of anterior chamber migration of the dexamethasone intravitreal implant (DEX-I) through a new type of scleral fixated lens, the Carlevale® intraocular lens (IOL) (Cutting Edge, Italy). Case Presentation: A 74-year-old pseudophakic man with a history of macular edema (ME) secondary to retinal vein occlusion had been receiving DEX-I injections every 4 months for 10 years. During follow-up, he spontaneously presented an IOL luxation into the vitreous cavity, treated surgically with explantation and Carlevale® IOL implantation. One month after this surgery, an injection of DEX-I was performed, due to recurrence of the ME. Seven days after, the patient presented DEX-I migration into the anterior chamber along with corneal edema, requiring implant removal. After aspiration through a 20-gauge catheter connected to a syringe corneal edema decreased in 7 days allowing an improvement in visual acuity. Conclusion: Migration of the DEX-I into the anterior chamber remains a potential complication in vitrectomized eyes with capsular defects, even with the use of scleral-fixated IOLs such as the Carlevale®, which features a large optic. This highlights the importance of careful patient selection and postoperative monitoring in such cases.

Topo-Tomography (TT) is a synchrotron-based X-ray diffraction imaging technique used to characterize grain shape and crystal orientation in polycrystalline samples. This work aims to provide a decisive and fundamental understanding of 3D grain shape and orientation field reconstruction from TT diffraction data. We derive mathematical expressions for the TT projection geometry, considering grain shape, intragranular lattice rotations, and elastic strains, under the assumption of kinematical diffraction. These expressions are simplified using approximations for small strain variations and grain size. The simplified expressions show that integrated TT projection images correspond to projections of a "pseudo" distorted grain volume. Its Fourier analysis provides insights into the feasibility of orientation field reconstruction from TT scans. We propose methods to expand data coverage, including using opposite scattering vectors and varying detector distance. A lower bound for orientation sampling resolution is derived and validated through simulations.

The strength of sapphire across several length scales has been studied by micro-cantilever bending tests on specimens with the a-plane perpendicular to the main loading direction. The combined machining of two types of FIB (Ga and plasma Xe) is used to produce specimens with a wide range of dimensions, with specimen heights ranging from a few microns to several tens of microns. All specimens exhibit a fracture surface along m-planes. These micro-bending strength results are compared with macroscopic bending results obtained on the same sample with the same orientation. A marked size effect is observed on the measured strength, ranging from around 20 GPa at the micrometric scale down to 650 MPa for macroscopic specimens. A comparison with data from literature on sapphire samples of different size is made. Statistical models are found unable to capture the size effect on the entire range of sample sizes. Graphical abstract