Andreas Mortensen

Oxide inclusions appear in steel as a subproduct of steelmaking. These are generally detrimental to alloy properties; however, variations exist in the extent to which different inclusions are harmful because their properties vary as a function of their chemical composition. We use nanoindentation to measure the local elastic modulus and hardness of individual oxide particles, produced by precipitation within liquid iron, that belong to the systems Al₂O₃–SiO₂–CaO and MnO–SiO₂–FeO. Measured inclusion hardness values are typically in the range of 8 to 13 GPa and can reach 26 GPa for alumina-rich inclusions. Calcium aluminates rich in alumina are significantly stiffer than iron, with elastic moduli that can reach 350 GPa. On the contrary, calcium aluminates that are expected as a result of successful calcium treatment (i.e., with less than about 80 wt pct Al₂O₃ content) have elastic moduli below that of iron. This is also the case for the wide range of calcium aluminosilicates and of manganese silicates studied here. In addition, silicates containing about 70 to 80 wt pct MnO are observed to have a fine multiphase structure and an elastic modulus of ≈ 180 GPa. Those inclusions thus emerge as possible candidates if one aims to minimise, in loaded steel, stress concentrations associated with matrix-inclusion elastic mismatch.

Chalcogenide glass exhibits a wide transmission window in the infrared range, a high refractive index, and nonlinear optical properties; however, due to its poor mechanical properties and low chemical and environmental stability, producing three-dimensional microstructures of chalcogenide glass remains a challenge. Here, we combine the fabrication of arbitrarily shaped three-dimensional cavities within fused silica molds by means of femtosecond laser-assisted chemical etching with the pressure-assisted infiltration of a chalcogenide glass into the resulting carved silica mold structures. This process enables the fabrication of 3D, geometrically complex, chalcogenide-silica micro-glass composites. The resulting products feature a high refractive index contrast that enables total-internal-reflection guiding and an optical quality roughness level suited for applications in the infrared.