Effect of Aging Heat Treatment at 400-600°C on the Microstructure and Tensile Properties of 15Cr-15Ni Ti-Stabilized Steel Cladding

This study investigates the effect of thermal aging on the microstructure and tensile properties of a 15-15Ti austenitic stainless steel in the baseline operating conditions of a sodium fast reactor, in the range between 400°C and 600°C. Samples that were aged at up to 600°C for 1000 hours exhibit no evidence of material recovery. Thus, after aging heat treatments, micro-hardness measurements do not decrease, and TEM analyses do not show any modification of the dislocation network. However, TEM examinations have indicated a new threshold for the precipitation of nanometric titanium carbides after an isothermal treatment at 500°C for about 5000 hours. Concerning the tensile properties, the aged states present a gain both in strength and in ductility compared to the initial cold-worked state. The large gain in ductility is observed for all of the temperatures tested (between 20°C and 400°C) and occurs concomitantly with an increase in the strain hardening rate of the material. One plausible hypothesis to explain this improvement of the mechanical behaviour relies on the nanometric titanium carbides formed during the aging process. These precipitates could act as obstacles that impede the motion of existing dislocations, thereby contributing an additional strain hardening mechanism, which would lead to greater strength and also delay the onset of strain localization.

Two-Dimensional Titanium Carbides (Ti3C2Tx) Functionalized by Poly(m-phenylenediamine) for Efficient Adsorption and Reduction of Hexavalent Chromium

Titanium carbides (MXenes) are promising multifunctional materials. However, the negative surface charge and layer-by-layer restacking of MXenes severely restrict their application in the field of anionic pollutants, including in hexavalent chromium (Cr(VI)). Herein, Ti3C2Tx MXenes was functionalized through in situ polymerization and intercalation of poly(m-phenylenediamine) (PmPD), then Ti3C2Tx/PmPD composites were obtained. Delightedly, Ti3C2Tx/PmPD composites exhibited positive surface charge, expanded interlayer spacing, and enhanced hydrophobicity. Furthermore, the specific surface area of Ti3C2Tx/PmPD composite was five and 23 times that of Ti3C2Tx and PmPD, respectively. These advantages endowed Ti3C2Tx/PmPD composite with an excellent adsorption capacity of Cr(VI) (540.47 mg g−1), which was superior to PmPD (384.73 mg g−1), Ti3C2Tx MXene (137.45 mg g−1), and the reported MXene-based adsorbents. The Cr(VI) removal mechanism mainly involved electrostatic adsorption, reduction, and chelation interaction. This study developed a simple functionalization strategy, which would greatly explore the potential of MXenes in the field of anionic pollutants.