Powder Particle Size Effects on Microstructure and Mechanical Properties of Mechanically Alloyed ODS Ferritic Steels

Reduced activation ferritic (RAF) steels are expected to be widely used in challenging nuclear industrial applications under severe thermo-mechanical regimes and intense neutron loads. Therefore, actual research panorama is facing the strengthening strategies necessary to maximize both performance and endurance under these conditions. Oxide dispersion strengthened (ODS) RAF steels are leader candidates as structural materials in fusion energy reactors thanks to the reinforcement obtained with a fine dispersion of nanosized oxides in their matrix. In this study, the influence of the initial powder particle size and the selected processing route on the final material has been investigated. Two RAF ODS steels coming from atomized pre-alloyed powders with nominal particle powder sizes of 70 and 30 µm and composition Fe-14Cr-2W-0.4Ti-0.3Y2O3 (wt. %) were manufactured by mechanical alloying. Alloyed powders were compacted by hot isostatic pressing, hot crossed rolled, and annealed at 1273 K. Initial powder particle size differences minimize after milling. Both steels present an almost completely recrystallized material and similar grain sizes. The same type and distributions of secondary phases, Cr-W-rich, Ti-rich, and Y-Ti oxide nanoparticles, have been also characterized by transmission electron microscopy (TEM) in both alloy samples. The strengthening effect has been confirmed by tensile and Charpy impact tests. The two alloys present similar strength values with slightly better ductile brittle transition temperature (DBTT) and ductility for the steel produced with the smaller powder size.

Study on the Effect and Mechanism of Alkali–Silica Reaction Expansion in Glass Concrete

The suppression of ASR expansion hazards of glass concrete has always been a key and hot issue in the research of glass concrete. According to the ASTM C1260-14 fast mortar rod method, glass sand and glass powder act as fine aggregate and auxiliary cementing material, respectively. The changes in expansion rate with different amounts of glass sand content and different particle sizes of glass powder in mortar rods were compared, and the effects of glass sand content and the glass powder particle size on the expansion of ASR were analyzed. SEM was used to compare and analyze the microstructure of mortar rods to explore the mechanism of ASR expansion of glass concrete, and the results showed that the addition of glass powder had a certain inhibitory effect on ASR expansion. The larger the particle size of glass powder was, the better the inhibition effect on ASR expansion and the longer its duration. Compared with the three groups of experiments of 0–13 μm, 13–38 μm, and 38–75 μm, it was found that the influence of the glass powder particle size on the expansion of ASR was weaker than that of dosage. The inhibitory effect of glass powder on ASR expansion is related to the fact that glass powder is more involved in pozzolanic reaction in the early hydration process.