[en] Highlights: • We characterize precipitates by physicochemical phase analysis, XRD, TEM, and etc. • Precipitation sequence of secondary phase during heat treatment has been revealed. • Carbide precipitation behavior explains the rationality of heat treatment process. - Abstract: The characterization of precipitates in X12CrMoWVNbN10-1-1 steel during the heat treatment was carried out for revealing the evolution of the precipitates. In addition to other microstructural parameters (such as dislocation and subgrains), the precipitate also plays an important role for microstructural stability which is a prerequisite for long term creep strength. In this paper, the precipitates during the heat treatment for this steel were characterized using physicochemical phase analyses and transmission electron microscopy. It was found that the Fe-rich M₃C carbides and Nb-rich MX particles were detected in the samples cooled in furnace from austenitization at 1080 °C for 16 h. However, after water cooling, only Nb-rich MX particles existed. During tempering at 570 °C for 18 h, the formation of Cr-rich M₇C₃ was detected but was replaced partially by Cr-rich M₂₃C₆. Additional Cr-rich M₂N nitride was also found. After two successive tempering (570 °C + 690 °C) for 24 h, Cr-rich M₇C₃ was completely replaced. The microchemical analyses of the extracted residues during heat treatment were also discussed. The results gave rise to an indication that the precipitation of precipitates nearly completed in first tempering and the transformation from Cr-rich M₇C₃ to Cr-rich M₂₃C₆ mainly occurred in the second tempering

[en] Quenching (AQ) and cryogenic treatments (QC) were conducted on the high-carbon SAE 52100 steel to investigate the mechanical stability of individual retained austenite (RA) by nano-indentation. The cross-sections of indented RA region prepared by focused ion beam (FIB) were examined by using transmission electron microscopy (TEM). For the first time, it was directly observed that some parts of RA grain, closest to the indent, in AQ specimen had transformed into strain-induced martensite (SIM). However, not any pop-in or transformation was detected in the indented QC specimen. This clearly indicates that the mechanical stability of RA in QC seems significantly enhanced, which is mainly attributed to the cryogenic treatment resulting in a higher carbon enrichment of RA compared to that in AQ. Furthermore, a higher load of external stress may need to trigger its martensitic transformation in QC specimen. - Highlights: • Mechanical stability of retained austenite was studied by nano-indentation and TEM. • The strain-induced martensite transformation in RA was observed under applied load. • Cryogenic treatment enhances mechanical stability of RA due to carbon enrichment.

[en] Retained austenite(RA) usually presents in the quenched Nuclear Pressure-Vessel SA508 Gr.3 steel. In the present work, the characteristic of RA decomposition and its effect on the impact toughness were investigated by microstructure observation, dilatometric experiments and Charpy impact tests. The results show that the RA transformed into martensite and bainite during tempering at 230 °C and 400 °C respectively, while mixture of long rod carbides and ferrite formed at 650 °C. The long rod carbides formed from RA decomposition decrease the critical cleavage stress for initiation of micro-cracks, and deteriorate the impact toughness of the steel. Pre-tempering at a low temperature such as 230 °C or 400 °C leading to the decomposition of RA into martensite or baintie can eliminate the deterioration of the toughness caused by direct decomposition into long rod carbides. The absorbed energy indicate that pre-tempering at 400 °C can drive dramatically improvement in the toughness of the steel. - Highlights: • The products of RA decomposition were localization observed by SEM and TEM. • Decomposition characteristic of RA were revealed during tempering at different temperature. • Impact toughness was dramatically improved by pre-tempering treatment.

[en] The microstructural evolution of reactor pressure vessel (RPV) steel and its effect on the mechanical properties during tempering at 650 °C were studied to reveal the time-dependent toughness and temper embrittlement. The results show that the toughening of the material should be attributed to the decomposition of the martensite/austenite constituents and uniform distribution of carbides. When the tempering duration was 5 h, the strength of the investigated steel decreased to strike a balance with the material impact toughness that reached a plateau. As the tempering duration was further increased, the material strength was slightly reduced but the material impact toughness deteriorated drastically. This time-dependent temper embrittlement is different from traditional temper embrittlement, and it can be partly attributed to the softening of the matrix and the broadening of the ferrite laths. Moreover, the dimensions and distribution of the grain carbides are the most important factors of the impact toughness. - Highlights: • The fracture mechanism of reactor pressure vessel (RPV) steels under impact load was investigated. • The Charpy V-notch impact test and the hinge model were employed for the study. • Grain boundary carbides play a key role in the impact toughness and fracture toughness. • The dependence of the deterioration of impact toughness on tempering time was analyzed for the first time.

[en] Through altering the solvents, we have obtained the Eu³⁺/Tb³⁺ ions-doped LnPO₄ (Ln = La, Gd) phosphors with different particle sizes, microstructures and morphologies via a facile solvo-thermal technology. X-ray powder diffraction (XRD), transmission electron microscope (TEM), and scanning electron microscope (SEM) have shown that the products using different solvents have various structures and morphologies. With the increase of DMA/water volume ratio, the microstructure has changed from hexagonal phase to monoclinic one, and the morphology from nanorod to nanoparticle, revealing the decreased oriented growth. The presence of DMA is an important factor in guiding the anisotropic growth of hexagonal lanthanide phosphates. Besides, N-methyl-2-pyrrolidone has been used as solvent to induce the Eu³⁺/Tb³⁺ ions-doped LnPO₄ (Ln = La, Gd) phosphors with different morphologies and structures. Finally, the photoluminescence behaviors of these nanocrystals have been investigated, which are dependent on their microstructures and morphologies.

[en] The quality and reliability of the civil nuclear safety equipment are very important to the safety of the nuclear facilities. In order to strengthen the regulation, improve equipment quality and maintain the efficient and sustainable development of civil nuclear safety, new measures to strengthen nuclear safety equipment supervision based on summing up good practice and analyzing the weakness shall be employed. (authors)

[en] The splitting phenomenon was detected in martensitic transformation of X12CrMoWVNbN10-1-1 steel using high resolution dilatometry under certain conditions. In-situ observation of austenite grain growth was carried out. Direct experimental results indicated that this splitting is not connected with the concentration gradient in the austenite resulting from the dissolution of carbonitrides during heating, but instead may be caused by the occurrence of abnormal grain growth.

[en] Catalytic conversion of CO₂ to CO (reverse water-gas shift reaction, RWGS) is one of the most promising technologies for CO₂ resource utilization. In this work, a sulfur-containing zirconia supported nickel catalyst (Ni/ZrO₂) was prepared to improve the CO₂ conversion while adjusting the CO₂ hydrogenation selectivity from CH₄ to CO. The effect of support size (80 nm, 120 nm, 200 nm and 320 nm) on the catalytic performance of RWGS was investigated. The results showed that the Ni/ZrO₂-80 sample with a smaller support size of 80 nm exhibited higher Ni dispersion and oxygen vacancy concentration, which not only exposed more active sites but also enhanced the adsorption and activation capacity of CO₂. For these reasons, the CO₂ conversion of 27.6% with 100% selectivity of CO was achieved over Ni/ZrO₂-80, and no catalyst deactivation was observed during the stability test for 50 h. This work provides a new idea for designing the RWGS catalyst with an outstanding CO₂ hydrogenation performance. (authors)

[en] Highlights: • The precipitates sequence of FB2 steel during tempering is proposed. • The effect of tempering temperature on the segregation behavior of interstitial atom and substitional is suggested. • The flux of Si and Co at the carbides/matrix interfaces may inlfuence the coarsening of carbides. The effect of tempering temperature on the precipitation reactions and elemental redistribution in 9Cr1.5Mo1CoB(FB2) steel has been studied using scanning electron microscope(SEM), transmission electron microscope(TEM), secondary ion mass spectrometry(Tof-SIMS) and atom probe technique (APT). The results show that water-cooling from normalization at 1100 °C produced lathy martensite. During tempering at 500 °C, only C and B atoms were segregated, and formed needle-like Fe₃(C, B); After tempering at 600 °C, the segregation of Cr, Mo and Mn showed noticeable difference, forming Cr + Mn + Mo + C + B and Mo + Cr + C + B clusters. Consequently, (Cr,Mo)₂(C,B), Cr-rich M₇(C,B)₃ and Cr-rich M₂₃(C,B)₆ were observed in sample tempered at 600 °C. And both (Cr,Mo)₂(C,B) and M₇(C,B)₃ particles were entirely replaced by Cr-rich M₂₃(C,B)₆ by enhancing the tempering temperature to 700 °C. Therefore, the evolution of carbides in FB2 steel during tempering at 500 °C–700 °C can be summarised as follows: Fe₃(C,B) → (Cr,Mo)₂(C,B) + Cr-rich M₇(C,B)₃ → Cr-rich M₂₃(C,B)₆. Besides, the Mo element in (V,Nb,Mo)(N,C) particles was gradually replaced by V and Nb with the increase of temperature from 600 °C to 700 °C. While Si and Co were rejected to the interfaces of carbides/matrix during tempering, forming a flux of Si and Co. Then, this flux may suppress carbides coarsening by retarding the diffusion of Cr, Mo and Mn from the matrix into carbides.

[en] In this paper, the lattice instability of γ-TiAl crystal under different loading modes was studied using a lattice dynamical finite-element method (LDFEM) and molecular dynamics (MD). The simulation results show that the lattice instability of γ-TiAl crystal is significantly influenced by loading modes and crystallographic orientations. In uniaxial loading, γ-TiAl crystal exhibits tension-compression asymmetry in critical stress. The stress–strain curves and the active slip systems obtained from LDFEM simulations are in agreement with those in MD simulations. In the nanoindentation of γ-TiAl crystal, surface orientation plays an important role in stress field, lattice instability and dislocation nucleation. The LDFEM accurately predicts the location of lattice instability and the active slip systems. The surface effect on lattice instability in nanoindentation was also proved by performing a cylindrical nanoindentation. (paper)