[en] Highlights: • Low cycle fatigue properties of CLAM steel were investigated at 450 °C and 550 °C. • CLAM steel showed the continuous softening up to fail failure under cyclic loading. The degree of softening increased with increasing temperature. • Dislocation density decrease and subgrain coarsening during the test process were the possible reasons for the cyclic softening of the CLAM steel. - Abstract: The low cycle fatigue behavior of China Low Activation Martensitic (CLAM) steel has been studied using a constant strain rate of 8 × 10"−"3/s with the strain amplitudes ranging from 0.3% to 0.8% at 450 °C and 550 °C. Cyclic stress response showed a gradual softening until complete failure. The fatigue life decreased with increasing test temperature, and the effect of temperature on fatigue life was more pronounced at lower strain amplitudes. The cyclic deformation behavior at different temperatures has been analyzed according to the hysteresis loop, and the mechanism of cyclic softening was interpreted in view of the changes taking place in dislocation density and lath structures. Evaluation of low cycle fatigue properties of CLAM steel at 450 °C and 550 °C can help in design of the Chinese Test Blanket Module (TBM) for the International Thermonuclear Experimental Reactor (ITER) and a future fusion power plant.

[en] In this paper the microstructure and mechanical properties of electron beam weld (EBW) joints for China low activation martensitic (CLAM) steel, which underwent a series of different post weld heat treatments (PWHTs) were studied. The aim of the study was to identify suitable PWHTs that give a good balance between strength and toughness of the EBW joints. The microstructural analyses were performed by means of optical microscope (OM) and scanning electron microscope (SEM). The mechanical properties were determined via tensile tests and Charpy impact tests. The results showed that the tensile strength of the as-weld joint (i.e. without any PWHT) were close to that of the base metal, but the impact toughness was only 13% of that of the base metal due to the existence of a delta-ferrite microstructure. To achieve a significant improvement in toughness a PWHT needs to be performed. If a one-step PWHT is applied tempering at 760 °C for 2 h gives EBW joints with high strength at a still acceptable toughness level. If a two-step PWHT is applied, a process involving quenching at 980 °C for 0.5 h followed by tempering at 740 °C or 760 °C for 2 h gives EBW joints with high strength and toughness properties. Whenever possible a two-step PWHT should be applied in favor of a one-step process, because of higher resulting strength and toughness properties

[en] Highlights: • High cycle fatigue properties of CLAM steel were investigated at 723 K and 823 K. • The condition fatigue limit at N = 10"7 were 275 MPa and 235 MPa at 723 K and 823 K. • Fatigue strength decreased when stress and temperature increased at 723 K and 823 K. • Dislocation density decrease and subgrain coarsening during the test process were the possible reasons for fatigue limit decrease. - Abstract: This paper highlights the results of a study on the high cycle fatigue strength and fracture mechanism of China Low Activation Martensitic (CLAM) steel. The high cycle fatigue test results showed that the fatigue strength of CLAM steel decreased with the temperature, and the condition fatigue strengths (N = 10"7) were 275 MPa and 235 MPa at 723 K and 823 K, respectively. The fractograph results indicated that the fractures were mainly initiated from the surface of the specimen.

[en] Highlights: • The welded joints of CLAM steel with different weld spacings have been fabricated with electron beam welding, and a simplified model of CLAM sheet was proposed. • The microstructure and mechanical properties such as microhardness, impact and tensile were investigated at different welding spacing for both conditions of as-welded and post weld heat treatment (PWHT). • The effect of the welding thermal cycle was significantly when the weld spacings were smaller than 4 mm. • When the weld spacing was small enough, the original microstructures would be fragmented with the high heat input. - Abstract: China low activation martensitic (CLAM) steel has been chosen as the primary structural material in the designs of dual function lithium-lead (DFLL) blanket for fusion reactors, China helium cooled ceramic breeder (HCCB) test blanket module (TBM) for ITER and China fusion engineering test reactor (CFETR) blanket. The cooling components of the blankets are designed with high density cooling channels (HDCCs) to remove the high nuclear thermal effectively. Hence, the welding spacing among the channels are small. In this paper, the welded joints of CLAM steel with different weld spacings have been fabricated with electron beam welding (EBW). The weld spacing was designed to be 2 mm, 3 mm, 4 mm, 6 mm and 8 mm. The microstructure and mechanical properties such as microhardness, impact and tensile were investigated at different welding spacing for both conditions of as-welded and post weld heat treatment (PWHT). The PWHT is tempering at 740 °C for 120 min. The results showed that the grain size in the heat affected zone (HAZ) increased with the increasing weld spacing, and the joint with small weld spacing had a better performance after PWHT. This work would give useful guidance to improve the preparation of the cooling components of blanket.

[en] A hot-dip aluminizing process is expected to produce aluminide coatings on structural materials to resist tritium permeation, corrosion, and magnetohydrodynamic (MHD) effects in the fusion reactor blanket. China Low Activation Martensitic (CLAM) steel, which is the candidate structural material for the LiPb blanket system in China, was coated with pure aluminum and with an Al–Si alloy. Factors affecting the thickness and morphology of the aluminide coatings were studied. After the hot-dipping treatment, FeAl₃ and Fe₂Al₅ were observed at the Al/steel interface. The existence of silicon in the molten aluminum suppressed the growth of Fe₂Al₅, built up the thickness of FeAl₃ slightly, and contributed to reducing the thickness of the intermetallic layer. The brittle phase of Fe₂Al₅ had completely transformed to ductile phases of FeAl₂, FeAl and α-Fe(Al) after high temperature heat-treatment in air. Kirkendall voids were found in the diffusion layer, due to the rapid interdiffusion of iron and aluminum during oxidation. Cracks and pores were observed on the coating surface and at the interlayer. Grazing incidence X-ray diffraction indicates the presence of α-Al₂O₃ in the oxide layer

[en] We report the effect of Ni-doping on the structural, dielectric and optical properties of Ba(Cd_1/3Ta_2/3)O₃ (BCT) ceramics. Rietveld analysis of the X-ray diffraction (XRD) data indicates that the BCT structure is similar to other Ba(B'_1/3B''_2/3)O₃ perovskites, although the Ta-O-Cd is distorted to an angle of ∼173deg; very close to our earlier theoretical prediction of 172deg. The XRD analysis also indicates that Ni doping significantly enhances the extend of Cd-Ta ordering in BCT. The temperature coefficient of resonant frequency decreases with Ni concentration up to 2 wt%. While the loss tangent of BCT is reduced at small levels of Ni doping (up to 0.5 wt%), it increases abruptly at higher concentrations. We found a correlation between the loss tangent of Ni-doped BCT samples and the intensity of a continuous absorption background in the optical spectra. This optical activity results from the presence of optically active point defects and is suggestive that these defects play an important role in the microwave loss in BCT ceramics. (author)

[en] The reactive adsorption of NO₂ over activated carbon (AC) was investigated at 50 C. Both the NO₂ adsorption and its reduction to NO were observed during the exposure of AC to NO₂. Temperature programmed desorption (TPD) was then performed to evaluate the nature and thermal stability of the adsorbed species. Adsorption and desorption processes have been proposed based on the nitrogen and oxygen balance data. The micropores in AC act as a nano-reactor for the formation of -C(ONO₂) complexes, which is composed by NO₂ adsorption on existing -C(O) complexes and the disproportionation of adsorbed NO₂. The generated -C(ONO₂) complexes are decomposed to NO and NO₂ in the desorption step. The remaining oxygen complexes can be desorbed as CO and CO₂ to recover the adsorptive and reductive capacity of AC. (author)

[en] Characteristics of matrix/matrix interface, i.e. grain boundary, and precipitate/matrix interface on China Low Activation Martensitic (CLAM) steel were analyzed by Atom Probe Tomography (APT), electron backscatter diffraction (EBSD) and transmission electron microscope (TEM), as well as the solute segregation behaviors on those interfaces. It is found that the Cr, Mn, C, Si and P were enriched on the matrix/matrix interface, while the segregation of Fe, W and V were not obvious. The compositions of nano-size carbide were mainly C, Ta and V, and VC particle formed associated with the TaC and they are inter-soluble to form the (V, Ta)C, which exhibited a ball coronary morphology with maximum diameter about 40 nm. The results showed that the Cr, W, P and Si were more easily to segregate at the V-rich side, which might weaken the adhesive strength of interface and consequently result in intergranular fracture. (paper)

[en] The neutron irradiation experiments for China Low Activation Martensitic (CLAM) steels were carried out in High Flux Engineering Test Reactor (HFETR), the effects of neutron irradiation on the hardening and embrittlement behavior of CLAM steels were investigated before and after neutron irradiation to 2.98 dpa at 430 ℃. The results showed that ultimate strength and yield stress of CLAM steel tested at room temperature are 710 MPa and 615 MPa, which decreased about 16 MPa and -0.5 MPa as compared with the unirradiated samples, respectively. And its Ductile to Brittle Transition Temperature (DBTT) shift was no obvious shift. While the upper shelf energy after irradiation was 217 J, which almost the same with that of unirradiated samples. The irradiation resistant of CLAM steel are slightly better than that of other Reduced Activation Ferritic/Martensitic (RAFM) steels under similar irradiation conditions. (authors)

[en] The China Low Activation Martensitic (CLAM) steel is one of 9Cr martensitic steels, and it has been selected as the primary candidate structural material for future fusion reactors in China. It is essential to understand the thermal stability of CLAM steel to ensure the operation safety during exposures at operating temperatures. In this paper, the thermal aging behavior of CLAM steel at 550 °C for 20000 h was studied. Microstructure evolution and mechanical property change were investigated. The results showed that Laves phase was mainly precipitated along the martensitic lath boundaries and grain boundaries in CLAM samples after aging for more than 4000 h, and its size increased faster than that of M₂₃C₆. The size of TaC had no obvious changed but its number increased after aging. The microstructure evolution resulted to degradation of the mechanical property, especially the ductile-to-brittle transition temperature (DBTT), which was increased from − 92 to − 43 °C after aging for 20000 h. The possible mechanism of DBTT increasing had been analyzed based on the interaction between precipitations and grain boundaries.