In this work, the tensile behavior and microhardness of 316L stainless steel fabricated by selective laser melting under different process parameters were investigated. The ultimate tensile strength ...decreased slightly with increasing energy input, while the opposite tendency was observed for the elongation to failure. Microstructure characterizations were performed to relate the pore morphology, melting pool geometry, solidification cell structure, and grain sizes to the mechanical performance of as-built samples. Fine grains with high fraction of low-angle grain boundaries and fine cellular structures with nano-inclusions are observed in the sample fabricated with a high scanning speed (1000 mm/s). As a result, the sample shows high ultimate tensile strength of up to 707 MPa, while maintaining a total elongation of 30%. The sample fabricated with a low scanning speed (800 mm/s) shows high ductility with total elongation to failure of 55%. The improved ductility is mainly attributed to the elimination of residual pores and melting pool boundaries, which result in brittle features in the as-built samples. The results indicate that selective laser melting may act as a physical metallurgy method to modify the microstructure, and thus improve the mechanical performance of metallic materials.
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•The scanning speed altered melting pool boundaries, residual pores, solidification cells, nano-inclusions and grain sizes.•High ultimate tensile strength was attributed to fine cellular structures and fine grains with low-angle grain boundaries.•Low scanning speed resulted in an enhanced ductility due to the minimization of residual defects and melting pool boundaries.
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•Representative studies were given with emphasis on methods for preparation of metal organic framework nanosheets.•Crucial technologies for characterization of metal organic framework ...nanosheets were evaluated.•Series of promising applications by metal organic framework nanosheets were surveyed and discussed.
With infinite assembly and ultrathin nature, metal-organic frameworks nanosheets (MOFNs), as an emerging family of two-dimensional (2D) materials, have attracted extensive interest in fields of material science, chemistry and nanotechnology. Here, we aim to review the recent advances of MOFNs. The assortments of their synthetic methods of top-down, bottom-up and combined strategies are discussed at first, including the comparison of their advantages and limitations. Then, some crucial techniques towards the morphology and microstructure characterization of MOFNs were introduced. We have also discussed the wide ranges of potential applications, especially molecular separation, catalyst, energy conversion, conduction, photofunction, electrochromism and sensing. Finally, the challenges and outlooks for these multi-functional 2D materials were prospected based on current achievements, as well as their unique architectural features.
The main aim of this study was to apply high-energy longer mechanical milling and spark plasma sintering (SPS) techniques to produce in-situ α-Ti/TiO2/TiC hybrid composites from commercially pure-Ti ...(CP–Ti, HCP structure) powders. The CP-Ti powders were subjected to different milling times (0, 20, 40, 60, 80, 100, and 120 h). The results showed that the powder samples milled for 120 h produced Ti, Ti3O5, TiO, TiO2 phases, and dissolved C atoms from the process control agent (toluene) which were then converted to α-Ti, TiO2, and TiC phases (formed in-situ composites) through spark plasma sintering. This was expected due to more reactivity in the 120 h sample as longer milling introduces severe and robust structural refinements. Structural evaluations with increasing milling time were carried out using XRD, HRSEM, and HRTEM. The synthesized powders were then consolidated by SPS at pressures of 50 MPa and 1323 K for 6 min. The micro-hardness results have shown that the hardness was started to increase from 1.40 GPa to 5.56 GPa with increasing milling time due to more dislocation and pinning effect produced by grain refinement and formed TiO2/TiC intermetallic particles enhancing the strength of α-Ti matrix. The α-Ti/TiO2/TiC in-situ hybrid composite bulk sample yielded an ultimate compressive strength of 1.594 GPa.
•The effects of process parameters and interactions on the laser repair performance of esophageal tissue were studied by designing laser power, scanning speed, defocusing amount and scanning path ...through orthogonal experiment.•The degree of thermal damage was assessed by calculating the esophageal microtissue characteristic parameters and the degree of collagen thermal deformation.•Laser power and interaction factor laser power and scanning path were the most important factors affecting the burst compression strength.•At laser power of 6 W, scanning speed of 150 mm/s, defocusing amount of 0 mm, and scanning path 3, the bursting pressure strength of esophageal tissue was highest at 93.3 mmHg, and the thermal damage of the tissue was minimum.
To study the influence of laser parameters on the mechanical properties and thermal damage of esophageal tissue, the experiment of laser repair of esophageal tissue incision is made. The effects of parameters including the laser power, scanning speed, defocusing amount, scanning path on the bursting pressure strength of esophageal tissue are analyzed. The influence of different energy densities on the appearance of esophageal tissue morphology, microstructure, and the degree of thermal denaturation of collagen is analyzed. The results showed that the laser power and the interaction factor of laser power × scanning path is the most important factor affecting the bursting pressure strength of esophageal tissues. The optimal parameters are laser power 6 W, scanning speed 150 mm/s, defocusing amount 0 mm, and scanning path 3, the highest bursting pressure strength of 93.3 mmHg is achieved. Meanwhile the esophageal tissues do not show obvious scarring, and the degree of thermal denaturation of tissue collagen is the smallest, which is only 1.6 × 10-5, the texture of the tissue microscopic images is uniformly changed, and the texture clarity is high.
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•Novel Ti-4Fe-3W/2TiC composite utilizing spark plasma sintering and hot extrusion.•Extruded composite at α+β exhibited yield strength of 1215 MPa at room temperature.•Extruded ...composite at β showed a consistent strength at high temperatures.•TiC dispersion was identical, while α morphology of the alloy matrixes was different.
Considering the high strength of titanium matrix composites (TMCs) at room and elevated temperatures, the aim of this study was to develop novel TMC Ti-4Fe-3W/2TiC (wt%) utilizing powder metallurgy and subsequent extrusion at different temperatures: the two-phase (α+β) and pure β phase regions. The TiC particle dispersion was almost identical in both composites with variation in the size distribution. However, there was a significant difference in the morphology of the α phase in the matrix. The α+β-extruded composite exhibited globular αp (grain size: 0.7 μm); in contrast, the β-extruded phase showed acicular αs (grain size: 1.5 μm). Additionally, α-Ti was the predominant phase in contact with TiC particles due to the semi-coherent relationship between these two phases. A remarkably high yield strength (1215 MPa) was achieved at room temperature in the α+β -extruded composite, while the β-extruded composite exhibited consistently improved strength at high temperatures. Morphological characterization using atomic force microscopy (AFM) revealed the β phase was slightly harder than the α phase, probably due to the solid solution of Fe and W that predominant in the β phase.
Chemically architectured high entropy alloys are an original concept of microstructure which is based on a metastable 3D network of composition fluctuations, named interphase. In the present work the ...evolution of CoCrFeMnNi-Ni architectured alloys at high temperatures was studied through long duration annealing at 500 and 800°C followed by microstructure characterization using scanning electron microscopy coupled with energy dispersive X-ray spectroscopy mapping and X-ray diffraction (XRD). Concentration evolution induced by the annealing was also modelled by diffusion simulations using DICTRA software. It results that the microstructure of CoCrFeMnNi-Ni chemically architectured alloys is stable at intermediate temperatures with no or slight microstructure evolution (below 500 or around 650°C depending on the initial thickness of the interphase). At higher temperature, architectured alloys tend to homogenize. Finally, a specific Rietveld XRD analysis was proposed for a quantification of phase fraction in high entropy alloys, applicable for architectured or not alloys.
•Chemically architectured alloys were annealed at 500 and 800°C for long duration.•Their microstructure is stable at intermediate temperatures.•They tend to chemically homogenize at higher temperature•The proposed Rietveld XRD analysis quantifies phase fraction in high entropy alloys
This work presents oxidation behaviours of Al-bearing Cr-based alloys GA1 (51Cr-22Al-13Mo-9Ta-5Si in at%) and GA2 (40Cr-33Al-13Mo-9Ta-5Si in at%) at 1100–1400 ˚C for up to 24 h. The formation of ...oxides on the surfaces was influenced by constituent phases; BCC phase was rich in Al and formed only α-Al2O3, complex oxides (Cr2O3, AlTaO4, CrTaO4, and Ta2O5) occurred on top of C14 Laves phase. Sufficient Al content is crucial to the formation of protective α-Al2O3, as GA2 was able to resist severe oxidation at 1400 ˚C with an oxidation weight gain of only 3.3 mg/cm2 after 24 h.
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•Al-bearing Cr-based alloys in this work contained BCC matrix and C14 phases.•The BCC phase was rich in Al and formed only α-Al2O3.•Complex oxides formed on top of C14 Laves phase and at phase boundaries.•Increasing Al content can enhance oxidation resistance from 1100 to 1400 °C.
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•Wire and arc additive manufacturing of HSLA steel was performed.•Microstructure and mechanical properties were related to the thermal cycles.•No preferential texture was developed, ...leading to near-isotropic mechanical properties.•As-built parts exhibited excellent ductility and high mechanical strength.
Wire and arc additive manufacturing (WAAM) is a viable technique for the manufacture of large and complex dedicated parts used in structural applications. High-strength low-alloy (HSLA) steels are well-known for their applications in the tool and die industries and as power-plant components. The microstructure and mechanical properties of the as-built parts are investigated, and are correlated with the thermal cycles involved in the process. The heat input is found to affect the cooling rates, interlayer temperatures, and residence times in the 800–500 °C interval when measured using an infrared camera. The microstructural characterization performed by scanning electron microscopy reveals that the microstructural constituents of the sample remain unchanged. i.e., the same microstructural constituents—ferrite, bainite, martensite, and retained austenite are present for all heat inputs. Electron backscattered diffraction analysis shows that no preferential texture has been developed in the samples. Because of the homogeneity in the microstructural features of the as-built parts, the mechanical properties of the as-built parts are found to be nearly isotropic. Mechanical testing of samples shows excellent ductility and high mechanical strength. This is the first study elucidating on the effect of thermal cycles on the microstructure and mechanical properties during WAAM of HSLA steel.
To optimize nuclear waste repository performance, the destruction of minor actinide elements, particularly Np and Am, in a neutron fast spectrum reactor is possible by incorporating these elements ...into nuclear fuel. Evaluating the performance of minor actinide containing fuel is of paramount importance to enabling this technology. However, such a task is challenging without an available domestic fast spectrum test reactor. A comparison of fuel performance tested in an available domestic thermal reactor at the Idaho National Laboratory, the Advanced Test Reactor, and in a fast spectrum reactor in France (Phénix) is presented here in this study. This study evaluates the capability of using a cadmium shrouded test position to mimic the power profile along the fuel radius present in fast spectrum reactors so that thermally driven phenomenon (e.g., constituent redistribution) can be evaluated in a thermal reactor and determined to be prototypical of a fast reactor. Thus, optical microscopy and scanning electron microscopy has been performed on irradiated 35U-29Pu-4Am-2Np-30Zr fuel samples (where the number preceding the element is the weight percent concentration) from the two mentioned reactors that present similar irradiation temperatures and power conditions. The results indicate that fuel performance phenomena are reproducible in the two irradiation conditions. The redistribution of Zr occurred in the same manner for the two samples. Similar partitioning of U-Pu-Zr phases was observed, and the behavior of Am was similar in the analyzed specimens. Finally, the overall microstructure evolution seems not to be affected by minor actinides addition compared to expected behavior of conventional U-19Pu-10Zr ternary metal fuels for both specimens. Slight differences in fuel cladding chemical interaction were, however, observed. This difference is likely driven by difference in cladding composition rather than irradiation conditions.
Following many years of evolutionary development, first at the National Synchrotron Light Source, Brookhaven National Laboratory, and then at the Advanced Photon Source (APS), Argonne National ...Laboratory, the APS ultra‐small‐angle X‐ray scattering (USAXS) facility has been transformed by several new developments. These comprise a conversion to higher‐order crystal optics and higher X‐ray energies as the standard operating mode, rapid fly scan measurements also as a standard operational mode, automated contiguous pinhole small‐angle X‐ray scattering (SAXS) measurements at intermediate scattering vectors, and associated rapid wide‐angle X‐ray scattering (WAXS) measurements for X‐ray diffraction without disturbing the sample geometry. With each mode using the USAXS incident beam optics upstream of the sample, USAXS/SAXS/WAXS measurements can now be made within 5 min, allowing in situ and operando measurement capabilities with great flexibility under a wide range of sample conditions. These developments are described, together with examples of their application to investigate materials phenomena of technological importance. Developments of two novel USAXS applications, USAXS‐based X‐ray photon correlation spectroscopy and USAXS imaging, are also briefly reviewed.
The ultra‐small‐angle X‐ray scattering (USAXS) facility at the Advanced Photon Source has been significantly upgraded to provide rapid USAXS scanning at high X‐ray energies together with associated pinhole small‐angle X‐ray scattering (SAXS) and wide‐angle X‐ray scattering (WAXS) measurements. Complete USAXS/SAXS/WAXS data can be obtained within 5 min, allowing flexible in situ and operando measurement capabilities under a wide range of conditions.
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