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The Hastelloy X superalloy is a widely used solid-solution Ni-based sheet alloy for gas turbines, aero-engine combustion chambers, and other hot-end components. To investigate the effect of microstructure, especially grain size, on its weldability, Hastelloy X alloy bars are homogenized, cold-rolled to thin sheets, and recrystallized under different conditions to obtain equiaxed grain microstructures with average grain sizes of ~5 μm, ~12 μm, and ~90 μm. The laser welding process is used for joining the alloy sheets, and then the alloy's weldability is investigated through microstructural and mechanical property characterizations. The microstructures in weld consist of coarse columnar grains with dendrite, and grain sizes of these columnar grains are almost the same when grain size of Hastelloy X base metal increases from ~5 μm to ~90 μm. Moreover, although all welds exhibit lower yield strengths (YS), ultimate tensile strengths (UTS), and elongations to fracture (EF) than the base metal, the degrees of reduction in them become slight when the grain size of base metal increases from ~5 μm to ~90 μm. [ABSTRACT FROM AUTHOR]

High temperature materials usually serve under extreme conditions. In order to ensure the safety and reliability of industrial application, it is very significant to clarify the microstructural evolution and mechanical properties at high temperature. The in situ experiment combining mechanical tensile testing and heating in the scanning electron microscope (SEM) is a feasible method to study the relationship between the microstructure, mechanical properties, and temperature. However, it was challenging to acquire images of high quality when the temperature exceeded 800 °C due to the effect of thermal electrons and the instability of loading conditions at high temperature. In this study, a mini-tensile apparatus was devised and installed in an ordinary SEM, which can achieve a stable loading of 0–2200 N and obtain high quality images in the temperature range of 1150 °C. A highly efficient heat source with multi-layer thermal insulation was designed to prevent the other parts of the apparatus from being affected by high temperature. A symmetrical tensile structure was developed to ensure that the region of interest was always within the field of view of the microscope during testing. Thermal electrons were suppressed to ensure that the sample can be clearly distinguished at 1150 °C. In order to ensure the testing reliability, standard carbon steel was used to calibrate the instrument. Finally, a Ni-based single crystal superalloy, as an example, was tested using this in situ tensile testing system at 1150 °C to verify the main functions and reliability of the apparatus. [ABSTRACT FROM AUTHOR]

Abstract: Mesporous hollow semiconducting materials have received much attention in recent years owing to their unique chemico-physical properties for applications in many fields. Herein, we firstly report a green, rapid, one-step route towards the facile fabrication of mesporous Ag2O nanotube via plasma etching of corresponding silver nanowire templates. Characterization by X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and high resolution transmission electron microscopy (HRTEM) techniques indicates that phase pure cubic Ag2O nanotube with mesporous structure were formed. Time-independent experiments demonstrate Kirkendall effect involved in forming hollow structure at nanoscale in solid–gas reaction. This green and simple strategy is expected to be extended for the rapid fabrication of similar hollow metal–oxide nanostructure and device. [Copyright &y& Elsevier]

Nickel-based GH3536 alloy exhibits high strength but low ductility when produced by selective laser melting (SLM), which hinders its widespread application in aerospace. This paper employed a 'two-step' method of heat treatment to optimize the microstructure of the SLM GH3536 alloy and investigated the mechanical properties. Tensile tests were conducted on SLM GH3536 alloy before and after heat treatment at 750 °C, using an in-situ high-temperature tensile stage. The relationship between the microstructural evolution and deformation behavior of the alloys was investigated by combining the in-situ tensile experiments and crystal plasticity finite element method (CPFEM). The results suggested that the elongation can be increased by 80% without a significant reduction in tensile strength. The improved elongation is attributed to the complete recrystallization, formation of annealed twins and serrated grain boundaries after heat treatment. The study also investigated the deformation behavior and fracture mode of the alloy before and after heat treatment. Discussion was done on the influence of the microstructure, particularly the twin and serrated grain boundaries on the alloy's plastic deformation. This study enhanced the understanding of plastic deformation of SLM GH3536 alloy and provided a valuable reference for the design and post-treatment of superalloy. • A two-step heat treatment method is proposed to prepare GH3536 alloy with high ductility and acceptable strength. • High-temperature microplastic deformation and damage of GH3536 alloy were observed in-situ SEM technique and its influencing factors were analyzed. • The effects of twins and serrated grain boundaries on the properties were simulated using the CPFEM model. [ABSTRACT FROM AUTHOR]

Abstract Laser direct melting deposited (LDMD) Ti-6Al-4V alloys are mainly used in aerospace fields. It is very important to study their deformation behavior as a function of the application conditions (i.e. temperature and stress). This work compared the dynamic microstructure evolution and mechanical properties of LDMD Ti-6Al-4V alloys at 23 ℃ and 650 ℃. A method based on in-situ scanning electron microscopy (SEM) tensile testing was used to identify the initiation of cracks and propagation mode of slip bands. The deformation mechanisms at low and elevated temperatures were discussed. The results showed that the strength decreased and the elongation increased with increasing temperature. These results were verified by the propagation modes of slip bands and opening of the active deformation systems. [ABSTRACT FROM AUTHOR]

Microstructure significantly affects materials' physical properties. Predicting and characterizing temporal microstructural evolution is valuable and helpful for understanding the processing-structure-property relationship but is rarely conducted on experimental data for its scarcity, unevenness, and uncontrollability. As such, a self-designed in-situ tensile system in conjunction with a scanning electron microscope was adopted to observe the grain evolution during the tensile process. We then used a deep learning-based model to capture grain growth behavior from the experimental data and characterize grain boundary and orientation evolution. We validated the framework's effectiveness by comparing the predictions and ground truths from quantitative and qualitative perspectives, using data from (1) a tensile experimental dataset and (2) a phase-field simulation dataset. Based on the two datasets, the model's predicted results showed good agreement with ground truths in the short term, and local differences emerged in the long term. This pipeline opened an opportunity for the characterization of microstructure evolution and could be easily extended to other scenarios, such as dendrite growth and martensite transformation. [Display omitted] • It's the first study using a deep learning method to predict and characterize temporal grain evolution on experimental data. • We accurately predict future grain evolution without any subjective assumptions and hand-crafted features. • We can provide valuable reference and guidance for future experiments based on the model's performance. • This pipeline opens a new way of shortening experimental time and characterizing temporal microstructure evolution. [ABSTRACT FROM AUTHOR]

Advanced single-crystal superalloys, developed to improve the high temperature capability of gas turbines, often underperform in low-temperature conditions. This limitation compromises the overall reliability of turbine blades under complex service environments. This study introduces a novel strategy to enhance the overall performance of a fourth-generation single-crystal superalloy. Rapid liquid-nitrogen quenching following the aging treatment promotes extensive nucleation of ultrafine γ′ particles (γ′ γ) with an average size of ∼10 nm, precipitated under extremely low supersaturation, as evidenced by high-resolution transmission electron microscopy (HRTEM) and atom probe tomography investigations. The combination of differential scanning calorimetry analysis, density functional theory calculations, and kinetic models verifies the high stability of γ′ γ particles at low-temperature conditions around 900 °C. HRTEM observations reveal Orowan bypassing and dislocation cutting of γ′ γ particles, leading to additional precipitation hardening by limiting dislocation motion in the γ phase and shear of primary precipitates. Consequently, a bimodal precipitation microstructure comprising γ′ γ particles and primary γ′ phase significantly reduces the strain rate of low-temperature creep and nearly doubles the creep rupture life at 800 °C/735 MPa. Simultaneously, high-temperature properties at 900 °C/392 MPa and 1100 °C/137 MPa remain comparable to those of the original microstructure as the primary γ/γ′ microstructure is minimally affected by rapid cooling. This advancement improves overall performance and redefines the importance of small precipitates, broadening microstructure design concepts for future superalloy development. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract During the growth process of a plasma electrolytic oxide (PEO) coating on an AZ-31 Mg alloy, electric breakdown inevitably occurs and causes local disintegration of the coating, thus forming breakdown pores that result in an increased coating porosity and suppressed corrosion resistance. Here, we report for the first time that the self-repairing capability of the PEO process can restore the coating after breakdown damage by decreasing the porosity, tuning the components and improving the corrosion resistance via the deposition of electrolyte anions into the breakdown pores. Based on detailed scanning electron microscopy and transmission electron microscopy characterizations of the PEO coatings processed in alkaline silicate electrolytes, it was found that the pores were repaired by silica fillings formed by the plasma-induced deposition of anions (SiO 3 2−) in the electrolyte. The plasma-deposited silica possesses short Si O bond lengths that are manifested by an Si-L 2,3 edge shift by ∼1.3 eV to higher energies. In addition, the presence of some amount of Mg together with a minor admixture of K indicates the contribution of ionic migration and plasma collisions to the self-repairing process in the PEO coating. Graphical abstract Image 1 Highlights • Self-repairing capability of PEO process could recover the coating from breakdown damage. • Breakdown pores are repaired by silica fillings. • Self-repairing process contributes to decreasing porosity and improving corrosion resistance of PEO coating. [ABSTRACT FROM AUTHOR]

This study compares the microstructure and tensile properties of Ti6Al4V components fabricated by laser direct metal deposition (LDMD) additive manufacturing (AM) in the transverse and longitudinal directions. The results show anisotropic tensile properties with the transverse direction having high tensile and fracture strengths and the longitudinal direction having a high elongation and reduction of cross section. The anisotropic mechanical properties are attributed to the anisotropic microstructural distribution. The transverse tensile specimen is composed of short columnar prior-β grains which grow perpendicular to the tensile direction, and have a lamellar structure. Along the β grain boundary, α GB and large α colonies were identified. However, the longitudinal specimen shows that the long β structure is parallel to the tensile axis and that the microstructure is composed of basket-woven α phases with shorter α plates and smaller colony sizes compared with those in the transverse specimen. The fracture mechanism induced by the anisotropic microstructure along the transverse and longitudinal directions was compared by examining the fracture process in real-time using uniaxial in-situ scanning electron microscopy (SEM) tensile testing. The results show that shear fracture, which is caused by the vertical β grain boundaries and large α colonies with long α plates, occurs in the transverse specimen. The shear mode is the main reason behind the enhanced tensile strength and fracture strength due to the high resistance to microcrack propagation. However, in the longitudinal specimens, symmetric necking behavior due to the fine α grains resulted in uniform deformation of the grains on both sides of the grain boundaries, inducing greater elongation. [ABSTRACT FROM AUTHOR]