Laser powder bed fusion (LPBF) is widely used for manufacturing nickel-based superalloy components with complex geometries; however, the process produces non-equilibrium microstructures characterized by directional grain growth, cellular substructures, and compositional segregation, which can lead to anisotropic mechanical behavior. In this study, the influence of multiple post-processing heat-treatment routes on the microstructural evolution and mechanical properties of LPBF-fabricated Inconel 625 (IN625) was systematically investigated by combining stress relief, hot isostatic pressing (HIP), and solution annealing. Microstructural characterization was performed using optical microscopy and scanning electron microscopy, while tensile properties were evaluated from room temperature to 700 °C. The HT3 condition resulted in a fully recrystallized, equiaxed grain structure with reduced segregation and minimal Nb-rich Laves phase, leading to nearly isotropic mechanical properties, with an ultimate tensile strength of approximately 880 MPa and an elongation exceeding 50%. Elevated-temperature testing demonstrated stable mechanical performance, with a localized strengthening effect near 600 °C attributed to dynamic strain aging. These results demonstrate that appropriate post-processing can effectively homogenize LPBF IN625 and improve its mechanical reliability.
We report the results of MeWO4 ceramics synthesis by the direct exposure of metal (Mg, Ca, Zn, W) oxides mixture to a high-power flux of high-energy electrons. The oxide powder particle sizes are 1–10 microns. The synthesis occurs with high efficiency in less than 1 s without the use of any additional substances and energy sources. The purpose of this work is to establish the main processes that ensure the effective synthesis of MgWO4, CaWO4, and ZnWO4 ceramics from ZnO, CaO, MgO, and WO4 oxides, which differ significantly in their physical and chemical properties. It has been found that the dependence of synthesis efficiency on the electron beam power density and the power density threshold at which synthesis begins varies significantly for simple metal oxides and is very close for the tungstates of these metals. The most probable explanation for the observed effect is redistribution of absorbed radiation energy. WO3 powder particles have a high absorptance of the incident electron radiation. The result is a cascade multiplication of primary electrons into secondary electrons with much lower energy. Secondary electrons are efficiently absorbed by MgO, CaO, and ZnO particles, leading to their efficient decomposition and the formation of a new phase.
Pyrophyllite is a 2:1 layered silicate with interest in ceramics, refractories, and several other important applications. In this work, an investigation into the thermal behaviour of several natural and purified pyrophyllite samples, including a pyrophyllite clay, has been conducted. A previous characterization of these samples has been carried out by AA, XRD, thermal analysis by thermo-dilatometry and DTA-TG, surface area, and SEM-EDX. Thus, relevant chemical, mineralogical, thermal, and textural data of these samples have been obtained. As a second step of this investigation, the thermal behaviour of these pyrophyllite samples has been investigated by XRD and SEM after several thermal treatments at 800, 1100 and 1150 °C during 24 h. The formation of dehydroxylated pyrophyllite as a crystalline phase in the samples was established after 1050 °C by XRD, and its permanency above this temperature, with little changes in morphological features, as revealed by SEM. When thermal treatment was progressive at higher temperatures (1300 °C) the following was evidenced by XRD: (a) the formation and crystallization of mullite (3Al2O3·2SiO2), with a progressive destruction of dehydroxylated pyrophyllite, and (b) the formation of cristobalite (SiO2). This later phase was formed by crystallization of the amorphous silica, detected as a hump by XRD, which is segregated in the solid-state reaction of formation of mullite. This treatment produces a new microstructure with elongated and needle-like crystals of mullite according to SEM observations. All these results have been found of interest for the preparation of ceramic materials, mullite-based ceramics, and refractories using these pyrophyllite samples.
