The effects of the solution heat treatment temperature on the precipitates, grain boundary evolution and response of the microhardness of Inconel 718 (IN718) superalloy fabricated by selective laser melting (SLM) were investigated. It was found that: (1) The long-chained Laves phases formed in the as-deposited condition dissolved into the matrix when the solution temperature rises above 980 °C. (2) The width-to-length ratio was maintained at approximately 1.6 when the solution was heated from 980 °C to 1080 °C, and dropped down to 1.03 when heated to 1130 °C. (3) Low-angle grain boundaries kept the same number fraction of 65% from 980 to 1080 °C as the as-deposited condition, and decreased dramatically from 1090 to 1130 °C to 4%. (4) Annealing twin boundaries occurred at 1090 °C with a number fraction of 3%, and quickly increased to 65% when heated to 1130 °C. It is concluded that the static recrystallization of IN718 fabricated by selective laser melting (SLM) occurred at 1090 °C and fast proceeded to full recrystallization at 1130 °C. The forming of annealing twins accompanies the recrystallization process and is an effective way to refine the recrystallized grain size.

The present study aims to investigate the orientation-dependent mechanical behaviors of ZnO single crystals under nanoindentation by molecular dynamics simulation. The load–indentation depth curves, atomic displacement, shear strain and dislocations for the c-plane, m-plane and a-plane ZnO single crystals were analyzed in detail. The simulation results showed that the elastic deformation stage of the loading curves for the three oriented ZnO single crystals can be described well by the Herz elastic contact model. The Young modulus values for the c-plane, m-plane and a-plane ZnO were calculated to be 122.5 GPa, 158.3 GPa and 170.5 GPa, respectively. The onset of plastic deformation occurred first in a-plane ZnO, then in m-plane ZnO, and lastly in c-planeZnO. The atomic displacement vectors in the three oriented ZnO single crystals were in good agreement with the primary activated slip systems predicted by the maximum Schmid factor. For the c-plane ZnO, the activated pyramidal {$11\overline{2}2$}<$11\overline{2}3$> slip system led to a complex dislocation pattern surrounding the indenter. A U-shaped prismatic half-loop was formed in the [$2\overline{11}0$] direction, confirming the activation of the prismatic {$10\overline{1}0$}<$11\overline{2}0$> slip system. For the m-plane ZnO, the activated prismatic {$10\overline{1}0$}<$11\overline{2}0$> slip system led to the preferential nucleation of dislocations along the $\left[\overline{11}20\right]$ and [$\overline{2}110$] directions. A prismatic loop was formed and emitted along the [$\overline{2}110$] direction, governed by a confined glide on {$10\overline{1}0$} planes. For the a-plane ZnO, the activated prismatic {$10\overline{1}0$}<$11\overline{2}0$> slip system led to dislocations concentrated in the [$\overline{1}\overline{1}20$] direction beneath the indentation pit, emitting a prismatic loop along this direction. Perfect dislocation (with a Burgers vector of 1/3 <$1\overline{2}10$>) is the dominant dislocation in the three oriented ZnO single crystals. The findings are expected to deepen insights into the anisotropic mechanical properties of ZnO single crystals, offering guidance for the development and applications of ZnO-based devices.

SiO₂ thin films are widely used in micro-electro-mechanical systems, integrated circuits and optical thin film devices. Tremendous efforts have been devoted to studying the preparation technology and optical properties of SiO₂ thin films, but little attention has been paid to their mechanical properties. Herein, the surface morphology of the 500-nm-thick, 1000-nm-thick and 2000-nm-thick SiO₂ thin films on the Si substrates was observed by atomic force microscopy. The hardnesses of the three SiO₂ thin films with different thicknesses were investigated by nanoindentation technique, and the dependence of the hardness of the SiO₂ thin film with its thickness was analyzed. The results showed that the average grain size of SiO₂ thin film increased with increasing film thickness. For the three SiO₂ thin films with different thicknesses, the same relative penetration depth range of ~0.4–0.5 existed, above which the intrinsic hardness without substrate influence can be determined. The average intrinsic hardness of the SiO₂ thin film decreased with the increasing film thickness and average grain size, which showed the similar trend with the Hall-Petch type relationship.

The microstructure and precipitates of INCONEL 718 alloy (IN718) fabricated by selective laser melting (SLM) are investigated. The matrix is comprised of the elongated γ grains along Z direction, tilting a few degrees. The microstructure mainly consists of a cellular–columnar structure with fine first dendrite arm space of 1–1.5 µm originated from the rapid solidification rate locally. The precipitates of the SLMed IN718 are confirmed to be a significant amount of Laves in the form of irregular bulk distribution, small amount of carbonitride and spherical Al₂O₃ particles in nanoscale. Some of the carbonitrides grow separately and some of the carbonitrides enwrap the Al₂O₃ fully or partly, forming the shell structure of the Al₂O₃–carbonitride. The reheating effect from the following layers to the previous layers have not reached the solid-state transformation temperature of the γ′ and γ″.

The present study aimed to experimentally evaluate the mechanical properties of Pb(In_1/2Nb_1/2)O₃–Pb(Mg_1/3Nb_2/3)O₃–PbTiO₃ (PIN–PMN–PT) bulk single crystals with different crystallographic directions using the nanoindentation technique. The load–indentation depth curves, elastic and plastic deformations, hardnesses, and Young’s moduli of [100]- and [110]-oriented 0.28PIN–0.43PMN–0.29PT bulk single crystals were investigated. Our results show that with an increase in the maximum indentation depth h_max, the plastic residual percentage increased for both the [100]- and the [110]-oriented single crystals. At each h_max, the plastic residual percentage of the [100]-oriented PIN–PMN–PT single crystals was less than that of the [110]-oriented PIN–PMN–PT single crystals. At h_max from 500 nm to 2000 nm, the plastic deformation was larger than the elastic deformation, and the plastic residual percentage was larger than 50% for both the [100]- and the [110]-oriented single crystals. This means that the plastic deformation dominated in the indentation process of PIN–PMN–PT single crystals. The indentation size effect on the hardness of the PIN–PMN–PT single crystals was apparent in the nanoindentation process. Both the hardness and the Young’s modulus of the [100]-PIN–PMN–PT single crystals were greater than those of the [110]-PIN–PMN–PT single crystals, which indicates that the PIN–PMN–PT single crystals had anisotropic mechanical characteristics.