Journal of Micromechanics and Molecular Physics

Lead-free (K${}_{0.5}$N${}_{0.5})$NbO₃ piezoelectric ceramics have drawn wide attention due to its environment-friendly and excellent piezoelectric performance. Since the difficulty of post-processing of ceramics limit its further development and practical application, three-dimensional (3D) printing technology has been developed in this work. A homogeneous piezoelectric ceramic suspension with 40 vol% modified (K${}_{0.5}$N${}_{0.5})$NbO₃ nanoparticles can be 3D printed well based on a stereolithography process. In addition, by the post heat treatment under different sintering temperature, a density value of 4.31g$\cdot$cm${}^{-3}$ with the relative density of about 96% was obtained in the sample sintered at 1120${}^{\circ }$C, which results in the larger dielectric constant and lower dielectric loss in this sample. These printed ceramics exhibit two successive phase transitions and reduce with increase of sintering temperature at measured temperature range.

Bovine serum albumin (BSA) is a familiar protein and often used as a model drug to test the adsorption efficiency of material, while the cytotoxicity of hybrid is overlooked. In this study, we synthesized hierarchical mesoporous flower-like Mg–Al layered double hydroxide (LDH) microspheres through anion surfactant mediated hydrothermal method. The scanning electron microscopic images demonstrated that 10S-LDH and 100S-LDH samples possessed a porous surface and the porosity structure were affected by the concentration of anionic surfactant, i.e., sodium dodecyl sulfonate (SDS). By being immersed in the BSA/phosphate buffer solution (PBS) solution, the 100S-LDH had a loading capacity about 44.6 mg/g. Compared to 1S-LDH and 10S-LDH, the SDS intercalated in 100S-LDH could form the hydrogen bond with BSA molecules and promote the adsorption efficiency. In the cytotoxicity test towards Raw264.7 cells, the hybrid of BSA and $x$S-LDH showed a superior biocompatibility to the raw LDH materials. The SDS intercalated Mg–Al LDH is expected to be used in the bioactive molecules delivery.

Laser powder bed fusion (L-PBF) is promising for producing metallic glasses (MGs) for its extremely high cooling rate and ability to manufacture complex geometrical components. However, the crystallization of MGs under different L-PBF parameters is not fully investigated, which has influences on the mechanical properties. In this study, we develop a multi-physics thermal-fluid flow model for the L-PBF process of MGs, run simulation cases for single tracks, and then analyze the molten pool morphology and crystallization behavior in the center and edge of the track, as well as the heat affected zone. The simulation results are validated against the experimental results in the literature and have provided deeper insight into the crystallization phenomenon observed in the experiments.

In comparison with the state-of-the-art Ni-based superalloys, refractory multiprincipal element alloys (MPEAs) exhibit considerably higher strengths at temperatures above 1600${}^{\circ }$C, which can be a significant potential required in the high demand for aerospace applications. However, the atomic-scale work-hardening behavior of such important materials during low-cycle loading remain unknown. Here, using molecular dynamics simulations, we study the low-cycle fatigue of nanocrystalline refractory multiprincipal element alloy with different grain sizes, to reveal the cyclic deformation, work hardening and damage mechanism. As a result, an extensive grain growth is observed during the cyclic deformation, thus driving the dynamic Hall–Petch strengthening mechanism. For the model with large grain size, the glide of partial dislocations with screw structure can be responsible for the deformation behavior under cyclic loading, and at small grain size the grain growth-coordinated deformation twinning can control the plastic process. The deformation twin boundaries generated during the cyclic loading show high stability, while the remaining high-angle grain boundaries are highly unstable. The initial softening followed by hardening depends upon the dislocation density and grain size. In particular, atomic-scale element segregation occurs after cyclic loading. This study gives a cyclic deformation micromechanism, and thus accelerates the design and development of superior fatigue-resistant refractory multiprincipal element alloy over a wide temperature range.

Yield strength (YS) is a key factor during design and application of Ni-based superalloys with complex compositions, hence it is of great significance to evaluate the YS prior to manufacturing. In this work, alloy diffusion-multiple technology was employed as a high-throughput way to yield the hardness dataset. Based on the composition and other descriptors, Pearson correlation coefficients, stability selection and feature importance were used to select the efficient feature variables. Thereafter, six different machine learning models were applied to predict the YS. Finally, the individual and interaction effect of Co and Mo could be effectively detected by the Gaussian process regression (GPR) model. The optimum composition of Ni-based superalloys with the largest YS at room temperature was determined using the trained GPR model and genetic algorithm. This method can be extended to predict the YS in other multicomponent alloys, such as Ti alloys, Co-based alloys, and high entropy alloys.

To facilitate the repairing and connecting processes for the non-main bearing TC4 alloy, a high-temperature (up to 1000${}^{\circ }$C) resistant adhesive that is converted to the composite of intermetallics and ceramics is prepared. The composition evolution of the adhesive, the structure changes in the bonding layer, the reaction process at interfaces and the fracture mode of joints are comprehensively studied to explore its bonding mechanism. The results show that chemical bonding mechanism based on the formation of Ti₅Si₃ plays a critical role at 600${}^{\circ }$C, and acts as the crucial one at elevated temperatures. As the reaction interlayer (2–5$\mu$m) is far thinner than the entire bonding layer (60–70$\mu$m), mechanical properties of the adhesive dominate the bonding performance, which is tied up with the composition and structure evolution. The differ of coefficient of thermal expansion (CTE) between the adhesive and the substrate remains lower than $3\times 10^{-6}$K${}^{-1}$ in range of 500–1000${}^{\circ }$C. Specifically, the formation of composites from intermetallics and ceramics improves the mechanical properties and heat-resistant of the adhesive. The bonding strength reaches $\sim$40MPa after pre-treatment at 1000${}^{\circ }$C without pressure, and remains over 30MPa within the normal operating temperature range of 500–700${}^{\circ }$C.