The Effect of Ethanol on Abnormal Grain Growth in Copper Foils

Single-crystal Cu not only has high electrical and thermal conductivity, but can also be used as a promising platform for the epitaxial growth of two-dimensional materials. Preparing large-area single-crystal Cu foils from polycrystalline foils has emerged as the most promising technique in terms of its simplicity and effectiveness. However, the studies on transforming polycrystalline foil into large-area single-crystal foil mainly focus on the influence of annealing temperature and strain energy on the recrystallization process of copper foil, while studies on the effect of annealing atmosphere on abnormal grain growth behavior are relatively rare. It is necessary to carry out more studies on the effect of annealing atmosphere on grain growth behavior to understand the recrystallization mechanism of metal. Here, we found that introduction of ethanol in pure argon annealing atmosphere will cause the abnormal grain growth of copper foil. Moreover, the number of abnormally grown grains can be controlled by the concentration of ethanol in the annealing atmosphere. Using this technology, the number of abnormally grown grains on the copper foil can be controlled to single one. This abnormally grown grain will grow rapidly to decimeter-size by consuming the surrounding small grains. This work provides a new perspective for the understanding of the recrystallization of metals, and a new method for the preparation of large-area single-crystal copper foils.

Precipitation Criterion for Inhibiting Austenite Grain Coarsening during Carburization of Al-Containing 20Cr Gear Steels

AlN precipitates are frequently adopted to pin the austenite grain boundaries for the high-temperature carburization of special gear steels. For these steels, the grain coarsening criterion in the carburizing process is required when encountering the composition optimization for the crack-sensitive steels. In this work, the quantitative influence of the Al and N content on the grain size after carburization is studied through pseudocarburizing experiments based on 20Cr steel. According to the grain structure feature and the kinetic theory, the abnormal grain growth is demonstrated as the mode of austenite grain coarsening in carburization. The AlN precipitate, which provides the dominant pinning force, is ripened in this process and the particle size can be estimated by the Lifshitz−Slyosov−Wagner theory. Both the mass fraction and the pinning strength of AlN precipitate show significant influence on the grain growth behavior with the critical values indicating the grain coarsening. These criteria correspond to the conditions of abnormal grain growth when bearing the Zener pinning, which has been analyzed by the multiple phase-field simulation. Accordingly, the models to predict the austenite grain coarsening in carburization were constructed. The prediction is validated by the additional experiments, resulting in accuracies of 92% and 75% for the two models, respectively. Finally, one of the models is applied to optimize the Al and N contents of commercial steel.

Microstructure and Magnetic Properties of La-Ca-Co Substituted M-Type Sr-Hexaferrites with Controlled Si Diffusion

La-Ca-Co substituted M-type Sr-hexaferrites (Sr0.3Ca0.4La0.3Fe9.8Co0.2O19-δ) were prepared by a solid-state reaction using two different procedures, where the SiO2 additive was mixed either before calcination (pre-Si) or after calcination (post-Si). At the same sintering temperature, smaller cell volumes and reduced saturation magnetization (Ms) values were obtained for samples processed with the pre-Si method than those with the post-Si method. This implied that the pre-Si method resulted in a greater degree of Si substitution into the M-type lattice and increased Fe extrusion out of the lattice. The grain growth behavior was controlled by the SiO2 amount and sintering temperature. It was found that abnormal grains occur with a bimodal distribution in the 0.5 wt% SiO2 samples sintered at 1240 °C, due to the increased critical driving force for growth caused by an increased amount of SiO2 addition. The Ms and coercivity values were altered with the control of Si diffusion and abnormal grain growth. The control of the additive diffusion behavior is one of the important keys in the material design under same materials compositions.

Grain Growth Kinetics of 0.65Ca0.61La0.26TiO3-0.35Sm(Mg0.5Ti0.5)O3 Dielectric Ceramic

The 0.65Ca0.61La0.26TiO3-0.35Sm(Mg0.5Ti0.5)O3[0.65CLT-0.35SMT] ceramic was prepared by the solid-state reaction method. The effects of sintering process on its microstructure and grain growth behavior were investigated. The Hillert model and a simplified Sellars model were established by linear regression, and the Sellars-Anelli model with a time index was established by using a nonlinear regression method. The results show that the grain size gradually increases with the increase of sintering temperature and holding time. Meanwhile, the sintering temperature has a more significant effect on the grain growth. The grain sizes of 0.65CLT-0.35SMT ceramic were predicted by the three models and compared with the experimentally measured grain size. The results indicate that for the 0.65CLT-0.35SMT ceramic, the Hillert model has the lowest prediction accuracy and the Sellars-Anelli model, the highest prediction accuracy. In this work, the Sellars-Anelli model can effectively predict the grain growth process of 0.65CLT-0.35SMT ceramic.