We report the influence of growth rate and external magnetic field on the eutectic lamellar spacing and properties of directionally-solidified Ag-Cu eutectic alloys. The results indicated that the relationship between the lamellar spacing of directionally-solidified Ag-Cu alloys and the growth rate matched the prediction of the Jackson-Hunt model, and the constant was 5.8 µm³/s. The increasing external magnetic field during solidification tilted the growth direction of the lamellar eutectics, and coarsened the eutectic lamellar spacing. These decreased the microhardness and strength of Ag-Cu alloys, but increased their electrical conductivity. The competitive strengthening contributions between the refinement of the eutectic lamellar spacing and the change in growth direction of the eutectics resulted in higher strength in the as-rolled sample with a 0.8 T magnetic field than with other samples, which was confirmed from higher relieved deformation energy using differential scanning calorimetry.

51CrV4 steel is extensively used in large-size damping springs for trains and vehicles. Quenching conditions play an important role in performance enhancement. The present work investigated the effects of various oil-bath temperatures and out-of-oil temperatures on the microstructure and the mechanical properties of this steel. The morphological examination focused on both the quenched martensite and the tempered troostite. Tensile and hardness tests were carried out to evaluate the mechanical properties. The results showed that a coarsening of the martensite occurred at a high oil-bath temperature. In addition, the size and fraction of bainite islands also increased with the increase of oil-bath temperature. In contrast, the carbide size and the intercarbide spacing both increased with the increase of oil-bath temperature. Thus, the tensile strength and the hardness both decreased with increasing oil-bath temperature in accordance with the Hall-Petch relationship. Correspondingly, the ductility increased as the oil-bath temperature increased. At a relatively high out-of-oil temperature, the martensite underwent an auto-tempering process, which led to the precipitation of many tiny carbide particles in the as-quenched martensite laths. This auto-tempering effect enhanced the width of large-sized carbides and reduced their length in the final microstructure. The intercarbide spacings increased with increasing out-of-oil temperature. As the oil-bath temperature increased, the tensile strength and hardness decreased, and the ductility increased. The fracture morphology was examined to explain the results of mechanical properties.

Fe-Cr-Co alloys precipitate nanosized α₁ particles through spinodal decomposition, and their magnetic performance is susceptible to influence by the shape and arrangement of α₁ particles. We studied spinodal decomposition during the heat treatment of Fe-Cr-Co alloys by both experimental and numerical simulation. Fe-Cr-Co alloys were fabricated first by directional solidification, followed by thermomagnetic treatment in a high magnetic field (HMF) and step aging. The experimental results show a spinodally decomposed structure consisting of nanosized α₁ particles. The applied HMF caused the α₁ phase to change into a rod-like shape. Moreover, a feather-like structure was observed near the grain boundary (GB), with slim α₁ rods regularly arranged along the direction perpendicular to the GB. With the shape change and alignment of the α₁ phase in the HMF, Fe-Cr-Co alloys show magnetic coercivity that is superior to those of samples without an HMF. To reveal the influence of HMF on phase transformations and the effect of GB, we conducted phase-field simulations of spinodal decomposition in the Fe-Cr-Co alloy. A migrating GB contributes to the elongation and arrangement of the α₁ phase in the regions where the GB has passed. Thus, the α₁ phase is arranged as parallel rods that are perpendicular to the GB. This GB effect consists of the effect of enhanced atomic mobility and the elastic energy. The α₁ rods are elongated along the direction of HMF. The simulation results indicate that the feather-like structure is caused by a combined effect of both the GB and HMF. It is shown that the model generates microstructures which are qualitatively similar to those observed experimentally.