Bainite transformation in steels is influenced by various factors. In the present work, bainite transformation in medium carbon high alloyed steel was investigated focusing on the influence of preexisting VC carbides on the morphology and transformation kinetics of the subsequently formed bainite. Hot-work die steels were held at 950 °C for various times to precipitate VC carbides, then rapidly cooled from 950 to 350 °C and held at this temperature for the bainite transformation. It is found that the bainite transformation was obviously accelerated by the preexisting VC carbides precipitated at the austenite region. The precipitation of carbides leads to a decrease in carbon concentration in the matrix, which decreases the effective activation energy and increases the highest temperature for the nucleation of bainite. Besides, bainite was observed to grow beside the VC carbides. It suggests that the VC carbides in the matrix act as nucleation sites for the bainite transformation. In the specimens, the bainite transformation is accelerated, and a higher fraction of bainite is formed when there are carbides in the matrix.

Porous carbon nanomaterials with significant capacitive performance were successfully prepared through a simple two-step process of thermal-polymerization and carbonization without an additional template. As a result, the as-prepared porous carbon nanomaterials of sample-A and sample-B exhibited an amorphous phase with low graphitization. And sample-A showed a moderate specific surface area of 476.39 m2/g, larger than that of sample-B (280.94 m2/g). The relatively high mass specific capacitance of 205.1 F/g at a scan rate of 5 mV/s and 211 F/g at a current density of 4 A/g was obtained by sample-A, which are higher than those of sample-B (82.6 F/g at 5 mV/s and 78.6 F/g at 4 A/g). Sample-A also showed excellent conductivity and superior cyclic stability with 94.19% capacitance retention after 5000 cycles, which are also higher than those of sample-B. This work proposed a cost-effective, green, and promising strategy for the large-scale preparation of porous carbon nanomaterial electrodes.

We address the competitive precipitation and coprecipitation of three types of secondary phases, i.e., Cu-rich precipitates (CRPs), reverted austenite (RA), and alloyed carbide, in a high-strength low-alloy steel with austenite reversion treatment at 675 °C by using electron back-scatter diffraction, transmission electron microscopy, and atom probe tomography. There is a strong competitive diffusion of Ni and Cu participating in austenite reversion and Cu precipitation with the fact that no CRPs are detected in and around the RA. Meanwhile, there is also a strong competitive diffusion of austenite stabilizing element Ni and carbide-forming elements Cr and Mo into the pre-existing C-rich zone, leading to the formation of nonequilibrium alloyed carbide deviating from the stoichiometric composition. On the other hand, the alloyed carbide and CRPs provide constituent elements for each other and make the coprecipitation thermodynamically favorable. The knowledge on the interactive formation of these three features provides versatile access to tailor the distributional morphology of CRPs, RA, and alloyed carbide via a multistage heat treatment and thus realize their beneficial effect on strength and toughness.

Atomic layer deposition (ALD) ZnO film as seed layer for growing aligned ZnO nanorods arrays is demonstrated. The effects of the deposition temperature and film thickness to the morphology of the ZnO nanorods are studied. The ALD is found to have its advantage over the conventional dip-coating method when being applied to three-dimensional (3D) substrates, as exemplified by the macroporous Si adn CNT arrays. As one example, the CNT-ZnO 3D hybrid nanostructures are obtained which might be useful for energy-related applications.