Shuai Lyu,Li Wang,Jianghao Zhang,Chen Liu,Junming Sun,Bo Peng,Yong Wang,Kenneth G. Rappé,Yuhua Zhang,Jinlin Li,Lei Nie
In order to understand the role of Co catalysts with different phases on Fischer–Tropsch synthesis, single-phase face-centered-cubic (fcc) and hexagonal-close-packed (hcp) Co were synthesized via a two-step approach, involving the formation of single-phase CoO materials followed by reduction in H2. The physicochemical properties of Co catalysts were thoroughly characterized by XRD, SEM, TEM, TPR, and H2 chemisorption. It was found that hcp-Co exhibits higher activity on hydrocarbon formation than fcc-Co in Fischer–Tropsch synthesis. For both catalysts, CO dissociation was suggested as the rate-determining step, on which hcp-Co presents ca. 40 kJ mol–1 lower activation energy than fcc-Co, in agreement with a reported computational study. As a result, hcp-Co is concluded to be the preferable phase for rational catalyst design.
Refractory high-entropy alloys (RHEAs) are celebrated for their exceptional yield strength and high-temperature stability, yet their wear performance remains insufficient. The wear behavior of these materials is largely governed by their deformation mechanisms and microstructural evolution during sliding. In this study, we synthesized an ultrafine-grained TiZrNbMoTa RHEA featuring a dual-phase microstructure comprising body-centered cubic (BCC) and hexagonal close-packed (HCP) phases. This unique microstructure enhances wear resistance via the in-situ formation of gradient nanostructured layers at room temperature (RT) and fish-scale-like amorphous-crystalline nanocomposite oxide layers at 600 °C during dry sliding. The RHEA exhibits wear rates of 1.15 × 10 −4 mm 3 /(N m) at RT and 9.85 × 10 −6 mm 3 /(N m) at 600 °C. At RT, a ∼3 µm thick subsurface deformation layer developed, with the upper 1.2 µm displaying distinct nanolayered structures, while the underlying grains bent and elongated along the sliding direction. At 600 °C, a protective fish-scale-like amorphous-crystalline nanocomposite oxide layer formed on the worn surface, thereby preventing direct contact between the alloy and the counterbody. This study presents a novel approach to enhancing wear resistance in BCC-HCP dual-phase TiZrNbMoTa RHEA, highlighting the critical role of nanostructured surface layers in enhancing performance under sliding conditions.
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