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• A new Co-based coating with excellent thermal-fatigue resistance was prepared. • The martensitic transformation only occurred in single cladding during TF process. • Boundaries of grain and γ/ε phase acted as the weak region for the crack initiation. The Co-based coating by laser deposition could improve the thermal-fatigue (TF) resistance of hot working dies but the effect of technology on properties remained to be studied further. This work investigated the influence of the microstructure and γ/ε transformation on the TF life of the Co-based coating of the AISI H13 hot work die steel. Direct laser deposition (DLD) layers were prepared on the steel surface using modified Co-based alloys, which increased the contents of Cr, W, and Ni. The single and duplex layers were made under precise conditions, and the difference in the TF test life was significant. Meanwhile, the hardness of the duplex layer coating was much higher than that of the single one in the TF process consistently. Various detection methods were adopted to characterize the Co-based coating structures and crack propagation during the TF test. The microstructure of the two deposition coatings uniformly included the γ-Co phase and M 23 C 6 crystalline phase. Moreover, after the TF experiment, the γ/ε transformation only occurred in the single layer as observed by transmission electron microscopy and electron backscattered diffraction. This indicated that the dilution of the base metal element distribution played a key role in reducing the stability of the γ-Co phase, which resulted in relatively low stacking fault (SF) energies, micro-hardness, a high fraction of the precipitate, and an early crack generation of the coating. This research was beneficial for understanding the microstructure, grain growth, γ/ε transformation, and crack propagation behavior in the DLD layers and TF test. [ABSTRACT FROM AUTHOR]

Schematic illustration of the structural evolution of Pt/LaCo x Ni 1−x O 3 /SiO 2 from LaCo x Ni 0.87−x Pt 0.13 O 3 /SiO 2. • A facile method for constructing stable and highly dispersed bi-active catalytic sites were proposed. • Pt clusters and oxygen vacancies could be constructed. • Pt/LaCo x Ni 1−x O 3 loaded on SiO 2 was obtained by using a perovskite-type oxide as the precursor. • The catalyst showed excellent activity and stability for CO oxidation. A new scheme for constructing bi-active sites of highly dispersed Pt and oxygen vacancies on a catalyst was put forward in this study. Pt/LaCo x Ni 1−x O 3 /SiO 2 was synthesized by reducing LaCo x Ni 0.87−x Pt 0.13 O 3 with the structure of perovskite loaded on silica. The catalytic performance for carbon monoxide oxidation over the catalysts were studied. The catalysts were characterized via using XRD, XPS, XAFS, N 2 adsorption–desorption, H 2 -TPR, TEM, O 2 and CO-TPD techniques. The results pointed out that nanocrystal lines of LaCo x Ni 0.87−x Pt 0.13 O 3 were supported on SiO 2. Pt clusters could be formed through reduction process at 300 °C and highly dispersed on catalyst's surface, and the catalyst transformed to Pt/LaCo x Ni 1−x O 3 /SiO 2 ; at the same time, oxygen vacancies also formed on the surface of LaCo x Ni 1−x O 3. The catalytic test revealed that LaCo 0.44 Ni 0.43 Pt 0.13 O 3 /SiO 2 displayed high activity and good stability for the oxidation of CO. The highly dispersed closely contact bi-active sites, the confinement of oxygen vacancies and strong interaction between Pt clusters and support were responsible for the significant catalytic activity and stability of LaCo 0.44 Ni 0.43 Pt 0.13 O 3 /SiO 2 catalyst. [ABSTRACT FROM AUTHOR]

• Enhanced hardness and deformation resistance are observed in surface modified layer. • Wear resistance is drastically improved by gas nitriding and laser surface hardening. • The gas nitriding processed P20 steel has superior corrosion resistance. Gas nitriding and laser surface engineering are popular technologies to improve the surface performance of steels. This study evaluates the effect of duplex treatment of gas nitriding and laser surface engineering on surface hardness, wear and corrosion resistance of P20 plastic mold steel. It is found that gas nitriding at 550 °C for 20 h with nitrogen potential of 0.18 generates a nitrided layer without nitrides, which drastically improves the wear resistance. Simultaneously, the corrosion resistance is also marginal improved by the gas nitriding. Laser surface hardening further elevates the surface hardness and wear resistance of the nitrided layer due to the formation of martensite. Besides, a small amount of austenite retains in surface layer after laser surface hardening, which may lead to the galvanic attack at the phase interface between martensite and retained austenite and deteriorate the surface corrosion resistance. Laser surface melting results in the denitrification of nitrided layer and the formation of holes at the bottom of melted layer, thus reducing the surface hardness and wear resistance. Meanwhile, the denitrified surface layer also exhibits a degraded corrosion resistance owe to the decreasing nitrogen content and the formation of mixed structure of martensite and retained austenite. [ABSTRACT FROM AUTHOR]