Pulsed wire discharge was used to prepare nanoparticles of molybdenum and its carbides from Mo wires in a gas mixture of argon and kerosene at pressures of 100, 50, and 25 kPa. The different pressures affected the carburization process and particle formation. The most effective pressure was 25 kPa, where the volume fraction of MoC was identified by Rietveld refinement of X‐ray diffraction data to be 98.4%. The particle size distribution was also obtained from transmission electron microscopy measurements, and the smallest geometric mean diameter was determined tobe 24.3 nm for the sample prepared at 25 kPa.

An aluminization process with controlled Al activity to form surface Ni(Al) zone was applied to fabricate ceramic nanorod array structures by using internal oxidation. The pack cementation with NaCl, Ni3Al and Al2O3 was adapted as the aluminization process to form surface Ni(Al) zone. With increasing Ni3Al concentration in pack powder mixture, Al content of surface Ni(Al) zone was increased. Nanorod array structures can be successfully obtained on Ni components with designed shape.

Yb2Si2O7/Yb2SiO5 composites dispersed with silicon carbide (SiC) possess a self‐crack‐healing ability that makes them promising top‐coat materials for multilayered environmental barrier coatings (EBCs) of SiC/SiC gas turbine blades. Stress‐induced surface cracks can be fully healed at high temperatures by the volume expansion of SiO2 glass and the newly formed Yb2Si2O7 in the composite. The reaction between SiO2 and Yb2SiO5 to form Yb2Si2O7 is considered a critical step that determines the high healing efficiency of this composite, therefore, Yb2SiO5 is considered as the secondary healing agent apart from the primary one, SiC. However, once all the healing agents have reacted, the composite can no longer promote its crack‐healing ability. To retain this property, in this work, Yb2SiO5 is regenerated by a heat treatment in water‐vapor atmosphere at 1073 K. X‐ray diffraction (XRD) and energy‐dispersive X‐ray spectroscopy (EDS) analyses show that the healing agent can be partially recycled after the treatment. In addition, the composite treated in water vapor demonstrates a greater crack‐healing ability compared with the untreated composite. These results open a new path for the development of gas turbine blades and high‐temperature components possessing permanent crack‐healing ability.

No abstract

Pure Ni was aluminized with an Ni3Al, NaCl and Al2O3pack powder mixture at 1100°C for 12 h. The Ni(Al) solid solution formed in aluminized Ni was internally oxidized at 1000°C for 2 to 12 h with a Co/CoO buffer. The internal oxidation zone consisted of 2 regions: granular precipitate zone near the surface and rod-like zone near the oxidation front. The growth of internal oxidation zone deviated from the parabolic law due to the non-constant Al profile developed by the aluminizing process. The granular zone grows linearly from the surface of the alloy.