This paper reviews the recent advances in the experimental and theoretical analysis of the high-temperature spreading of molten metals and oxides. Results obtained in the analysis of simple non-reactive systems are compared with current theories developed for room-temperature liquids. These results outline the critical role in spreading at high-temperature of the local dissipation at the triple solid–liquid–vapor junction. However, in most high-temperature systems, the substrate cannot be described as an ideal solid – rigid and insoluble – and the movement of the triple junctions is accompanied by other phenomena such as ridging, interdiffusion, and chemical reactions (reactive spreading). The effect of these phenomena is outlined and a framework for the theoretical analysis of reactive spreading emerges. This framework is based on the division of the reactive spreading process into its constituent steps, and the identification of the step that drives spreading and controls its kinetics. A key aspect of the analysis is the description of the structure of the triple junction and the identification of the relative kinetics of the movement of the liquid and the other phenomena that accompany spreading.

Kinetics of high-temperature spreading

For studying the evolution of the η phase in cemented carbides with the CoNiFeCr high entropy alloy binder, we prepared low-carbon, medium-carbon, and high-carbon cemented carbides with a 0.2 wt% difference in the C content using SHIP. The results showed that the η phase morphology was sensitive to the carbon content. When the carbon content was 4.5%, the η phase was abundant and uniformly dispersed. When the carbon content increased to 4.7%, the η phase amount decreased and became locally aggregated in large clusters, showing typical segregation. When the carbon content was further increased to 4.9%, the η phase disappeared. The η phase clusters exhibited a sharp contrast between inner and outer parts. The inner part showed the presence of the η phase, WC with small and round grains, and a small amount of binder. The outer part had only WC with large grain and sharp grains, and a large amount of binder. In addition to the inherent η phase brittleness, the η phase segregation resulted in a large hardness dispersion and a further toughness decrease. 

Effect of the carbon content on the morphology evolution of the η phase in cemented carbides with the CoNiFeCr high entropy alloy binder

For studying the evolution of the η phase in cemented carbides with the CoNiFeCr high entropy alloy binder, we prepared low-carbon, medium-carbon, and high-carbon cemented carbides with a 0.2 wt% difference in the C content using SHIP. The results showed that the η phase morphology was sensitive to the carbon content. When the carbon content was 4.5%, the η phase was abundant and uniformly dispersed. When the carbon content increased to 4.7%, the η phase amount decreased and became locally aggregated in large clusters, showing typical segregation. When the carbon content was further increased to 4.9%, the η phase disappeared. The η phase clusters exhibited a sharp contrast between inner and outer parts. The inner part showed the presence of the η phase, WC with small and round grains, and a small amount of binder. The outer part had only WC with large grain and sharp grains, and a large amount of binder. In addition to the inherent η phase brittleness, the η phase segregation resulted in a large hardness dispersion and a further toughness decrease.

Wenyan Luo

Papers

Wetting behaviors and interfacial characteristics of molten AlxCoCrCuFeNi high-entropy alloys on a WC substrate