Solidify Your Knowledge with this Metals Solidification Quiz!

Understanding Solidification in Metals

• All metals start as a liquid and are heated until molten and poured into a mold to form a casting, which can be further processed to create different shapes and structural sections.
• Casting and fusion welding involve rapid solidification, which affects the microstructure and performance of the final structure.
• The phase diagram and underlying equilibrium conditions provide a good canvas to start developing an understanding of solidification.
• The binary isomorphous Ni-Cu system, with an overall composition of 35 wt % Ni, can be used to understand solidification.
• As temperature decreases, solidification events take place, and the final solid contains the same amount of nickel as the overall composition to minimize the Gibbs energy of the system.
• Small, discrete nucleation of solid occurs, and each of these sites grow in size as temperature decreases to form 'grains.'
• Equilibrium conditions do not reflect what happens in industry, where raw, unmachined casting is produced in minutes, and fusion welding thermal transients are measured in seconds or milliseconds.
• Solidification starts with a nucleation event, and homogeneous nucleation occurs rarely in nature, requiring a pure liquid cooled significantly below its equilibrium freezing temperature.
• All metals, even pure ones, are polycrystals, making it difficult to refine a metal to 100% purity and ensuring consistent temperature everywhere.
• Heterogeneous solidification occurs when preferential sites or interfaces exist, triggering solidification preferentially at those locations.
• The process of solidification needs to be understood at the atomic scale to understand how casting and fusion welding affect the microstructure.
• Small changes in temperature and cooling rate can have significant impacts on the microstructure, making it essential to carefully control these parameters in industrial processes.