Influence of carbon diffusion from a steel capsule on the porosity formation in a MMC coating layer during hip cladding
Abstract
A multi-material inert anode for aluminium production has been manufactured via Hot Isostatic Pressing (HIP) Cladding by coating Metal-Matrix-Composite (MMC) powder on a nickel base alloy core through diffusion bonding in a steel capsule. Post heat treatment carried out after capsule removal in air shows foaming of the MMC coating. This porosity formation was found to be produced by CO2 release: C diffusion from the capsule to the MMC under high pressure during the HIP cycle could easily lead to CO2 formation. To prevent such foaming, a diffusion barrier was designed and inserted between the capsule and the MMC powder before HIP cladding. At the end of the process chain, the microstructure and the carbon content of the anode were characterized. The anode benefited from the designed diffusion barrier and a carbonless dense MMC coating layer that complies with the application requirements could be produced.
