Minimizing solidification shrinkage and tailoring the microstructure of precious metals

Feeding solidification shrinkage is one of the main challenges when casting a metallic component and this challenge becomes particularly acute when dimensions are reduced because temperature differences are more shallow across small castings, making conventional strategies, namely the implementation of risers coupled with thermal gradients across the mold, less potent [1]. This study will seek to address the issue by placing focus on the development of nearly zero solidification shrinkage alloys Such alloys are produced by adding elements into the alloys that, as opposed to the majority of existing systems, tend to form covalently bonded structures that expand upon solidification. These expanding elements, namely germanium and silicon, usually are prone to lower the mechanical properties, in particular by reducing the elongation to fracture. Goals of the present study are to examine in detail the microstructure of noble metals containing Si or Ge additions, measure by dilatometry their volumetric evolution between room temperature and temperatures at which they are fully molten, to explain their microstructural evolution, infer how it may be tailored and if relevant explore heat treatments that will increase the ductility and/or homogeneity of the metal. If time allows the project will also include tensile testing of alloyed metal samples thus produced.

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[1] L. Borasi, E. Casamenti, R. Charvet, C. Dénéréaz, S. Pollonghini, L. Deillon, T. Yang, F. Ebrahim, A. Mortensen, Y. Bellouard, 3D metal freeform micromanufacturing, Journal of Manufacturing Processes. 68 (2021) 867–876.