Cobalt-Chromium Solidification Modeling for Use in Additive Manufacturing

by Dorothy Waskow

Mentor: Douglas Matson; funding source: Nathan Gantcher Student Summer Scholars Fund

This research sought to determine properties of cobalt-chromium under rapid solidification. This research is relevant to the additive manufacturing industry. Cobalt-chromium is used in medical implants and dental implants because it is non-toxic and biocompatible. In order to make these implants, metal additive manufacturing is used. Selective laser melting and electron beam melting are two common forms of metal additive manufacturing. In both instances, metal powders are heated up rapidly and fused together then cooled rapidly. This rapid solidification can lead to unpredicted phases and microstructures, as there is not enough time for the metal to go through all of the phases as it would in a standard cooling. Rapid solidification can also lead to microcracks, micropores, and other defects in the material. In order to understand the material and ensure longevity of the product, the phases that form during rapid solidification need to be understood. This research looked at modeling those phases and predicting what would form. Thermocalc software was used to create phase diagrams for cobalt-chromium. These diagrams show what phase would form at a given temperature and mole percent composition, ranging from 100% cobalt to 100% chromium. This will help us to understand the metal better in order to make a uniform part where the whole piece has the same phase and microstructure. Future work will lead to adding a third material to this prediction. This software can be used to make ternary diagrams for cobalt-chromium-molybdenum and cobalt-chromium-tungsten. Additionally, there will be lab work done in the future to experimentally test the accuracy of these diagrams as well as determine the properties of cobalt-chromium, cobalt-chromium-molybdenum, and cobalt-chromium-tungsten. Understanding the properties will allow us to strategically vary the bead size in the powders of the additive manufacturing to make sure the properties of the final product are uniform and desired.