Thermokinetically Driven Microstructural Evolution in Laser‐Based Directed Energy‐Deposited CoCrMo Biomedical Alloy

The present work investigated additive manufacturing of CoCrMo alloy via laser-based directed energy deposition process. A range of five different laser powers are used for the fabrication of fully dense and metallurgically sound CoCrMo samples. The solidification parameters including temperature gradient, growth rate, and the cooling rate are computationally predicted in each case, using a multitrack multilayer model. The variation in these computationally predicted solidification parameters with the different laser powers used in fabrication is linked to the evolution of microstructural features within the laser additively deposited CoCrMo samples. Evolution of epsilon-hexagonally close-packed (HCP) martensites from gamma-face-centered cubic (FCC) phase, along with variation in thickness of these martensitic laths with respect to the varying solidification parameters associated with the laser additive deposition, is identified and investigated. The multitrack, multilayer thermokinetic model not only provides the spatial and temporal signatures of laser-based directed energy deposited process, but uniquely considers the influence of pre- and postheating on microstructural evolution with their correlation with experimental observations.