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

Abstract

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 ε‐hexagonally close‐packed (HCP) martensites from γ‐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.

Surface Nanostructures Enhanced Biocompatibility and Osteoinductivity of Laser-Additively Manufactured CoCrMo Alloys

“…The CoCrMo alloy was first prepared by the L-DED process using Ambit Mini Mill system equipped with a Nd/YAG laser (1.06 μm wavelength), as previously reported. 19 Commercially available CoCrMo alloy powder was melted at the focal plane of the laser beam (550 W laser power, 1 mm in diameter) using argon as the carrier gas and deposited onto the substrate at a linear velocity of 15 mm/s. A laser scanning pattern was employed with a 0.6 mm overlap between consecutive laser tracks and a 90° rotation after each layer.…”

“…Among these methods, selective laser melting and laser-directed energy deposition (L-DED) have been reported to fabricate the CoCrMo alloy. In comparison with other approaches, L-DED offers several advantages, including enhanced long-term stability, reduced risk of coating delamination, improved corrosion resistance, and the ability to create implants with complex structures directly. – Our previous study revealed that the extremely high cooling rates during the L-DED process resulted in the formation of a fine subgrain morphology and nonuniform distribution of Co and Mo, which facilitated the generation of stable surface nanostructures with different aspect ratios (AR) through selective etching during the subsequent potentiodynamic polarization (PDP) process. Our preliminary study showed that these surface nanostructures promoted adhesion and proliferation of preosteoblast MC3T3 cells …”