Additively manufactured characteristics of carbon fibers deposited from alkane precursors

Abstract

Laser Chemical Vapor Deposition (LCVD) is an additive processing technique in which freestanding fibers are deposited. This is accomplished by the thermal dissociation of a precursor gas under a translating laser focal point. In this study the relationships between deposited carbon fiber growth regimes based on precursor chemistry, microstructure, mechanical properties, and processing conditions are compared. The precursor gases include gases from the alkane family, i.e., methane (CH4), ethane (C2H6), and propane (C3H8) and the alkene family, i.e., ethylene (C2H4). Each of these gases offer differences in molecular geometry, the amount of carbon and hydrogen present per molecule, and molecular weight. In the hyperbaric growth condition, these variances reveal different abilities to access either the surface-reaction kinetic limited or mass transport limited growth regimes. The deposited fibers morphology revealed either a core shell or nodular structure with each of these morphologies a function of the accessible growth regime. The fracture stress for the different fibers, in each of the accessible growth regimes, are compared revealing a strength dependence that is linked to the extent of graphitization (via Raman spectroscopy characterization). Collectively, these outcomes fundamentally address how precursor chemistry is a critical variable in the manipulation of the processing-structure-property space in LCVD carbon fibers.