The ability to print polymeric materials at a high volume rate (~1000 in3/hr) has been demonstrated by Oak Ridge National Lab's (ORNL) Manufacturing Demonstration Facility (MDF) and shows promise for new opportunities in Additive Manufacturing (AM), particularly in the rapid fabrication of tooling equipment for prototyping. However, in order to be effective, the polymeric materials require a metallic coating akin to tool steels to survive the mechanical and thermal environments for their intended application. Thus, the goal of this project was to demonstrate a pathway for metallizing Big Area Additive Manufactured (BAAM) polymers using a Twin Wire Arc (TWA) spray coating process. Key problems addressed in this study were the adhesion of sprayed layers to the BAA1V1 polymer substrates and demonstration of hardness and compression testing of the metallized layers.
Aerosol Deposition (AD) is a unique thick film deposition technology that is capable of depositing ceramic, metallic, or composite films through the acceleration, impact and consolidation of dry, fine sized (~0.1-1μm) particle feedstock delivered by a carrier gas towards a substrate [akedo]. Additionally, the use of fine particle feedstock is necessary in order for typically brittle materials (i.e., ceramics) to exhibit sufficient plasticity and non-brittle fracturing that is the key mechanism to coating consolidation [Sarobol], resulting in a dense, nano-crystalline grain size deposition.
Thermal spray deposited WC-CoCr coatings are extensively used for surface protection of wear prone components in a variety of applications. Although the primary purpose of the coating is wear and corrosion protection, many of the coated components are structural systems (aero landing gear, hydraulic cylinders, drive shafts etc.) and as such experience cyclic loading during service and are potentially prone to fatigue failure. It is of interest to ensure that the coating and the application process does not deleteriously affect the fatigue strength of the parent structural metal. It has long been appreciated that the relative fatigue life of a thermal sprayed component can be affected by the residual stresses arising from coating deposition. The magnitude of these stresses can be managed by torch processing parameters and can also be influenced by deposition effects, particularly the deposition temperature. In this study, the effect of both torch operating parameters (particle states) and deposition conditions (notably substrate temperature) were investigated through rotating bending fatigue studies. The results indicate a strong influence of process parameters on relative fatigue life, including credit or debit to the substrate's fatigue life measured via rotating bend beam studies. Damage progression within the substrate was further explored by stripping the coating off part way through fatigue testing, revealing a delay in the onset of substrate damage with more fatigue resistant coatings but no benefit with coatings with inadequate properties. Finally, the results indicate that compressive residual stress and adequate load bearing capability of the coating (both controlled by torch and deposition parameters) delay onset of substrate damage, enabling fatigue credit of the coated component.