Additive manufacturing has become increasingly popular due to its reduced geometric constraints compared to traditional manufacturing processes. To date, the main factors limiting additive manufacturing usage in structural applications are cost per part, time to manufacture, and inferior mechanial properties compared to in-service solutions. Currently additive manufacturing in metals is costly, time consuming, and often results in highly inhomogenous microstructures with complex material responses. These constraints often limit metal additive manufacturing usage to one-off prototypes or unique/custom applications such as those found in the biomedical field. Polymer-based additive manufacturing systems are relativly inexpensive, but resultant mechanical properties often limit usage in strucutral applications.
Enhancing the mechanical functionality of plastic additively-manufactured parts can be achieved by electroforming a metal sheath onto a fused deposition modeling® (FDM) substrate.The structure of the disparate phase metal-polymer hybrid is shown in Figure 1 where it is possible to see the nickel, copper and ABS layers. Typically, when a shell is made very thin it is subject to localized failure. The hybrid architecture allows a reduction in wall thickness via functional support of the shell.
The deformation modes observed indicated the mechanical properties of the shell significantly exceeded the bulk values. In order to properly optimize the hybrid architecture, the properties of the electroformed material must be characterized. The impact of process parameters on the grain structure of electroformed films has been evaluated. It is known that the growth rate is often slow and linked to the microstructure of the deposit; which can impact mechanical properties.
Previous studies have looked at the microstructural evolution of Ni elecrodeposits and have observed columnar grains. Conflicting information is reported about how the columnar grains evolve. Anisotropy of the grain morphology and the textures that develop during electrodeposition suggests that properties of a coating would vary in the growth direction compared to the transverse direction. Most literature studies report only the properties perpendicular to the growth direction, and lack tension data on the properties in the growth direction.
A new method is needed to fully evaluate the anisotropic mechanical properties of these deposits as standard macroscale ASTM samples would result in significant measurment error due to the evolution of the microstructure along the growth direction of the deposit.This paper seeks to fill gaps in the current literature by characterizing both the growth direction and transverse properties of electrodeposited nickel and copper films using micro-tension samples. We have investigated electrodeposits from three different plating bath chemistries under processing conditions determined to produce a constant growth rate, and relates the resulting properties back to the microstructure.