Fatigue performance of high-strength low-alloy DED-Arc components with low-pressure cold spray coating

Abstract

Additive manufacturing using the directed energy deposition-arc (DED-Arc) process enables the production of customized structural components from high-strength low-alloy (HSLA) steels. The layer-wise deposition results in surface waviness, which affects the as-built components’ fatigue resistance. Additionally, the HSLA steel requires reliable corrosion protection for use in structural applications. This study investigates the applicability of low-pressure cold spray (LPCS) Zn + Al2O3 coatings on as-built HSLA DED-Arc components with regard to fatigue performance and corrosion resistance. Multiple thin-walled components were manufactured using two different DED-Arc parameter sets, resulting in varying surface topographies. Selected components were coated with LPCS Zn + Al2O3, and a subset of those was subjected to cyclic corrosion testing (CCT). From the thin-walled components, several sets of fatigue specimens were extracted in deposition direction and geometrically characterized using 3D scanning, before and after CCT. Surface height parameters and volumetric geometry were analyzed, followed by uniaxial fatigue testing (stress ratio R = 0.1), together with four-camera digital image correlation (DIC) measurements of displacements at selected load cycles. The LPCS process enabled successful coating deposition with average Zn + Al2O3 thicknesses of approx. 500 µm, and the CCT confirmed its effective cathodic corrosion protection for the DED-Arc HSLA material. Differences in surface topography and fatigue strength were observed depending on the applied DED-Arc process parameters, resulting in fatigue strengths ranging from FAT 80 to FAT 125. While LPCS Zn + Al2O3 coating slightly increased surface height parameters, it did not affect fatigue strength compared to uncoated as-built components. Both the as-coated and corrosion-exposed conditions exhibited fatigue strength of FAT 125.