Wire arc additive manufacturing of ER70S-6/316L bimetal joint

Abstract

Additive manufacturing has been a transformative approach to industrial production. It delivers advantages of improved mechanical properties, complex geometries, and simplified fabrication. Wire arc additive manufacturing (WAAM) has the highest deposition rate among various metal additive manufacturing techniques. The WAAM process usually starts to print the first layer on a starting substrate. The substrate could be a functional part of the WAAM-built components. Therefore, the interface of the WAAM-built structure and the substrate should be studied. In this work, the ER70S-6 wall was built directly using WAAM process on a 316L stainless steel substrate. Metallurgical study was conducted to investigate bonding of the two materials at the interface and revealed a diffusion of alloying elements from the substrate to the interface, and the upper layers of as-built structure and formation of martensite phase at the interface regions and ferrite at the upper layers. In addition, microhardness test and tensile test were conducted to investigate the mechanical properties of the bimetal joint. Microhardness test revealed the variation of hardness property along the layers, and the notable boost was obtained at the first layer with an average peak value of 354.4 ± 11.2 HV. Tensile test conducted with DIC analysis revealed that high tensile strain deformation shifted from the 316L substrate to the WAAM ER70S-6 side of the material where necking and fracturing occurred as the weakest point. The interface of the bimetal joint exhibited a very low tensile strain which was attributed to the transformation of a martensite phase in this region.