Investigation of Functionally Graded Materials Developed by Wire Arc Additive Manufacturing Process Assisted by Friction Stir Processing

Abstract

The demand of advanced materials is growing in a very steeped manner, especially in the engineering sectors like, aerospace, nuclear, automobile and power generation. The materials of these components are required to serve in harsh working conditions. The working life of such industrial components are very important and possibilities of catastrophic failures of these components cannot be accepted in such sectors. The development of materials for these applications, is very time consuming and costly process. Hence, functionally gradient materials (FGM) can be one of the possible solutions. Many additive manufacturing (AM) has applied to fabricate bulk metal based FGM. However, wire arc additive manufacturing would be one of the most prominent and economical fabrication methods. In this work, Ni-based FGMs specific alloys such as Inconel 625, ERNiCrMo-10, Nichrome 80/20, and pure Ni weld spools were selected as a raw material. The development of Ni-Cr-Mo-based functionally graded materials (FGMs) was carried out by using gas tungsten arc welding (GTAW) based wire and arc additive manufacturing (WAAM) process. The GTAW process parameters for FGMs were optimized to get good weld bead geometry. The optimized process parameters are used for further development of FGMs. The post treatment of developed FGMs were also carried out by using innovative approach of friction stir processing (FSP). This post treatment is mainly intended for mitigation of developed stresses during FGMs development and maintained the material homogeneity in the FGMs structure. The FSP process parameters has been optimized and based on the observations, rotation speed is the most influencing parameter to control the intentions. The effect of water cooling is also investigated on the developed FGMs. The developed FGMs were investigated in detailed by using various metallurgical and mechanical tools and techniques. The microstructural evolution of FGMs produced through WAAM, observing a combination of dendritic and columnar grains in the as-deposited samples. Through, FSP post-processing, these structures transform into fine recrystallized grains with oriented deformation direction after FSP. It also affects the distribution of CrNi3 and MoNi4 precipitates. The microhardness gradually increases from the bottom to top of the samples in the as-deposited state. The FSP processed samples shown significant improvement in the microhardness. The investigations reveal variations in tensile strength along the gradient direction of the FGMs, with increasing Cr and Mo content correlating with higher tensile strength and microhardness. Further, the trimetallic FGMs using stainless steel (ER316L), duplex steel (ER2205), and Inconel 718 (IN718) via gas metal arc welding (GMAW) based WAAM has been also investigated. The metallurgical examinations uncover distinct boundaries between different alloy compositions and the presence of metal carbides and Lave phases. The mechanical characterization of these FGMs demonstrates a steady increase in hardness along the built direction, with variations at alloy interfaces. The tensile tests reveal increased tensile strength along the built direction, accompanied by reduced strain.