Fabrication, analysis, and modelling of SS316L & IN625 FGMs and alloys by twin wire arc additive manufacturing

Abstract

The research paper focused on the fabri cation of functionally graded materials (FGMs) and alloys using the TIG-based wire arc additive manufacturing (WAAM-TIG) process. The study explores two types of functionall y graded materi als (FGMs) i.e., continuous (CGFGM) and sandwich structures (SW-FGMs) with varying gradients. By precisely controlling the weight percentage of SS316L and IN625 materi als using individual wire feeding systems, defect-free depositions are achieved through the optimization of process parameters. Energy dispersive X-ray spectroscopy (EDS) analysis reveals a gradual variation in the distribution of Ni and Fe elements in CG-FGMs, while alternating peaks are observed in SW-FGMs. Microstructure analysis shows a smooth transition from equiaxed to columnar dendrites in CG-FGMs, while SW-FGMs exhibit a heterogeneous behav ior. Hardness measurements indicate a steady increase in CG-FGMs and a wavy pattern in SW-FGMs. X-ray diffraction (XRD) analysis confirms the formation of the desired austenitic phase, with peak height variations correlating to changes in microslruclure and hardlless. The specific wear rale decreases wilh illcreas illg Ni COlilelll in CG-FGMs, while in SW-FGMs, it shows a strong dependency on the adopted des ign. In stati stical study, response surface design analysis was conducted using central composite design (CCD). Regression models were developed to evalu ate factors' effects on responses such as hardness, fract ure toughness, scratch hardness, spec ific wear rate, and coefficient of friction (COF) that exhibited the R2 values ranging between 0.65 to 0.9. Composition is found to be the main factor influencing the mechanical properties, while current and speed affect bead geometry. Quadratic models were detemlined to be the most suitable for most responses. The optimal conditions for maximizing hardness and fracture toughness and minimizing wear rate were identified as a composition of 3 (3: I), current of 205 A, and voltage of 200 mm/min. The predicted values for the selected parameters were also presented, along with an overall composite des irability value of 0.63. Keywords: Additive manufacturing, functionally graded materi al, directed energy deposition, design of experiments, CCD, SS3 16L, IN625.