## 1 Introduction  
Additive manufacturing (AM) offers additional advantages compared to subtractive manufacturing, including greater geometric freedom and less material waste. Metal additive technologies are classified into two categories, the directed energy deposition (DED) and powder bed fusion (PBF) types. Among DED methods, approaches employing wire feedstock and powder feedstock have been reported [1; 2; 3]. Wire arc additive manufacturing (WAAM) is a DED method that utilizes an arc as a heat source and metal wire as a feedstock. This method can be easily implemented with existing welding equipment and robots, resulting in lower initial construction costs compared to those of other AM methods. Additionally, WAAM has gained popularity for its ability to produce large metal components with high deposition rates and efficient material utilization. Moreover, several studies have been conducted on weld monitoring and its integration into WAAM processes [4]. Bimetallic structures are designed with locally tailored properties to handle different loads and operating conditions, leading to much more efficient performances. Bimetallic structures belong to the multi-material component category, typically consisting of two distinct metals that offer complementary attributes, such as mechanical, thermophysical, electrical, optical, and resistance to corrosion or oxidation [5]. Stainless steel 308L (SS308L) is an austenitic stainless steel known for its durability, high biocompatibility, moderate high-temperature properties, and excellent corrosion resistance. Because of these properties, SS308L is applied in various industries, including nuclear power plants, ship construction, oil refining, and automotive manufacturing [6]. Inconel625, a nickel-based superalloy, is widely used in the aerospace and nuclear industries because of its exceptional mechanical properties and wide service temperature range. Its excellent weldability has led to numerous studies on additive manufacturing and its application in various fields [7]. Stainless-steel-Inconel bimetallic products have been custom engineered to endure diverse operating conditions and external forces. They are utilized across nuclear power plants, industrial gas turbines, shipbuilding, and oil refineries, thanks to their superior thermal, mechanical, electrical, and corrosion properties compared to those of traditional single-metal products. For example, Inconel is chosen for high-temperature operating components in oil reformer towers, due to its mechanical durability and corrosion resistance, while stainless steel is used for rotating shafts that operate at lower temperatures [8]. Using a GMAW-WAAM system, [PERSON] and [PERSON] deposited austenitic stainless steel followed by a nickel-based alloy. They observed an interface without defects that showed a significant decrease in hardness [9]. [PERSON] et al. researched an interweaving deposition strategy for steel-nickel bimetallic components using GTA-WAAM. By depositing overlapping beads at the same time, they achieved a complex inter-locking microstructure. This, combined with the strengthening effect from the mixing of Fe and Ni, led to a strong bond at the interface [10]. Despite their good properties, both stainless steel and Inconel present significant challenges in machining via conventional subtractive manufacturing methods, leading to rapid tool wear and low material removal rates. Additive manufacturing offers a solution to these issues. However, the high heat input generated during WAAM results in defects such as distortion, residual stresses, coarse columnar grains, mechanical anisotropy, pores, and thermal cracks, all attributed to the substantial heat that is generated during the process and the subsequent rapid cooling rates. To mitigate these issues, numerous studies have proposed different types of inter-layer rolling devices, demonstrating that these can reduce residual stresses, mechanical anisotropy, and transform the columnar grain structure into an equiaxed grain structure [11; 12; 13].