OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 27 No. 3 2025 Introduction Nickel-based alloys are widely used for manufacturing critical components across various industries, including aerospace, power generation, petrochemical, and marine sectors. This widespread application is attributed to their combination of high corrosion resistance and mechanical strength at moderately elevated temperatures. The high strength of these alloys is achieved through a specific phase composition, which in turn is determined by the presence of particular alloying elements and the corresponding strengthening mechanisms [1–3]. Traditionally, the most common method for producing components from nickel alloys is casting, followed by heat treatment to form the desired phase structure [4]. However, this approach has several significant drawbacks. These include chemical element segregation, the presence of large undesirable Laves phase inclusions and eutectics [5, 6], as well as an uneven distribution of strengthening phases across the cross-section of the workpiece [7]. Moreover, many complex-shaped components are assembled into a single combined structure using welding techniques. Additive manufacturing technologies present a promising alternative for producing nickel alloy components, as evidenced by analysis of strengthening mechanisms in these alloys and their manufactured parts [8–12]. This approach offers several key advantages: (1) it addresses the challenge of fabricating geometrically complex components; (2) the rapid cooling rates characteristic of additive processes minimize chemical segregation; (3) the layer-by-layer deposition induces repeated thermal cycling, which can promote in situ precipitation of strengthening phases during the build. Moreover, the ability to create hybrid structures reduces the consumption of expensive materials. As a result, the microstructure and phase composition of additively manufactured materials are anticipated to differ significantly from those produced via conventional methods. Despite the growing interest in this topic in the scientific literature, a comprehensive understanding of the microstructural and phase characteristics of various alloys produced by additive technologies is still lacking. This is primarily due to the wide variability in processing methods and parameters used in different studies. Furthermore, in the case of hybrid structures produced via additive manufacturing, identifying the patterns of structure and phase formation becomes an even more complex task [13–15]. Consequently, the purpose of this work is to investigate the structural features of gradient layers in «steel – nickel alloy – steel» systems fabricated by direct laser deposition. Research methods Research materials For sample fabrication, powders of Inconel 625 nickel-based alloy (particle size: 50–70 μm) and AISI 316L stainless steel (particle size: 15–45 μm) were used (Fig. 1). A 50×50×5 mm plate made of 0.12 C-18 Cr-10 Ni-Ti stainless steel served as the substrate. The chemical compositions of the initial materials are presented in Table 1. Sample preparation Dissimilar joints were fabricated at the Khristianovich Institute of Theoretical and Applied Mechanics SB RAS using a “Cladding and Welding Complex Based on a Multi-Axis Robotic Arm and a 3 kW Fiber Laser (IPG Photonics) with a Wavelength of 1.07 μm”. Direct laser deposition (DLD) was employed as the processing method, where powder is delivered through a coaxial nozzle into a localized melt pool generated by laser radiation. The high scanning speed and rapid cooling rates inherent in this technique minimize thermal gradients and reduce the likelihood of secondary phase formation in the joint region. Argon served as the shielding gas. Detailed deposition parameters are provided in Table 2 [16]. The samples were fabricated in a unidirectional manner. Sequentially, four layers of each material were deposited in the order: steel – nickel alloy – steel. Each subsequent layer overlapped the previous layer by 50%, which was intended to ensure a smooth transition between the materials.
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