In recent years, to harness the combined properties of different materials to enhance performance and reduce costs, the topic of joining dissimilar alloys has attracted significant attention from researchers. Titanium alloys and stainless steels, as two important materials with extensive applications in various industries such as oil and gas, automotive manufacturing, etc., offer various advantages regarding physical, chemical, and mechanical properties. Today, selective laser melting (SLM) and electron beam melting (EBM) methods are utilized in these industries due to their ability to produce complex parts with superior or equivalent properties compared to conventional methods. Given the size limitations of parts produced by these methods, studying their joining processes for broader industrial applications has become a focus of attention. In this research, the joining of 316L stainless steel (SS) to Ti-6Al-2Sn-4Zr-2Mo titanium alloy, produced by additive manufacturing, was carried out using the transient liquid phase (TLP) bonding process at two temperatures of 980°C and 1020°C and durations of 30, 60, and 120 minutes, employing a BNi-2 interlayer under vacuum conditions of 10⁻⁵ bar. To examine the microstructure of the joints obtained, optical microscopy and scanning electron microscopy (SEM) equipped with energy-dispersive X-ray spectroscopy (EDS) were utilized. Additionally, the mechanical properties of the joints were eva‎luated using shear strength testing and microhardness testing, and the fracture surfaces of the joints were analyzed using X-ray diffraction (XRD). The results of this study indicate that with increasing temperature and time, the isothermal solidification zone, which contains a titanium-rich phase, expands, while the non-isothermal solidification zone, containing titanium boride and titanium-nickel compounds, decreases. Notably, the diffusion zones on the side of the base metals also increase with rising time and temperature. However, in the case of stainless steel, the formation of M3B2 compounds reduces the desired bonding properties. The shear strength results of the joints at 980°C showed an increase in strength up to 118 MPa with increasing time, attributed to a higher rate of isothermal solidification. However, at 1020°C, with increasing bonding time, strength was decreased due to the reduction of titanium boride compounds and the increase of M3B2 phases. The microhardness test results showed that the highest hardness values were associated with the non-isothermal solidification zone located at the center of the joint. According to the X-ray diffraction investigations of the failure surface of joints, the formation of brittle phases of NiTi2 in the non-isothermal freezing area, as well as phases of FeTi and M3B2 borides in the penetration area of stainless steel, causes the failure of joints from these areas.

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عبدالله صبوري

بهزاد نيرومند , ابوذر طاهري زاده