<p>Corrosion of joints at high temperatures is a major challenge in industrial applications. This study examines the effect of interlayer thickness (38, 76, and 100&#xa0;µm) on the hot corrosion behavior of Hastelloy X superalloy joints bonded via transient liquid phase bonding in a Na₂SO₄–V₂O₅ eutectic at 900&#xa0;°C. It is hypothesized that a thinner interlayer improves corrosion resistance by forming a stable oxide layer. To validate this, corrosion products, microstructural evolution, and elemental composition were analyzed using X-ray diffraction, optical microscopy, field emission scanning electron microscopy, and energy-dispersive spectroscopy. Results show that the 38&#xa0;µm interlayer enhances resistance due to the formation of a protective Cr₂O₃, NiCr₂O₄, and NiO oxide layer. In contrast, increasing the thickness to 100&#xa0;µm intensifies elemental diffusion, leading to a higher concentration of boride and silicide compounds in the diffusion affected zone, reducing corrosion resistance. Initially, corrosion forms a dense Cr₂O₃–NiO oxide layer. However, after 20&#xa0;h, vanadium (V) reacts with the alloy, forming NaVO₃, while sulfur (S) infiltration leads to Ni, Cr, and Mo-based sulfides, promoting intergranular corrosion. The formation of NaVO₃ and SO₃, along with Cr₂O₃ depletion, further accelerates degradation over time.</p> Graphical Abstract <p></p>