In light of the continuous advancements in high-entropy alloys and the widespread use of high-strength metals such as titanium alloys in modern industries, this research focuses on investigating the dissimilar joining process between a high-entropy alloy (Co–Cr–Fe–Mo–Ni) with high entropy and the titanium alloy TC4(Ti-6Al-4V) using the transient liquid phase bonding process at constant times and variable temperatures. The joining process at a constant time of 90 minutes and temperatures of 890, 960, 1000, and 1050℃ was performed using a copper interlayer. The selected high-entropy alloy exhibits excellent mechanical and corrosion properties. On the other hand, TC4 alloy, belonging to a category of titanium alloys, is widely used in various industries, including aerospace, due to its excellent mechanical properties, corrosion resistance, and favorable strength-to-weight ratio. The joining of these two alloys together, considering their desirable mechanical properties, poses a technical challenge. To eva‎luate the microstructure of different zones created in the joint, optical and electron microscopes were utilized. The energy-dispersive X-ray spectroscopy capability of the scanning electron microscope was employed to analyze the concentration and distribution of elements in the joint interface and predict possible formed phases. In the assessment of the mechanical properties of the joints, the connection at a temperature of 960℃ exhibited the highest strength of 138 megapascals due to the complete homogenization of the co-solidification zone and achieving element penetration equilibrium in different regions of the joint. Subsequently, at a temperature of 1000℃, the strength decreased to 108 megapascals. The strength reduction at 1000℃, considering the presence of the co-solidification zone, was attributed to the formation of more brittle intermetallic compounds such as Fe2Ti, FeTi, and Cr2Ti in the common phase between the high-entropy alloy and the interlayer. The highest hardness at all temperatures was observed in the region affected by penetration on the side of the high-entropy alloy. The high hardness in this region is attributed to the presence of brittle and fracture-prone intermetallic compounds such as CoCr(Ti-Mo), FeTi, and Fe2Ti. With an increase in temperature up to 1050℃, the joint region generally underwent morphological changes, and in the ASZ (Adiabatic Shear Zone) region at this temperature, titanium and cobalt eutectoids were formed. Examination of the joint fracture surfaces revealed a brittle fracture pattern due to the presence of cleavage planes. Furthermore, sheet-like fracture surfaces were observed at all temperatures. By utilizing transient liquid phase bonding analysis, one of the solid-state joining processes used for joining alloys sensitive to high temperatures and melt formation, the study contributes to the understanding of the joining behavior of these dissimilar alloys.

علي اشرفي

بهزاد نيرومند , قاسم عظيمي روئين