## 1 Introduction
[3] reported that friction-welded alloy 718 joints, prior to STA process, friction-welded alloy 718 joints displayed lower hardness and tensile properties in the weld zone compared to the BM. The IN718 friction welds prepared from ST showed a fine grain structure in the weld zone due to DRX, which enhanced the hardness. [PERSON] et al. [7] reported that PWHT improved the microhardness and tensile strength properties of friction welds compared to the as-welded condition, because of the modification of the microstructure and the formation of \(\gamma^{\prime}\) and \(\gamma^{\prime\prime}\) precipitates. IN718 is a highly alloyed material that is prone to alloying element segregation and formation of unsolicited phases at the grain boundaries, which are high-energy sites. [PERSON] et al. [8] utilized a homogenization heat treatment at 1066 \({}^{\circ}\)C to reduce boron (B) segregation at grain boundaries in cast IN718. This treatment increased the resistance to HAZ microfissuring, while significantly decreasing the volume percentage of NbC and Laves phases. Friction welding parameters are crucial to the welding process, including spindle rotation speed, friction pressure, upset pressure, friction time, and burn-off length. [PERSON] et al. [5] examined the influence of friction welding parameters on dissimilar IN718/SS410 rotary friction welds, by varying the rotation speed and friction pressure. They found that increasing the rotating speed and friction pressure enhanced the tensile strength values. The maximum tensile strength of 718 MPa was attained at a rotating speed of 1500 rpm and a friction pressure of 189 MPa. [PERSON] et al. [9] investigated the mechanical and metallurgical properties of dissimilar IN718 to SS410 rotary friction welded joints. They observed that the process parameters, such as forging time (10 s), friction pressure (220 MPa), and rotating speed (1300 rpm), could be used to optimized the maximum tensile strength (652 MPa). [PERSON] et al. [10] reported that the IN718-SM45C dissimilar friction joints displayed the highest fatigue and tensile properties at 10 s of heating time. A further increase in heating time reduced the mechanical performance. [PERSON] et al. [11] reported that rapid thermal and mechanical stress cycles altered the microstructure of IN718 friction welded joints. They also found that the upset pressure during welding severely affected the weld zone width, with a higher upset pressure yielding a narrower weld zone width. The friction weld zone of alloy 718 revealed an average grain size of about 2-5 um in the DRX zone near the weld interface. Precipitate dissolution can occur in the weld zone and TMAZ/HAZ of the IN718 alloy welds, due to the high temperatures encountered during friction welding exceeding the solvus temperatures of the strengthening precipitates. [PERSON] et al. [12] investigated the influence of process parameters on the microstructure and mechanical properties of friction-welded joints between AISI 1040 and AISI 304L steel. Four microstructurally unique zones were identified in the weldment, namely, the friction-affected zone (FDZ), thermo-mechanically affected zone (TMAZ), heat-affected zone (HAZ), and base metal (BM). The width of the FDZ and HAZ was mainly influenced by the friction time and rotational speed. The tensile strength of the dissimilar continuous drive friction-welded joint was increased by increasing the rotation speed and decreasing the friction time. [PERSON] et al. [13] studied the mechanical properties of dissimilar AISI 304L/AISI 4340 steel friction-welded joints as a function of rotation speed. They concluded that sufficient welding strength could be achieved by keeping the friction time as short as possible, while the friction pressure, forging pressure, and rotation speed should be as large as feasible. [PERSON] et al. [14] investigated the mechanical properties and grain structure development of alloy 718 tube joints produced using the rotary friction welding process.