This study investigates linear friction welding of GH4169 alloy for aero-engine integrally blisks, with particular focus on elucidating the mechanisms by which combined pre- and post-weld heat treatments influence microstructural evolution and corrosion behavior of welded joints. Microstructural characterization reveals that composite heat treatment promotes the formation of large-scale spherical γ′ and disc-shaped γ′′ phases in the Base Material (BM), while in the Thermo-Mechanically Affected Zone (TMAZ), original precipitates coarsen and fine γ′ and γ′′ phases reprecipitate. Additionally, needle-like δ phases precipitate along grain boundaries. The synergistic effect of grain refinement and precipitation strengthening results in superior joint mechanical properties, including a microhardness of 540 HV_0.5, a tensile strength of 1400 MPa, and a fracture elongation of 18%, with the joint strength comparable to that of the BM. Electrochemical analysis shows that the joint exhibits significantly lower corrosion resistance than the BM, due to enhanced micro-galvanic coupling between the γ-matrix and precipitated γ′ or γ′′ phases. This is evidenced by an increase in corrosion current density from 1.62×10^-6 A/cm² of BM to 3×10^-6 A/cm² of joint. High-temperature molten salt corrosion tests indicate that corrosion mainly occurs through the combined action of oxides and soluble salts. The joint shows accelerated corrosion, reaching a peak value in the average corrosion rate of 269.9 g/m²/h, characterized by a fine-grained microstructure and loosely oxide films. The electrochemical impedance of these is measured at 1.83 kΩ ·cm², attributed to thermo-mechanical effects. In contrast, the coarse-grained BM forms dense and protective oxide layers, with a higher impedance of 14.20 kΩ ·cm² and a lower peak corrosion rate of 134.9 g/m², reflecting more stable corrosion behavior. This work deciphers how heat treatment controls corrosion resistance through the regulation of precipitate distribution in welded joints, providing valuable guidelines for the optimization of integrated welding and heat treatment process in blisk production.

GH4169 joints manufactured by Linear Friction Welding (LFW) are subjected to tensile test and stair-case method to evaluate the High Cycle Fatigue (HCF) performance at 650 ℃. The yield and ultimate tensile strengths are 582 MPa and 820 MPa, respectively. The HCF strength of joint reaches 400 MPa, which is slightly lower than that of Base Metal (BM), indicating reliable quality of this type of joint. The microstructure observation results show that all cracks initiate at the inside of specimens and transfer into deeper region with decrease of external stress, and the crack initiation site is related with microhardness of matrix. The Electron Backscattered Diffraction (EBSD) results of the observed regions with different distances to fracture show that plastic deformation plays a key role in HCF, and the Schmid factor of most grains near fracture exceeds 0.4. In addition, the generation of twins plays a vital role in strain concentration release and coordinating plastic deformation among grains.

Linear Friction Welding (LFW) technology was used to realize the welding of GH4169 superalloy, and the effect of welding parameters on the microstructure, mechanical properties and corrosion behavior of the joint was analyzed. The results show that there is a positive correlation between the weld hardness and the tensile strength. With the gradual increase of heat input and welding pressure, the joint quality is gradually improved, but the heat affected zone is not significantly increased. The smaller the grain size of the weld, the higher the strength and plasticity of the joint. With the increase of the joint shortening amount, the corrosion resistance of the weld first gradually increases. However, when the shortening reaches a certain level, the corrosion resistance of the joint becomes little changed. With the increase of solution temperature, the corrosion current density increases and the polarization impedance decreases. The higher the corrosion temperature, the worse the corrosion resistance of the joint. There is no significant correlation between the joint strength and the corrosion resistance. The corrosion resistance of the joint can be enhanced without changing the joint mechanical properties by reducing the welding frequency and amplitude or increasing the welding pressure.

Numerical simulation and experimental research on Linear Friction Welding (LFW) for GH4169 superalloy were carried out. Based on the joint microstructure and mechanical properties, a suitable welding process was determined, which provided an important theoretical basis for the manufacture and repair of aeroengine components such as the superalloy blisk. The results show that the joint strain rate gradually increases with the increase of welding frequency, and the deformation resistance of the thermoplastic metal increases in the welding process, resulting in the interface thermoplastic metal not being extruded in time to form a flash, so the joint shortening amount gradually decreases. The thermoplastic metal in the center of the welding surface is kept at high welding temperature for a long time, resulting in the decrease of the joint strength. The microhardness of the joint shows a “W” distribution perpendicular to the weld, and most of the joints break in the Thermo-Mechanically Affected Zone (TMAZ) with high tensile strength and low elongation. When the welding area is increased without changing the aspect ratio of the welding surface, the interface peak temperature increases gradually, and the joint shortening amount decreases with the increase of the welding interface size.

In this study, a new linear friction welding (LFW) process, embedded LFW process, was put forward, which was mainly applied to combination manufacturing of long or overlong load-carrying titanium alloy structural components in aircraft. The interfacial plastic flow behavior and bonding mechanism of this process were investigated by a developed coupling Eulerian-Lagrangian numerical model using software ABAQUS and a novel thermo-physical simulation method with designed embedded hot compression specimen. In addition, the formation mechanism and control method of welding defects caused by uneven plastic flow were discussed. The results reveal that the plastic flow along oscillating direction of this process is even and sufficient. In the direction perpendicular to oscillation, thermo-plastic metals mainly flow downward along welding interface under coupling of shear stress and interfacial pressure, resulting in the interfacial plastic zone shown as an inverted “V” shape. The upward plastic flow in this direction is relatively weak, and only a small amount of flash is extruded from top of joint. Moreover, the wedge block and welding components at top of joint are always in un-steady friction stage, leading to non-uniform temperature field distribution and un-welded defects. According to the results of numerical simulation, high oscillating frequency combined with low pressure and small amplitude is considered as appropriate parameter selection scheme to improve the upward interfacial plastic flow at top of joint and suppress the un-welded defects. The results of thermo-physical simulation illustrate that continuous dynamic recrystallization (CDRX) induces the bonding of interface, accompanying by intense dislocation movement and creation of many low-angle grain boundaries. In the interfacial bonding area, grain orientation is random with relatively low texture density (5.0 mud) owing to CDRX.

The Ti17(α + β)-Ti17(β) dual alloy-dual property blisk produced using Linear Friction Welding (LFW) is considered as high-performance component in advanced aeroengine. However, up to now, microstructure evolution and relationship between microstructure and micro mechanical properties of LFWed Ti17(α + β)/Ti17(β) dissimilar joint have not been thoroughly revealed. In this work, complex analyses of the phase transformation mechanisms of the joint are conducted, and phase transformations in individual zones are correlated to their microhardness and nanohardness. Results reveal that α dissolution occurs under high temperatures encountered during LFW, which reduces microhardness of the joint to that of Ti17(α + β) and Ti17(β). In Thermo-Mechanically Affected Zone of Ti17(α + β) (TMAZ-(α + β)) side joint, a large number of nanocrystalline α phases form with different orientations. This microstructure strengthens significantly by fine grains which balances partial softening effect of α dissolution, and increases nanohardness of α phase and microhardness of TMAZ-(α + β). Superlattice metastable β phase precipitates from metastable β in Weld Zone (WZ) during quick cooling following welding, because of short-range diffusion migration of solute atoms, especially β stabilizing elements Mo and Cr. The precipitation of the superlattice metastable β phase results in precipitation strengthening, which in turn increases nanohardness of metastable β and microhardness in WZ.