With the continuous advancement of laser deposition repair technology, its applications have expanded from static aero-engine components to rotating parts, with the GH4169 compressor blade being a notable example of this demand. The limited space between blades restricts the use of linear friction welding repair, while laser deposition repair technology effectively restores the geometric integrity of damaged parts. However, challenges such as deformation damage, degradation of the forging matrix, non-uniform macrostructures in the repaired region, and the formation of fusion cracks significantly impair the mechanical properties of repaired components. Conventional repair methods for nickel-based high-temperature alloys, relying on forging and conventional heat treatments, often result in pronounced matrix grain growth, leading to severe performance deterioration. Although low-temperature solution treatment achieves static strength comparable to forged materials, it suffers from reduced fatigue strength, restricting the repaired part suitability for long-term, high-temperature alternating load environments. This limitation stems from the inability of low solution-treatment temperatures to dissolve all Laves phases in the repaired region, which act as sites for crack initiation and propagation during subsequent service, thereby preventing full restoration of mechanical properties. To address these issues, this study employs pulse current processing in the laser deposition repair of GH4169 alloy, offering an effective solution to these critical challenges and advancing the performance of repaired components.

In this study, GH4169 alloy is selected as the base material. Laser deposition repair is employed to fabricate the repaired GH4169 alloy, after which tensile specimens are prepared using wire cutting. The specimens underwent solution treatment, followed by pulse current processing, during which the pulse current parameters—frequency and energization time—are varied systematically in orthogonal tests. Measured real-time temperatures are recorded at the midpoint of parallel section of the specimen using thermocouples during the pulse current treatment. The influence of pulse current on the mechanical properties of the laser deposition repaired GH4169 alloy is subsequently evaluated through tensile testing. Furthermore, the effects of pulse current on the dissolution of the Laves phase and the precipitation of the γ″ phase are analyzed using optical microscope (OM), scanning electron microscope (SEM), and transmission electron microscope (TEM).

In the absence of pulse current, the alloy exhibits a distinct columnar crystal structure aligned along the deposition direction, characterized by multilayered deposition bands. The dendritic Laves phase predominantly appears as elongated strips, with occasional granular forms [Fig. 3(a)]. Under the influence of pulse current, driven by the combined effects of Joule heating and the electromagnetic field, the morphology of the Laves phase transforms with increased energization time. Initially, the thin and short strips evolve into larger granular or island-like distributions, eventually forming a discontinuous fine granular structure (Fig. 4). Concurrently, the volume fraction of the Laves phase decreases significantly (Fig. 5).

In this study, the microstructure and mechanical properties of the laser deposition repaired GH4169 alloy are significantly enhanced through pulse current treatment. The dissolution of the Laves phase during pulse current application can be attributed to two primary mechanisms. First, the pulse current promotes the diffusion of solute atoms, thereby providing the necessary energy for the dissolution of the Laves phase. Second, it reduces the energy barrier for the dissolution process while inducing the generation of a high density of dislocations within the alloy, which further facilitates the phase dissolution. The reduction in the size and volume fraction of the brittle Laves phase significantly improves the alloy mechanical strength. Specifically, the volume fraction of the Laves phase in the repaired area decreases from 2.24% in the absence of pulse current to 0.85%, 0.77%, and 0.57% following treatment with a 40 Hz pulse current for 5, 10, and 20 min, respectively. Correspondingly, the tensile strength increases by 18%, 20%, and 23%, with alloy strength progressively improving with longer energization time. Furthermore, the pulse current treatment satisfies both thermodynamic and kinetic conditions necessary for the precipitation of the γ″ phase. The size of the γ″ phase increases with prolonged energization time, and its precipitation in the repair zone is attributed to the reduction in activation energy for solute atom diffusion caused by the pulse current. Additionally, the dissolution of the Laves phase releases a significant amount of Nb atoms back into the matrix, while the temperature rise during energization satisfies the thermodynamic requirements for γ″ phase precipitation. The γ″ phase, acting as a reinforcement, exerts a pinning effect on dislocations. This effect becomes more pronounced as the γ″ phase grows larger, resulting in enhanced dislocation resistance and a corresponding increase in the alloy strength.