Objective K4169 hightemperature alloys exhibit high strength, plasticity, and heatcorrosion resistance in the middle and lowtemperature ranges and are particularly suitable for manufacturing aircraft engines. The ascast state of the K4169 alloy is prone to severe elemental segregation, resulting in deteriorated welding performance. The presence of liquation cracks in the heataffected zone significantly reduces the safety and operational reliability of the product. To enhance the quality of repairs, laser pretreatment is employed to adjust the composition, structure, and phase distribution of the base material while reducing its strength and hardness to improve the liquation crack sensitivity of the matrix material. However, a systematic study of the prelaser treatment process for K4169 nickelbased hightemperature alloys has not been carried out. In particular, the influence of the base material' s structure on crack initiation mechanisms is not well understood. Therefore, this study emphasizes the necessity of employing pretreatment processes to regulate the K4169 alloy base material before repair, and conducts indepth research on the sensitivity and mechanisms of liquation cracks in the repaired specimen's heataffected zone. The results of this study have significant implications for the highquality repair of nickelbased hightemperaturealloy components in aerospace.Methods This study employed a homogenization+solution+aging treatment and homogenization+hot isostatic pressing+ solution+aging treatment on a K4169 alloy substrate prior to repair, followed by repair experiments using the laser deposition process with synchronized powder feeding for different substrate microstructures. The repaired specimens subjected to the homogenization+ solution+aging treatment were denoted LDR, whereas those subjected to the homogenization+hot isostatic pressing+solution+ aging treatment were denoted LDR -K9. The process parameters included a laser power of 1600 W, scanning speed of 8 mm/s, scanning speed of 1 rad/min, overlap rate of 40%, and laser diameter of 3 mm. Subsequently, the crosssections of the heattreated substrate and repaired specimens were ground and polished, followed by corrosion using a solution of hydrochloric acid, nitric acid, and hydrofluoric acid (80 mL HCl+7 mL HNO 3 +13 mL HF). The microstructures of the substrate specimen crosssections and the distribution and characteristics of cracks in the repaired specimens were observed using an OLYMPUS GX 51 optical microscope (OM) and a ZEISS Sigma300 scanning electron microscope (SEM). Energydispersive spectroscopy (EDS) was employed to characterize the distribution of elements in the substrate region. Phase analysis was performed using a Bruker d2 -phaser Xray diffractometer (XRD). Microhardness measurements of the repair, heataffected, and substrate zones were conducted using an HVS -1000Z Vickers hardness tester under a 1.96 N load for 15 s. Tensile tests were performed using an INSTRON5982 universal testing machine at a strain rate of 0. 5 mm/min.
Results an...
