| Ni-base superalloy blades welding repair always serves as one of the hot and difficult issues in the joining fields. The K465 Ni-base superalloy blades repairing by vacuum electron beam brazing (VEBB) has been studied in this paper. The weldability of K465 alloy is poor, and VEBB is a method only for local heating, these two factors induce the generation of heat stress in the joints during brazing and hot cracks easily formation in the joints after brazing. Therefore, basing on the analysis of composition and distribution of the interfacial reaction products of the joints and heat stress distribution during brazing, a beam current gradual transition heat input control VEBB repair method of K465 Ni-base superalloy blades has been developed, and the crack-free joints of K465 Ni-base superalloy blades have been obtained by VEBB repair.Development and choice of the filler metal is the key factor of VEBB K465 Ni-base superalloy. Considering the requirement of VEBB on the filler metal, a new Ni-base filler metal with good high temperature property is developed by mechanical alloying. The effect of VEBB parameters on the spreading area and the mechanical property of the joints with BNi-2, Bпp27 and No.1 self-made filler metal were carried out, No.1 self-made filler metal was chosen as the filler metal for VEBB study.According to the experimental results of interface reactions on the K465 Ni-base superalloy interface, it was found that the VEBB parameters had a direct effect on the formation and distribution of the interface reaction products. There are five reaction products in the repaired joints interface, they are Ni-baseγsolid solution, Ni2Si, Ni3B, Ni3Si and Ni3Al.The experimental results show that interface reaction products do not change with the electron beam brazing parameters varying, but shape and quantity of reaction products are effectively affected. When the electron beam current is small or heating time is short, the quantity of Ni-baseγsolid solution is large in the brazed joint interface. While the electron beam current is large or heating time is long, the content of Ni2Si, Ni3B, Ni3Si and Ni3Al increases, but the content of Ni-baseγsolid solution decreases in the brazed joint interface. At the same time, the size of Ni2Si become larger, and the distribution of Ni2Si is concentrated on interface between filler metal and base material.Effects of brazing parameters on joint tensile strength and fracture position are investigated. The joint strength improves as the electron beam current and heating time increase. When the strength comes to the maximum, it declines with the electron beam current and heating time increase. In this work, the largest tensile strength could reach 760MPa, 82 percent of that of base material, when the current is 2.7mA, heating time is 200s and focus current is 1800mA.Hot cracks easily occurred during VEBB repairing K465 Ni-base superalloy simulating blades with non-through slot. Mostly, cracks occur from the seam and base metal next to the joining interface, then the cracks go along the whole seam. This is mainly because the hot stress is large. Tensile fractures usually appear at the seam and base metal near the seam, which belong to brittle transcrystalline fracture. While simulating blades with through slot rarely produce cracks.The cooling time of crack initiation was got by analyzing simulating blades with non-through slot. The distribution of temperature and stress was calculated. The results showed that stress concentration area was 1.3~2.4mm away from the center of the specimens. And the stressσY in Y axis direction was higher thanσX in X axis direction, the maximum tensile stress reached to was 935MPa. Most of the cracks were in X axis direction. Comparing the tensile stress distribution ofσX in X axis direction andσY in Y axis direction of simulating blades with non-through and through slot, the tensile stress of simulating blades with non-through slot was less than that of simulating blades with non-through slot at the same position. The residual tensile stress in the joints was 826MPa, resulting in low stress fracture of the through slot specimens joints.According to the above results, a beam current gradual transition heat input control method was developed, which could obtain crack-free joints of of K465 Ni-base superalloy blades by VEBB. The procedure as follows: application of brazing preheating step-by-step increasing beam current and step-by-step decreasing beam current slow-cooling after brazing, which were used to control brazing thermal cycle and release the heat stress. Finally, macro crack-free joints of K465 Ni-base superalloy simulating blades with non-through slot have been obtained by this method. X-ray diffraction was applied to measure the residual stress distribution by beam current gradual transition heat input control method.The crack-free joints of K465 Ni-base superalloy blades with non-through slot and through slot were repaired by beam current gradual transition heat input control VEBB method. The results showed there was no crack or any other welding defects by X-ray detection.
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