Laser Melting Deposition Repairing Research Of GH4169Alloy

GH4169alloy, which is a nickel-iron base superalloy with excellent comprehensive properties between-253～650℃, is one of the highest strength high-temperature alloy at temperatures below650℃, and is widely used in aviation, aerospace, marine, nuclear industry, oil industry and other fields. But the structural parts of GH4169alloy may be damaged inevitably in the process of processing and service. Since direct discard will increase the cost of production and service, it becomes a meaningful research to repaire the damaged GH4169alloy structural components. Due to the strict control of heat input, laser melting deposition repairing technique makes little deformation and small heat-affected zone. And the repairing area won’t peel off easily because the dense cladding area is metallurgical bonded to the substrate. Laser melting deposition technique gains practical application in the repairing of parts because of these advantages.As the most commonly used lasers, CO2laser and YAG laser are widely applied in medical, cutting, welding, heat treatment, solid forming, surface cladding and other fields. In this study, repairing layers on substrate are prepared by CO2and YAG laser melting deposition respectively according to the require of repairing to study the effect of parameters on the geometry of deposition layers, and the effect of process parameters and heat treatment on the microstructure and mechanical properties. The main conclusions are as follows:(1) The cross-section geometry of single bead deposition layer in CO2laser melting deposition process has been studied, and it is found that less power and larger scanning speed can reduce the heat-affected zone under the assurance of the melting geometry, and the carrier gas flow rate should be taken as5L/min.(2) The cross-section geometry of several beads deposition layers in YAG laser melting deposition process has also been studied, and it is found that the pulse width has almost no influence on the morphology of the repairing zone, and the overlap should be taken as0.8mm; Two preferred process parameters are gained according to the favorable surface shape:current240A, powder feed rate1.36g/min, overlap0.8mm, pulse width2.5-3.5ms; current280A, powder feed rate2.26g/min, overlap0.8mm, pulse width2.5-3.5ms.(3) The repairing zone of samples by CO2and YAG laser melting deposition is composed of columnar dendrites, which is dense with no defect and microscopic cracks, and the interface is metallurgically bonded. The heat-affected zone in the CO2laser melting deposition repairing experiment is deeper with recrystallization. And the repairing zone of YAG laser melting deposition has finer microstructure and lighter heat-affected zone with grain boundary remelting.(4) After heat treatment, the elongation of samples by CO2laser melting deposition repairing reaches forging state level, and the STA sample has the highest tensile strength, which is1078MPa reaching84.5%of forging state. The weak point is the repairing zone; Among all the YAG laser melting deposition repairing samples, DA sample has the highest tensile strength, which is1223MPa reaching95.8%of forging state level; The yield strength exceeds the forging state level; The HSTA sample has the highest elongation reaching the cast level, and the weak point is the heat-affected zone.