Fundamental Research On Repairing Of TC11Titanium Alloy Blades By Laser Cladding Deposition

Compared with other conventional repair technology, laser cladding deposition presents advantages of high precision, small heat input and influence to substrate, superior performance of deposited materials, high bonding strength and so on. This process has become a key method of research and development in remanufacturing field recently. The recovery of shape and performance for damaged blade is a necessary condition in high quality repair. Based on the background of repairing a blisk in TC11titanium alloy, fundamental researches including controls of cladding size and microstructure in repaired part are studied in this paper.In order to improve the aerodynamic efficiency of compressor blisk, the blade is generally designed in an irregular twist surface contour. To accurately restore the shape of such broken blade, track of laser scanning should be designed strictly according to the height of the area to be repaired. Therefore, control and prediction on the size of cladding layer has become an urgent basic problem for blade repairing. The cross-sectional area of single laser cladding layer by lateral powder feeding is set as the target control parameter in this study. The main work and conclusions in this regard are as follows:(1) By defining the powder transport ratio as the mass ratio of powder particles fed into the molten pool to all powders transported, based on the conservation of mass, powder transport models for flow field with cylindrical and Gaussian distribution, and corresponding analytical formula of powder transport ratio are proposed. Then, the target parameter for different process parameters (laser power, scanning speed, powder feed rate) are calculated. Although modified theoretical predictions are still larger than experimental results, above two models could reflect the effects of process parameters on the cross-sectional area and the Gaussian model is more reasonable. (2) Based on the Gaussian powder flow field, powder transport ratios according to arbitrary adjustments of injection condition parameters (de focusing distance, powder-feeding angle, pool width) could be calculated by geometrical relationship of plane vectors.Microstructure of material is one of important factors affecting parts performance. Micro structure of TC11titanium alloy blades after repaired by laser cladding deposition shows widmanstatten structure in profiling zone, mixed structure with gradual transition in heat affected zone (HAZ), and equiaxed structure in initially forged substrate. To improve service lives of repaired blades, controls on the first two regional microstructures in thin-walled parts are investigated from experimental and theoretical aspects. Size of initial β grain, thickness of intragranular single a phase (for materials as deposited), and distribution of equiaxed a phase (for materials with mixed structure in HAZ) are set as target control parameters. In this aspect, main conclusions are summarized as follows:(1) In experimental studies, size of initial β grain could be reduced by decreasing laser power or increasing scanning speed, and intragranular lamellar a phase could be refined with the rise of laser power, scanning speed, and interlayer stay time. In theoretical research, characteristic parameters of temperature field for different process parameters are compared, such as peak temperature, duration time above P phase transition, temperature gradient at the solid-liquid interface, cooling rate below β phase transition. For effects on the target parameter, predictions and experimental results could be in good agreement. According to above theoretical analysis, microstructure control of deposited materials in TCI1titanium alloy can be realized by adjustment of process parameters.(2) Experimental results indicate that transition of equiaxed to lamellar phase and thermal influence on forged substrate are weakened with the reduction of laser power, increase of scanning speed and interlayer stay time. In theoretical research, based on the modified JMA equation, diffusion transformation model for the complicate thermal history during laser cladding deposition is established. Distributions of equiaxed a phase in HAZ corresponding to different process parameters are calculated. A positive correlation between transition of equiaxed phase and duration time, peak temperature in heating stage can be deduced. After comparing the temperature field parameters in HAZ, influences of process parameters on the target parameter are obtained. The theoretical prediction is in accordance with experimental results, so the model could be used as basis for microstructure control in H AZ of forged thin-walled parts.Combined with above fundamental researchs, a damaged blisk in TC11titanium alloy is repaired in high-quality by using an optimized technology program.