The Research Of The Temperature Field Evolution In The Process Of Laser Metal Deposition

The vigorous development of aerospace undertaking the requirements of aircraft engine are more thrust and efficiency. Almost all the commercial and military advanced engine obtained single crystal turbine and guide blade by the method of directional solidification. The blade may be damaged in machining and service process, which may cause blade discard as useless, so the technology of damaged blade repair become the problem that need to be addressed. Epitaxial laser metal forming(E-LMF) which combine the technology of laser engineered net shaping(LENS) and directional solidification can obtain directional solidification epitaxial from the substrate. Repairing the damaged turbine by this technology can restore the blade geometrical shape and dimensional accuracy, but also keep the good performance.Temperature field, the evolution of which not only response the shape of molten pool, temperature changing and liquid flow intuitively but also have great influence on the formation of microstructure and the residual stress inside the parts, is an important parameter. To understand the thermal behavior in the molten pool in laser forming process, the three dimensional transient model is used to study the evolution of temperature field in the process of making a vertical wall with technology of the coaxial laser cladding forming(LMD: laser metal deposition or LENS: laser engineered net shaping), and the processed materials are nickel-base superalloy Rene80. Firstly, the interaction between laser and the powder during the powder falling process is simulated, and its possible effect on the temperature field of molten pool is analyzed. After that, the evolution of temperature field during the vertical wall manufacturing process is studied. By numerical simulation the change of phase(solid/liquid, and mushy zone) and the liquid flowing are considered and the parameters are based on optimized vertical wall manufacturing experiments.It is found that short of interaction happen between laser and powder particles before the powder down to the substrate surface from the end of the nozzle, the highest temperature of powder particles rise to about 1200 K which is below 1593.15 K, which is the melting point of Rene80. Therefore, the temperature of powders are well short of the melting point and can not be melted. According to the results, it can be estimated that the absorption of laser by the powders is approximately 5%. However, due to the small quality of the powders, the energy from the powders is too small to the absorption energy by substrate, and is neglected in the research of the temperature field.Considering of the change of solid-liquid phase, the powder injection and fluid flow comprehensively, the model of temperature field in the process of forming vertical wall by laser cladding is established. During the manufacture of the first four layers, the temperature of the molten pool and internal parts is increased significantly with the increase of forming layer, and temperature distribution in molten pool becomes irregular. With the increase of forming layers to the fifth layer, there are not larger changes on the temperature in molten pool and to stabilize. Besides the irregular temperature distribution in molten pool, the shape of molten pool changes a lot, that the width and depth of molten pool has increased, and this makes the vertical wall shape- "narrow below and width above", the instability of the forming process in early time is revealed. Moreover, the results of the simulation and measured are nearly same.