Effects Of Outfield Assistant On The Microstructure And Mechanical Properties Of Net Shaping Al₂O₃-YAG Eutectic Ceramics

Al₂O₃-YAG eutectic ceramic is considered to be the new generation of high temperature structural material in the field of aerospace engine due to their high strength,excellent thermal shock resistance and excellent high temperature creep resistance.As one kind of additive manufacturing technology,laser engineered net shaping?LENS?has the advantages of no need of fixtures and moulds,no limitation of batch size and low cost.This technology can process hard and brittle materials such as eutectic ceramics.As the preferred high temperature material,the microstructure of Al₂O₃-YAG is the key factor influencing its comprehensive performance and operational effects.Therefore,it is of great significance to research the microstructure of Al₂O₃-YAG eutectic ceramics.In this paper,Al₂O₃-YAG thin-walled samples were fabricated by laser engineered net shaping.The effects of outfield such as temperature field by means of water-cooled and ultrasonic field by means of ultrasonic vibration-substrate on the microstructure of Al₂O₃-YAG were studied.The main research contents are as follows:?1?The microstructure characteristics and formation mechanism of Al₂O₃-YAG microstructure were analyzed and researched from two perspectives:the first perspective is the internal factors such as physical properties and the solidification kinetics.The second perspective is the change of supercooling caused by solidification condition changing.It lays a theoretical foundation for the feasibility of forming Al₂O₃-YAG with outfield intervention.?2?Determination of reasonable process parameters for Al₂O₃-YAG preparation.By establishing a mathematical model of double-bead single-layer and single-bead multi-layer structure,the overlap ratio?and the Z-axis lift amount?Z were deduced.The reasonable values were determined by mathematical model combining experiments.Because scanning speed V is an important parameter especially for microstructure in LENS process,single-factor experiments of scanning speed V were designed,and a thin-walled sample with good macroscopic appearance is the final target to determine the optimum scanning speed.?3?The effects of water-cooled constant-temperature substrate on the microstructure and mechanical properties of Al₂O₃-YAG.The temperature of substrates was measured using an NI 9213 thermocouple.Combining the results of temperature acquisition,the phase composition and microstructure of Al₂O₃-YAG were analyzed by the X-ray diffraction?XRD?and scanning electron microscope?SEM?.The hardness,fracture toughness,and friction and wear properties of different samples formed on different substrates were tested and compared.The relationship between microstructure and mechanical properties and its mechanism was revealed.Finally the effects of temperature field intervention of water-cooled constant-temperature substrate on the Al₂O₃-YAG microstructure and mechanical properties were obtained.?4?Al₂O₃-YAG thin-wall experiments was designed and carried out by ultrasonic-assisted laser engineered net shaping?LENS?with different power densities?0W/cm²,0.65 W/cm²,1.30 W/cm²,1.95 W/cm²?.The phase composition,microstructure characteristics and mechanical properties of Al₂O₃-YAG thin-wall samples formed with different ultrasonic power densities were examined.The effects of ultrasonic assisted on microstructure and mechanical properties were analyzed.