High Temperature Heat Treatment Process Of Al₂O₃ Ceramics Prepared By Directed Laser Deposition

Al₂O₃ ceramic material has the characteristics of high melting point,low density,oxidation resistance and corrosion resistance.,and has broad application prospects in the manufacture of hot section components of aero-engines with large thrust-to-weight ratio.Directed laser deposition forming technology is a type of rapid additive manufacturing technology based on directed energy deposition with synchronous feeding,which can realize the rapid preparation of ceramic structural parts with near-net size,and has the advantages of simple process and short production cycle.However,due to the existence of solidification defects,Al₂O₃ ceramics by directed laser deposition have the problem of low flexural strength,which limits its further application and development in more fields.In response to this problem,high temperature heat treatment process is used to improve the flexural strength of Al₂O₃ceramic structural parts prepared by directed laser deposition.The microstructure,macro morphology and mechanical properties of samples before and after high temperature heat treatment are examined to analyze the influence mechanism of the high temperature heat treatment process on the Al₂O₃ ceramics and the regularity between the mechanical properties of the Al₂O₃ ceramics and the process parameters of high temperature heat treatment.The main research contents and conclusions are as follows:（1）There are thin-film two-dimensional structure and defects with narrow and long ravine-shaped pore between the grains of Al₂O₃ ceramic samples prepared by directed laser deposition.The surface of crystal grains is step-shaped.The results show that the hardness of Al₂O₃ ceramics is 1878 HV,the fracture toughness is 2.85 MPa·m^1/2,the flexural strength is270 MPa,and the phase composition isα-Al₂O₃ phase.（2）After the single factor experiments of heat treatment time and heat treatment temperature,the microstructure of Al₂O₃ ceramic samples is detected.It found that with the increase of the heat treatment temperature,the film-like two-dimensional structure gradually disappeared,the steps on the surface of the crystal grains also disappeared,and the ravine-like voids gradually healed into linear pores.The impurities in the grain boundary of the sample surface gradually melt and evaporate with the increase of the heat treatment temperature,and the grain boundary gradually becomes a continuous and complete line from the intermittent pores.As the heat treatment time increases,the ravine-shaped voids become linear,and their size gradually decreases;the depth of the grain boundary on the surface of the sample gradually increases.After the high temperature heat treatment,the phase composition of the Al₂O₃ceramic sample is stillα-Al₂O₃ phase.（3）After the single factor experiments of heat treatment time and heat treatment temperature,the macroscopic morphology and mechanical properties of Al₂O₃ ceramic samples are tested.It found that the quality,size and surface roughness of Al₂O₃ ceramic samples did not change significantly after high temperature heat treatment.In terms of mechanical properties,the hardness and fracture toughness of Al₂O₃ ceramics did not changed significantly,but the flexural strength improved significantly.The flexural strength of Al₂O₃ceramics increases with the increase of heat treatment temperature.After high temperature heat treatment at 1600℃,the flexural strength reaches 494 MPa,an increase of 82.96%.The flexural strength of Al₂O₃ ceramics increases first and then decreases with the increase of heat treatment time.After 15 hours of high temperature heat treatment,the flexural strength reached548 MPa,an increase of 102.96%.