Directed Laser Deposition Of Al₂O₃-ZrO₂ Composite Ceramics

Al₂O₃-ZrO₂ composite ceramic material combines the high strength of Al₂O₃ ceramic and excellent toughness of ZrO₂ ceramic,and has excellent comprehensive mechanical properties.As a new generation of alternative high temperature structural materials,Al₂O₃-ZrO₂ composite ceramics have an important application prospect in the hot end parts of high performance aeroengine and heavy gas turbine.Directed laser deposition?DLD?is a newly developed technology for manufacturing three-dimensional near net-shaping components of melt-grown ceramics,which has advantages of fast response time,flexible material composition design,simple process and low energy consumption.Different from the traditional method of powder sintering,microstructure of Al₂O₃-ZrO₂ composite ceramics prepared by DLD has typical solidification characteristics,and the obtained microstructure has the interface shared by oxygen atoms,which can still maintain excellent strength and good stability at high temperature.Aiming at Al₂O₃-ZrO₂ composite ceramic material system,this paper uses DLD technology to rapidly prepare composite ceramics with different composition ratios,and studies the influence of material ratios,process parameters and high temperature heat treatment on the microstructure and properties of composite ceramics.The main research contents and conclusions are as follows:?1?Al₂O₃-ZrO₂ composite ceramics with different composition ratios of hypoeutectic,eutectic and hypereutectic were prepared by using the same process parameters.The influence rule and mechanism of composition ratios on the microstructure and mechanical properties were studied.On this basis,the optimal composition ratio with comprehensive mechanical properties was selected.Results show that the hypoeutectic ceramic has the highest microhardness?AZ30 sample?,the eutectic ceramic has the highest flexural strength?237MPa?,and fracture toughness reaches the maximum at hypereutectic ratio(AZ60 sample fracture toughness is 5.91 MPa·m^1/2).AZ30 sample has the best comprehensive mechanical properties.Its microhardness is 1972 HV.Flexural strength reaches 230 MPa,which is close to the eutectic ratio,and fracture toughness is 4.62 MPa·m^1/2.?2?After determining the optimal composition ratio,the single-factor experimental method was used to study the effects of scanning speed,laser power and z-axis increment on the microstructure and performance of AZ30 sample prepared by direct laser deposition.Results show that as the scanning speed increases,crack density of the sample gradually decreases,showing an inverse proportional curve trend.Flexural strength increases first and then decreases with the increase of scanning speed.With the increase of laser power,crack density of the ceramics decreased,the primary grain size of?-Al₂O₃ increased,and flexural strength firstly increased and then decreased.The influence of z-axis increment on crack density is not obvious.However,flexural strength of sample increases first and then decreases.According to results of single-factor experiment,the optimal parameters are as follows:laser power P=275 W,scanning speed v=400 mm/min,z-axis increment?z=0.5 mm.Based on the optimization of process parameters,the crack free Al₂O₃-ZrO₂ complex structure was successfully prepared by using these parameters,and the cylinder sample has excellent performance.?3?Aiming at the requirements of high-temperature materials for the hot end parts of aeroengine and gas turbine,AZ30 cylinder samples were prepared by using the optimized process parameters,and high-temperature performance and high-temperature stability of the materials were studied.Results show that after heat treatment at 1600?for 10 hours,microstructure of the prepared samples shows a dot like or strip like ZrO₂ dispersed in Al₂O₃matrix.The quality of the sample remains unchanged,the length increases slightly,and the surface phase after heat treatment is the same as that before heat treatment.Residual strength of the sample is 180 MPa and the residual hardness is 1850 HV.After high temperature heat treatment,the performance changes little compared with that at room temperature,which shows that Al₂O₃-ZrO₂ composite ceramics have good high temperature stability,and it is worth further application in the hot end components of aeroengine and gas turbine.In this paper,directed laser deposition technology was used to prepare multi-composition ratios Al₂O₃-ZrO₂ melt-grown composite.The range of composition ratio and process parameters with excellent comprehensive mechanical properties were obtained,which provides theoretical guidance and technical reference for the selection of Al₂O₃-ZrO₂composite system and process conditions.