Study On Digital Holography Observation Method Of High Speed Moving Copper Matrix Composite Particles

The study of the atomisation mechanism of copper matrix composite melt containing reinforcing particles is important for improving the preparation process of in-situ synthesis,so non-contact observation means digital holographic observation method is used to study the atomisation process of high temperature,high speed,opaque copper matrix composite melt droplets.The paper designs a coaxial digital holographic observation system for the atomisation process of molten droplets of copper matrix composites and conducts experiments to observe the atomisation process of high speed moving copper matrix composite particles.Main research elements of the thesis:A coaxial digital holographic optical observation system was designed,combining a telecentric lens with a coaxial digital holographic optical path to achieve a measurement distance of 750mm;stray light was suppressed by a 532nm ultra-narrowband filter and polarised light;a sampling method that two high-speed cameras with simultaneous and asynchronous triggering was also proposed to improve the sampling frame rate.The resolution of the coaxial digital holographic observation system was calibrated by the USAF1951 standard resolution plate,and its resolution reached 22.1μm;the recognition accuracy and magnification were calibrated by the 100μm standard dot diffraction plate,and the recognition accuracy was 101.3μm±10.8μm,and the magnification was 1.The relationship between the reconstructed hologram distance and the actual object distance obtained from this measurement system is 1:1.The z-axis focusing algorithm uses the local brightness gradient variance method,and the z-axis positioning error of this method is 2.6mm,which is consistent with the depth of field of the telecentric lens.The accuracy of the verification measurement system of the coaxial digital holographic observation system and the accuracy of the speed matching algorithm are verified by simulated atomization experiments.The atomization field of 50μm standard particles was measured,and the average particle sizes at the sampling heights of 8mm,15mm and 24mm were 49.8μm,48.7μm and 50.0μm respectively,which was consistent with the theoretical values.The nearest-neighbor matching method combined with particle feature information is used to match particles,and then the velocity ranges of 50μm standard particle atomization field at different sampling heights are 1.1m/s～3.7m/s,1.4m/s～4.9m/s and 1.7m/s～5.2m/s,respectively.The results show that the maximum and minimum velocities of particles increase with the increase of sampling height,which is consistent with the theory.The atomization field of copper powder particles with main particle sizes ranging from 38μm to 53μm,75μm to 90μm and 90μm to 106μm was also simulated and measured.The results show that 66%of the particles are in the nominal range at different heights,which is consistent with the off-line measurement results of copper powder particles.The atomisation field of high-temperature and high-speed copper matrix composite particles was observed by a coaxial digital holographic measurement system with a sampling height of 112mm,and two consecutive hologram frames were processed to consider the particles with good focusing effect as correctly identified particles,obtaining a correct particle identification rate of 85%for the atomisation field;the three-dimensional velocity and particle size spectrum distribution of the atomisation field was also processed,with the three-dimensional velocity range of 3.73m/s～40.56m/s.The measured results are consistent with the simulation results of the atomization field of high temperature and high speed copper matrix composite particles under the same conditions.The experimental results show that the coaxial digital holographic measurement system is capable of measuring the atomisation field of high speed copper matrix composite particles.The atomisation process of the copper matrix melt can be monitored by the coaxial digital holographic measurement system,and the equivalent particle size,3D position,morphological characteristics and 3D velocity of the atomised melt can be obtained,which can further investigate the atomisation mechanism of the copper matrix melt.Ultimately,the cooling time of the composite melt and the degree of particle segregation of the reinforcing particles can be reduced by means of aerosolised powder production.