Mechanism And Process Study Of Laser Microstructure Processing Of SiC/SiC Composites

Turbines are important components of aero-engines that work in harsh and complex environments for long periods of time and are subject to challenges such as high temperatures,corrosion and wear.Conventional homogeneous materials can hardly meet the new service requirements,and silicon carbide fiber reinforced silicon carbide(SiC/SiC)components work together to provide better performance than homogeneous materials,and are widely used in harsh environments.Nanosecond laser processing has the characteristics of high processing efficiency,wide processing range and high processing accuracy,which can better meet the processing requirements of this paper.However,thermal damage phenomena such as oxidation build-up,heat affected zone(HAZ),delamination and microcracking can occur when processing SiC/SiC composites with nanosecond laser,affecting the mechanical properties of the target material.In this paper,nanosecond laser etching process research,laser-target material interaction mechanism,thermal stress coupling analysis and experimental research work on different solution-assisted laser processing are carried out for high quality etching of SiC/SiC composites.The specific research contents are as follows:To address the problem of thermogenic damage during nanosecond laser processing,nanosecond laser etching experiments were carried out to investigate the influence of laser parameters on the shape and size of SiC/SiC composites.Firstly,the ablation threshold of SiC/SiC composites was determined,which is a prerequisite for high-quality processing without oversaturation.Based on the correlation coefficients of the nanosecond laser parameters with the width and depth of the microstructure,the laser parameters with the highest correlation were selected for the experiments.The experimental results show that the width and depth of the microstructure show a tendency to increase first and then to saturate with the increase of energy density.The oxidation phenomenon in the process of nanosecond laser interaction with SiC/SiC composites becomes more significant with the increase of processing number,processing power and repetition frequency,and the change trend slows down with the increase of scanning speed.The thermal accumulation effect that occurs during laser etching experiments tends to cause stress concentration on the surface and inside of the material,which further leads to delamination,HAZ,microcracking and other problems.Since it is impossible to accurately grasp the characteristic change pattern inside the material by relying on experiments and microscopic equipment photography alone,this paper establishes a three-dimensional temperature field model with the help of simulation software to simulate the action process of pulsed laser with SiC/SiC composites and observe the corresponding temperature field and stress-strain change pattern of the material under the influence of different parameters of the laser.The simulation results show that when the nanosecond laser interacts with SiC/SiC composites,a large amount of thermal energy acts on the surface of the matrix,and the three-dimensional complex model generates thermal stresses with the change of energy density,and the higher the energy density the higher the temperature,and the corresponding stress-strain is larger.Due to the special characteristics of the structure of SiC/SiC composites,the SiC component contained in the material is prone to react with oxygen in the air under high temperature environment.In this paper,the auxiliary processing environment is changed in an attempt to avoid the phenomenon of thermogenic damage during the processing of SiC/SiC composites.By forming a closed-loop feedback research scheme through experiment-simulation-experiment,it was found that the machining contour of the microstructure obtained by machining in the waterassisted environment is clear and complete,and the taper of the groove wall of the microgroove structure is small,and the microhole structure is a U-shaped hole,which is the ideal hole type.At the same time,oxidation,delamination,fiber pullout and HAZ were significantly improved,and heat damage free machining of SiC/SiC composites was achieved.