Cf/C-SiC烧蚀行为及激光复合超声磨削可行性研究

Cf/C-SiC Ablative Behavior and Feasibility of Laser Assisted Ultrasonic Grinding

目的揭示激光与Cf/C-SiC陶瓷基复合材料相互作用机理,分析激光能量密度对材料形性演变的影响规律。提出Cf/C-SiC陶瓷基复合材料激光复合超声磨削加工方案,探究硬脆材料多能场复合加工的可行性。方法使用不同能量密度的激光束扫描Cf/C-SiC陶瓷基复合材料表面,以明确材料烧蚀行为。在材料表面预制不同间距的平行纹理沟槽,进而对比传统磨削、超声辅助磨削和激光复合超声磨削的加工效果,同时研究不同扫描间距的预制沟槽对磨削效果的影响规律。结果陶瓷基复合材料(CMC)在激光作用下可呈现2种截然不同的状态,改性状态时材料以氧化等热化学变化为主,样件内出现热影响区和裂纹区。烧蚀状态时材料以热物理和热机械变化为主,样件内出现烧蚀凹坑、重铸层、热影响区和裂纹区。纤维束中界面经整体脱黏后,裂纹向下延伸并发生偏转。基体中的裂纹多起源于纤维界面处,并在扩展过程中发生偏转、分叉。激光烧蚀作用可改变材料的可加工性,有利于后续超声磨削加工。激光复合超声磨削的两方向磨削力相较传统磨削分别减小了51.4%和56.5%,同时表面粗糙度Sa可降低至4.228μm。结论激光复合超声磨削可有效降低磨削力和加工表面粗糙度,从而提高加工质量,该方法在实现硬脆材料高质量低成本加工方面具有较大的潜能。

The work aims to reveal the interaction mechanism between laser and Cf/C-SiC ceramic matrix composites,and analyze the effect of laser energy density on the shape evolution of the materials.A scheme of laser assisted ultrasonic grinding for Cf/C-SiC machining is proposed,and the feasibility of multi-energy field machining of hard and brittle materials is explored.In this work,a laser beam with different energy density was used to scan the surface of Cf/C-SiC ceramic matrix composite to investigate the effect of laser on the ablation pits,heat affected zone and crack zone.Then,parallel texture grooves with different spacing were preset on the surface of the material,and the machining effects of traditional grinding,ultrasonic assisted grinding and laser assisted ultrasonic grinding were compared.Meanwhile,the effect of laser prefabricated grooves with different scanning spacing on ultrasonic grinding was studied.The surface temperature of the sample was measured by infrared thermal imager.The macro and micro morphology and element composition of the sample section were analyzed by ultra-depth of field microscope,scanning electron microscope and energy spectrometer.The grinding force and machining quality were measured by dynamometer and 3D surface optical profilometer.Under the action of laser,CMC showed two different states.In the modified state,the material was dominated by oxidation and other thermochemical changes.The materials underwent oxidation of SiC phase,C fiber and pyrolytic carbon,liquefaction of Si phase,formation of gaseous SiO,and evaporation of SiO2 after liquefaction,and the cross section had heat affected zone and crack zone,in which the continuous phase in the heat affected zone disappeared.In the ablative state,in addition to the reaction in the modified state,sublimation of SiC phase,C fiber and pyrolytic carbon interface,SiC decomposition and Si phase gasification also occurred.At this time,the material was mainly corroded by thermophysical and thermomechanical reaction,and there were ablative pits,recast layers,heat affected zones and crack zones in the sample section.The formation of pits and cracks was conducive to subsequent machining.When the interface of the fiber bundle underwent the whole debonding,the cracks extended downward and deflected.The cracks in the matrix mostly originated at the fiber interface,and were deflected,bifurcated and bridged during the process of expansion,and there were both transgranular and intergranular fractures at the same time.When the laser scanning spacing was 2,1 and 0.5 mm,the average depth of the laser prefabricated groove was 547,568 and 677μm,respectively.The average grinding force in X direction and Y direction was 0.248 N and 0.403 N,and the surface roughness was about 4.228μm.Compared with traditional grinding,the average grinding force in both directions was reduced by 51.4%and 56.5%,and the surface roughness could be reduced.The results show that laser assisted ultrasonic grinding can effectively reduce the grinding force,and can reduce the roughness of the machined surface to a certain extent,so as to improve the machining quality.For hard and brittle materials,laser combined ultrasonic grinding has great potential in increasing grinding parameters,improving efficiency and realizing high quality and low-cost machining.