摘要
玻璃等硬脆材料上的微结构应用广泛,然而,利用超快激光在硬脆材料上实现高质量微结构加工仍然面临着质量和效率不能兼顾的问题。本文研究了飞秒激光(900 fs)在石英玻璃上加工微孔阵列时的裂纹产生及扩展机制,并通过激光功率的梯度动态调控,实现了对裂纹产生及扩展的有效控制。研究结果表明,加工过程中裂纹的形成和扩展可分为4个阶段:第一阶段,孔底熔融物凝固引起微裂纹产生;第二阶段,孔底裂纹通过孔壁向外扩展;第三阶段,向外扩展的裂纹在孔周形成环形裂纹;第四阶段,孔阵列中的多个环形裂纹连接形成裂纹网络。虽然降低激光功率可以抑制裂纹的形成,但是加工效率也会随之降低。采用“先低功率后高功率”的梯度功率加工策略可以在保证加工效率的同时抑制裂纹的扩展。微孔阵列加工过程中温度的原位测量结果表明:激光吸收率的提高可使最大温度差下降45%;与恒定功率加工相比,梯度功率加工时工件的最大温度差下降了31%,峰值功率最大温度差下降了44%。梯度功率加工抑制裂纹的机理是:初始时的低功率加工增大材料的表面粗糙度,提高材料对激光的吸收率,减小材料内部的热应力,并使孔深发展至一定程度,进而使得后续切换到高功率加工时孔底裂纹无法通过孔壁向外扩展。本文所提出的梯度功率加工策略可被广泛应用于硬脆材料上微结构的激光加工。
Objective The rapid advancement of ultrafast laser technology has opened new avenues for precision manufacturing,particularly in fabricating microstructures on hard and brittle materials,such as glass.However,achieving highquality microstructure fabrication on such materials remains challenging owing to their inherent properties,including high hardness and brittleness.Therefore,this study aims to investigate and optimize the methods for ultrafast laser microstructuring of hard and brittle materials,focusing on the influence of laser power on crack formation,propagation,and processing efficiency.We propose a gradient power processing strategy to enhance machining quality while maintaining processing efficiency.The importance of this study lies in its potential to mitigate issues related to crack generation and propagation during ultrafast laser processing of hard and brittle materials,thereby enhancing quality and efficiency.Furthermore,the findings can expand the application of microstructures on hard and brittle materials in advanced technological fields.Methods A femtosecond laser with a wavelength of 1030 nm,pulse duration of 900 fs,and Gaussian beam profile was employed herein.Microholes arrays were processed in quartz glass(0.15 mm thick)at a constant pulse frequency of 10 kHz and an average scanning speed of 0.1 m/s.The experimental procedure involved initially investigating the generation and propagation mechanisms of cracks during machining.Subsequently,the processing effects of varying laser power on quartz glass were compared to analyze the relation between processing power,crack formation,and processing efficiency.Based on these analyses,a gradient power processing strategy was proposed.Insitu temperature measurements were taken during processing to validate the effectiveness of the proposed strategy in reducing the temperature gradient and minimizing thermal stress generation.Results and Discussions 1.During ultrafast laser processing of quartz glass,crack propagation can be divided into four stages:a)solidification of the melt at the bottom of the hole creates microcracks,b)these cracks propagate outward through the hole wall,c)the outwardpropagating cracks form annular cracks around the hole,and d)the connection of multiple annular cracks within the microhole array leads to processing failure(Fig.2).2.Comparative analysis of the impact of different laser powers on machining effects reveals that lowpower processing effectively reduces recast layer formation and thermal stress generation but decreases processing efficiency(Fig.3).Therefore,a gradient power processing strategy is proposed to optimize processing quality while maintaining efficiency.The effects of different gradient power strategies on machining surface quality and efficiency are explored.The results show that a lower and gradual power gradient yields better processing outcomes.This is attributed to the smooth transition of power from low to high,leading to a gradual temperature increase,thereby avoiding notable temperature gradients.This effectively suppresses crack formation and propagation,thus achieving an optimized balance between efficiency and quality(Fig.4).3.Insitu temperature measurements are used to compare temperature variations during microhole array processing of quartz glass under constant and gradient power conditions.The results indicate that gradient power processing reduces the maximum temperature in the initial processing stage and lowers the temperature at each power level,allowing the processing temperature to stabilize quickly(Fig.5).4.The crack suppression mechanism of gradient power processing includes the following:in the initial stage,lowpower processing increases surface roughness,enhancing laser absorption and promoting heat dissipation through phase transition in subsequent stages,thereby reducing thermal stress.With increasing power,the hole depth has already developed to a certain extent,resulting in a reduced stress concentration at the hole wall.This reduces crack propagation along the hole wall and blocks the crack path(Fig.6).Conclusions This study investigates the mechanisms of crack initiation and propagation during microhole array fabrication on quartz glass using 900 fs laser pulse and demonstrates the effective suppression of crack formation and expansion through a gradient power dynamic regulation strategy.The findings reveal that crack formation and propagation occur in four stages and that adopting a“lowpowertohighpower”gradient power processing strategy can suppress crack propagation without compromising processing efficiency.Insitu temperature measurements indicate that gradient power processing considerably reduces the maximum temperature difference,enhancing fabrication process stability.Furthermore,the crack suppression mechanism of gradient power processing involves the initial lowpower phase that increases surface roughness to enhance laser absorption,reduce internal thermal stress,and allow the hole depth to reach a critical level.Transitioning to highpower processing subsequently prevents crack propagation from the bottom of the hole to the sidewalls.The proposed gradient power processing strategy is broadly applicable to laser micromachining of hard and brittle materials and holds considerable potential for various applications.
作者
聂烨辉
张博武
张朋辉
黄志楷
赵宽
阿占文
Nie Yehui;Zhang Bowu;Zhang Penghui;Huang Zhikai;Zhao Kuan;A Zhanwen(School of Mechanical Engineering,Qinghai University,Xining 810016,Qinghai,China;Department of Mechanical Engineering,Tsinghua University,Beijing 100084,China)
出处
《中国激光》
北大核心
2025年第8期286-293,共8页
Chinese Journal of Lasers
基金
国家自然科学基金(52305479)。
关键词
超快激光加工
梯度功率
硬脆材料
裂纹
ultrafast laser processing
gradient power
hard and brittle materials
cracks
