雷达功率组件的金刚石微通道热沉激光加工工艺

为研究雷达功率组件金刚石微通道热沉的加工难题,开展了飞秒激光加工多晶金刚石微流道的工艺研究,仿真模拟了飞秒激光作用于金刚石表面的温度场分布,以及诱导去除过程,理论与实验研究了金刚石的烧蚀阈值,系统研究了激光能量、扫描速度、扫描次数、焦点位置等参量及其优化工艺参数对金刚石微槽尺寸的影响规律。结果表明:当飞秒激光功率大于0.3 W时,激光作用于金刚石的最高温度超过材料去除的气化温度,温度最高位置处于光斑中心,功率不会改变温度场的分布情形;飞秒激光加工金刚石的烧蚀阈值为1.80 J/cm2,金刚石微槽深度与激光功率、扫描次数正相关,与扫描速度负相关,与正负离焦量基本成对称分布关系,而金刚石微槽表面宽度则变化不明显;在激光功率为5 W,扫描速度为100 mm/s,扫描次数为30,离焦量为-0.5 mm的优化参数下,加工出的金刚石微槽结构形状规则,截面侧壁锥度控制在3°以内,表面无残渣、裂纹、崩边等缺陷,且内部也无裂纹等缺陷,加工一致性较高,实现了微通道的 “冷”加工,可满足雷达功率组件金刚石热沉对微通道的高质量加工要求。     

飞秒激光单路径刻蚀硅微槽深度研究

对飞秒激光在单晶硅片上单路径加工微槽进行了研究。在固定激光频率和进给深度的条件下,对不同激光功率、扫描次数以及扫描速度对微槽深度的影响展开对比试验,通过COMSOL软件对激光加工硅片温度分布及微槽内激光反射进行数值分析。研究发现,微槽截面形状与激光能量分布特点相关,高频飞秒激光的热累积效应易氧化微槽底部,限制了激光对其的进一步加工;等离子体的屏蔽效应则使得微槽深度随着扫描速度先增大后减小。     

飞秒激光烧蚀不锈钢的实验研究

进行了飞秒激光烧蚀不锈钢(SUS420)的工艺实验研究。采用波长为780nm,脉宽为164fs,频率为1k Hz的飞秒激光照射不锈钢。对比分析了长短脉冲激光烧蚀不锈钢的作用过程,计算了单脉冲飞秒激光烧蚀不锈钢的烧蚀阈值和烧蚀阈值随脉冲数量改变的累计系数,研究了不同激光参数烧蚀不锈钢的工艺规律。结果表明:飞秒激光烧蚀金属材料的过程中对加工区域周围具有较小的热影响;单脉冲飞秒激光烧蚀不锈钢的烧蚀阈值为0.25J/cm2,烧蚀阈值随脉冲数量改变的累计系数为0.68;飞秒激光脉冲能量对烧蚀孔孔径的增加比较明显,脉冲数量对烧蚀孔孔深的增加比较显著。     

飞秒激光无碎屑加工不锈钢血管支架

经皮冠状动脉植入血管支架是解决心血管堵塞的主要手段.管状心血管支架主要采用纳秒激光加工,但存在热效应大、熔渣碎屑残留、以及复杂后处理等问题.因此,利用高重复频率红外飞秒激光对不锈钢血管支架进行加工,研究飞秒激光烧蚀作用机理,分析材料的去除过程,研究激光能量密度、平台进给速度、激光脉冲重复频率等加工工艺参数对加工表面的影响规律,研究结果表明:高重复频率低能量密度下飞秒激光加工具有良好的表面质量和加工效率;在激光能量密度、脉冲重复频率、进给速度、气体压力分别为1.99J/cm2、100 kHz、24.6 mm/min、0.1 MPa时,实现了热影响区小、无碎屑残留且没有重凝层的高质量血管支架切割,并且在其表面加工了直径为30 μm的储药孔.     

选区激光熔化医用316L多孔结构的多目标工艺优化

为解决选区激光熔化技术成形医用多孔结构成形质量较差的问题,研究了工艺参数对316L成形样件致密度、孔隙率差值和表面粗糙度的影响,结合灰色关联分析方法建立了多元非线性预测模型。结果表明,预测模型的拟合度可达96.85%,最优工艺参数分别为激光功率250 W、扫描速度800 mm/s、扫描间距0.08 mm。优化后的灰色关联度达0.9195,得到样件的致密度为99.25%,孔隙率差值为0.60%,表面粗糙度均值为4.39 μm。致密度与激光功率正相关,随着致密度的增大,扫描速度和扫描间距呈现先增大再减小的趋势,孔隙率差值和表面粗糙度与激光功率、扫描速度、扫描间距均保持先减小再增大的趋势。结合激光体能量密度概念,揭示了工艺参数影响成形质量的原因,体能量密度为109.65～145.83 J/mm3时粉末的熔化状态最好。     

等离子体吸收对飞秒激光烧蚀绝缘材料的影响

以自由电子运动的速率方程模型为基础,研究了飞秒脉冲激光对绝缘材料的烧蚀机理,考虑了等离子体对激光能量的吸收效应,建立了激光强度与电子数密度及等离子体吸收系数三者相互耦合的数学模型,计算出飞秒激光烧蚀绝缘材料时的烧蚀阈值,分析了考虑等离子体吸收效应对烧蚀阈值的影响,通过与不考虑等离子体吸收所得结果相比较说明该效应是影响烧蚀阈值的一个重要因素.     

飞秒激光正交线扫描诱导表面微纳结构

通过控制激光偏振与扫描方向,利用飞秒脉冲激光正交线扫描的微加工方式,在硅和不锈钢表面诱导出了规则分布的复合表面微纳结构并分析了激光能量密度对微纳表面结构形成的影响。实验显示:当激光的能量密度接近材料烧蚀阈值时,在硅表面诱导出了周期条纹嵌套纳米孔的双层复合二维结构,在不锈钢表面则诱导出了依赖于激光偏振方向的纳米点阵列分布,分析认为纳米点阵列是由周期条纹结构边缘发生断裂而生成的。另外,当激光的能量密度大于材料烧蚀阈值时,在硅和不锈钢表面会烧蚀出规则分布的微米级孔洞结构。实验结果表明:第一次扫描诱导出的表面微纳结构增加了对入射激光的吸收,促进入射激光与表面等离子体波的耦合,加强了后扫描的烧蚀效果,使得后扫描诱导出的微纳结构占主导。文中提出的正交线扫描的加工方式为微纳表面结构的制备提供了新的思路。     

水射流引导激光制造Inconel 718合金沟槽结构的研究

为了探究水射流引导激光(WJGL)技术在Inconel 718合金上制造沟槽结构的规律特征,在自行研发的水导激光设备上设计并进行了多组单因素实验,分析了水射流速度和激光能量密度对沟槽结构的深度、宽度以及毛刺尺寸的影响规律。实验结果表明,激光能量密度对沟槽结构尺寸的影响程度要高于水射流速度,在喷嘴孔径固定不变的条件下,激光能量密度和水射流速度对沟槽结构宽度的影响很小。采用孔径为0.5 mm的喷嘴,当水射流速度固定为60 m/s,激光功率密度为40 J/cm²时,获得最大沟槽平均深度为523μm;当激光能量密度为10 J/cm²时,获得最窄沟槽平均宽度为403μm;当激光能量密度为40 J/cm²时,获得最小毛刺平均尺寸为54μm。根据理论分析得出,水导激光技术去除Inconel 718合金的机制是通过激光烧蚀并熔化材料,水射流将熔融物冲刷去除。     

纳秒激光加工和热处理对纯铝表面润湿性的影响

采用纳秒激光加工技术在纯铝板表面制备微纳米结构,之后进行150℃×2h的热处理,研究激光扫描间距(0.0050.020mm)、扫描速度(1001 700mm·s~(-1))与热处理对激光烧蚀表面润湿性的影响。结果表明:不同工艺参数下激光烧蚀后纯铝板表面均形成了相对规则的微纳米网格结构;激光烧蚀后的纯铝板表面为超亲水表面,再经热处理后变为疏水表面或超疏水表面;随着扫描速度和扫描间距的增大,激光烧蚀和热处理后,纯铝板表面的接触角变化不明显,滑动角增大,表现出不同程度的润湿性;在激光扫描速度为100mm·s~(-1),扫描间距为0.005mm下激光烧蚀与热处理后,纯铝板表面微纳米结构致密,其接触角为155.6°,滑动角为4°,超疏水性最佳。     

激光诱导等离子体加工蓝宝石微结构及其润湿性

激光诱导等离子体刻蚀技术在蓝宝石表面微结构制作方面具有独特的优势。通过控制变量法研究了激光能量密度、靶材和蓝宝石之间的距离和扫描速度对激光诱导等离子体加工蓝宝石微槽的微观形貌和几何尺寸的影响规律。通过正交试验研究了激光诱导等离子体工艺参数对蓝宝石表面微结构接触角的影响,发现扫描线间距对接触角的影响最大,靶材和蓝宝石之间的距离和激光能量密度次之,扫描速度的影响最小。当激光能量密度为6.3 J/cm²,扫描线间距为200μm,靶材和蓝宝石之间的距离为150μm,扫描速度为10 mm/s时,蓝宝石表面微结构的接触角为136°,表现出良好的疏水性;当激光能量密度为7.4 J/cm²,扫描线间距为50μm,靶材和蓝宝石之间的距离为100μm,扫描速度为5 mm/s时,蓝宝石表面微结构的接触角为29°,具有较好的亲水性,并且长时间放置后表面接触角基本保持不变。通过扫描电镜观察发现,蓝宝石表面的微结构上分布着许多纳米颗粒,这些微纳结构共同影响蓝宝石的润湿性。     

ENERGY DEPOSITION AND NON-THERMAL ABLATION IN FEMTOSECOND LASER GROOVING OF SILICON

Ultra-short pulsed laser ablation of crystalline silicon is characterized by a complicated heat diffusion and material removal process. In this research, a computational investigation is undertaken to understand the temperature distribution and heat effect in femtosecond laser grooving of silicon. Energy accumulation and threshold fluence of silicon ablation by femtosecond lasers are estimated through solving coupled energy balance equations. Thermal and optical properties of the material are considered in the calculations. The possible non-thermal ablation process and ablation geometry are analyzed for the case of succession of laser pulses. Thermal-mechanical response induced by temperature gradient is discussed around the laser ablation region. The agreement between the model calculations and experimental results show that this research provides an efficient thermal analysis method of the explosive laser-silicon interaction process, and a feasible way to optimize process parameters with minimum thermal damages.     

Ablation of copper by a scanning Gaussian beam of a femtosecond laser pulse

This study investigated ablation from a copper metal surface using a scanning femtosecond laser beam with a Gaussian beam profile. A method was developed herein to calculate the ablation profile with experimentally identified parameters (e.g., effective focused Gaussian incident beam radius, ablation threshold fluence, effective energy penetration depth). The results show the relationship between the maximum ablation depth and maximum ablation width. The calculated ablation profile agrees well with the experimental measurements.     

Fabrication of porous copper surfaces by laser micromilling and their wetting properties

Porous copper surfaces show their great merits in the applications of chemical reaction, sound absorption and heat transfer. In this study, a laser micromilling method is proposed to fabricate porous surfaces with homogeneous micro-holes and cavities of the size about 1–15 μm on pure copper plates in a one-step process. The laser micromilling was performed by a pulsed fiber laser via the multiple–pass reciprocating scanning strategy. Based on the measurement of scanning electron microscope (SEM) and 3D laser scanning confocal microscope, the formation of surface structures was investigated together with the laser ablation mechanisms. The effects of laser processing parameters, i.e., laser fluence, scanning speed, number of scanning cycles and scanning interval, on the formation and surface morphology of porous surfaces were systematically assessed. Furthermore, the wettability of the porous copper surfaces was also evaluated by measuring the static contact angle of water. The results showed that the laser fluence played the most significant role on the formation of porous copper surfaces. The average depth and surface roughness of porous copper surfaces increased with increasing the laser fluence and number of scanning cycles while decreased with the increase in scanning interval. The scanning speed played little influence on the formation of porous copper surfaces. These results can be closely related to the variation of energy density and re-melting process during the laser micromilling process. Moreover, all the copper porous surfaces were found to be hydrophobic. The contact angle of porous copper surfaces was significantly dependent on laser fluence, but weakly affected by the scanning speed and number of scanning cycles.     

0Cr18Ni9不锈钢箔的飞秒激光烧蚀

利用飞秒激光对厚度为20 μm的0Cr18Ni9不锈钢箔进行了表面烧蚀、微细切割等试验,并研究了不锈钢箔的烧蚀特性。首先,根据烧蚀区域的直径和脉冲能量的关系,得到了0Cr18Ni9不锈钢箔的单脉冲烧蚀阈值,并估算了飞秒激光的束腰半径。然后,对飞秒激光切割不锈钢箔的边缘进行金相观察并测试了切割试件的电阻率,以确定飞秒激光切割对不锈钢箔的热影响。最后,对切割试件进行X射线衍射分析(XRD),以确定飞秒激光切割对不锈钢箔物相组成的影响。实验结果表明:飞秒激光的束腰半径为10.416 μm;厚度为20 μm的0Cr18Ni9不锈钢箔的单脉冲烧蚀阈值为0.455 J/cm²;飞秒激光切割后试件的金相组织处于回复阶段,因此金相组织不会产生明显变化;飞秒激光切割后不锈钢箔的物相组成没有变化,但物相的相对含量发生了改变。     

Ablation drilling of invar alloy using ultrashort pulsed laser

Drilling a hole in Invar alloy is accomplished by using a nanosecond pulsed Nd:YAG laser. However, this process has a few problems, such as heat effect and poor edge quality. Therefore, the ablation properties of the Invar alloy were investigated by using an ultrashort pulsed laser, which is a regenerative amplifier Ti:sapphire laser with a 1 kHz repetition rate, a 184 fs pulse duration, and a 785 nm wavelength. To study the ablation characteristics of the Invar alloy, we measured the ablation shape, width, and ablated depth at the energy fluence of a single pulse. The optimal condition for hole drilling is a z-axis transfer depth of 4 μm, a circular feed rate of 0.2 mm/s, and a pulse energy of 26.4 μJ. A fine circular hole without burrs and thermal damage were obtained under the optimal processing conditions. The ultrashort pulsed laser system is an excellent tool for micro-hole drilling in Invar alloys without heat effects and poor edge quality.     

Effect of Transverse Current Injection on the Grinding of Cemented Carbide

Cemented carbide (WC-Co) samples with dimensions of 5 20 mm 3 were ground using a reciprocating table surface grinding machine. Direct electrical current with densities of 0–120 A cm _2 were injected along the length of the sample during grinding. The hardness, structure, and composition of the processed surfaces were examined using Vickers indentation, profilometry, metallographic optical microscopy and scanning electron microscopy (SEM), with scattered electrons (SE), backscattered electrons (BSE) and energy dispersive specroscopy (EDS). The surface roughness increased up to a factor of 2.6 at J = 60 A cm _2 at a cutting depth of 0.06 mm, and the microhardness increased up to 28% with J = 120 A cm _2 at a depth of cut 0.06 mm, in comparison with samples ground without injected current. The atomic concentration ratio WC/Co increased by a factor of 2 at the surface and decreased by a factor of 5 at a depth of 3 _m, when the injected current density was 60 A cm _2 .     

Design of energy optimization for laser polymer joining process

Different laser heat inputs were applied on the gray-colored acrylonitrile butadiene styrene (ABS) plastic using fixed laser power and variable scanning speeds to join ABS- and polycarbonate (PC)-based polymers. Experiments with a laser power between 6 and 8 W and a scanning speed of 1,500, 3,000, and 4,500 mm/min were used for the joining. Heat-affected zone (HAZ) and melt zone measurements were performed to find the joining energy threshold, and the mechanical properties of welds were evaluated. At the low scanning speed, the total heat input at the given area resulted in carbonization damage on the surface. However, energy distributed laser beam joining process by galvanometers resulted in secure and sound weld joining quality. Damage threshold was calculated as 127 J/cm² with relatively less sensitivity of scanning speed. However, the ablation threshold was measured to be 215, 281, and 424 J/cm² for the scanning speed of 4,500, 3,000 and 1,500 mm/min, respectively.     

纳秒激光加工2.5维Cf/SiC复合材料的烧蚀孔洞特征

针对新型材料2.5维碳纤维增强陶瓷基（Cf/SiC）复合材料采用传统机械加工难以去除加工的问题，采用纳秒激光烧蚀2.5维Cf/SiC复合材料，烧蚀后采用扫描电子显微镜观察其烧蚀孔洞形貌特征，并分析其烧蚀去除机制，讨论激光加工参数对烧蚀孔径的影响。研究表明，Cf/SiC复合材料的激光烧蚀区域出现烧蚀孔洞、重凝、纤维断口、末端气胀，以及长轴与纤维方向一致的椭圆形材料性能变化区域等烧蚀现象；激光烧蚀Cf/SiC复合材料过程中存在氧化的化学变化现象；烧蚀产生的孔径随烧蚀功率的增加和烧蚀时间的延长而增大，烧蚀时间和烧蚀功率均较大时，可能存在烧蚀孔洞被重凝材料堵塞或部分堵塞的情况。计算出纳秒激光的束腰半径为223 μm，纳秒激光烧蚀Cf/SiC复合材料的烧蚀阈值为0.32 J/cm2。