Dual-Step Sintering of Metal Nanoparticles with Femtosecond Laser Pulses

飞秒激光脉冲双步烧结金属纳米颗粒

• 批准号: 1934357
• 负责人: Yaguo Wang
• 金额: $ 34.71万
• 依托单位: University of Texas at Austin
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2019
• 资助国家: 美国
• 起止时间: 2019-10-15 至 2023-11-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1934357&HistoricalAwards=false
• 关键词: Dual; Step; Sintering; Metal; Nanoparticles

Selective laser sintering of metal particles, an additive manufacturing process, has great potential in the manufacture of metal components with complex geometries. Current systems which utilize nanosecond and continuous-wave lasers to sinter (bond) the metal particles can suffer from high porosity and high residual stresses. Femtosecond lasers, with a pulse duration of less than 10^-12 s, have high associated power and a limited heat affected zone, and thus can effectively sinter metal nanoparticles to produce dense parts with reduced residual stresses. That said, challenges remain in the effective sintering of metal nanoparticles with femtosecond lasers as the high-power pulses can ablate (remove) the particles before they are sintered resulting in incomplete printed features. To address this problem, a double-pulse train strategy is planned, whereby the first laser pulse will heat the particles to a level below where ablation occurs, while the second pulse will induce the required sintering. Successfully widening the femtosecond laser processing window will facilitate the manufacture of metal components with complex, small-scale geometries and high mechanical/electrical/thermal integrity; a combination that offers potential for industries requiring precision components for critical applications, i.e. aerospace. The small associated heat affect zone implies the approach could also positively impact the manufacture of flexible electronics. Additionally, this award will provide research training for minority graduate and undergraduate students, and will generate teaching materials for dissemination through Research Experience for Teachers (RET) programs in the Austin, Texas region.Non-thermal ablation by femtosecond lasers is widely used in high-precision manufacturing, where the rapid accumulation of hot electrons can cause the breaking of atomic bonds and facilitate the removal of unnecessary material. This is beneficial in the shaping of bulk materials. However, in the sintering of metal nanoparticles, hot electrons can result in ablation and seriously jeopardize the effectiveness of the desired process outcomes. To achieve proper sintering, metal nanoparticles must be partially melted, which requires increasing the lattice temperature above a certain threshold. Hot electron effects however occur much faster than electron-phonon coupling, hence preventing the desired increase of lattice temperature. A two-step sintering strategy is proposed that will use a double-pulse train to suppress the hot electron effects while still promoting sintering across a broad range of experimental conditions. To achieve this the mechanisms of femtosecond-laser interaction with noble metal nanoparticles (silver, copper, gold) must first be understood. The mechanisms will be investigated using ultrafast broad-band transient absorption spectroscopy, and transient thermoreflectance measurements during femtosecond laser sintering experiments. Modified two-temperature models will be developed to analyze experimental data and to provide a foundation from which viable processing windows can be isolated. Knowledge delivered through this research will reveal the dynamic process of femtosecond-laser sintering of metal nanoparticles and bridge the long-standing gap between theoretical predictions and conventional sintering outcomes.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

金属颗粒的选择性激光烧结是一种添加剂制造过程，在具有复杂几何形状的金属组件的制造方面具有巨大的潜力。使用纳秒和连续波激光器烧结（键）的当前系统可能会遭受高孔隙率和高残余应力。飞秒激光器的脉冲持续时间小于10^-12 s，具有高相关功率和有限的热影响区，因此可以有效地烧结金属纳米颗粒，以产生残留应力减少的密集部分。也就是说，挑战仍然存在于具有飞秒激光器的金属纳米颗粒的有效烧结中，因为高功率脉冲可以在颗粒烧结之前消除（去除）颗粒，从而产生不完整的印刷特征。为了解决这个问题，计划了双脉冲训练策略，从而将第一个激光脉冲将颗粒加热到发生消融的位置，而第二个脉冲将诱导所需的烧结。成功扩大飞秒激光处理窗口将有助于具有复杂，小规模的几何形状和高机械/电气/热完整性的金属组件的制造；一种组合，为需要关键应用的精确组件（即航空航天）提供了潜力。相关的热量影响区域意味着该方法也可能对柔性电子产品的生产产生积极影响。此外，该奖项将为少数群体研究生和本科生提供研究培训，并将通过在德克萨斯州奥斯汀地区的教师（RET）计划来生成教学材料，以供众多激光器进行高精度制造中的毫无用处，在高精度制造中广泛使用，可以使电子材料的快速累积构成Antom bearts of Athomic and and of and aTOM intol and and of and and，又可以弥补了Antom intos and a and of Atsomic and and and of and aTOM的型号。 这对于散装材料的塑造是有益的。但是，在金属纳米颗粒的烧结中，热电子会导致消融并严重危害所需过程结果的有效性。为了达到适当的烧结，必须部分融化金属纳米颗粒，这需要将晶格温度提高以上以上。然而，热电子效应的发生速度要比电子 - 音波耦合的速度快得多，从而阻止了晶格温度所需的升高。提出了两步烧结策略，该策略将使用双脉冲列车来抑制热电子效应，同时仍在各种实验条件下促进烧结。为了实现这一目标，必须首先了解飞秒激光量与高贵金属纳米颗粒（银，铜，金）的机制。该机制将使用超快宽带的瞬态吸收光谱以及在飞秒激光烧结实验期间的瞬时热室感式测量进行研究。将开发经过修改的两个温度模型来分析实验数据，并提供一个可以隔离可行处理窗口的基础。通过这项研究提供的知识将揭示金属纳米颗粒烧结的动态过程，并弥合了理论预测和常规烧结成果之间的长期差距。该奖项反映了NSF的法定任务，并通过评估该基金会的知识分子功能和广泛的影响来评估NSF的法定任务。

项目成果

Thermal properties of copper nanoparticles at different sintering stages governed by nanoscale heat transfer

铜纳米颗粒在不同烧结阶段的热性能受纳米级传热控制

• DOI: 10.1016/j.addlet.2022.100114
• 发表时间: 2023
• 期刊: Additive Manufacturing Letters
• 作者: Jeong, Jihoon;Wang, Yaguo
• 通讯作者: Wang, Yaguo