Optical in-situ analysis of the cavitation damage on technical alloys under repeated single bubbles

重复单气泡作用下技术合金空化损伤的光学原位分析

• 批准号: 451715773
• 负责人: Dr.-Ing. Stefanie Hanke
• 金额: --
• 依托单位: Lehrstuhl für Werkstofftechnik
• 依托单位国家: 德国
• 项目类别: Research Grants
• 资助国家: 德国
• 项目状态: 未结题
• 来源: https://gepris.dfg.de/gepris/projekt/451715773?language=en
• 关键词: Optical; situ; analysis; cavitation; damage

With time, cavitation – that is, the formation and collapse of gas bubbles in liquids – can damage the surface even of high-strength materials. The resistance of materials to cavitation is typically investigated using ultrasound sonotrodes. Due to the large number and stochastic nature of the acoustically generated bubbles, in general the resulting damage cannot be assigned to individual bubble events. However, by means of focused laser pulses it is possible to generate individual bubbles that are precisely reproducible in location and time. Besides many studies on the fluid dynamics of the collapsing bubble, some works examine the effect of such individual bubbles on a deformable solid surface. With few exceptions, the sample is from a soft material, such that the deformation resulting from a single bubble can be correlated with its dynamics. However, it is unclear how these results can be transferred to higher-strength materials.The proposed project aims at this knowledge gap between microscopically uncontrolled damage to technical alloys by acoustic cavitation on one hand and precisely reproducible loading on soft materials by individual bubbles on the other. Series of single bubbles will provide defined, repeated stress on surfaces of technical alloys. The dynamics of each bubble are recorded by imaging, then after each bubble collapse the incremental increase in damage is recorded in situ by optical microscopy, and this is complemented by high-resolution ex-situ techniques to yield a detailed picture of the damage evolution. This enables examining the development of damage during the incubation and erosion phases in unprecedented spatio-temporal resolution, as well as correlating the details of the collapse processes with material changes. In parallel, standard tests with a sonotrode are performed to put this damage into context with what is generally known about the materials’ cavitation resistance.First, microscopy optics are integrated into an existing single-bubble experiment and synchronized with high-speed visualization of the bubbles. Using samples from a soft material, this in-situ imaging is validated by ex-situ confocal microscopy. In a second step, series of tests are carried out on NiAl bronze and 316L steel in order to develop semi-automated methods to efficiently evaluate the very large data sets and to correlate in-situ and ex-situ microscopy. Finally, these methods are used in experiments on both materials, in which the number of bubbles, their distance from the sample surface, and the bubble diameter are varied. Ex-situ, the damage mechanisms in the technical alloys are analyzed in detail by high-resolution electron microscopy and compared with samples from experiments with ultrasonic cavitation according to ASTM G32. The extensive data generated in this project will be made publicly accessible, in particular for modeling work outside of the project.

随着时间的推移，空化现象（即液体中气泡的形成和破裂）甚至会损坏高强度材料的表面。通常使用超声波焊极来研究材料的抗空化能力。由于声学产生的气泡数量众多且具有随机性，通常所造成的损害不能归因于单个气泡事件。然而，通过聚焦激光脉冲，可以产生在位置和时间上可精确再现的单个气泡。除了对破裂气泡的流体动力学的许多研究之外，一些工作还研究了此类单个气泡对可变形固体表面的影响。除少数例外，样品均来自软材料，因此单个气泡产生的变形可以与其动力学相关。然而，目前尚不清楚如何将这些结果转移到更高强度的材料上。拟议的项目旨在解决一方面声空化对技术合金造成的微观不受控制的损坏与另一方面单个气泡对软材料的精确再现的负载之间的知识差距。系列单个气泡将在技术合金的表面上提供限定的、重复的应力。通过成像记录每个气泡的动态，然后在每个气泡破裂后，通过光学显微镜原位记录损伤的增量，并辅以高分辨率异位技术，以生成损伤演变的详细图片。这使得能够以前所未有的时空分辨率检查孕育和侵蚀阶段的损害发展，并将倒塌过程的细节与材料变化相关联。同时，使用超声波发生器进行标准测试，将这种损坏与材料的抗空蚀性相结合。首先，将显微镜光学器件集成到现有的单气泡实验中，并与气泡的高速可视化同步。使用软材料的样品，通过异位共焦显微镜验证了这种原位成像。第二步，对 NiAl 青铜和 316L 钢进行一系列测试，以开发半自动化方法来有效评估非常大的数据集并将原位和异位显微镜关联起来。最后，这些方法用于两种材料的实验，其中气泡的数量、距样品表面的距离以及气泡直径都是不同的。通过高分辨率电子显微镜对技术合金的损伤机制进行了异位详细分析，并与根据 ASTM G32 的超声波空化实验中的样品进行了比较。该项目中生成的大量数据将可供公众访问，特别是对于项目外的建模工作。