Ultrasonic Attenuation Due to Grain Boundary Scattering in Pure Niobium
Ultrasonic Attenuation Due to Grain Boundary Scattering in Pure Niobium
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DOI：
10.1007/s10921-010-0068-2
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发表时间：
2010-03
影响因子：
2.8
通讯作者：
F. Zeng;S. Agnew;B. Raeisinia;G. Myneni
中科院分区：
文献类型：
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作者：
F. Zeng;S. Agnew;B. Raeisinia;G. Myneni
实验证实了各种颗粒散射理论的存在，但在利用超声表征微观结构方面仍存在一些突出问题。在本研究中，高纯Nb被用作没有外在散射中心(例如，空洞、沉淀物、第二相粒子等)的模型材料。经常规冷轧和再结晶热处理后，在不同温度(600~800℃)下进行超高真空退火，获得了一系列显微组织。超声波衰减是作为每个样品的频率的函数测量的。对于中等粒度的样品(通常为∼50μm)，衰减服从指数为n∼1.6的幂函数关系，这与经典随机散射理论的预测值n=2相近。然而，定量比较表明，观测到的衰减比经典理论预测的要高。虽然Stanke-Kino统一粒子散射理论仍然低估了衰减的大小，但它可以解释这种频率依赖性比传统理论预测的要低的原因。无论如何，由此得到的经验关系为实际的粒度测量提供了一种有用的方法，并且具有可接受的不确定度。讨论了某些板材/板材典型的层状组织结构的影响。
Experimental confirmation of various grain scattering theories exist but there are still outstanding questions concerning the characterization of microstructure using ultrasound. In this study, high purity niobium serves as a model material devoid of extrinsic scattering centers (e.g., voids, precipitates, second phase particles etc.) A range of microstructures were obtained by annealing in ultrahigh vacuum at different temperatures (600–800°C) after routine cold-rolling and recrystallization heat treatment. Ultrasonic attenuation is measured as a function of a frequency for each sample. For the samples with an intermediate grain size (typically ∼50 μm), attenuation follows a power law dependence on frequency with an exponent ofn∼1.6, which is close to the prediction,n=2, of classical Stochastic scattering theory. However, quantitative comparison shows that the observed attenuation is higher than predicted by the classical theory. The Stanke-Kino unified grain scattering theory may provide an explanation for the lower frequency dependence than traditional theories predict, though it still under predicts the magnitude of the attenuation. In any event, the resulting empirical relations provide a useful approach for practical grain size measurement with an acceptable level of uncertainty. The effect of a layered microstructure typical of some sheets/plates is discussed.