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Grain-Size Distribution Effects on the Attenuation of Laser-Generated Ultrasound in α-Titanium Alloy

1
Laser Institute, Qilu University of Technology (Shandong Academy of Sciences), Jinan 250103, China
2
Department of Materials Research, Avic Manufacturing Technology Institute, Beijing 100024, China
*
Author to whom correspondence should be addressed.
Materials 2019, 12(1), 102; https://doi.org/10.3390/ma12010102
Received: 27 November 2018 / Revised: 13 December 2018 / Accepted: 21 December 2018 / Published: 29 December 2018
(This article belongs to the Special Issue Deformation, Fatigue and Fracture of Materials)
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Abstract

Average grain size is usually used to describe a polycrystalline medium; however, many investigations demonstrate the grain-size distribution has a measurable effect on most of mechanical properties. This paper addresses the experimental quantification for the effects of grain-size distribution on attenuation in α-titanium alloy by laser ultrasonics. Microstructures with different mean grain sizes of 26–49 μm are obtained via annealing at 800 °C for different holding times, having an approximately log-normal distribution of grain sizes. Experimental measurements were examined by using two different theoretical models: (i) the classical Rokhlin’s model considering a single mean grain size, and (ii) the improved Turner’s model incorporating a log-normal distribution of grain sizes in the attenuation evaluation. Quantitative agreement between the experiment and the latter model was found in the Rayleigh and the Rayleigh-to-stochastic transition regions. A larger attenuation level was exhibited than the classical theoretical prediction considering a single mean grain size, and the frequency dependence of attenuation reduced from a classical fourth power to an approximately second power due to a greater probability of large grains than the assumed Poisson statistics. The provided results would help support the use of laser ultrasound technology for the non-destructive evaluation of grain size distribution in polycrystalline materials. View Full-Text
Keywords: grain-size distribution; laser ultrasonics; α-titanium alloy; ultrasonic attenuation grain-size distribution; laser ultrasonics; α-titanium alloy; ultrasonic attenuation
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Bai, X.; Zhao, Y.; Ma, J.; Liu, Y.; Wang, Q. Grain-Size Distribution Effects on the Attenuation of Laser-Generated Ultrasound in α-Titanium Alloy. Materials 2019, 12, 102.

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