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Article

Correlation between Laser-Ultrasound and Microstructural Properties of Laser Melting Deposited Ti6Al4V/B4C Composites

1
Laser Institute, Qilu University of Technology (Shandong Academy of Sciences), Jinan 250103, China
2
Tech Institute for Advanced Materials, College of Materials Science and Technology, Nanjing Tech University, Nanjing 210009, China
*
Author to whom correspondence should be addressed.
Academic Editor: Zhiwei Liu
Metals 2021, 11(12), 1951; https://doi.org/10.3390/met11121951
Received: 28 October 2021 / Revised: 26 November 2021 / Accepted: 30 November 2021 / Published: 3 December 2021
The presence of large microtextured clusters (MTC) composed of small α-phase crystallites with preferred crystallographic orientations in 3D printed near-α titanium alloys leads to poor mechanical and fatigue properties. It is therefore crucial to characterize the size of MTCs nondestructively. Ti6Al4V/B4C composite materials are manufactured using Laser Melting Deposition (LMD) technology by adding an amount of nano-sized B4C particles to the original Ti6Al4V powder. TiB and TiC reinforcements precipitating at grain boundaries stimulate the elongated α crystallites and coarse columnar MTCs to equiaxed transition, and microstructures composed of approximately equiaxed MTCs with different mean sizes of 11–50 μm are obtained. Theoretical models for scattering-induced attenuation and centroid frequency downshift of ultrasonic waves propagating in such a polycrystalline medium are presented. It is indicated that, the studied composite material has an extremely narrow crystallographic orientation distribution width, i.e., a strong degree of anisotropy in MTCs. Therefore, MTCs make a dominant contribution to the total scattering-induced attenuation and spectral centroid frequency downshift, while the contribution of fine α-phase crystallites is insignificant. Laser ultrasonic inspection is performed, and the correlation between laser-generated ultrasonic wave properties and microstructural properties of the Ti6Al4V/B4C composites is analyzed. Results have shown that the deviation between the experimentally measured ultrasonic velocity and the theoretical result determined by the Voigt-averaged velocity in each crystallite is no more than 2.23%, which is in good agreement with the degree of macroscopically anisotropy in the composite specimens. The ultrasonic velocity seems to be insensitive to the size of MTCs, while the spectral centroid frequency downshift is approximately linear to the mean size of MTCs with a goodness-of-fit (R2) up to 0.99. Actually, for a macroscopically untextured near-α titanium alloy with a relatively narrow crystallographic orientation distribution, the ultrasonic velocity is not correlated with the properties of MTCs, by contrast, the central frequency downshift is dominated by the size and morphology of MTCs, showing great potentials in grain size evaluation. View Full-Text
Keywords: laser-ultrasonics; laser melting deposition; metal composites; ultrasonic scattering; centroid frequency shift laser-ultrasonics; laser melting deposition; metal composites; ultrasonic scattering; centroid frequency shift
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MDPI and ACS Style

Xu, W.; Bai, X.; Sun, Z.; Meng, X.; Guo, Z. Correlation between Laser-Ultrasound and Microstructural Properties of Laser Melting Deposited Ti6Al4V/B4C Composites. Metals 2021, 11, 1951. https://doi.org/10.3390/met11121951

AMA Style

Xu W, Bai X, Sun Z, Meng X, Guo Z. Correlation between Laser-Ultrasound and Microstructural Properties of Laser Melting Deposited Ti6Al4V/B4C Composites. Metals. 2021; 11(12):1951. https://doi.org/10.3390/met11121951

Chicago/Turabian Style

Xu, Wanwei, Xue Bai, Zhonggang Sun, Xin Meng, and Zhongming Guo. 2021. "Correlation between Laser-Ultrasound and Microstructural Properties of Laser Melting Deposited Ti6Al4V/B4C Composites" Metals 11, no. 12: 1951. https://doi.org/10.3390/met11121951

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