In-situ laser ultrasonic grain size measurement in superalloy INCONEL 718

Garcin, Thomas; Schmitt, Jean-Hubert; Militzer, Matthias

doi:10.1016/j.jallcom.2016.01.222

Cited by 67 publications

(24 citation statements)

References 23 publications

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“…For a longitudinal wave propagating in the polycrystalline medium, three sources of the measured ultrasonic attenuation mainly exist [28,32]. The most important source arises from attenuation by scattering, αs, and is attributed to interactions between waves and grain boundaries due to inhomogeneities in elastic properties or in density between adjacent grains, which is of interest in the present case.…”

Section: Resultsmentioning

confidence: 99%

“…The third one is involved with attenuation by internal friction and is frequency-independent. It is generally negligible with respect to the scattering phenomenon [28,33]. Generally, for a longitudinal wave propagating along the z direction from z=z1 to z=z2, the total attenuation per unit length, expressed in dB/mm, is evaluated by comparing the amplitude spectrum A measured in each waveform:αitalictotal( f ) = αs+αd+αf =20z2−z1log10A(z2, f )A(z1, f ) ,…”

Section: Resultsmentioning

confidence: 99%

“…The ability to use ultrasonic attenuation for grain size characterization in polycrystalline materials has been demonstrated by experimental measurements [24,25,26,27,28]. Correlation of the experimentally measured attenuation to a single mean grain size are usually established.…”

Section: Introductionmentioning

confidence: 99%

“…Correlation of the experimentally measured attenuation to a single mean grain size are usually established. Nevertheless, some studies found the distribution of grain sizes could affect the accuracy of the experimental confirmation of the classical theories [7,27,28]. For example, Zhang et al [27] carried out the measurements of the dependence of ultrasonic attenuation on mean grain size in copper samples in the Rayleigh frequency region.…”

Section: Introductionmentioning

confidence: 99%

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

Bai

Zhao

et al. 2018

Materials

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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.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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

Bai

Zhao

et al. 2018

Materials

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“…Abnormal grain growth (AGG) refers to a subset of grains that will grow excessively at the expense of surrounding normal grains leading to an obvious size advantage of the abnormal grains [1,2]. The AGG phenomenon has been observed in many materials, including steels [3][4][5][6][7][8][9][10][11], aluminum alloys [12,13], super alloys [14][15][16], ceramics [17][18][19][20][21], nanocrystalline materials [22][23][24][25] as well as thin films [25][26][27][28]. AGG is of important technological relevance and must be controlled in the thermal processing of polycrystalline materials.…”

Section: Introductionmentioning

confidence: 99%

Phase Field Modelling of Abnormal Grain Growth

2019

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Heterogeneous grain structures may develop due to abnormal grain growth during processing of polycrystalline materials ranging from metals and alloys to ceramics. The phenomenon must be controlled in practical applications where typically homogeneous grain structures are desired. Recent advances in experimental and computational techniques have, thus, stimulated the need to revisit the underlying growth mechanisms. Here, phase field modelling is used to systematically evaluate conditions for initiation of abnormal grain growth. Grain boundaries are classified into two classes, i.e., high- and low-mobility boundaries. Three different approaches are considered for having high- and low-mobility boundaries: (i) critical threshold angle of grain boundary disorientation above which boundaries are highly mobile, (ii) two grain types A and B with the A–B boundaries being highly mobile, and (iii) three grain types, A, B and C with the A–B boundaries being fast. For these different scenarios, 2D simulations have been performed to quantify the effect of variations in the mobility ratio, threshold angle and fractions of grain types, respectively, on the potential onset of abnormal grain growth and the degree of heterogeneity in the resulting grain structures. The required mobility ratios to observe abnormal grain growth are quantified as a function of the fraction of high-mobility boundaries. The scenario with three grain types (A, B, C) has been identified as one that promotes strongly irregular abnormal grains including island grains, as observed experimentally.

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