Scatter in nonlinear ultrasonic measurements due to crystallographic orientation change induced anisotropy in harmonics generation

Abstract

Present study endeavors to establish the physical basis of an unprecedented trend in scatter, observed in nonlinear ultrasonic (NLU) parameter, associated with varying degree of crystallographic orientation change across crystallites in a polycrystalline material. It is shown that this scatter arises due to anisotropy in harmonics generation as a result of orientation change of slip systems in polycrystals with respect to the wave propagation direction. A near α titanium alloy has been taken as a model alloy to demonstrate this effect of crystallographic orientation change vis-à-vis change in the orientation of slip systems. Scale of crystal orientation change is shown to have a strong correlation with the degree of scatter in NLU measurements. Further, the study establishes the dominating effect of the scale of crystalline orientation change on harmonics generation as compared to variation in other microstructural parameters such as dislocation density, interface structure etc. Frequency distribution analysis of the scatter indicates that the distribution depends on the colony size which exhibits a linear correlation with standard deviation value. The dislocation string vibration model has been extended for harmonics generation in polycrystalline aggregates to explain the trend in the scatter during measurement of NLU parameter in the material.

Nonlinear ultrasonic characterization of precipitation in 17-4PH stainless steel

“…It is interesting to point out that the measurement variation in the air cooled compared to water-quenched 345 samples is consistent with previous results [35], where the authors measured the variation of β measurements for different cooling times. Faster cooling times correlated with a smaller measurement variation.…”

“…The purpose of this Thermal aging of 17-4PH in this paper will focus on aging times below peak aging, since overaging causes a decrease in the hardness. These measurements are interpreted using the precipitate-pinned dislocation model [15], along with hardness measurements, thermo-electric power 35 (TEP) measurements, transmission electron microscopy (TEM), and atom probe tomography (APT). These measurements and model provide insight into how precipitate parameters can be extracted from measurements of β.…”

Ultrasonic Attenuation Based Inspection Method for Scale-up Production of A206–Al2O3 Metal Matrix Nanocomposites

“…This nonuniformity of ultrasonic attenuation is quite similar to the phenomenon of large anisotropies of the acoustic backscattering found in titanium alloys [34][35][36][37]. In these alloys (e.g., Ti6242, T i-6 A H V [38][39][40]), there exist microtextures or colonies of crystallites sharing a common crystallographic orientation over a long range.…”

“…In these alloys (e.g., Ti6242, T i-6 A H V [38][39][40]), there exist microtextures or colonies of crystallites sharing a common crystallographic orientation over a long range. For example, Mukhopadhyay et al [36] measured the nonlinear ultrasonic (NLU) parameters at different locations of /[ heat treated near a titanium alloys under different cooling rates. For example, Mukhopadhyay et al [36] measured the nonlinear ultrasonic (NLU) parameters at different locations of /[ heat treated near a titanium alloys under different cooling rates.…”

Characterization of annealing in polycrystalline copper using harmonic generation technique

“…Karthik et al [17,18] observed that nonlinearities generate static displacement component in addition to higher harmonic contents. The scatter in nonlinearity parameter with crytallographical orientations was observed by Mukhopadhyay et al [19].…”