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

Review of Second Harmonic Generation Measurement Techniques for Material State Determination in Metals

Abstract: This paper presents a comprehensive review of the current state of knowledge of second harmonic generation (SHG) measurements, a subset of nonlinear ultrasonic nondestructive evaluation techniques. These SHG techniques exploit the material nonlinearity of metals in order to measure the acoustic nonlinearity parameter, $$\beta $$ . In these measurements, a second harmonic wave is generated from a propagating monochromatic elastic wave, due to the anharmonicity of the crystal lattice, as well as the presence of microstructural features such as dislocations and precipitates. This article provides a summary of models that relate the different microstructural contributions to $$\beta $$ , and provides details of the different SHG measurement and analysis techniques available, focusing on longitudinal and Rayleigh wave methods. The main focus of this paper is a critical review of the literature that utilizes these SHG methods for the nondestructive evaluation of plasticity, fatigue, thermal aging, creep, and radiation damage in metals.

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

Abstract: This research is part of a broader effort to develop a nondestructive evaluation technique to monitor radiation damage in reactor pressure vessel steels, the main contributor being copper-rich precipitates. In this work, 17-4PH stainless steel is thermally aged to study the effects of copper precipitates on the acoustic nonlinearity parameter. Nonlinear ultrasonic measurements using Rayleigh waves are performed on isothermally aged 17-4PH. Results showed a decrease in the acoustic nonlinearity parameter with increasing aging time, consistent with evidence of copper precipitation from hardness, thermo-electric power, transmission electron microscopy, and atom probe tomography measurements.

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

Abstract: A206–Al2O3 metal matrix nanocomposite (MMNC) is a promising high performance material with potential applications in various industries, such as automotive, aerospace, and defense. Al2O3 nanoparticles dispersed into molten Al using ultrasonic cavitation technique can enhance the nucleation of primary Al phase to reduce its grain size and modify the secondary intermetallic phases. To enable a scale-up production, an effective yet easy-to-implement quality inspection technique is needed to effectively evaluate the resultant microstructure of the MMNCs. At present the standard inspection technique is based on the microscopic images, which are costly and time-consuming to obtain. This paper investigates the relationship between the ultrasonic attenuation and the microstructures of pure A206 and Al2O3 reinforced MMNCs with/without ultrasonic dispersion. A hypothesis test based on an estimated attenuation variance was developed and it could accurately differentiate poor samples from good ones. This study provides useful guidelines to establish a new quality inspection technique for A206–Al2O3 nanocomposites using ultrasonic nondestructive testing method.

An Experimental Investigation on the Influence of Annealed Microstructure on Wave Propagation

Abstract: In this work grain growth associated with isochronous annealing in polycrystalline pure copper is studied using nonlinear ultrasonic method. In isochronous annealing, holding time is constant but annealing temperatures vary. It is observed that, grain growth due to isochronous annealing significantly influences the ultrasonic nonlinearity parameter, β. A decrease in nonlinearity parameter with increase in grain size is noticed. Further, micro-hardness measurements as well as metallographic results are presented to underscore the utility of the nonlinear ultrasonic method in gauging the progress of annealing. As the time and effort involved in this method is less, with suitable calibration, this method may be gainfully employed for determination of grain size on annealing.

Characterization of microstructural changes due to prolonged thermal exposure of directionally solidified Ni-base super alloy CM 247LC using ultrasonic.

Abstract: The high temperature strength of directionally solidified Ni-base super alloy CM 247LC strongly depends on the morphology, volume fraction, size and size distribution of γ′ precipitate (Ni3Al) in the FCC γ matrix. The microstructure of the alloy is engineered to achieve the right combination of these parameters that provides the required high temperature strength and creep resistance. The alloy contains high volume fraction of coherent γ′ precipitates having near cubic shape. High temperature exposure of gas turbine components made out of the alloy leads to coarsening of the γ′ precipitates and broadening of the γ matrix channel. This in turn, adversely affects the high temperature mechanical properties of the alloy. The present study endeavours to non-destructively characterize such detrimental changes in the microstructure that controls the mechanical properties and limits the life of components. The microstructural changes of the fully heat treated alloy exposed at 980 °C for different hours (100–1200) of thermal exposure have been characterized using ultrasonic methods. Changes in microstructural parameters due to different hours of thermal exposure have been correlated with changes in ultrasonic velocity, ultrasonic attenuation coefficient and second order acoustic nonlinearity parameter. It is observed that the change in attenuation is predominantly by absorption of the ultrasonic wave due to dislocation damping in the γ channels. Nonlinear ultrasonic parameter changes with thermal exposure predominantly due to the alteration of dislocation precipitate interaction. A dislocation precipitation interaction model for ultrasonic wave distortion has been used to explain the observed variation in nonlinear parameter. A microstructural parameter has been identified that varies in a similar way as ultrasonic attenuation and second order ultrasonic parameter. It is shown that variations in the acoustic non-linearity parameter follow the trend more closely with the identified microstructural parameter.

Theory of Mechanical Damping Due to Dislocations

Abstract: A quantitative theory of damping and modulus changes due to dislocations is developed. It is found that the model used by Koehler of a pinned dislocation loop oscillating under the influence of an applied stress leads to two kinds of loss, one frequency dependent and the other not. The frequency dependent loss is found to have a maximum in the high megacycle range. The second type of loss is a hysteresis loss which proves to be independent of frequency over a wide frequency range which includes the kilocycle range. This loss has a strain‐amplitude dependence of the type observed in the kilocycle range. The theory provides a quantitative interpretation of this loss.

On the process of transition of the cubic-body-centered modification into the hexagonal-close-packed modification of zirconium

Abstract: Summary The process of transition of the cubic-body-centred modification into the hexagonal-close-packed modification of zirconium can be described by means of a combination of shearing- and dilatation-processes parallel to definite crystallographic directions. The transition has, therefore, “homogeneous” or “oriented” character. See for particulars the detailed summary at the end of the paper.

Nonlinear ultrasonic characterization of fatigue microstructures

Abstract: Dislocation dipole substructures formed during metal fatigue are shown to produce a substantial distortion of ultrasonic waves propagating through the fatigued material. A model of ultrasonic wave-dislocation dipole interactions is developed that quantifies the wave distortion by means of a material nonlinearity parameter (beta). Application of the model to AA2024-T4 predicts a value of p approximately 300% larger in material cyclically loaded for 100 kcycles in stress-control at 276 MPa and R=0 than that measured for virgin material. Experimental measurements show a monotonic increase in p as a function of the number of fatigue cycles that closely approaches the predicted increase. The experiments also suggest that the relevant dislocation substructures are localized in the material.

Room temperature deformation and mechanisms of slip transmission in oriented single-colony crystals of an α/β titanium alloy

Abstract: Primary creep at low homologous temperatures and low stresses has been widely reported in α/β Ti alloys. Creep in these alloys is dependent on microstructure, with the colony microstructure showing the least creep resistance. There exists a Burgers orientation relationship between the α and the β phase, which has been assumed to allow for easy slip transmission across the α/β interfaces. Constant strain rate and creep tests were performed on single-colony crystals of a near-α alloy oriented for slip along different prismatic slip systems in the α phase. A distinct anisotropy in the deformation behavior of different colony crystals is found. The origin of this anisotropy is due to the relative misalignment of the slip systems between the α and the β phases which results in the formation of residual dislocations during slip transmission. A simple model is presented based on the accumulation of residual dislocations at both the α/β interface and the α matrix, which provides insight into the mechanism of slip transmission, strain hardening and primary creep of these colony structures.