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Abstract
Ultrasonic attenuation and velocity were measured in commercially pure titanium over an ultrasonic frequency range from 10 to 50 mc/s before and after heating in hydrogen. The two ultrasonic quantities changed by large amounts when the metal was heated in hydrogen at temperatures near 550°C. The main feature is that the attenuation decreased with the increasing hydrogen content.The changes induced by heating in hydrogen resulted mainly from the appearance of titaniumhydrogen phases although hydrogen in solution may also have had an effect. Similar treatment of the titanium in vacuum, oxygen, and nitrogen did not produce appreciable changes in attenuation, velocity, or microstructure.Unfortunately the use of attenuation measurement work at these frequencies is in early stages of development and no unique identification of the mechanisms involved can be given at present. As a consequence this paper is limited to discussion of the experimental observations and effects.RésuméL'attenuation et la vitesse ultrasoniques ont été mesurées dans du titane commercialement pur, dans un intervalle de fréquences allant de 10 à 50 me/sec, avant et après un chauffage dans de l'hydrogène. Les deux grandeurs ultrasoniques changeaient dans des proportions considérables quand le métal était chauffé dans l'hydrogène aux températures proches de 550°C. La caractéristique principale de ce changement était que l'atténuation diminuait quand la teneur en hydrogène augmentait. Les changements produits par le chauffage dans l'hydrogène étaient dus, ayant tout, à l'apparition de phases titane-hydrogène, quoique l'hydrogène en solution eût aussi pu avoir un certain effet. Un traitement similaire du titane dans le vide, l'oxygène et l'azote n'a pas produit de changements appréciables de l'atténuation, de la vitesse ou de la microstructure. L'emploi des mesures de l'atténuation à ces fréquences est encore fort peu développé et il est impossible, en ce moment, d'interpréter les mécanismes impliqués d'une façon unique. Par conséquent, dans cet article, on se borne à discuter les observations et les effets expérimentaux.ZusammenfassungUltraschalldämpfung und -geschwindigkeit wurden in technisch reinem Titan vor und nach Glühen in Wasserstoff in einem Ultraschallfrequenzbereich zwischen 10 und 50 mc/sec gemessen. Wird das Metall bei etwa 500°C in Wasserstoff geglüht, so ändern sich die beiden Eigenschaften stark. Die Haupterscheinung ist die mit zunehmendem Wasserstoffgehalt abnehmende Dämpfung.Die durch Glühen in Wasserstoff hervorgerufenen Eigenschaftsveränderungen beruhen in erster Linie auf dem Auftreten von Titan-Wasserstoff-Phasen, obwohl auch der gelöste Wasserstoff wirksam sein kann. Entsprechende Versuche mit Titan im Vakuum, in Sauerstoff oder Stickstoff rufen keine nennswerten Änderungen in Dämpfung, Schallgeschwindigkeit oder Feinstruktur hervor.Leider sind die Dämpfungsmessungen in diesen Frequenzbereichen erst im Anfangsstadium ihrer Anwendung, und es kann im Augenblick kein eindeutiger Nachweis der verschieden zugrunde liegenden Elementarvorgänge gegeben werden. Deshalb beschränkt sich die vorliegende Arbeit auf eine Diskussion der experimentellen Beobachtungen.
The use of ultrasonic testing for the inspection of thick section weldments in titanium alloys requires careful acoustic characterization of the materials and weldments in question. In the present work ultrasonic wave velocity measurements were performed on a series of test specimens of titanium alloy weldments and base plate material. Data provided by x-ray diffraction analysis and scanning electron microscopy were correlated with the ultrasonic results.
Dissolved oxygen contamination during GTA and GMA welding of titanium alloys can result in severe embrittlement of the weld region. In order to evaluate the feasibility of ultrasonic testing for quantitatively detecting the presence of interstitial gas contamination in weldments of Ti-6211, ultrasonic wave velocity and ultrasonic attenuation measurements were performed on a series of five specimens with nominal oxygen levels of 0.07, 0.14, 0.20, 0.24 and 0.29 percent by weight. Density measurements, in addition to the ultrasonic wave velocity data, enabled relative determination of elastic moduli. Variations in the ultrasonic data were correlated with results from scanning electron microscopy and hardness testing.
The presence of oriented regions of displaced atoms (directional radiation damage) produced by a beam of approximately collimated fission neutrons in silicon single crystals has been observed by an ultrasonic double refraction method. The effects observed are anisotropic velocity or modulus changes which do not appear to be accompanied by attenuation changes. The irradiated crystal shows a very pronounced ultrasonic double refraction effect with waves propagated at right angles to the bombardment direction together with the absence of such a double refraction effect when the waves are propagated in the direction of the bombarding neutrons. Separate, independent, ultrasonic velocity measurements indicate that the irradiation has lowered the velocities perpendicular to the bombardment direction in a manner entirely consistent with the double refraction measurements. The observed velocity effects are not accompanied by detectable attenuation changes and are therefore not connected with dislocation damping phenomena.
Summary Internal friction in titanium (99.9% Ti) containing 4, 12 and 26 at. % of hydrogen has been investigated. With 12 and 26 at.
% of hydrogen two peaks were observed: one about 600 K and another at 250 K. The first is associated with the eutectoidal
transformation in the Ti−H system. The other has a relaxation character, and its parameters are similar to those for Hasiguti
peaks. It probably results from the deformation caused by the precipitation of the γ-phase during the eutectoidal transformation.
Pulse techniques for the measurement of attenuation in solids have been extended and refined sufficiently to obtain dependable measurements over a frequency range from 5 to 50 megacycles. Understanding of the relative importance of beam spreading, geometrical boundaries, and method of coupling has been improved. Coupling by means of water buffer and direct mounting is discussed in detail.
Attenuation measurements in the frequency range from 5 to 50 megacycles have been made on chrome molybdenum steel specimens, and these measurements have shown large differences in ultrasonic attenuation for samples of the same chemical composition but different heat treatment. The resulting differences are connected with anisotropy which appears in the photomicrographs. The attenuation measurements are quite sensitive to heat treatment and other factors. The application of the methods to metallurgical problems and the physics of solids is suggested.
When high frequency longitudinal and transverse sound waves are sent through a multicrystalline rod of metal, attenuation losses result because of scattering and diffusion of sound waves by the grains. When the grain size is less than one-third of the wave-length, these losses are due to Rayleigh fourth power law scattering and are proportional to the grain volume. The scattering factor depends on the anisotropy of the elastic constants. Two different factors are obtained, one for shear waves and one for longitudinal waves. These factors have been evaluated for cubic and hexagonal metals. From the measured elastic constants the only metals with a low loss are aluminum, magnesium, and tungsten. The calculations indicate that the losses for aluminum and magnesium are about equal for longitudinal waves, but for shear waves magnesium has a very low shear loss. It has been found experimentally that magnesium has nearly as low a loss as fused quartz.
Experiments with higher frequencies show that when the wave-length is one-third of the grain size or less, the transmission process becomes a diffusion process similar to the propagation of a heat wave. The grain sizes determine the mean free path, and the loss becomes inversely proportional to the grain diameter. An approximate formula for diffusion losses has been obtained which agrees closely with the experimental values.
- Kirschfeld