Measuring and testing – Vibration – By mechanical waves
Reexamination Certificate
1999-12-03
2002-05-28
Williams, Hezron (Department: 2856)
Measuring and testing
Vibration
By mechanical waves
C073S597000, C073S598000, C073S602000, C073S627000
Reexamination Certificate
active
06393916
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to titanium inspection methods and systems. In particular, the invention relates to methods and systems for inspecting titanium using ultrasonic energy.
Nondestructive evaluation by ultrasonic inspection and ultrasonic inspection testing is a known material testing and evaluation method. Ultrasonic testing typically requires that detectable flaws possess different acoustic behaviors from bulk material under similar ultrasonic inspection. This different behavior permits the ultrasonic inspection technique to detect flaws, grains, imperfections, and other related microstructural characteristics for a material.
Materials with large, elastically anisotropic grains, such as, but not limited to, cast ingots of steels, titanium alloys, and nickel alloys, are often difficult to evaluate by ultrasonic testing. The difficulties arise, at least in part to, because sound waves, which are used for ultrasonic inspection, can be partially reflected from grains, and represent a background “noise.” The generated background noise can mask flaws in the material, and is thus undesirable.
Ultrasonic inspection techniques have been developed that use focused ultrasonic beams to enhance a flaw fraction within any instantaneously insonified volume of material. These developed ultrasonic inspection techniques can identify indications based both on maximum signal, as well as signal to noise. A scattering of sound in a polycrystalline metallic material body, which is also known in the art as an attenuation of a propagating sound wave, can be described as a function of at least one of the following: grain dimensions, intrinsic material characteristics, and ultrasound frequency. Typically, three different functional relationships among scattering, frequency, and grain dimensions have been described. These are:
for &lgr;>2&pgr;D, a=Tv
4
&THgr;, termed “Rayleigh” scattering;
for &lgr;<2&pgr;D or &lgr;≡D, a=Dv
2
&Sgr;, termed “stochastic” or “phase” scattering; and
for &lgr;<<D, a∝1/D, termed “diffusion” scattering;
where a is attenuation, &lgr; is wavelength of the ultrasound energy, v is frequency of the ultrasound energy, D is an average grain diameter, T is a scattering volume of grains, and &THgr; and &Sgr; are scattering factors based on elastic properties of the material being inspected.
The microstructure of a material can determine the applications in which the material can be used, and the microstructure of a material can limit the applications in which the material can be used. The microstructure can be determined by measuring the scattering of sound waves in a material. The scattering of sound in a material, such as titanium, is sensitive to its microstructure. The titanium microstructure's sound scattering sensitivity can be attributed to &agr;Ti particles that are arranged into “colonies.” These colonies typically have a common crystallographic (and elastic) orientation, and these colonies of &agr;Ti particles can behave as large grains in the titanium material. An individual &agr;Ti particle might be about 5 &mgr;m in diameter, however, a colony of &agr;Ti particles could be greater than about 200 &mgr;m in diameter. Thus, the size contribution attributed to sound scattering sensitivity from &agr;Ti particles could vary over 40-fold among differing microstructures. Additionally, the sound scattering sensitivity due to &agr;Ti particles could change between that from randomly oriented &agr;Ti particles to that from &agr;Ti particles within oriented colonies of &agr;Ti particles.
Colony structures are formed during cooling a titanium alloy from a high temperature as &bgr;Ti transforms to &agr;Ti . There is a crystallographic relation between the &agr;Ti and the parent &bgr;Ti grain, such that there are only three crystallographic orientations that &agr;Ti will take when forming from a given &bgr;Ti grain. If the cooling rate is high and there is uniform nucleation of &agr;Ti throughout the grain, neighboring &agr;Ti particles have different crystallographic orientations, and each behave as distinct acoustic scattering entities. However, if there are only a few sites of &agr;Ti nucleation within the &bgr;Ti grain, then the &agr;Ti particles in a given area all grow with the same crystallographic orientation, and a colony structure results. This colony becomes the acoustic entity. Since a colony is formed within a &bgr;Ti grain, the colony size will be less than the &bgr;Ti grain size. The size of &bgr;Ti grains and the nature of &agr;Ti particles colony structures are important variables that influence ultrasonic noise and ultrasonic inspection in single phase and two-phase titanium alloys and materials. Therefore, the size of &bgr;Ti grains and the nature of &agr;Ti particles in colony structures may influence ultrasonic inspection techniques, methods, and results by creating undesirable noise during ultrasonic inspection. While thermomechanical processing techniques, which rely on dynamic recrystallization in the &agr;+&bgr; temperature range to achieve uniform fine grain (UFG) &agr;Ti particles and prevent colony formation, have been developed to improve titanium microstructure, defects may remain in the titanium material. These defects may be undesirable for some titanium material applications.
Thus, in order to have acceptable titanium for certain applications, it is desirable to provide an ultrasonic inspection process that accurately determines the nature of noise during ultrasonic inspection. The ultrasonic inspection method should determine if ultrasonic noise is attributed to a defect in the titanium material, or is due to other factors.
Therefore, a need exists for an ultrasonic inspection method for determining material characteristics and properties. Further, a need exists for an ultrasonic inspection method for determining processed titanium characteristics and properties. Furthermore, a need exists determining material configurations and characteristics for accurate ultrasonic inspection methods.
SUMMARY OF THE INVENTION
In one aspect of the invention, an ultrasonic inspection method for determining acceptability of material for microstructurally sensitive applications is provided. The method comprises providing a material, directing ultrasonic energy of ultrasonic inspection to the material; scattering reflected energy in the material; determining an amount of noise generated by the ultrasonic inspection; and characterizing the material as acceptable if the amount of noise corresponds to a preset noise level.
In another aspect of the invention, a system for implementing the method, as embodied by the invention is provided. The ultrasonic inspection system for determining acceptability of material for microstructurally sensitive applications comprises means for providing a material, means for directing ultrasonic energy of ultrasonic inspection to the material; means for scattering reflected energy in the material; means for determining an amount of noise generated by the ultrasonic inspection; and means for characterizing the material as acceptable if the amount of noise corresponds to a preset noise level.
These and other aspects, advantages and salient features of the invention will become apparent from the following detailed description, which, when taken in conjunction with the annexed drawings, where like parts are designated by like reference characters throughout the drawings, disclose embodiments of the invention.
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The Journal of The Acoustical Society of America, Revised Grain-Scattering Formulas and T
Bewlay Bernard Patrick
Deaton, Jr. John Broddus
Gigliotti, Jr. Michael Francis Xavier
Gilmore Robert Snee
General Electric Company
Johnson Noreen C.
Saint-Surin Jacques
Santandrea Robert P.
Williams Hezron
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