Metal treatment – Process of modifying or maintaining internal physical... – Heating or cooling of solid metal
Reexamination Certificate
2000-01-11
2002-05-14
Sheehan, John (Department: 1742)
Metal treatment
Process of modifying or maintaining internal physical...
Heating or cooling of solid metal
C148S670000, C148S671000, C148S421000
Reexamination Certificate
active
06387197
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to methods for ultrasonic noise reduction in titanium-containing materials. In particular, the invention relates to methods for ultrasonic noise reduction in titanium alloy forgings.
Nondestructive evaluation by ultrasonic inspection and ultrasonic inspection testing is a known material testing and evaluation method. Ultrasonic testing typically requires that items to be detected possess high acoustic reflectance behaviors from bulk material under ultrasonic inspection. This different behavior permits the ultrasonic inspection technique to detect flaws, large and/or abnormal 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. The scattering of sound in a polycrystalline metallic material body, which is also known in the art as 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 the attenuation, &lgr; is the wavelength of the ultrasound energy, v is the 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 evaluated 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 no larger 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 at least one of the &bgr; and the &agr;+&bgr; temperature ranges 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, particularly those that are fatigue-life limiting applications.
There are a number of patents directed to ultrasonic inspection titanium alloys. For example, U.S. Pat. No. 5,631,424, entitled “Method For Ultrasonic Evaluation Of Materials Using Time Of Flight Measurements” issued to Nieters et al, and U.S. Pat. No. 5,533,401, entitled “Multizone Ultrasonic Inspection Method And Apparatus” issued to Gilmore, and assigned to General Electric, the entire contents of which are fully incorporated by reference herein. The ultrasonic inspection results for titanium, as described in these patents, may be dependent on the processing of the titanium and its structural configurations. Various processing methods for titanium and some structural configurations may result in generated noise during ultrasonic inspection, such as, but not limited to, generated high-ultrasonic noise, and may not provide desirable ultrasonic inspection results.
The high-ultrasonic noise that is generated during ultrasonic inspection of titanium-containing articles is undesirable. The generated noise can present problems in determining acceptable titanium microstructures, as the noise can lead to at least one of, but not limited to, a reduced possibility of detecting defects, increased ultrasonic inspection times, increased part inventory, and, possibly titanium parts needing to be scrapped because they can not be accurately inspected.
Therefore, a need exists for titanium processing and formation methods that can provide ultrasonic inspection of the formed titanium with reduced noise. Further, a need exists for titanium processing and formation methods that provide enhanced ultrasonic inspection of the formed titanium, in which the titanium comprises large diameter articles, such as titanium forgings.
SUMMARY OF THE INVENTION
Accordingly, a method is set forth for processing titanium into a titanium article, in which the titanium exhibits enhanced ultrasonic inspection characterization for determining its acceptability in microstructurally sensitive titanium applications. The method for processing titanium comprises providing titanium at a temperature above its &bgr;-transus temperature; quenching the titanium from a temperature above the &bgr;-transus temperature, the step of quenching titanium forming fine grain &agr;-plate microstructure in the titanium; and deforming the quenched titanium into a titanium article, the step of deforming the quenched titanium transforming the &agr;-plate microstructure into discontinuous-randomly textured &agr; particles. The discontinuous-randomly textured cc particles lead to a reduction in ultrasonic noi
Bewlay Bernard Patrick
Franczak Jacek Marian
Furrer David Ulrich
Gigliotti, Jr. Michael Francis Xavier
Shen Gangshu
Johnson Noreen C.
Oltmans Andrew L.
Santandrea Robert P.
Sheehan John
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