Patent Grant
10011885
Field of Technology
The present disclosure relates to methods for producing titanium and titanium alloy articles. In particular, certain non-limiting aspects of the present disclosure relate to methods including producing a hydrogenated titanium or titanium alloy, deforming (working) the titanium or titanium alloy, and subsequently dehydrogenating the material to reduce the hydrogen content of an article. In certain non-limiting embodiments of the method of the present disclosure, the method provides a titanium or titanium alloy article having an ultra-fine α-phase particle size, e.g., an average α-phase particle size of less than 10 microns in the longest dimension.
Description of the Background of the Technology
Titanium alloys are used in a variety of applications for their advantageous balance of material properties including strength, ductility, modulus, and temperature capability. For example, Ti-6Al-4V alloy (also denoted “Ti-6-4 alloy”, having a composition specified in UNS R56400) is a commercial alloy that is widely used in the aerospace and biomedical industries.
Titanium has two allotropic forms: a “high temperature” beta (“β”)-phase, which has a body centered cubic (“bcc”) crystal structure; and a “low temperature” alpha (“α”)-phase, which has a hexagonal close packed (“hcp”) crystal structure. The temperature at which the α-phase transforms completely into the β-phase as a titanium alloy is heated is known as the β-transus temperature (or simply “β-transus” or “Tβ”). Conventional processing of cast ingots of titanium alloys to form billets or other mill products generally involves a combination of deformation steps above and below the β-transus depending on the desired structure and material property requirements for a given application.
A finer α particle size can result in higher tensile properties, improved fatigue strength, and improved ultrasonic inspectability for the titanium alloy article. The conventional approach to achieving a finer α particle size in titanium alloy articles usually involves managing complicated thermo-mechanical processing, for example, rapid quenching from the β-phase field followed by relatively large amounts of hot working or strain in the α+β phase region and possibly a post-deformation anneal in the α+β phase region to enhance particle refinement. In particular, to achieve the finest α particle size, hot working at very low, and perhaps marginally practical, temperatures and using relatively low, controlled strain rates is required. However, there are manufacturing limits to what can be achieved with this conventional approach, due to increased forging loads, lower process yields due to cracking, and lack of or limits of practical strain rate control, especially at large section sizes. The conventional approach may also be limited by an increasing tendency to form small voids or pores in the alloy under certain processing conditions such as low temperatures and/or high strain rates. This phenomenon is known as “strain-induced porosity” or “SIP.” The presence of SIP in the alloy can be particularly deleterious to the alloy properties and can result in significant process yield loss. In severe cases, additional and costly processing steps, such as hot-isostatic pressing, may be required to eliminate SIP that has formed. Thus, there has developed a need for methods for producing titanium alloy articles having a finer α particle size while avoiding limits imposed by the hot working temperature and/or the strain rate.
The present disclosure, in part, is directed to methods and alloy articles that address certain of the limitations of conventional approaches for producing titanium alloy articles. Certain embodiments herein address limitations of conventional techniques for achieving a finer α particle size in certain titanium and titanium alloy articles. One non-limiting aspect of the present disclosure is directed to a method of producing an article selected from a titanium article and a titanium alloy article. The method comprises: melting feed materials with a source of hydrogen to form a molten heat of a titanium or titanium alloy; casting at least a portion of the molten heat to form a hydrogenated titanium or titanium alloy ingot; deforming the hydrogenated ingot at an elevated temperature to form a worked article comprising a cross-sectional area smaller than a cross-sectional area of the hydrogenated ingot; and dehydrogenating the worked article to reduce a hydrogen content of the worked article. In certain non-limiting embodiments of the method, the dehydrogenated article comprises an average α-phase particle size of less than 10 microns in the longest dimension. In certain non-limiting embodiments of the method, the titanium or titanium alloy is selected from the group consisting of commercially pure titanium, a near-α titanium alloy, an α+β titanium alloy, a near-β titanium alloy, and a titanium aluminide alloy.
Another non-limiting aspect of the present disclosure is directed to a method of producing an α+β titanium alloy article. The method comprises: melting feed materials with a source of hydrogen to form a molten heat; casting at least a portion of the molten heat to form a hydrogenated ingot of an α+β titanium alloy; deforming the hydrogenated ingot at a temperature initially in a β phase field and subsequently in an α+β+δ phase field to form a worked article comprising a cross-sectional area smaller than a cross-sectional area of the hydrogenated ingot; and vacuum heat treating the worked article to reduce a hydrogen content of the worked article.
Another non-limiting aspect of the present disclosure is directed to a method of producing an α+β titanium alloy article. The method comprises: melting feed materials with a source of hydrogen to form a molten heat; casting at least a portion of the molten heat to form a hydrogenated ingot of an α+β titanium alloy; deforming the ingot at a first elevated temperature to form an initial worked article comprising a cross-sectional area smaller than a cross-sectional area of the hydrogenated ingot; hydrogenating the initial worked article at a second elevated temperature; deforming the initial worked article at a third elevated temperature to form an intermediate worked article having a cross-sectional area smaller than a cross-sectional area of the initial worked article; and vacuum heat treating the intermediate worked article to reduce the hydrogen content of the intermediate worked article.
Features and advantages of the methods and alloy articles described herein may be better understood by reference to the accompanying drawings in which:
It should be understood that the invention is not limited in its application to the arrangements illustrated in the above-described drawing. The reader will appreciate the foregoing details, as well as others, upon considering the following detailed description of certain non-limiting embodiments of methods and alloy articles according to the present disclosure. The reader also may comprehend certain of such additional details upon using the methods and alloy articles described herein.
In the present description of non-limiting embodiments and in the claims, other than in the operating examples or where otherwise indicated, all numbers expressing quantities or characteristics of ingredients and products, processing conditions, and the like are to be understood as being modified in all instances by the term “about.” Accordingly, unless indicated to the contrary, any numerical parameters set forth in the following description and the attached claims are approximations that may vary depending upon the desired properties one seeks to obtain in the methods and alloy articles according to the present disclosure. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.
The present disclosure, in part, is directed to methods and titanium and titanium alloy articles that address certain of the limitations of conventional approaches for achieving a finer α particle size in certain titanium alloy articles. Referring to
More generally, the methods described herein may be used in connection with the preparation of ingots and other articles of any of commercially pure titanium, near-α titanium alloys, α+β titanium alloys, near-β titanium alloys, and titanium aluminide alloys. Non-limiting examples of near-α titanium alloys that can be processed in accordance with various non-limiting embodiments of the methods disclosed herein include Ti-8Al-1Mo-1V alloy (having a composition specified in UNS R54810). Non-limiting examples of α+β titanium alloys that can be processed in accordance with various non-limiting embodiments of the methods disclosed herein include Ti-6Al-2Sn-4Zr-2Mo alloy (having a composition specified in UNS R54620), Ti-6Al-4V alloy (having a composition specified in UNS R56400), and Ti-6Al-6V-2Sn alloy (having a composition specified in UNS R56620). Non-limiting examples of near-β titanium alloys that can be processed in accordance with various non-limiting embodiments of the methods disclosed herein include Ti-5Al-2Sn-2Zr-4Mo-4Cr alloy (also denoted “Ti-17” alloy, having a composition specified in UNS-R58650), Ti-6Al-2Sn-2Zr-2Cr-2Mo-0.15Si alloy (also denoted “Ti-62222” alloy), and Ti-4.5Al-3V-2Mo-2Fe alloy (also denoted “SP-700” alloy). Non-limiting examples of titanium aluminide alloys that can be processed in accordance with various non-limiting embodiments of the methods disclosed herein include Ti-24Al-11Nb alloy and super-α2 based Ti-25Al-10Nb-3V-1Mo alloy. It will be appreciated by those skilled in the art that the foregoing alloy designations refer only to nominal concentrations, on a weight percent of total alloy weight basis, of certain major alloying elements contained in the titanium alloy, and that these alloys may also include other minor additions of alloying elements, as well as incidental impurities, that do not affect the designation of the alloys as near-α titanium alloys, α+β titanium alloys, near-β titanium alloys, and titanium aluminide alloys. Moreover, although the present description references certain specific alloys, the methods and alloy articles described herein are not limited in this regard. As will be understood, the starting materials may be selected by an ordinarily skilled practitioner so as to provide an alloy ingot having the desired composition and other desired properties.
According to certain non-limiting embodiments, at least a portion of the hydrogenated ingot produced in the melting and casting steps according to the present methods has a hydrogen content greater than 0 to 1.5%, by weight based on the total weight of the hydrogenated ingot. According to certain other non-limiting embodiments, the hydrogen content of at least a portion of the hydrogenated ingot is 0.05% to 1.0%, by weight. In yet other non-limiting embodiments, at least a portion of the hydrogenated ingot has a hydrogen content of 0.05% to 0.8%, or 0.2% to 0.8%, by weight. Depending on the composition for the particular alloy article, a hydrogen content greater than 1.5% by weight may promote cracking during cooling to room temperature and, therefore, may not provide the requisite material properties.
The conventional approach to introducing hydrogen in a titanium alloy article is post-melt, through a heat treatment of the solidified alloy in the presence of hydrogen. This conventional approach relies on solid-state diffusion of hydrogen and, therefore, typically requires a high temperature heat treatment for a lengthy period of time, increasing significantly with section size. In contrast, certain non-limiting embodiments of methods of producing an α+β titanium alloy article or other titanium or titanium alloy articles according to the present disclosure include melting feed materials with a source of hydrogen to provide a hydrogenated titanium or titanium alloy ingot. In other words, a hydrogen source is present during the production of the molten heat and hydrogen from the source is incorporated into the cast material. According to certain non-limiting embodiments, the hydrogen source is present during the melting and casting (solidification) steps, which are performed simultaneously.
The hydrogen may be incorporated into the cast titanium or titanium alloy in the form of, for example, hydride precipitation or interstitial solid solution, in the titanium or titanium alloy matrix, although the hydrogen may be present in any form promoted by the alloy composition and processing conditions. As further explained below, titanium and titanium alloy articles processed according to various embodiments of methods according to the present disclosure can result in improved workability and process yields and thereby decrease production costs, and/or can achieve finer α particle size than is possible via conventional titanium conversion methods. Moreover, as further explained below in connection with certain embodiments herein, by maintaining the hydrogenated state through the final hot worked and rough-machined article, the annealing times needed for dehydrogenation (i.e., reducing hydrogen content) can be relatively short and economically practical.
In certain non-limiting embodiments, the source of hydrogen may be, for example: a gaseous environment comprising a partial pressure of hydrogen in contact with the molten feed materials; a gaseous environment comprising a partial pressure of hydrogen and an inert gas (e.g., helium or argon) in contact with the molten feed materials; and/or one or more hydrogen-containing materials (such as, for example, titanium hydride powder, hydride titanium chips or turnings) that are melted along with other feed materials. Those having ordinary skill, upon reading the present description, may identify additional sources of hydrogen that could be used in methods according to the present disclosure to increase the hydrogen content of a titanium or titanium alloy article. It is intended that all such additional hydrogen sources are within the scope of the present invention.
With continuing reference to
In certain non-limiting embodiments of the present methods, the hydrogenated ingot is deformed at a temperature initially in a β phase field (block 120) of the particular alloy, and is subsequently deformed in an α+β+δ phase field (block 130) of the alloy to form a worked article comprising a cross-sectional area smaller than a cross-sectional area of the hydrogenated ingot. In certain embodiments of the present method involving deformation in the β phase field and subsequently in the α+β+δ phase field, the alloy is an α+β titanium alloy. Conventional processing of cast ingots of α+β alloys to form billets or other mill products typically involves an initial deformation of the material above the β-transus (i.e., in the β phase field) to break up the cast structure of the ingot. Without intending to be bound to any theory, providing an α+β titanium alloy article with an increased hydrogen content using methods according to the present disclosure may improve the hot workability or ductility of the α+β titanium alloy by decreasing the β-transus temperature of the alloy and stabilizing the alloy's β phase.
In certain non-limiting embodiments of methods according to the present disclosure, a titanium or titanium alloy article made by casting a melt produced by melting feed materials with a source of hydrogen is initially deformed at a temperature slightly above the β-transus temperature to form an intermediate billet (block 120). Deforming the titanium or titanium alloy article according to various non-limiting embodiments disclosed herein may involve deforming a portion of the article or the entire article. Further, as used herein, phrases such as “deforming at” and “deforming the body at,” etc., with reference to a temperature, a temperature range, or a minimum temperature, mean that at least the portion of the object to be deformed has a temperature at least equal to the referenced temperature, within the referenced temperature range, or at least as high as the referenced minimum temperature during the deformation. Non-limiting examples of methods of deforming the titanium or titanium alloy articles that may be used in accordance with various non-limiting embodiments disclosed herein include one or a combination of forging, cogging, extrusion, drawing, and rolling. For example, according to one specific non-limiting embodiment, deforming at least a portion of the article at a temperature T1 can comprise forging the article at a condition wherein at least a portion of the article is at temperature T1. With regard to α+β titanium alloys, because increasing the hydrogen content of an α+β titanium alloy decreases the β-transus temperature, the temperature of the initial β forging operation can be lower compared to conventional processing, in which the hydrogen content of the alloy may be lower. Utilizing a lower temperature during the initial β forging operation can provide benefits such as minimizing β-grain size and retaining a higher density of dislocations which can facilitate microstructural refinement during subsequent processing.
Still referring to block 120 of
According to certain non-limiting embodiments, the hydrogen-containing intermediate billet formed from the melt is cooled to form hydride precipitates in the intermediate billet. The hydrogen content of the hydrogenated ingot can promote a eutectoid phase transformation of the form βα+β+δ (titanium hydride) when held at a temperature in an α+β+δ phase region. As used herein, phrases such as “hold at” and the like, with reference to a temperature, temperature range, or minimum temperature, mean that at least a desired portion of the titanium or titanium alloy is maintained at a temperature at least equal to the referenced or minimum temperature, or within the referenced temperature range. In certain non-limiting embodiments, the titanium or titanium alloy is cooled in a controlled manner through the eutectoid transus to room temperature. Alternatively, the material is cooled in a controlled manner to below the eutectoid transus, held (aged) at a temperature or in temperature range below the eutectoid transus for a period of time to develop a more homogeneous distribution of hydrogen, and then cooled in a controlled manner to room temperature. The δ-phase precipitates can be used to refine the α+β microstructure and potentially facilitate the formation of a finer α particle size compared to conventional processing, as further explained below. Although the present description references α+β titanium alloys, the methods and alloy articles described herein are not limited in this regard. It is to be appreciated that, in other non-limiting embodiments of methods according to the present disclosure, various modifications can be made without departing from the spirit and scope of the disclosure as will be apparent to those skilled in the art. Such changes and modifications are within the scope and teachings of this disclosure as defined in the claims appended hereto.
With continuing reference to
In certain non-limiting embodiments, the hydrogenated ingot is cylindrical. In further embodiments, the hydrogenated ingot may assume other geometric forms, and the cross-section may be, for example, roughly rectangular. According to certain non-limiting embodiments disclosed herein, deforming the hydrogenated ingot into the final billet may comprise deforming or otherwise working the ingot in one or more passes or steps, to attain a total percent reduction in cross-sectional area of at least 15% up to 98% during the hot working.
According to certain non-limiting embodiments involving processing of a Ti-6-4 titanium alloy article, the temperature in the α+β+δ phase region of the α+β titanium alloy at which the ingot is worked (block 130) is less than 800° C. The δ-phase hydride precipitates formed in embodiments herein may facilitate the formation of a finer α particle size compared to conventional processing. Without intending to be bound to any theory, the δ-phase hydride precipitates can act as nucleation sites for recrystallization of the α phase during the hot working, and also can act as pinning sites to stabilize the refined α particles.
According to certain non-limiting embodiments, a method of producing a Ti-6-4 titanium alloy article according to the present disclosure comprises deforming a hydrogenated ingot cast from an ingot prepared using a hydrogen source as described herein, at a first elevated temperature to form an initial worked article comprising a cross-sectional area smaller than a cross-sectional area of the hydrogenated ingot, and hydrogenating the initial worked article at a second elevated temperature (block 150). In certain non-limiting embodiments, hydrogenation during melt processing (block 100) is used to increase hydrogen to an intermediate content lower than a desired final content, and the balance of the desired hydrogen is then added to hydrogenate the alloy by a subsequent short-time, high-temperature heat treatment applied, for example, after the β forge. The further hydrogenated alloy may be additionally processed to precipitate titanium hydride particles as detailed above.
With continuing reference to
According to certain non-limiting embodiments, the final article provided is dehydrogenated (block 180) in either the as-worked or rough machined condition to reduce a hydrogen content of the final article. As used herein, “dehydrogenating” means to reduce the hydrogen content of the final article to any degree. In certain non-limiting embodiments, dehydrogenating the article reduces the hydrogen content to no greater than 150 ppm. In certain non-limiting embodiments, dehydrogenating the final article may reduce hydrogen content in the final article to any suitable reduced hydrogen content to inhibit or avoid low temperature embrittlement and/or to meet industry standard chemistry specifications for the particular alloy. During the dehydrogenation process, the δ-phase (titanium hydride) precipitates may decompose and leave behind a relatively fine α+β microstructure with morphologies that range from slightly acicular to equiaxed, depending on processing conditions.
In certain non-limiting embodiments, the dehydrogenation treatment produces a dehydrogenated worked article. In various non-limiting embodiments, the dehydrogenated worked article comprises an average α-phase particle size less than 10 microns in the longest dimension. In further non-limiting embodiments, the dehydrogenated worked article can comprise an average α-phase particle size of less than 3 microns in the longest dimension. In further non-limiting embodiments, the dehydrogenated worked article can comprise an average α-phase particle size of less than 1 micron in the longest dimension. The refined α+β microstructure can improve the mechanical properties of the final article and/or improve ultrasonic inspectability. One ordinarily skilled in the art can readily determine the α-phase particle size for the dehydrogenated worked article by microscopy.
According to certain non-limiting embodiments, dehydrogenating the article includes vacuum heat treating the article. In certain non-limiting embodiments, vacuum heat treating the article comprises heating the final article in substantial vacuum at a temperature sufficient to remove at least a portion of hydrogen from the article. Although only a limited number of methods of dehydrogenation are described herein, the present invention is not so limited. Those having ordinary skill may readily determine a suitable dehydrogenation technique for a particular hydrogenated worked article.
Maintaining the titanium or titanium alloy article in its hydrogenated state all the way to a final worked or rough-machined condition can result in numerous process advantages including, for example, improved yield (less cracking), lower forging flow stresses, lower allowable hot working temperatures, improved machinability, and significantly reduced dehydrogenation annealing times. The changed process conditions can produce a final titanium or titanium alloy article with an ultra-fine structure and improved tensile strength, fatigue resistance, and ultrasonic inspectability.
Although the foregoing description has necessarily presented only a limited number of embodiments, those of ordinary skill in the relevant art will appreciate that various changes in the methods and other details of the examples that have been described and illustrated herein may be made by those skilled in the art, and all such modifications will remain within the principle and scope of the present disclosure as expressed herein and in the appended claims. It is understood, therefore, that the present invention is not limited to the particular embodiments disclosed or incorporated herein, but is intended to cover modifications that are within the principle and scope of the invention, as defined by the claims. It will also be appreciated by those skilled in the art that changes could be made to the embodiments above without departing from the broad inventive concept thereof.
This patent application claims the benefit of co-pending U.S. Provisional Patent Application Ser. No. 62/114,194, filed on Feb. 10, 2015, which is hereby incorporated herein by reference in its entirety.
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| Number | Date | Country | |
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| 20160230239 A1 | Aug 2016 | US |
| Number | Date | Country | |
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| 62114194 | Feb 2015 | US |
