Patent Application
20250146114
The present disclosure is drawn to the field of metal processing, and specifically, to improvements in techniques for super transus processing of titanium, zirconium, and/or hafnium materials.
This section is intended to introduce the reader to various aspects of art, which may be related to various aspects of the present invention that are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present invention. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.
Hydrogen processing of titanium materials has previously been used as a method to refine the α+β microstructure during lower temperature (i.e., below the β transus temperature) heat treatments for additively manufacture components (see U.S. Pat. No. 11,624,105B2) and powder metallurgy sintering processes to refine the microstructure and improve densification (see U.S. Pat. No. 9,816,157B2).
However, processing certain materials, such as titanium alloys, above the β transus temperature is often required in order to homogenize the microstructure, reduce the flow stress to enable mechanical working (rolling, forging, etc.), or prevent cracking during mechanical working. Unfortunately, traditional titanium processing above the β transus temperature causes significant growth of the β grain size and is mainly dependent on the maximum processing temperature. The large grain sizes caused by super transus processing cause poor mechanical properties (including, e.g., strength, ductility, fatigue strength, etc.) and often require additional processing. Conventional techniques to reduce the prior β grain size require deformation to break apart prior β grains or permanent alloying to limit their growth.
Thus, an improved technique for controlling the microstructure when processing titanium materials above the β transus temperature is desirable.
Various deficiencies in the prior art are addressed below by the disclosed compositions of matter and techniques.
In various aspects, a method for grain growth mitigation in titanium, zirconium, and/or hafnium materials may be provided. The method may include heating a titanium, zirconium, and/or hafnium material in a processing atmosphere to a first temperature above a β transus temperature of the titanium, zirconium, and/or hafnium material. At a point in time before the titanium, zirconium, and/or hafnium material is at the first temperature, the method may include introducing hydrogen gas into the processing atmosphere to achieve a predetermined hydrogen partial pressure in the processing atmosphere. The method may include holding the titanium, zirconium, and/or hafnium material at the first temperature in the processing atmosphere at the predetermined hydrogen partial pressure for a first holding time.
In some embodiments, after holding, the method may include cooling to a second temperature less than the first temperature. The method may include removing hydrogen gas from the processing atmosphere at the second temperature. In some embodiments, after cooling to the second temperature, the method may include annealing in an inert gas or vacuum atmosphere. The method may include cooling to a third temperature less than the second temperature.
In some embodiments, after holding, the method may include directly heating in an inert or reactive atmosphere. In some embodiments, after holding, the method may include cooling in an inert or reactive atmosphere.
In some embodiments, the titanium, zirconium, and/or hafnium material may include titanium. In some embodiments, the titanium, zirconium, and/or hafnium material may include zirconium or hafnium. In some embodiments, the titanium, zirconium, and/or hafnium material may include an alloy. In some embodiments, the alloy may include titanium and may further include zirconium and/or hafnium.
In some embodiments, the first holding time may be no more than 24 hours, such as no more than 8 hours. In some embodiments, the predetermined hydrogen partial pressure may be less than 0.5 atm.
Additional objects, advantages, and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the present invention and, together with a general description of the invention given above, and the detailed description of the embodiments given below, serve to explain the principles of the present invention.
It should be understood that the appended drawings are not necessarily to scale, presenting a somewhat simplified representation of various features illustrative of the basic principles of the invention. The specific design features of the sequence of operations as disclosed herein, including, for example, specific dimensions, orientations, locations, and shapes of various illustrated components, will be determined in part by the particular intended application and use environment. Certain features of the illustrated embodiments have been enlarged or distorted relative to others to facilitate visualization and clear understanding. In particular, thin features may be thickened, for example, for clarity or illustration.
The following description and drawings merely illustrate the principles of the invention. It will thus be appreciated that those skilled in the art will be able to devise various arrangements that, although not explicitly described or shown herein, embody the principles of the invention and are included within its scope. Furthermore, all examples recited herein are principally intended expressly to be only for illustrative purposes to aid the reader in understanding the principles of the invention and the concepts contributed by the inventor(s) to furthering the art and are to be construed as being without limitation to such specifically recited examples and conditions. Additionally, the term, “or,” as used herein, refers to a non-exclusive or, unless otherwise indicated (e.g., “or else” or “or in the alternative”). Also, the various embodiments described herein are not necessarily mutually exclusive, as some embodiments can be combined with one or more other embodiments to form new embodiments.
The numerous innovative teachings of the present application will be described with particular reference to the presently preferred exemplary embodiments. However, it should be understood that this class of embodiments provides only a few examples of the many advantageous uses of the innovative teachings herein. In general, statements made in the specification of the present application do not necessarily limit any of the various claimed inventions. Moreover, some statements may apply to some inventive features but not to others. Those skilled in the art and informed by the teachings herein will realize that the invention is also applicable to various other technical areas or embodiments.
The disclosed method enables reduced β grain size for titanium materials that are being processed above the temperature at which the material undergoes and allotropic transformation from the room temperature α phase to the high temperature β phase. This temperature is known at the β transus temperature. Reducing the β grain size improves mechanical properties.
In various aspects, a method for grain growth mitigation in titanium, zirconium, and/or hafnium materials may be provided. The method may include heating a titanium, zirconium, and/or hafnium material in a processing atmosphere to a first temperature above a β transus temperature of the titanium, zirconium, and/or hafnium material. The first temperature may be below the melting temperature of the material. In some embodiments, the first temperature may be from about 700° C. to about 1500° C. In some embodiments, the first temperature may be from about 900° C. to about 1300° C. The processing atmosphere may be free of hydrogen while heating. The processing atmosphere may be inert to the titanium, zirconium, and/or hafnium material. The processing atmosphere may include a noble gas, such as argon.
In some embodiments, the titanium, zirconium, and/or hafnium material may include titanium. In some embodiments, the titanium, zirconium, and/or hafnium material may include zirconium or hafnium. In some embodiments, the In some embodiments, the titanium, zirconium, and/or hafnium material may include an alloy. In some embodiments, the titanium alloy may include titanium, and may further include zirconium and/or hafnium.
In certain non-limiting specific examples, the titanium, zirconium, and/or hafnium material may be commercially pure (CP) titanium metal, CP zirconium metal, or nuclear grade hafnium metal. The material may be at least 99% or 99.2% by weight pure metal. If the material is an alloy, non-limiting alloying materials include a metalloid and/or a transition metal. Non-limiting examples of alloying materials include V, Al, Si, Mo, W, Ta, Nb, Cr, Ni, Co, Cu, Mg, Pt, Pd, B, and/or Sn. In some embodiments, the alloying material may be a beta stabilizer. The term “beta stabilizer” refers to an element that is added to the titanium, zirconium, and/or hafnium material that stabilizes the beta crystal structure and may lower the alpha-to-beta transformation temperature. Non-limiting examples of beta stabilizers include, e.g., vanadium, niobium, tantalum, molybdenum, manganese, iron, chromium, cobalt, nickel, copper, and silicon.
In some embodiments, the material may include up to 49% by atomic concentration of these alloying materials. In some embodiments, the material may include up to 40% by atomic concentration of these alloying materials. In some embodiments, the material may include up to 30% by atomic concentration of these alloying materials. In some embodiments, the material may include up to 20% by atomic concentration of these alloying materials. In some embodiments, the material may include 2-10% by atomic concentration of these alloying materials. In some embodiments, the material may include small amounts of other elements, such as iron, oxygen, carbon, nitrogen, hydrogen, or yttrium. In some embodiments, the material may include no more than 2% or no more than 1% of these other elements.
At a point in time before the titanium, zirconium, and/or hafnium material is at the first temperature, the method may include introducing hydrogen gas into the processing atmosphere to achieve a predetermined hydrogen partial pressure in the processing atmosphere. For example, in some embodiments, hydrogen may be introduced when the temperature is below the β transus temperature. In some embodiments, hydrogen may be introduced when the temperature is above the β transus temperature, but less than the first temperature. The point is preferably after the heating has begun.
In some embodiments, hydrogen may be introduced when the temperature is at least 200° C. In some embodiments, hydrogen may be introduced when the temperature is at least 500° C. In some embodiments, hydrogen may be introduced when the temperature is at least 1000° C. In some embodiments, hydrogen may be introduced when the temperature is no more than 1400° C. In some embodiments, hydrogen may be introduced when the temperature is no more than 1100° C. In some embodiments, hydrogen may be introduced when the temperature is no more than 800° C.
The hydrogen partial pressure may be greater than 0.01 atm. In some embodiments, the hydrogen partial pressure may be at least 0.5 atm. In some embodiments, the hydrogen partial pressure may be at least 1 atm. In some embodiments, the hydrogen partial pressure may be less than 0.5 atm. In some embodiments, the hydrogen partial pressure may be no more than 10 atm.
The method may include holding the titanium, zirconium, and/or hafnium material at the first temperature in the processing atmosphere at the predetermined hydrogen partial pressure for a first period of time (a first holding time). There is no meaningful limit to the length of time the material may be held at the first temperature. In some embodiments, the first period of time may be no more than 48 hours. In some embodiments, the first period of time may be no more than 24 hours. In some embodiments, the first period of time may be no more than 12 hours. In some embodiments, the first period of time may be no more than 8 hours. In some embodiments, the first period of time may be no more than 4 hours. In some embodiments, the first period of time may be no more than 1 hour. In some embodiments, the first period of time may be at least 1 minute. In some embodiments, the first period of time may be at least 1 hour. In some embodiments, the first period of time may be at least 4 hours.
After holding for the first period of time at the first temperature in the processing atmosphere at the predetermined hydrogen partial pressure, the titanium, zirconium, and/or hafnium material may be processed further using any desired technique.
In some embodiments, after holding for the first period of time, the method may include cooling to a second temperature. In some embodiments, the second temperature may be below a β transus temperature of the titanium, zirconium, and/or hafnium material and above the decomposition temperature of a δ phase, about 200° C. for some materials. The decomposition temperature of a substance is the temperature at which the substance begins to chemically decompose. The decomposition temperature will differ based on the composition of the material (i.e., different metals and alloys will have different decomposition temperatures of the δ phase). In some embodiments, the second temperature may be room temperature.
The method may include removing hydrogen gas from the processing atmosphere at the second temperature. This can remove at least a portion of hydrogen from the titanium, zirconium, and/or hafnium material.
In some embodiments, the process may include keeping the material at the second temperature in the hydrogen-free processing atmosphere for a second period of time (a second holding time).
There is no meaningful limit to the length of time the material may be held at the second temperature in the hydrogen-free processing atmosphere. In some embodiments, the second period of time may be no more than 48 hours. In some embodiments, the second period of time may be no more than 24 hours. In some embodiments, the second period of time may be no more than 12 hours. In some embodiments, the first period of time may be no more than 8 hours. In some embodiments, the second period of time may be no more than 4 hours. In some embodiments, the second period of time may be no more than 1 hour. In some embodiments, the second period of time may be at least 1 minute. In some embodiments, the second period of time may be at least 1 hour. In some embodiments, the second period of time may be at least 4 hours.
The volume fraction of β phase material can vary, such as from 0% to 100%, depending on the composition of the titanium, zirconium, and/or hafnium material, and the maximum temperature and cooling rate used during the heat treatment. For example, it could be as low as 0% for commercially pure materials, or as high as 100% for beta alloys that have enough beta stabilizing elements in them to stabilize the beta phase at room temperature.
In some embodiments, after cooling to the second temperature, the method may include annealing in an inert gas or vacuum atmosphere. In some embodiments, the annealing temperature may be 200° C. to 900° C., such as 500° C. to 800° C. There is no meaningful limit to the length of time the material may be annealed. In some embodiments, such anneals may be performed for 10 seconds-48 hours, depending on the size of the material and the type of furnace.
After cooling to a second temperature and performing some processing of the material, the method may include cooling to a third temperature less than the second temperature. In some embodiments, the third temperature may be a temperature less than 50° C. In some embodiments, the third temperature may be a temperature of −50° C. to 50° C.
In some embodiments, after holding for the first period of time, the method may include directly heating in an inert or reactive atmosphere.
In some embodiments, after holding for the first period of time, the material may be aged. Any known aging technique may be used. In some embodiments, the material may be cooled to room temperature and heated up to an aging temperature. Alternately, the temperature can be ramped down directly from the heat treatment temperature to the aging temperature. The material can be held at the aging temperature to further refine the microstructure. In some embodiments, the aging temperature may be no more than 1000° C. In some embodiments, the aging temperature may be from about 200° C. to about 700° C. By aging, the material may experience precipitation of secondary phase(s), which can increase the strength of the material.
Several ½″ rod Ti-6Al-4V samples were heat treated at different temperatures, times, and H2 partial pressures. Referring to
A heat treatment profile used for the various examples can be seen in
After the intermediate holding, the parts were then heated to a maximum holding temperature, Tmax, and held at temperature for a desired time. The parts were then cooled in hydrogen to a temperature 202 at which hydrogen was turned off, and the atmosphere gradually became inert due to flowing Ar. The samples were then cut, polished, and etched to reveal the microstructure and imaged.
Various modifications may be made to the systems, methods, apparatus, mechanisms, techniques, and portions thereof described herein with respect to the various figures, such modifications being contemplated as being within the scope of the invention. For example, while a specific order of steps or arrangement of functional elements is presented in the various embodiments described herein, various other orders/arrangements of steps or functional elements may be utilized within the context of the various embodiments. Further, while modifications to embodiments may be discussed individually, various embodiments may use multiple modifications contemporaneously or in sequence, compound modifications and the like.
Although various embodiments which incorporate the teachings of the present invention have been shown and described in detail herein, those skilled in the art can readily devise many other varied embodiments that still incorporate these teachings. Thus, while the foregoing is directed to various embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof. As such, the appropriate scope of the invention is to be determined according to the claims.
The invention described herein may be manufactured and used by or for the Government of the United States for all governmental purposes without the payment of any royalty.
