Metal structure and associated method

Abstract

The present disclosure relates to an α+β titanium alloy material for use in high-strain impact applications, wherein the material has an α+β lamellar microstructure, with secondary α precipitates within the β phase, as well as a heat treatment method and an additive manufacturing process of making said α+β titanium alloy material.

Description

METAL STRUCTURE AND ASSOCIATED METHODTechnical Field

[0001] The present disclosure relates to a metal structure and method of forming same, in particular a titanium alloy structure with improved mechanical properties.Background of the Disclosure

[0002] Additive manufacturing processes (also referred to as 3D printing) generally involve the successive and selective deposition of layers of material according to a 3D computer model to form a structure. Among the benefits of additive manufacturing processes are the relatively fast production time and relative ease of forming complex geometrical shapes, enabling net-shape or near net-shape manufacturing. A number of additive manufacturing processes exist for a variety of materials, ranging from polymers, metals, to ceramics. For metals, the processes typically begin with a metal powder which is spread in a layer and heated, for example by laser or electron beam.

[0003] Titanium alloys, such as Ti6A14V, are one example of metal materials used in additive manufacturing processes, however the produced structures show inferior mechanical properties compared to the same alloy as processed by conventional thermomechanical methods such as hot rolling or hot pressing. This has prevented the use of these additive manufacturing processes to produce metal structures for a number of applications, in particular where a comparatively high strength, hardness, fracture resistance, or a particular shearing behaviour is required, for example in aerospace, high-pressure environment, and structural applications.Summary of the Invention

[0004] According to a first aspect, there is provided an a+P titanium alloy material, wherein the material has an a+P lamellar microstructure, with secondary a precipitates within the P phase.

[0005] In some embodiments, the P phase comprises 9.5% or less of the microstructure; and wherein the secondary a precipitates comprise 2% or more of the microstructure.

[0006] In some embodiments, the P phase comprises 8% or more and 9.5% or less of the microstructure; and wherein the secondary a precipitates comprise 5% or more of the microstructure.

[0007] In some embodiments, the titanium alloy is Ti6A14V or Ti6242.

[0008] In some embodiments, the material has an initial acicular martensitic a phase microstructure prior to undergoing a heat treatment.

[0009] In some embodiments, the heat treatment is carried out at a temperature between 25°C and 75°C below the P-transus temperature of the alloy material.

[0010] In some embodiments, the heat treatment is carried out for a time period between about 0.5 hours and about 2 hours.

[0011] In some embodiments, the material is cooled at a rate between about 2°C / s and 5°C / s.

[0012] In some embodiments, the material is in a predetermined shape formed by an additive manufacturing process.

[0013] In some embodiments, the material is used in a high strain-rate impact application.

[0014] According to a second broad aspect, there is provided a method of producing an a+P titanium alloy structure, comprising: subjecting an a+P titanium alloy structure with a microstructure comprising an acicular martensitic a phase to a heat treatment; wherein the heat treatment is carried out at a temperature between 25 and 75°C below the P-transus temperature of the a+P titanium alloy structure.

[0015] In some embodiments, the heat treatment is carried out for a time period between about 0.5 hours and about 2 hours.

[0016] In some embodiments, the method further comprises cooling the structure at a cooling rate between about 2°C / s and 5°C / s.

[0017] In some embodiments, the metal material is formed on a substrate.

[0018] In some embodiments, the titanium alloy structure is produced by an additive manufacturing process.

[0019] In some embodiments, the additive manufacturing process is a laser powder bed fusion process.

[0020] In some embodiments, the a+P titanium alloy is Ti6A14V or Ti6242.

[0021] In some embodiments, the titanium alloy structure is shaped for use in a high strainrate impact application.

[0022] In some embodiments, the a+P titanium alloy structure is an a+P titanium alloy material according to the first aspect.

[0023] According to a third broad aspect, there is provided an additive manufacturing process, comprising: forming a structure in a predetermined shape from an a+P titanium alloy metal powder; subjecting the structure to a heat treatment step carried out at a temperature between 25°C and 75°C below the P-transus temperature of the a+P titanium alloy.

[0024] In some embodiments, the heat treatment is carried out for a time period between about 0.5 hours and about 2 hours.

[0025] In some embodiments, the method further comprises cooling the structure at a cooling rate between about 2°C / s and 5°C / s.

[0026] In some embodiments, the metal material is formed on a substrate.

[0027] In some embodiments, the a+P titanium alloy is Ti6A14V or Ti6242.

[0028] In some embodiments, the titanium alloy structure is shaped for use in a high strainrate impact application.

[0029] In some embodiments, the a+P titanium alloy structure is an a+P titanium alloy material according to the first aspect.

[0030] Other aspects, features, and advantages will become apparent from the following detailed description when taken in conjunction with the accompanying drawings, which are a part of this disclosure and which illustrate, by way of example, principles of the inventions disclosed.Brief Description of the Figures

[0031] The present disclosure will become better understood from the following detailed description of various non-limiting embodiments thereof, described in connection with the accompanying figures, wherein:

[0032] FIGURE 1 shows an SEM image of the micro structure of a Ti6A14V titanium alloy following laser powder bed fusion.

[0033] FIGURE 2 shows an SEM image of the micro structure of a Ti6A14V titanium alloy following laser powder bed fusion and heat treatment.

[0034] FIGURE 3 shows a comparison of the relative V50 performance of titanium alloys manufactured using different methods.

[0035] FIGURE 4A shows a plot of the relationship between total P phase and ballistic limit improvement for a range of example compositions.

[0036] FIGURE 4B shows a plot of the relationship between secondary a phase and ballistic limit improvement for the same compositions shown in FIGURE 4A.Detailed Description

[0037] The inventors have found that titanium alloy structures produced by additive manufacturing processes, have inferior mechanical properties compared to their conventionally thermomechanic ally processed equivalents. As a result, the titanium alloy structures formed by additive manufacturing processes may be unsuitable in applications where their conventionally processed equivalents are suitable. This presents an issue as the conventional thermomechanical methods are far more limited in the shapes which can be produced, as treatments such as hot rolling and pressing necessarily change the shape of the structure.

[0038] The inventors have developed a heat treatment process which at least partially addresses the problem of inferior mechanical properties in additively manufactured titanium structures. In particular, this process is applicable to the class of titanium alloys called a+p alloys, so named because both a and P phases are stable. This class may also include near-a and near-P alloys. As used in this specification, the term a+P alloys is intended to refer to titanium alloys which contain both a and P phases and transform martensitically uponquenching from temperatures above the P-transus temperature. For titanium alloys, a range of additive manufacturing processes such as wire-arc, directed energy deposition (DED), electron beam melting (EBM) or laser powder bed fusion (LPBF) produce mechanically inferior structures compared to conventional thermomechanical methods. The as-formed a+P titanium alloy has a martensitic structure when formed by additive manufacturing processes. Martensite, sometimes referred to as a’, is a phase characterised by a distorted hexagonal close packed lattice structure. Martensite has a high strength but low ductility. The present heat treatment results in the formation of a lamellar micro structure with coarse a phase and P phase, and the precipitation of secondary a particles from the P phase, resulting in an a+P microstructure with secondary a particles present in the P phase. Otherwise stated, some of the P phase is transformed (diffusionally precipitated) into secondary a phase during the heat treatment. This microstructure provides superior mechanical properties compared to the structure pre-heat treatment. Without wishing to be bound by theory, this is thought to relate to the precipitation of secondary a particles during the heat treatment. The secondary a phase may provide local resistance to the progression of adiabatic shear bands (ASB) due to local strengthening of the P phase in which they precipitate, while the coarse primary a and P phases retain a relatively high ductility. These superior mechanical properties may enable the alloy to be used in applications in which a non heat-treated structure of the same alloy would not be suitable, such as in high pressure environment, aerospace, structural, or protective applications.

[0039] In particular, the alloy material may be useful for high strain-rate impact applications, which are typically considered to refer to strain rates in the range of 102s’1to 106s’1. Many materials show different behaviours when undergoing high strain-rate deformations compared to low strain-rate or quasistatic deformations, and the required material properties differ if they are expected to survive high-strain rate impacts, such as during an automobile or aeroplane crash or when being hit by space or other high velocity debris. In these applications, the failure of titanium alloys is usually due to the formation of ASB which form due to intense strain localisation in the absence of heat extraction from the area, due to low thermal conductivity in titanium alloys. The ductility of the present micro structure allows for a large degree of absorption of the impact energy through plastic deformation, while also hindering ASB progression through the material. Advantageously, the micro structure is also free from the presence of continuous grain boundary a, which is continuous a phase at the prior P grain boundary, which has been found to increase the failure rate. The absence of continuous grainboundary a is attributed to the initial martensitic microstructure formed by additive manufacturing processes, such as laser powder bed fusion.

[0040] As a specific example, Ti6A14V, a titanium alloy belonging to the a+P class of titanium alloys, forms an acicular or needle-shaped martensitic a-phase micro structure when produced by a LPBF process, among other additive manufacturing processes. The heat treatment process converts this microstructure to an a+P lamellar microstructure, with secondary a precipitates within the P phase.

[0041] Advantageously, the heat treatment process does not result in a shape change of the titanium alloy structure, enabling the resultant heat-treated structure to retain the complex geometry created by a near-net shape process such as additive manufacturing, while also featuring comparable mechanical properties to the conventionally thermomechanically processed equivalent. The ability to form the structure into a near-net shape is advantageous because the conventionally thermomechanically processed equivalents must be welded or mechanically fastened together to create complex shapes. Any welds necessarily change the local micro structure around the weld site, and any mechanical fastening methods produce areas of stress concentration at the join. These create areas of inferior mechanical properties and may result in the conventionally thermomechanically processed structure being unusable.

[0042] The heat treatment is preferably carried out at a temperature which is selected to be between about 25°C and 75°C below the P-transus temperature, which is the temperature at which the hexagonal close packed a phase completely transforms to the body centered cubic P phase. The P-transus temperature varies for different titanium alloys, and may be anywhere between 900°C and 1050°C for typical a+P alloys. If the P-transus temperature is exceeded, recrystallization and excessive grain growth will occur, and if the temperature is more than 75°C below the P-transus temperature, there will be insufficient P-phase metastability to allow secondary a phase to diffusionally precipitate from the P phase. When the heat treatment is carried out in the range of about 25°C and 75°C below the P-transus temperature, the resultant microstructure is an a+P lamellar microstructure, with finer, secondary a precipitates in the P phase. This heat treatment can be performed, for example, in a vacuum-capable furnace. The temperature of the heat treatment will determine the volume fraction of a and P phases in the resultant micro structure.

[0043] In preferred embodiments, the heat treatment is carried out for a time period of between about 0.5 and about 2 hours. The time period is selected to ensure that diffusion-driven phase changes take place. In some circumstances, the time period may include the ramp up in temperature, for instance when heated in a furnace, if those temperatures facilitate diffusion. Otherwise stated, the heat treatment is preferably carried out for at least 0.5 hours above a temperature threshold, the threshold being selected to facilitate active diffusion. For example, when Ti6A14V is the alloy, this threshold may be 700°C.

[0044] The heat-treated structure is preferably cooled at a rate between approximately 2°C / s and 5°C / s, more preferably from approximately 3°C / s to 4°C / s. This may correspond to air-cooling of the material, for instance in a laboratory setting, but may also correspond to fan cooling in, for example, industrial settings. In other embodiments, argon cooling or other known cooling methods may be used, provided they can provide the required cooling rate. The exact cooling rate required will be dependent on the thickness of the structure, but should be selected to maintain the a+P lamellar microstructure, and to allow precipitation of secondary a phase within the P phase. Control over the cooling rate will determine the formation of the secondary a precipitates and the volume fraction of the retained and residual P phases in the resultant micro structure.

[0045] Preferably, the metal structure is formed by an additive manufacturing process, also referred to as 3D printing. A person skilled in the art will understand the term additive manufacturing to refer to a number of different techniques, including but not limited to laser powder bed fusion (LPBF), directed energy deposition (DED), electron beam melting (EBM) or wire-arc methods (WAAM). In preferred embodiments, the structure is formed by a laser powder bed fusion (LPBF) process, as this has been found to result in an acicular martensitic a phase microstructure optimal for the heat treatment method. Other additive manufacturing processes and processing parameters may be used, provided they result in a martensitic microstructure. This may thus apply to a large range of additive manufacturing techniques and processes. Additive manufacturing provides a number of advantages over conventional thermo-mechanical processes, the foremost being that these processes allow the creation of shapes with complex geometries relative to thermomechanical processes. Additive manufacturing is also a comparatively fast process. This is especially useful, for example, when the titanium alloy structure is used as a replacement component of a larger structure, enabling rapid repair of the larger structure. Additive manufacturing processes also producecomparatively less waste compared with conventional methods, which is important due to the high material cost of titanium alloys, and to reduce the environmental impact of producing the alloy structure.

[0046] Alternatively, the structure may be formed on a substrate, for example applied as a coating on a substrate with a predetermined shape, so as to retain the predetermined shape when removed from the substrate. In other embodiments, the substrate may be retained, with the alloy forming a permanent coating. In these embodiments, the substrate is chosen from a material which can withstand the heat treatment temperatures without losing its shape. Otherwise stated, the structure is preferably formed by a near-net shape forming process, that is to say that the shape in which the structure is formed initially is close to or is the final shape for the structure's intended purpose.

[0047] The heat treated titanium alloy has a microstructure of an a+P lamellar structure, with secondary a precipitates within the P phase. More specifically, the micro structure consists of alternating course primary a phase and P phase. Within the P phase are fine secondary a phase precipitates. These precipitates preferably have an acicular or needle-like shape. The secondary a phase is diffusionally precipitated from the P phase, as opposed to other forms of secondary a phase such as continuous grain boundary a which forms at the prior grain boundaries and secondary martensite, which is martensite retained in the micro structure through the use of water quenching or other rapid cooling techniques.

[0048] Advantageously, alloys which have undergone this heat treatment show improved mechanical properties relative to the same alloys pre-treatment, and as the heat treatment step does not cause any shape change, the structure maintains the shape it was formed with. This allows the complex geometries made possible by additive manufacturing to be used in applications which require an increased strength, hardness, reduced tendency to fracture, or specific failure characteristics, such as the tendency to form localized fractures or to shear when failure occurs. For example, the produced structure may be suitable for high strain rate impact and / or high-pressure applications, or as part of a shield surface surrounding a turbine, or as a material for orbital debris mitigation.

[0049] In some embodiments, the titanium alloy is Ti6A14V, which is also referred to by the names TC4 and Ti64. Ti6A14V is an a+P alloy, forming both an a phase and a P phase on cooling, the specific amounts of each phase being controllable by the heat treatment process.In other embodiments, the titanium alloy is Ti6242, a titanium ‘near-a’ alloy, which also forms an a phase and P phase on cooling. It will be understood that other titanium a+P alloys, may also be suitable as a starting material, provided that they result in a similar initial martensitic microstructure when formed by an additive manufacturing process. Other metal materials may also benefit from the heat treatment process, and may also show improved mechanical properties as a result of the heat treatment.Examples

[0050] The present disclosure will become better understood from the following examples of non-limiting embodiments.

[0051] A titanium alloy structure was produced using Ti6A14V powder in a laser powder bed fusion system (SLM250HL by SLM Solutions) with the following settings:Powder layer thickness: 30 pm Power: 100WScanning speed: 375 mm / min

[0052] The person skilled in the art will understand that in other embodiments, other settings may be used to produce the initial titanium alloy structure, and these settings may not be directly transferrable to other LPBF systems. Further, in other embodiments, other additive manufacturing methods may be used to form the structure. Preferably, the settings are chosen to control the speed at which the meltpool solidifies so that a martensitic structure forms.

[0053] An SEM image of the micro structure of the Ti6A14V structure post-LPBF and prior to heat treatment is shown in FIGURE 1. This image shows a martensitic (a’ -phase) structure with acicular or needle-like morphology. The micro structure shows a high density of twins and defects, and no P-phase is detectable microscopically.

[0054] The Ti6A14V structure then underwent a heat treatment process, wherein the structure was heated in a furnace at 950°C for a period of 2 hours. The P-transus temperature for Ti6A14V is considered to be 995±5°C, and this temperature was chosen as being 45° to 50°C below this temperature. In this embodiment, the structure was heated isothermally, that is to say, added to the furnace when the furnace was at temperature, though it will be understood that in other embodiments, the structure may be added while the furnace is heating to the hold temperature. The structure was then cooled by removing the structure from the furnace andallowing it to cool in air, which corresponds to a cooling rate of approximately 3°C / s to 4°C / min. Other experiments have shown that similar microstructures can be obtained with a cooling rate up to 5°C / s and as low as 2°C / s.

[0055] Further experiments have shown similar microstructures are formed when the structure was placed in a vacuum furnace at room temperature and heated at 9°C / min to 950°C, and held for a soak time of 1 hour, before being cooled under forced argon cooling with a cooling rate of approximately 1.6°C / s to 2°C / s.

[0056] An SEM image of the microstructure of the Ti6A14V structure following heat treatment at 950°C for a period of 2 hours and cooled at a rate between approximately 3°C / s to 4°C / s is shown in FIGURE 2. The martensitic micro structure shown in FIGURE 1 has decomposed to form a-lamellae (1) and P phase (2) between said lamellae. Further, secondary a precipitates (3) can be seen within the P phase. Additionally, there are areas where there are no precipitates within the P phase. These can be referred to as residual P phase. As these are present within the P phase, they can be differentiated from grain-boundary a, which was not observed in the micro structure.

[0057] As an indication of the suitability for high strain-rate impact applications of the produced material, a test was carried out to measure the difference in ballistic limit velocity for titanium alloys produced by this method. The ballistic limit velocity (V50) value is a measure of the projectile velocity at which the likelihood that the material is penetrated is 50%. FIGURE 3 compares the difference in velocity to the minimum acceptable value set by the MIL-DTL- 46077G standard, which relates to wrought titanium alloys for ballistic armour applications and is thus a suitable benchmark for high strain-rate impact applications. Ballistic impacts represent the lower end of the high strain rate range, in a range of 102to 103s1and provide a relatively simple assessment of the material’s response to high strain rate impacts, compared to more complex and inaccessible forms of testing such as hypervelocity testing. FIGURE 3 shows the difference in velocity for Ti6A14V structures manufactured by additive manufacturing processes (4A, 4B), commercial Ti6A14V plates produced by traditional thermomechanical means (5A, 5B), and Ti6A14V structures manufactured by additive manufacturing processes which have further undergone the heat treatment detailed above (6A, 6B, 6C). The alloys formed by additive manufacturing but without heat treatment (4A, 4B), which have a microstructure similar to that shown in FIGURE 1, show inferior results compared to the commercially produced Ti6A14V plates (5A, 5B), falling short of theminimum standard for the equivalent wrought titanium alloy set by MIL-DTL-46077G. The additive manufactured Ti6A14V structures which have undergone the heat treatment step (6 A, 6B, 6C) show comparable or improved performance compared to the non-additive manufactured Ti6A14V plates (5A, 5B). Unlike the traditionally manufactured plates, however, the additive manufactured alloys can be formed into complex geometries and thus avoid the need for welding or fastening methods that the traditionally manufactured structures require to form similar shapes.

[0058] A number of plates with varying compositions were fabricated using the present method outlined above and also subjected to the ballistic limit velocity testing, after which they were analysed to determine the relative fractions of primary a phase, residual P phase, secondary a phase, transformed P phase, retained P phase, and the total P phase, with a view to correlating the ballistic limit improvement, which is the ballistic limit velocity subtracting the minimum standard set by MIL-DTL-46077G. These results are shown in FIGURE 4A, which compares the ballistic limit velocity of the compositions against the total P phase present and FIGURE 4B, which compares the ballistic limit velocity of the compositions against the amount of secondary a phase present. The total P phase (ptot) is the total amount of P phase present, including both the residual P phase (without any transformed P phase observed) and the retained P phase (the P phase remaining after a precipitation). The secondary a phase (asec) corresponds to the precipitated a phase, observed as fine, acicular precipitates in FIGURE 2. These measurements allow the implicit calculation of the total a phase (atot) by subtracting the Ptot value from 100%, and the primary a phase by subtracting the asec value from the atot.

[0059] FIGURE 4A shows that for Ptot values over 9.5%, the ballistic limit improvement was generally below 20 m / s, while for ptot values below 9.5%, the ballistic limit improvement was 20 m / s or greater. This suggests that the maximum ptot should preferably be 9.5% or less. FIGURE 4B shows that the compositions that showed at least 20 m / s ballistic limit improvement almost all had asec values above 2%. This suggests that asec should preferably make up more than 2% of the microstructure. Three exemplary compositions are circled in FIGURES 4 A and 4B. These have a P tot value between 8% and 9.5% and an sec value of 5% or more. The high asec value may account for the one outlier in FIGURE 4A. The volume fraction of a and P can be controlled by setting a different heat treatment temperature, while the formation of secondary a and the final volume fractions can be controlled by altering the cooling rate following the heat treatment.

[0060] The produced alloy may be beneficial for high strain-rate applications, for example, for micrometeroid and orbital debris mitigation applications, structural applications, and in the aerospace and automobile industry. As an example, the alloy may be formed into a complex shape by an additive manufacturing process to fit the profile of a satellite or spacecraft without the need to weld sections of the alloy produced by conventional thermomechanical processes together to form the complex shape, which would compromise the structural integrity.

[0061] In the foregoing description of certain embodiments, specific terminology has been resorted to for the sake of clarity. However, the disclosure is not intended to be limited to the specific terms so selected, and it is to be understood that each specific term includes other technical equivalents which operate in a similar manner to accomplish a similar technical purpose.

[0062] In this specification, the word “comprising” is to be understood in its “open” sense, that is, in the sense of “including”, and thus not limited to its “closed” sense, that is the sense of “consisting only of’. A corresponding meaning is to be attributed to the corresponding words “comprise”, “comprised” and “comprises” where they appear.

[0063] The reference in this specification to any prior publication (or information derived from it), or to any matter which is known, is not, and should not be taken as, an acknowledgement or admission or any form of suggestion that prior publication (or information derived from it) or known matter forms part of the common general knowledge in the field of endeavour to which this specification relates.

[0064] In addition, the foregoing describes only some embodiments of the invention(s), and alterations, modifications, additions and / or changes can be made thereto without departing from the scope and spirit of the disclosed embodiments, the embodiments being illustrative and not restrictive.

[0065] Furthermore, invention(s) have described in connection with what are presently considered to be the most practical and preferred embodiments, it is to be understood that the invention is not to be limited to the disclosed embodiments, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the invention(s). Also, the various embodiments described above may be implemented in conjunction with other embodiments, e.g., aspects of one embodiment may be combined withaspects of another embodiment to realize yet other embodiments. Further, each independent feature or component of any given assembly may constitute an additional embodiment.

Claims

The claims defining the invention are as follows:

1. An a+P titanium alloy material, wherein the material has an a+p lamellar microstructure, with secondary a precipitates within the P phase.

2. The a+P titanium alloy material of claim 1, wherein the P phase comprises 9.5% or less of the microstructure; and wherein the secondary a precipitates comprise 2% or more of the microstructure.

3. The a+P titanium alloy material of claim 2, wherein the P phase comprises 8% or more and 9.5% or less of the micro structure; and wherein the secondary a precipitates comprise 5% or more of the microstructure.

4. The a+P titanium alloy material of any one of the preceding claims, wherein the titanium alloy is Ti6A14V or Ti6242.

5. The a+P titanium alloy material of any one of the preceding claims, wherein the material has an initial acicular martensitic a phase microstructure prior to undergoing a heat treatment.

6. The a+P titanium alloy material of claim 5, wherein the heat treatment is carried out at a temperature between 25°C and 75°C below the P-transus temperature of the alloy material.

7. The a+P titanium alloy material of either claim 5 or 6, wherein the heat treatment is carried out for a time period between about 0.5 hours and about 2 hours.

8. The a+P titanium alloy material of any one of claims 5 to 7, wherein the material is cooled at a rate between about 2°C / s and 5°C / s.

9. The a+P titanium alloy material of any one of the preceding claims, wherein the material is in a predetermined shape formed by an additive manufacturing process.

10. The a+P titanium alloy material of any one of the preceding claims, wherein the material is used in a high strain-rate impact application.

11. A method of producing an a+P titanium alloy structure, comprising: subjecting an a+P titanium alloy structure with a microstructure comprising an acicular martensitic a phase to a heat treatment; wherein the heat treatment is carried out at a temperature between 25 and 75 °C below the P-transus temperature of the a+P titanium alloy structure.

12. The method of claim 11, wherein the heat treatment is carried out for a time period between about 0.5 hours and about 2 hours.

13. The method either of claim 11 or 12, wherein the method further comprises cooling the structure at a cooling rate between about 2°C / s and 5°C / s.

14. The method of any one of claims 11 to 13, wherein the metal material is formed on a substrate.

15. The method of any one of claims 11 to 14, wherein the titanium alloy structure is produced by an additive manufacturing process.

16. The method of claim 15, wherein the additive manufacturing process is a laser powder bed fusion process.

17. The method of any one of claims 11 to 16, wherein the a+P titanium alloy is Ti6A14V or Ti6242.

18. The method of any one of claims 11 to 17, wherein the titanium alloy structure is shaped for use in a high strain-rate impact application.

19. The method of any one of claims 11 to 18, wherein the a+P titanium alloy structure is an a+P titanium alloy material according to any one of claims 1 to 10.

20. An additive manufacturing process, comprising: forming a structure in a predetermined shape from an a+P titanium alloy metal powder; subjecting the structure to a heat treatment step carried out at a temperature between 25°C and 75°C below the P-transus temperature of the a+P titanium alloy.

21. The process of claim 20, wherein the heat treatment is carried out for a time period between about 0.5 hours and about 2 hours.

22. The process either of claim 20 or 21, wherein the method further comprises cooling the structure at a cooling rate between about 2°C / s and 5°C / s.

23. The process of any one of claims 20 to 22, wherein the metal material is formed on a substrate.

24. The process of any one of claims 20 to 23, wherein the a+P titanium alloy is Ti6A14V or Ti6242.

25. The process of any one of claims 20 to 24, wherein the titanium alloy structure is shaped for use in a high strain-rate impact application.

26. The process of any one of claims 20 to 25, wherein the a+P titanium alloy structure is an a+P titanium alloy material according to any one of claims 1 to 10.

Images