Method for producing a body from a ti / nb / ta alloyed powder

Abstract

The present invention relates to a method for producing a body from a Ti / Nb / Ta alloyed powder, a body produced according to this method, and the use of a Ti / Nb / Ta alloyed powder for producing a body by laser powder bed fusion.

Description

[0001] Process for producing a body from a Ti / Nb / Ta alloy powder

[0002] The present invention relates to a method for producing a body from a Ti / Nb / Ta alloy powder, a body produced by this method and the use of a Ti / Nb / Ta alloy powder for producing a body by means of laser-based powder bed melting.

[0003] Ti / Nb / Ta alloys have great potential for medical applications, particularly as implants in dentistry and orthopedics. In particular, the advancing developments in additive manufacturing techniques offer the possibility of producing implants that are individually tailored to the patient's needs.

[0004] A challenge in the production of three-dimensional objects using additive manufacturing techniques is the determination of process parameters, which is essential for obtaining high-quality parts. Particularly in production using laser beam powder bed fusion (LB-PBF), which is preferred for metal powder processing, a number of different parameters must be correlated and optimized. The influence of parameters such as laser power, the speed at which the laser is moved across the powder bed, the spacing of the melting tracks, the laser focus, and the powder bed thickness on the structure of the microstructure obtained during the printing process can only be evaluated through systematic variation and subsequent assessment of the components in a complex process.

[0005] In their article "Highly Anisotropie steel Processed by Selective Laser Melting," published in Met. Mat. Trans. 44b (2013) 795, T. Niendorf et al. describe the production of austenitic stainless steel samples using a high-energy laser system. The resulting microstructure is characterized by the formation of a coarse-grained, columnar structure with a (001) texture in the build direction when very high laser energy is applied. In contrast, lower energy input results in a fine-grained, more isotropic microstructure. In "The effect of laser energy input on the microstructure, physical and mechanical properties of Ti-6AI-4V alloys by selective laser melting" by DK Do et al., published in Virt. Phys. Protoyping, 11 (2016) 41, describes the microstructure development and mechanical properties of L-PBF-processed Ti-6AI-4V.The laser power is kept constant and the energy input is controlled via the scanning speed.

[0006] In "Influence of the Energy Density for Selective Laser Melting on the Microstructure and Mechanical Properties of Stainless Steel" in Metals 10 (2020) 919, C. Donik et al. describe the influence of laser power in L-PBF on the microstructure (density) and some mechanical properties such as UTS, YS and elongation at break.

[0007] In "Microstructure and mechanical characterization of SLM processed Haynes® 2300," T. Bauer et al. (ETH Zurich Library, https: / / doi.org / 10.3929 / ethz-a-010584903) describe the mechanical properties of Haynes 230, a Ni / Cr / W / Mo alloy, as a function of the applied laser energy.

[0008] In his article "High-Power Laser Materials Processing: Lasers, Beam Delivery, Diagnostics, and Applications III", published in PROCEEDINGS OF SPIE, V. 8963, F. Dorsch summarizes the results of his investigations into the influence of printing parameters in SLM on the geometry of the component.

[0009] In "Multi-material model for mesoscopic analysis of porosity evolution during laser powder-bed fusing TiNbTa powder mixture", published in Computational Material Science 198 (2021) 110674, M. Xia et al. present a model for investigating the processes during printing of Ti / Nb / Ta powder mixtures using laser-based powder bed fusing (LPBF).

[0010] In their article "Influence of laser powder bed fusion process parameters on the properties of CuZn42 components: case study of the laser surface energy density," published in Progress in Additive Manufacturing (2023) 8:843-855, A. Gatto et al. describe a model for predicting density, hardness, and the relative proportions of the brass phases in the system as a function of the surface energy density (SED). According to the model, a linear relationship between hardness and density can be observed. The processes described in the prior art have the disadvantage that the energy applied by laser always influences the porosity of the produced samples, so that the production of high-density components, such as those required for implant technology, can only be achieved with very specific, narrowly defined process parameters.

[0011] Therefore, there is still a need for processes that allow the targeted adjustment of the properties of three-dimensional components while maintaining high density using different process parameters. In particular, it would be desirable if the phase constitution, and thus properties such as strength and elongation at break, could be adapted to the requirements of the specific application of the component at full density.

[0012] Within the scope of the present invention, it was surprisingly found that with the aid of additive manufacturing, the phase composition of titanium-based alloys can be specifically adjusted and, at the same time, properties such as strength and elongation at break can be specifically adjusted by the energy introduced, while at the same time components with consistently very high densities are obtained.

[0013] A first subject of the present invention is therefore a method for producing a body comprising the steps: a) providing a first layer of a Ti / Nb / Ta alloy powder and treating the layer by melting with a laser beam that delivers an energy with a surface energy E_Ai. b) applying a further layer of a Ti / Nb / Ta alloy powder on the treated first layer and treating the further layer by melting with a laser beam that delivers a surface energy E_Ai; c) repeating step b) to obtain the additively manufactured body; characterized in that the adjustment of the phase composition and at least one of the properties selected from the group consisting of elongation at break A (E_Ai), hardness VH (E_Ai), tensile strength R m (E_Aj) and the yield strength po2 is determined depending on the surface energy E_Ai of the body. Surface energy E_Ai in the context of the present invention is understood to be the energy provided by the laser beam per unit area. This can be represented by Equation 1:

[0014] P represents the laser power in watts (W), v s quantifies the scanning speed of the laser with which it is guided over the powder bed with the unit mm / s and H s The hatch width, i.e., the distance between the individual lines traversed by the laser, measured in mm. E_Ai can be determined equivalently for pulsed systems, whereby the above-mentioned scan speed can be replaced by the product of pulse duration and pulse spacing.

[0015] The method according to the invention enables the additive manufacturing of dense components with a specifically adjusted phase composition and specifically adjustable properties such as elongation at break, ductility, hardness, tensile strength and / or yield strength, without the usually observed change or fluctuation in the density of the components being observed.

[0016] Within the scope of the present invention, the density of the additively manufactured components can be determined, unless otherwise stated, using optical methods, gravimetrically, or by means of a pycnometer. For the determination using optical methods, micrographs of the body can be used, for example.

[0017] For the purposes of the present invention, "dense" means a body having a porosity of less than 1%, determined by optical porosity analysis.

[0018] The elongation at break A, which is a measure of the ductility of a structure, can be determined in a tensile test on metal or metallic materials according to DIN EN ISO 6892-1 or ASTM E 8.

[0019] The hardness VH can be determined according to the Vickers hardness test according to ISO 6507 / ASTM E384. The tensile strength R m and yield strength R p0 2 can be determined in tensile tests on metal or metallic materials according to DIN EN ISO 6892-1 or ASTM E 8.

[0020] The method according to the invention is particularly intended for the production of components with a high density. Therefore, an embodiment is preferred in which the body has a density of more than 99.0%, preferably more than 99.6%, particularly preferably more than 99.9%, as determined by micrographs of the body.

[0021] Within the scope of the method according to the invention, mechanical properties of the component such as hardness, tensile strength, elongation at break, and yield strength are controlled using the applied energy. To achieve a variation of the properties within the body, the applied energy can be varied. Therefore, an embodiment is preferred in which the surface energy E_Ai used to treat the layers is varied. In this way, for example, a gradient in the body's mechanical properties can be imposed, or areas exposed to particular stress can be specifically reinforced or their ductility increased.

[0022] The process according to the invention is tailored to Ti / Nb / Ta alloys, with particular preference being given to embodiments in which the Ti / Nb / Ta alloy powder has a composition xTi / yNb / zTa, with the mass fraction x of titanium (Ti) preferably being 61 to 72 mass%, the mass fraction y of niobium (Nb) preferably being 21 to 32 mass% and the mass fraction z of tantalum (Ta) preferably being 3 to 11 mass%, in each case based on the total mass of the alloy powder.

[0023] Within the scope of the method according to the invention, it was surprisingly found that, with the aid of the applied energy, not only the mechanical properties but also the crystallographic composition can be adjusted while maintaining a constant chemical composition of the body, without this having a negative impact on the density of the body. Therefore, an embodiment is preferred in which the body has a crystal phase composition Z (F-Aj) as a function of the applied surface energy E_Ai. Furthermore, an embodiment of the method according to the invention is preferred in which the phase composition of the body is adjusted by the surface energy E_Ai.

[0024] The process according to the invention allows the production of three-dimensional bodies with high precision through layer-by-layer construction. In a preferred embodiment, the powder is applied in a layer thickness of 10 to 90 μm, preferably 15 to 35 μm.

[0025] Suitable powders that can be used in powder-bed-based processes are known to those skilled in the art. For example, WO 2019 / 197376 describes Ti / Nb / Ta alloy powders for additive manufacturing. Spherical powders that have sufficient flowability to be applied as a powder layer have proven particularly suitable. In a preferred embodiment, the alloy powder is therefore a spherical powder. Suitable powders can be obtained, for example, using EIGA (Electrode Induction-melting Gas Atomization) processes, plasma spherodization, ultrasonic atomization, or wire atomization.

[0026] In order to adapt further properties of the body produced by the method according to the invention, the alloy powder used can contain additional components. These are preferably one or more metals selected from the group consisting of Zr, Hf, Mo, W, and Sn. In a preferred embodiment, their proportion is 2 to 10 mass%, preferably 3 to 7 mass%, particularly preferably 4 to 6 mass%, based on the total weight of the alloy powder. In a further preferred embodiment, the alloy powder used according to the invention contains no more than 10 mass% of other components besides Ti, Nb, and Ta.

[0027] Particularly in the field of orthopedic implants, it may be necessary to adapt implants so that different regions of the implant have different mechanical properties. This can be achieved within the scope of the method according to the invention, in particular, by varying the surface energy E_Ai, so that bodies are accessible that have mechanical properties that vary across their cross-section. In this context, an embodiment is therefore preferred in which the body has a gradient with respect to at least one of the properties selected from the group consisting of elongation at break, ductility, hardness, yield strength, and tensile strength. The gradient is preferably achieved by varying the surface energy E_Ai.

[0028] A further subject of the present invention is a body which is obtainable by means of the process according to the invention, wherein the body has a phase composition and at least one of the properties selected from the group consisting of elongation at break A (E_Ai), hardness VH (E_Ai), tensile strength R m (E_Aj) and the yield strength R p o2 in each case as a function of the surface energy E_Ai and wherein the body has a density of more than 99.0%, preferably more than 99.6%, particularly preferably more than 99.9%, determined on micrographs of the body using optical porosity analysis.

[0029] In a preferred embodiment, the body according to the invention preferably has a gradient with respect to at least one of the properties selected from the group consisting of elongation at break, ductility, hardness and tensile strength.

[0030] In a particularly preferred embodiment, the body is an implant, preferably a dental, orthopedic, craniofacial and / or spinal implant.

[0031] A further object of the present invention is the use of a Ti / Nb / Ta alloy powder for producing a body by means of laser-based powder bed melting, wherein the body has a phase composition and at least one of the properties selected from the group consisting of elongation at break A (E_Ai), hardness VH (E_Ai), tensile strength R m (E_Aj) and the yield strength R p o2 in each case as a function of the surface energy E_Ai and wherein the body has a density of more than 99.0%, preferably more than 99.6%, particularly preferably more than 99.9%, determined on micrographs of the body using optical porosity analysis.

[0032] Within the scope of the present invention, it was surprisingly found that the phase composition, while maintaining a constant composition, as well as the mechanical properties of bodies made from a Ti / Nb / Ta alloy powder can be adjusted by the energy input during processing by means of selective laser beam melting. Therefore, a further subject of the present invention is a method for adjusting at least one of the properties selected from the group consisting of tensile strength, elongation at break, ductility, yield strength, and hardness of an optically dense body made from a Ti / Nb / Ta alloy powder by means of selective laser beam melting, characterized in that the property is adjusted by varying the surface energy E_Ai during laser beam melting.

[0033] Furthermore, it was surprisingly found that the surface energy E_Ai of the applied laser beam also significantly influences phase development. This generally depends primarily on the chemical composition of the alloy. Titanium-rich Ti / Nb / Ta alloys generally crystallize preferentially in hexagonal or orthorhombic, martensitic crystal structures. Niobium- and / or tantalum-rich Ti / Nb / Ta alloys, on the other hand, generally crystallize preferentially in a body-centered cubic crystal structure. In the present case, however, it was surprisingly found that the formation of the crystalline phase is influenced by the surface energy E_Ai depending on the applied energy of the laser beam. A lower surface energy E_Ai results in the preferential formation of crystal structures with larger hexagonal or orthorhombic components.In contrast, a higher surface energy E_Ai of the laser beam results in the preferential formation of body-centered cubic crystal structures. Therefore, a further subject of the present invention is a method for adjusting the crystal phase composition of an optically dense body made of a Ti / Nb / Ta alloy powder by means of selective laser beam melting, characterized in that the property is adjusted by adjusting and / or varying the surface energy E_Ai during the laser beam melting.

[0034] The present invention is described in more detail with reference to the following examples, which are in no way to be understood as a limitation of the inventive concept.

[0035] An alloy with the composition Ti-27Nb-6Ta was processed by laser-based powder bed fusion to a specimen with a density of greater than 99.94%, determined by optical porosity analysis, and its properties were determined. Figure 1 shows the tensile strength values ​​and elongation at break of the produced specimen derived from a stress / strain diagram as a function of the surface energy E_Ai. While the tensile strength of approximately 770 MPa at E_Ai = 1.5 J / mm 2 to approx. 700 MPa at E_Ai = 2.85 J / mm 2 reduced, the elongation at break decreases in return from approx. 22 % at E_A = 1.5 J / mm 2 to approx. 34% at E_Ai = 2.85 J / mm 2 to.

[0036] From the comparison of the X-ray diffraction patterns of the powder with three differently manufactured samples, as shown in Figure 2, it can be seen that a higher energy input is clearly associated with the increase of the body-centered cubic phase (so-called beta phase). While the powder crystallizes orthorhombic in a «" phase, with E_Ai = 1.45 J / mm 2 In addition to the orthorhombic phase, the additively manufactured material also exhibits reflections to a small extent that indicate the formation of a body-centered cubic ß-phase. The intensity of the corresponding reflections attributable to the ß-phase increases significantly with increasing energy input. Furthermore, strong texture effects are also observed, which are particularly confirmed by the increasing intensity of the 200 reflection of the ß-phase material.

[0037] High-energy synchrotron diffraction experiments allow further detailed conclusions about the phase constitution of the additively manufactured Ti-27Nb-6Ta structures. Figure 3a shows the corresponding diffraction patterns of the additively manufactured Ti-27Nb-6Ta, prepared with E_Ai = 1.45 J / mm 2 , E_Ai = 2.05 J / mm 2 and E_Ai = 2.78 J / mm 2 All diffraction patterns indicate the presence of the bcc-ß equilibrium phase and the martensitic nonequilibrium o" phase with orthorhombic structure. The lattice parameters are aß = 0.3286 nm and a a - = 0.2930 nm / c0" = 0.4694 nm. Apart from these two phases, no other components such as hexagonal close-packed (hcp) o- or hexagonal o'-martensite are detected.

[0038] As can be seen from the diffraction patterns and especially from the enlarged view in Figure 3b, both the number of diffraction peaks and their positions are consistent, indicating an α" + β two-phase microstructure for all processed Ti-27Nb-6Ta materials. However, taking into account the different processing parameter sets, the diffraction peaks differ significantly in intensity. In general, differences in signal intensity can be attributed to significant differences in the volume fractions of the phases present, but also in their texture components. The assessment of the phase constitution was carried out using Rietveld analysis, which enabled a detailed and quantitative evaluation of the phase fractions. Accordingly, for [Ti-27Nb-6Ta] with E_Ai = 1.45 J / mm 2manufactured Ti-27Nb6Ta has a balanced phase composition in which the o"-martensite slightly dominates. In contrast, the Ti-27Nb-6Ta microstructure after processing with parameter set E_Ai = 2.78 J / mm 2 mainly from the body-centered cubic ß-phase. In other words, the volume fraction of the martensitic α"-phase decreases with increasing energy input during PBF-LB / M.

Claims

Patent claims:

1. A method for producing a dense body, comprising the steps of: a) providing a first layer of a Ti / Nb / Ta alloy powder and treating the layer with a laser beam which delivers an energy input with a surface energy E_Ai; b) applying a further layer of a Ti / Nb / Ta alloy powder to the treated first layer and treating the further layer with a laser beam which delivers an energy input with a surface energy E_Ai; c) repeating step b) to obtain the additively manufactured body; characterized in that the adjustment of the phase composition and at least one of the properties is selected from the group consisting of elongation at break A (E_Ai), hardness VH (E_Ai), tensile strength R. m (E_Aj) and the yield strength R p o2 is dependent on the surface energy E_Ai.

2. Method according to at least one of the preceding claims, characterized in that the body has an optical density of more than 99.0%, preferably more than 99.6%, particularly preferably more than 99.9%, determined by micrographs of the body.

3. Method according to claim 1, characterized in that the surface energy E_Ai used for treating the layers is varied.

4. A method according to at least one of the preceding claims, characterized in that the Ti / Nb / Ta alloy powder has a composition xTi / yNb / zTa with 61 < x < 72; 21 < y < 32 and 3 < z < 11, where x, y, z express the proportions in mass percent based on the total mass of the alloy powder.

5. Process according to at least one of the preceding claims, characterized in that the powder is applied in a layer thickness of 10 to 90 pm, preferably 15 to 35 pm.

6. Method according to at least one of the preceding claims, characterized in that the alloy powder is a spherical powder.

7. The method according to at least one of the preceding claims, characterized in that the alloy powder further comprises one or more metals selected from the group consisting of Zr, Hf, Mo, W and / or Sn.

8. A method according to claim 7, characterized in that the proportion of the one or more metals in the alloy powder is not more than 10 mass%, based on the total mass of the alloy powder.

9. Method according to at least one of the preceding claims, characterized in that the body has a gradient with respect to at least one of the properties selected from the group consisting of phase composition, elongation at break, hardness and tensile strength.

10. Body obtainable by a process according to at least one of claims 1 to 9, characterized in that the body has a phase composition wherein the body has a phase composition and at least one of the properties selected from the group consisting of elongation at break A (E_Ai), hardness VH (E_Ai), tensile strength R. m (E_Aj) and the yield strength R p o2 in each case as a function of the surface energy E_Ai and wherein the body has a density of more than 99.0%, preferably more than 99.8%, particularly preferably more than 99.97%, determined on micrographs of the body.

11. Body according to claim 10, characterized in that the body is an implant, preferably a dental, orthopedic, craniofacial and / or spinal implant.

12. Use of a Ti / Nb / Ta alloy powder for producing a dense body by laser-based powder bed melting, wherein the body has a phase composition and at least one of the properties selected from the group consisting of elongation at break A (E_Ai), hardness VH (E_Ai), tensile strength R. m (E_Aj) and the yield strength R PO2, each as a function of the surface energy E_Ai, and wherein the body has a density of more than 99.0%, preferably more than 99.6%, particularly preferably more than 99.9%, determined on micrographs of the body.

13. A method for adjusting at least one of the properties selected from the group consisting of phase composition, tensile strength, elongation at break, yield strength, and hardness of an optically dense body made of a Ti / Nb / Ta alloy powder by means of selective laser beam melting, characterized in that the properties are adjusted by varying the surface energy during laser beam melting.

14. A method for adjusting the phase composition of an optically dense body made of a Ti / Nb / Ta alloy powder by means of selective laser beam melting, characterized in that the adjustment of the phase composition is carried out by varying the surface energy during Laser beam melting takes place.

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