Powder-in-tube type titanium deposition wire

Abstract

The powder-in-tube deposited wire includes a hollow tubular portion of titanium and a core portion filled in the tubular portion. The core portion occupies (30)% to (80)% by volume of the deposited wire. The core portion includes compacted elongated powder of titanium and optionally other compacted powders selected from the group consisting of aluminum, vanadium, aluminum-vanadium, chromium, molybdenum, boron, niobium, tantalum, nickel, zirconium, silicon, copper, tin, iron, and palladium. Due to the high volume of the core portion, the fabrication process of the wire is not very complicated.

Description

Technical Field

[0001] The present invention relates to a powder-in-tube type deposition wire, a method for producing such a deposition wire, and a specific use of such a deposition wire.

Background Art

[0002] The essence of additive manufacturing is to fabricate parts by adding controlled material layers, as opposed to machining that removes materials.

[0003] As an example, 3D printing can be realized using welding wires of titanium or titanium alloys.

[0004] Titanium has advantageous properties, namely, a high strength-to-weight ratio (as strong as steel but half its weight), excellent corrosion resistance, and good mechanical properties at elevated temperatures. Therefore, welding wires of titanium or titanium alloys are well-known in the art.

[0005] U.S. Patent No. A-4,331,857 discloses a welding wire including a hollow tubular portion of titanium and a core portion filled in the tubular portion. The core portion is formed from a powder for compacting alloying.

[0006] Conventional welding techniques such as TIG welding require working in a protective atmosphere and / or the use of an activator (flux) to improve the quality of welding.

[0007] Chinese Patent No. 107363433 discloses a wire for titanium-based alloy flux cored welding, which includes a metal sheath and an internal active agent core. The welding wire is composed of an outer skin and an internal active welding agent core. The metal sheath is a titanium strip having a titanium content of 98% or more and a hydrogen content of 0.015% or less. The internal active agent core consists of metal powder, B powder, Si powder, and an activator. The metal powder includes Ti, Co, Mn, Ni, and Cu. The activator includes chlorides, fluoroaluminates, MgF2, and SrF2. The mass percentages of the powder, B powder, Si powder, and active components are as follows: Ti is 16% - 34%, Co is 0.2% - 0.4%, Mn is 0.8% - 1%, Ni is 1% - 3%, Cu B is 2% - 6%, Si is 0.10% - 0.25%, chlorides are 1% - 5%, fluoroaluminates are 12% - 16%, MgF2 is 5% - 15%, and SrF2 is 20% - 60%.

[0008] With the evolution of deposition techniques for additive manufacturing, the requirements regarding accuracy and deposition rate have become more stringent, thus necessitating the development of a new type of deposition wire. In metal additive manufacturing, recent techniques perform direct energy deposition (DED). The energy source can include a laser, an electron beam, a MIG / MAG arc, or a plasma arc. For example, powder deposition using powder for selective laser melting (SLM) or laser cladding is slower compared to wire-based DED. Therefore, new deposition wires are being developed.

[0009] Chinese Patent No. 108000004 discloses a method for preparing a titanium flux cored wire of a titanium matrix composite material for 3D printing.

[0010] Welding wires or deposition wires for titanium or titanium alloys are still expensive and complex to manufacture. This is due to many diameter reduction steps and many intermediate heat treatments.

Summary of the Invention

Problems to be Solved by the Invention

[0011] A general object of the present invention is to avoid or at least mitigate the drawbacks of the prior art.

[0012] A specific object of the present invention is to provide a deposition wire that is not so complicated to manufacture and is compatible with the latest deposition techniques.

[0013] Another object of the present invention is to reduce the number of steps required to manufacture the deposition wire.

Means for Solving the Problems

[0014] According to a first aspect of the present invention, a powder-in-tube type deposition wire is provided. The deposition wire includes a hollow tubular portion of titanium and a core portion filled in the tubular portion. The core portion occupies 25% to 85% by volume, for example 27% to 80% by volume, for example 30% to 75% by volume of the complete deposition wire. The core portion includes compacted elongated powder of titanium and optionally also other compacted powders selected from the group consisting of aluminum, vanadium, aluminum-vanadium, chromium, molybdenum, boron, niobium, tantalum nickel, zirconium, silicon, copper, tin, iron, and palladium.

[0015] Aluminum-vanadium powder is more preferred than vanadium powder because vanadium powder is very expensive.

[0016] Aluminum and vanadium (either vanadium itself or aluminum-vanadium) are the most preferred elements to be used in an aviation deposition wire. Chromium and molybdenum are also preferred for an aviation deposition wire.

[0017] Boron is a very interesting element with respect to its grain refinement property. Boron is a nano-sized grain refinement element. Boron powder has an acidic oxide (B2O3) layer around its surface, and this layer absorbs some moisture. Since metal oxides are generally basic, the surfaces of boron and metal powders can be integrally attached.

[0018] Since the amount of boron is very small, boron can also be mixed in a solution and then sprayed onto the dry mixing powder. After mixing, the powder can be dried in an oven.

[0019] Alternatively, all the powders can be mixed in a solvent and fed into a U-profile as a slurry.

[0020] Preferably, the core part occupies more than 40% by volume, for example more than 50% by volume, of the fully deposited wire.

[0021] The deposited wire may have a butt welding seam or a laser welding seam. However, the most preferred embodiment is a cold welding overlap seam.

[0022] The advantageous effects of the present invention are as follows. Compared with the welding wire of U.S. Patent No. A-4,331,857, the volume portion of the powder material is considerably large. This means that the energy required to reduce the diameter of the deposited wire to its final value is considerably small. The titanium powder in the core is a major contributing factor to the improvement of workability. The titanium powder will elongate during diameter reduction, provide continuous powder flow, and minimize powder locking. Therefore, the number of reduction steps required in the form of a stretching step or a rolling step is reduced. Also, since the number of reduction steps required is reduced, the need for intermediate heat treatment is reduced or eliminated. Although the tensile strength level may be lost with a higher volume portion of the powder material, the tensile strength achieved with the deposited wire of the present invention is substantially sufficient for use as a deposited wire. Moreover, as will be described in more detail hereinafter, the final tensile strength of the deposited wire depends on the degree of reduction, whether the last process step is a heat treatment, and the initial tensile strength of the tube portion.

[0023] The tubular portion must have a minimum volume percentage of 15% to enable the first reduction step. If the minimum volume percentage of the tubular portion is less than 15%, the strip forming the tubular portion is at risk of breaking.

[0024] The compacted elongated powder of titanium can originate from non-spherical sponge powder or spherical sponge powder. The non-spherical sponge powder of titanium is considerably cheaper than the spherical powder of titanium. The spherical titanium powder can be plasma atomized powder. In one embodiment, all of the compacted elongated powder of titanium originates from non-spherical sponge powder. In another embodiment, all of the compacted elongated powder of titanium originates from spherical sponge powder. The non-spherical powder results in a more uneven grain structure than the spherical powder.

[0025] In a preferred embodiment, the compacted elongated titanium powder is at least partially derived from non-spherical sponge titanium powder and partially from spherical sponge titanium powder. This means that the titanium powder initially placed on the titanium strip to produce the deposition wire is a mixture of spherical titanium powder and non-spherical sponge titanium powder.

[0026] Since the compacted elongated titanium powder can also be derived from recycled powder or turnings, it can contribute to a circular economy. In one embodiment, all of the compacted elongated titanium powder is derived from recycled powder or turnings. In another embodiment, the compacted elongated titanium powder is derived from both recycled powder and non-recycled spherical sponge powder. Recycled powder and turnings also result in a more uneven grain structure than spherical powder.

[0027] Surprisingly, it has been found that the final properties of the deposition wire of the present invention also depend on the type of powder materials used and their mixing. Both higher tensile strength and elongation were obtained with deposition wires using non-spherical sponge titanium powder compared to spherical titanium powder.

[0028] Preferably, the titanium powder has more than 65% of the volume of the core part. More preferably, more than 80% of the volume of the core part consists of titanium powder.

[0029] In one embodiment, there is no other compacted powder present in the core part. That is, all of the powder present in the core part is titanium. This results in a deposition wire of only titanium and inevitable impurities.

[0030] Preferably and generally, the deposition wire contains 0.15 wt% or less, for example 0.10 wt% or less, of carbon.

[0031] Most preferably and generally, the deposition wire contains 1.0 wt% or less, for example 0.50 wt% or less, for example 0.20 wt% or less, of oxygen.

[0032] Titanium wires comply with strict specification limits, particularly with respect to impurities such as C, O, H, N. In particular, the oxygen content in the deposited wire is important because it leaves a TiOx layer on the newly deposited layer during welding or additive manufacturing, requiring machining of the newly deposited layer before depositing subsequent layers, resulting in additional costs and a source of defects in the weld bead or additive manufactured part, thus adversely affecting the deposition process. According to ASTM, the specification limit for O is 0.18 wt% for grade 1 and 0.40 wt% for grade 4.

[0033] Therefore, it is necessary to balance and adjust the volume fraction of non-spherical sponge powder or recycled powder and turnings of titanium using either Ti strip material or spherical powder of titanium so that too much oxygen is not trapped during the wire production process.

[0034] Due to the diameter reduction, the powder material in the core part is compacted and elongated. The size of the voids between the compacted and elongated powders is reduced to a minimum. These voids only appear occasionally.

[0035] The deposited wire according to the first aspect of the present invention has a final diameter of less than 6.0 mm, such as less than 5.0 mm, such as less than 4.0 mm, such as less than 3.6 mm, such as less than 2.5 mm, i.e., the outer diameter of the reduced tubular part. In automatic wire feeding in an automatic process such as MIG welding and in arc-based (plasma, laser) additive manufacturing (3D printing), the typical diameter range is 1.0 mm to 1.6 mm. In manual wire feeding, such as in TIG welding, a diameter range greater than 2.0 mm is used. In electron beam or laser additive manufacturing (3D printing) or other processes targeting very high deposition rates, an even larger diameter range, such as greater than 2.5 mm or greater than 3.6 mm, is used.

[0036] According to a second aspect of the present invention, there is provided a method for producing a powder-in-tube type deposited wire. The method includes the following steps: a) providing a strip of titanium; b) providing a powder of titanium and optionally another powder selected from the group consisting of aluminum, vanadium, chromium, molybdenum, boron, niobium, and tantalum; c) placing the powder of titanium and the other powder on the strip; d) closing the strip so as to form a tube around the core portion of the powder of titanium and the other powder, wherein the core portion occupies 30% to 80% by volume of the tube and the core portion; e) reducing the diameter of the tube by rolling or stretching in various rolling or stretching steps. The method includes steps a) to e).

[0037] In certain embodiments, one or more intermediate heat treatments are applied between various subsequent rolling or stretching steps.

[0038] In other embodiments, such intermediate heat treatment is not necessary.

[0039] To avoid oxidation, at least steps c) to d) are preferably carried out in an inert atmosphere.

[0040] In a highly preferred embodiment of step d), closing the strip includes creating an overlap of the strip. The overlap of the strip is cold-welded during diameter reduction. This working method enables the creation of a seamless core wire, avoids hot welding above all, and substantially reduces the risk of titanium powder fire.

Brief Description of the Drawings

[0041]

Fig. 1a-1d

Fig. 2

Fig. 3

Mode for Carrying Out the Invention

[0042] The powder-in-tube type titanium deposition wire is produced as follows.

[0043] Referring to FIG. 1a, the starting material is, for example, a titanium strip 10 having a thickness of 0.7 mm.

[0044] FIG. 1b illustrates the second step in which the titanium strip 10 is deformed into a U shape. Titanium powder, aluminum powder, and aluminum-vanadium powder (all referred to by reference numeral 12) are placed on the deformed strip 10. For a wire weight of 100 kg, about 30 kg of Ti powder is required, about 6.4 kg of Al-V powder, and an additional amount of about 3.8 kg of Al powder.

[0045] FIG. 1c illustrates the third step. The strip 10 having the powder 12 is closed to create an overlap 14 of 60° to 90°. The outer diameter of the closed strip is 6.0 mm.

[0046] Next, the closed strip is subjected to various reduction steps to its final outer diameter of 1.30 mm. The cross-section of the final deposition wire 16 of the powder-in-tube type is shown in FIG. 1d. By the various reduction steps, the powder 12 is made into a long shape and becomes fibers 12'. The thickness of the strip 10' is reduced. The strip 10' may show a local thickness 18 which is the destination of the welding of the tube.

[0047] Figure 2 shows a photograph by optical microscopy of the cross-section of the final deposition wire 16 of the powder-in-tube type. The outer diameter is 1.27 mm. The average thickness of the strip is 0.225 mm. The ratio of the core volume to the total volume is 41.6%. It is possible to clearly distinguish between the core part 12' with long powder and the deformed strip part 10'.

[0048] Figure 3 also shows a photograph by optical microscopy of the cross-section of a preferred embodiment of the deposition wire 16 of the powder-in-tube type. The difference from the embodiment of Figure 2 is that in the preferred embodiment of Figure 3, a cold-weld overlap seam is used to close the tube. The trace of this overlap can be seen at the bottom of Figure 3 and is indicated by arrow 19.

Example

[0049] Test Results Tensile tests were performed on the following three different titanium deposition wires. 1) Ceweld ER Ti-1 commercially available welding wire of 100% titanium with a final diameter of 1.199 mm. 2) The deposition wire according to the present invention having a core volume portion of 44.5%, provided that the core is initially filled with non-spherical sponge titanium powder and the final diameter is 1.261 mm. 3) The deposition wire according to the present invention having a core volume portion of 52.8%, provided that the core is initially filled with spherical titanium powder and the final diameter is 1.273 mm.

[0050]

Table 1

[0051]

Table 2

[0052] In the deposition wire of the present invention, despite the fact that there is a core portion initially filled with powder, the strength and load values of the deposition wire of the present invention are significantly higher than those of the prior art welding wire. This is mainly due to the fact that the prior art welding wire is subjected to a final heat treatment, while the deposition wire of the present invention is end cold deformed without a final heat treatment. When two deposition wires of the present invention are compared, the sample INV2 using non-spherical sponge titanium powder has the highest strength and force values. The sample INV3 using spherical titanium powder has the lowest elongation value.

[0053] In addition, despite the fact that it has been cold deformed, the sample INV2 has a higher total elongation than the sample INV3.

[0054] By mixing both non-spherical sponge titanium powder and spherical titanium powder in various ratios, either the desired strength or the desired elongation (within a certain limit) can be determined.

[0055] For example, by mixing 50% non-spherical sponge titanium powder and 50% spherical titanium powder, it is possible to obtain a 1.25 mm diameter deposition wire having a total elongation of at least 2% and a tensile strength of at least 800 MPa.

[0056] Impurity limits The upper limits (in weight %) for C, O, and H concentrations are set by ASTM standards for pure titanium and titanium alloys. They are reported in the following table for grades 1 to 4 of pure titanium and grade 5 of titanium alloys.

[0057]

Table 3

[0058] The contents of C, O, and H in the three samples were measured by combustion analysis (LECO) and reported in the following table.

[0059]

Table 4

[0060] In all three samples, including Sample 2INV which contains a mixture of spherical titanium powder and non-spherical sponge titanium powder, all measured values are below the upper limit recommended by ASTM for different Ti grades.

Explanation of Symbols

[0061] 10 Titanium strip 10’ Titanium strip after cross-section reduction 12 Titanium powder and other added powders 12’ Long titanium and other powders after cross-section reduction 14 Overlap 16 Final deposited wire 18 Thickness of the titanium strip due to welding 19 Trace of cross-section due to welding overlap

Claims

1. A powder-in-tube type deposition wire, wherein the deposition wire includes a hollow tubular portion of titanium and a core portion filled in the tubular portion, the core portion occupies 25% to 85% by volume of the deposition wire, the core portion includes compacted elongated powder of titanium and optionally other compacted powder selected from the group consisting of aluminum, vanadium, aluminum-vanadium, chromium, molybdenum, boron, niobium, tantalum, nickel, zirconium, silicon, copper, tin, iron, and palladium, the compacted elongated powder of titanium is at least partially derived from non-spherical sponge powder of titanium, deposition wire.

2. The deposition wire according to claim 1, wherein the core portion occupies more than 40% by volume of the deposition wire.

3. The deposition wire according to claim 1 or claim 2, wherein the deposition wire has a cold welding overlap seam, a butt welding seam, or a laser welding seam.

4. The deposition wire according to claim 1 or 2, wherein the compacted elongated powder of titanium is at least partially derived from recycled powder or turnings of titanium.

5. The deposition wire according to claim 1 or 2, wherein the titanium powder has more than 65% by volume of the core portion.

6. The deposition wire according to claim 5, wherein there is no other compacted powder present in the core portion.

7. The deposition wire according to claim 1 or 2, wherein the deposition wire contains 0.15% by weight or less of carbon.

8. The deposition wire according to claim 1 or 2, wherein the deposition wire contains 1.0% by weight or less of oxygen.

9. The deposition wire according to claim 1 or 2, wherein the deposition wire has a final diameter (i.e., the outer diameter of the tubular portion) of less than 6.0 mm.

10. A method for producing a powder-in-tube type deposition wire, the method comprising the following steps: a) providing a strip of titanium; b) providing a powder of titanium containing at least partially non-spherical sponge powder of titanium and optionally other powder selected from the group consisting of aluminum, vanadium, chromium, molybdenum, boron, niobium, and tantalum; c) placing the titanium powder and the other powder on the strip; d) closing the strip so as to form a tube around the core portions of the titanium powder and the other powder, wherein the core portions occupy 30% to 80% by volume of the tube and the core portions; e) reducing the diameter of the tube by rolling or drawing in various rolling or drawing steps; A method for producing a deposited wire, comprising:

11. The method for producing a deposited wire according to claim 10, wherein one or more intermediate heat treatments are applied between the rolling or drawing steps.

12. The method for producing a deposited wire according to claim 10 or 11, wherein at least steps c) to d) are performed in an inert atmosphere.

13. The method for producing a deposited wire according to claim 10 or 11, wherein the step d) of closing the strip includes creating an overlap of the strip.

14. The method for producing a deposited wire according to claim 10, wherein the titanium powder at least partially comprises recycled titanium powder or turnings.

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