NICKEL-BASED ALLOY POWDER

Abstract

A nickel-based alloy powder for additive manufacturing having in weight %:C:0.09 to 0.17, Ti:3.8 to 4.5, Zr:>0.06, W:1.8 to 2.6, and Al:3.0 to 3.8 is disclosed.

Claims

1. A nickel-based alloy powder for additive manufacturing comprising in weight %: C: 0.09 to 0.17, Ti: 3.8 to 4.5, Zr: >0.06, W: 1.8 to 2.6, Al: 3.0 to 3.8 and optionally one or more of the elements selected from: Cr: 15.7 to 17.0, Co: 3.0 to 9.0, Ta: 1.5 to 2.5 Mo: 1.0 to 2.5 Nb: 0.7 to 1.2 B: 0.008 to 0.012 O: <0.04 N: <0.03 the remainder being nickel and inevitable impurities.

2. The nickel-based alloy powder according to claim 1, wherein the powder comprises: Cr: 15.7 to 17.0, Co: 3.0 to 9.0, Ti: 3.8 to 4.5, Al: 3.0 to 3.8, W: 1.8 to 2.6, Ta: 1.5 to 2.5, Mo: 1.0 to 2.5, Nb: 0.7 to 1.2, C: 0.09 to 0.17, Zr: >0.06, B: 0.008 to 0.012, the remainder being nickel and inevitable impurities.

3. The nickel-based alloy powder according to claim 1, wherein the composition comprises 0.07 to 0.15 Zr.

4. The nickel-based alloy powder according to claim 1, wherein the composition comprises >0.08 to 0.12 Zr.

5. The nickel-based alloy powder according to claim 1, wherein the powder comprises 3.9 to 4.3 Ti.

6. (canceled)

7. The nickel-based alloy powder according to claim 1, wherein the powder comprises 3.2 to 3.6 Al.

8. The nickel-based alloy powder according to claim 1, wherein the powder comprises 2.0 to 2.4 W.

9. (canceled)

10. The nickel-based alloy powder according to claim 1, wherein the powder comprises 1.8 to 2.0 Ta.

11. The nickel-based alloy powder according to claim 1, wherein the powder comprises 1.5 to 2.0 Mo.

12. The nickel-based alloy powder according to claim 1, wherein the powder comprises 0.8 to 1.0 Nb.

13. The nickel-based alloy powder according to any claim 1, wherein the powder comprises 0.09 to 0.14 C.

14. (canceled)

15. The nickel-based alloy powder according to claim 1, wherein the powder comprises <0.025 O.

16. (canceled)

17. The nickel-based alloy powder according to claim 1, wherein the powder comprises <0.15 N.

18. The nickel-based alloy powder according to claim 1, wherein the powder comprises: Cr: 16.0 to 17.0, Co: 8.0 to 9.0, Ti: 3.9 to 4.3, Al: 3.2 to 3.6, W: 2.0 to 2.4, Ta: 1.8 to 2.0, Mo: 1.5 to 2.0, Nb: 0.8 to 1.0, C: 0.09 to 0.14, Zr: 0.07 to 0.15. B: 0.008 to 0.012, the remainder being nickel and inevitable impurities.

19. A method of producing the nickel-based alloy powder, the method comprising the steps of the atomising a liquid stream of molten metal having a composition according to claim 1.

20. The method according to claim 19, wherein the powder is produced by liquid atomisation, gas atomisation or centrifugal atomisation.

21. The method according to claim 19 wherein the atomised powder is annealed.

22. The method of producing a three-dimensional component by additive manufacturing which comprises the step of: i. providing a layer of the nickel-based alloy powder according to claim 1 on a build platform; ii. selectively fusing regions of the powder to form a first component layer; iii. providing a further layer of powder on the build platform and selectively fusing said further powder layer to form a subsequent component layer, and iv. repeating step (iii) as required to produce the three-dimensional component.

23. The nickel-based alloy component having the composition according to claim 1.

24. A method of using the powder according to claim 1 comprising the step of employing the powder in an additive manufacturing process.

Description

DETAILED DESCRIPTION OF THE DRAWING

[0068] Embodiments of the present invention are explained in more detail below with reference to figures.

[0069] FIG. 1 shows an additive manufacturing apparatus according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0070] In order that the invention may be more clearly understood one or more embodiments thereof will now be described, by way of example only.

[0071] According to the present invention there is provided an IN-738LC nickel-based superalloy powder (E1) for use in additive manufacturing applications, the composition of which is shown in Table 1 below.

[0072] In order to produce a component by additive manufacturing there is provided an additive manufacturing apparatus 10. The AM apparatus 10 comprises at least one container 11 which is configured to hold and dispense the powder 12 according to the present invention. The container 11 is funnel shaped at its lower end and an electronic valve 13, configured to control the flow of powder 12 from the container 11, is provided in the funnel portion of the container. The electronic valve 13 is controlled by a control unit (not shown) which is in communication with both the electronic valve 13 and a personal computer or similar device (not shown).

[0073] The container 11 is funnel shaped at its lower end and an electronic valve 13, configured to control the flow of powder 12 from the container 11, is provided in the funnel portion of the container. The electronic valve 13 is controlled by a control unit (not shown) which is in communication with both the electronic valve 13 and a personal computer or similar device (not shown).

[0074] The AM machine 10 also comprises a build platform 14 located below the container 11 that is configured to move in the y-direction. Arranged above the build platform 14 is a wiper 15. The wiper 15 is moveable from a first position in which the wiper 15 is held clear of the powder 12 (when present on the build platform) to a second position in which the wiper 15 engages the powder 12. The wiper is also operable for spreading powder 12 across the build platform 14 to form a layer of powder 12 having a substantially uniform thickness. In particular, the wiper 15 is operable to move from one side of the build platform 14 to the other once the wiper 15 has been brought into engagement with the powder 12 on the build platform 13.

[0075] The apparatus 10 also comprises a heat source 16 for selectively melting powder particles within a given layer into a pre-determined shape. In this example the heat source 16 is a laser beam, but it will be appreciated that electron beam, microwave or plasma heat sources could alternatively be used. Prior to commencing the additive manufacturing process, a 3D model of the component to be produced is generated using computer aided design (CAD) software on a personal computer or similar device. For example, the component may be a gas turbine engine component.

TABLE-US-00001 TABLE 1 Alloy (wt %) Cr Co Ti Al W Ta Mo Nb C Zr B Ni Cl 16.00 8.50 3.40 3.40 2.60 1.75 1.75 0.90 0.11 0.05 0.010 Bal C2 15.76 8.43 3.61 3.36 1.84 2.46 1.47 0.48 0.11 0.018 0.0089 Bal C3 15.66 8.26 3.75 3.43 1.9 2.26 1.47 0.49 0.083 0.034 0.0055 Bal C4 15.88 8.30 3.31 3.51 2.62 1.90 1.75 0.90 0.10 0.02 0.011 Bal C5 16.00 8.30 3.30 3.50 2.60 1.90 1.80 0.91 0.1 0.03 0.011 Bal C6 12.0 0 0.60 5.5 0 0 5.20 2.50 0.15 0.06 0.01 Bal C7 8.23 9.25 0.81 5.63 9.42 3.26 0.51 0.09 0.08 0.011 0.018 Bal C8 22.3 19.2 3.60 1.80 1.90 1.50 0.00 1.00 0.16 0.13 0.005 Bal El 16.0 8.30 3.90 3.50 2.40 1.91 1.75 0.90 0.10 0.08 0.009 Bal E2 16.39 8.68 4.04 3.66 2.17 1.5 1.53 0.71 0.11 0.11 0.0099 Bal

[0076] The CAD model is then subjected to finite element analysis (FEA) which is a computerised method for predicting how a product reacts under various physical conditions such as stress. The CAD files are then converted into .STL files which can be understood by the additive manufacturing apparatus 10. The 3D model generated by the CAD software is then sliced electronically to obtain a series of 2D layers, which each define a planer cross section through the model of the component. The computer then outputs a signal to the control unit to open the electronic valve 12 of a container 11 so that the powder 12 is dispensed from the container 11. To ensure that the layer of powder 12 has a substantially uniform thickness, the wiper 15 is brought into engagement with the powder 12 and is then moved back and forth so that powder is spread across the build platform 14 until the desired layer thickness is obtained. The wiper 15 is then retracted and held out of contact with the powder 12. In forming the layer of powder 12 it will be appreciated that a proportion of the powder 12 will be wiped from the surface of the build platform 14. This powder is collected in a collection chamber 17 so that this unfused powder 12 can be re-used and reintroduced into the container 11 or into a further container (not shown).

[0077] Selected regions of powder 12 corresponding with the desired shape of the component are then irradiated with a laser beam 16 which causes particles in the layer to fuse and form a solid mass on cooling. In this example a 3D energy density of between 60 and 80 J/mm.sup.−3 was used, although it will be appreciated that the value of each parameter (laser power (W), scan velocity (mm/s), hatch distance (μm) and layer thickness (μm) can be varied. For example, when additively manufacturing nickel-based super alloys, a scan velocity of 600-1200 mm/s and hatch distances between 50 and 115 μm are typically used.

[0078] The build platform 14 is then lowered and another layer of powder is dispensed from the container 11 and the above described process of forming a layer with uniform layer thickness and irradiating selected regions with a laser beam 16 is repeated until the component is formed.

[0079] The components were then analysed to determine their crack susceptibility by measuring crack density. Crack density was determined by counts per unit area. Using an area of 0.25 mm.sup.2 (500×500 μm) square, 20 measurements were taken from each sample, enabling a statistically safe determination of an average per mm.sup.2 with 95% confidence level error. The 20 measurements were split across multiple micrographs depending on how many were taken per sample; for the case of a 5×5×5 mm cube this would be 5 measurements per micrograph, 4 micrographs per sample. In addition, micrographs were taken across specific regions of the sample (central, edge, top corner and bottom corner) in order to remove local bias. A crack severity scale is given below in Table 2:

TABLE-US-00002 Table 2 Crack severity scale 1 2 3 4 5 Cracks per mm.sup.2 0 1-5 6-10 11-20 21+

[0080] A crack severity rating (CSR) of 1 (cracks) is considered to be acceptable. However, a crack severity rating of 2 to 5 is considered unacceptable for most applications.

TABLE-US-00003 TABLE 3 Example Cl C2 C3 C4 C5 C6 C7 C8 El E2 CSR 4 4 3 4 4 5 5 4 1 1

[0081] The inventors found that components produced from the composition according to the invention (E1) and E2 exhibited reduced hot crack susceptibility relative to a commercially available nickel-based superalloy (C1) having a zirconium content of 0.05 wt %. Thus, contrary to current industry beliefs, it has been found that increasing the content of zirconium to above 0.06 wt % reduces the alloy's susceptibility to hot cracking in additive manufacturing processing. Moreover, improvements in rupture strength were observed which has been attributed to the E1 alloy composition containing an increased content of zirconium relative to the C1 alloy.

[0082] The C2 alloy received a crack severity rating of 4. The high number of cracks observed for this alloy has been attributed to it having a zirconium content of 0.06 wt % or less and a titanium content below 3.8 wt % which means there is insufficient high temperature strengthening during additive manufacturing. Similar results were obtained for the C4 and C5 alloys which also contained less than 3.8 wt % titanium and 0.06 wt % or less zirconium.

[0083] The C3 alloy received a crack severity rating of 3. Despite this alloy having a low carbon content (0.083 wt %) which would decrease solution strengthening, the reduced number of cracks relative to the C2, C4 and C5 alloys is believed to be due to the C3 alloy containing a higher content of titanium (3.75 wt %) and zirconium (0.034 wt %).

[0084] The C6 and C7 alloys both received a crack severity rating of 5. This is due to these alloys containing 0.06 wt % or less of zirconium, less than 3.8 wt % of titanium and more than 3.8 wt % of aluminium. As discussed above, a titanium content of less than 3.8 wt % results in reduced high temperature strengthening, whereas an aluminum content above 3.8 wt % increases the alloy's susceptibility to hot cracking during additive manufacturing. Moreover, the absence of tungsten in the C6 alloy means that there is no tungsten for forming carbides or for contributing to solid solution strength and therefore such alloys exhibit an increased cold crack susceptibility. In the case of the C7 alloy which contains a significant amount of tungsten (9.42 wt %) it is also believed that the high tungsten content contributes to increasing the hot crack susceptibility of the alloy.

[0085] Despite the C8 alloy having a zirconium content above 0.06 wt %, it was found to be very susceptible to hot cracking and received a crack severity rating of 4 (11-20 cracks). This increased hot crack susceptibility has been attributed to the C8 alloy having a titanium content below 3.8 wt % and a low aluminium content (1.8 wt %).

[0086] The above embodiment is described by way of example only. Many variations are possible without departing from the scope of the invention.