Control of solidification in laser powder bed fusion additive manufacturing using a diode laser fiber array
A method of method of forming or repairing a superalloy article having a columnar or equiaxed or directionally solidified or amorphous or single crystal microstructure includes emitting a plurality of laser beams from selected fibers of a diode laser fiber array corresponding to a pattern of a layer of the article onto a powder bed of the superalloy to form a melt pool; and controlling a temperature gradient and a solidification velocity of the melt pool to form the columnar or single crystal microstructure.
1. A method of forming or repairing a superalloy article having a columnar or equiaxed or directionally solidified or amorphous or single crystal microstructure, the method comprising:
emitting a plurality of laser beams from selected fibers of a diode laser fiber array corresponding to a pattern of a layer of the article onto a powder bed of the superalloy to form a melt pool; and
controlling a temperature gradient and a solidification velocity of the melt pool to form the columnar or equiaxed or directionally solidified or amorphous or single crystal microstructure, the controlling comprising controlling a decay rate of a laser energy of each of the plurality of laser beams to control a cooling period of the melt pool.
2. A method according to claim 1 , wherein the laser energy is decreased at 10 W/s to provide a is cooling period.
3. A method according to claim 1 , wherein the laser energy is decreased at 1 W/s to provide a 10 s cooling period.
4. A method according to claim 1 , wherein the laser energy is decreased at 0.1 W/s to provide a 100 s cooling period.
5. A method according to claim 1 , wherein controlling the temperature gradient and solidification velocity comprises heating a substrate that supports the powder bed and/or heating a prior layer of the article formed by solidification of a prior melt pool.
6. A method according to claim 5 , wherein heating the substrate comprises heating the substrate to a temperature below the melting temperature of the substrate.
7. A method according to claim 1 , wherein the average output power of each diode laser is up to 5 W-10 W.
8. A method according to claim 1 , wherein a diameter of each laser beam is 0.01 mm.
9. A method according to claim 1 , wherein each laser beam is emitted for 5-50 ms.
10. A method according to claim 1 , wherein an efficiency of the diode laser fiber array is 0.5.
11. A method according to claim 1 , wherein an energy distribution of each laser beam is a top hat.
12. A method according to claim 1 , wherein the melt pool has a depth of 20 μm-150 μm.
13. A method according to claim 12 , wherein the melt pool has a width 3-100,000 times the depth of the melt pool.
14. A method according to claim 1 , wherein a particle size of the superalloy powder is 10 μm-150 μm.
15. A method according to claim 14 , wherein a particle size of the superalloy powder is 40 μm.
16. A method according to claim 1 , wherein the superalloy is a Ni-based superalloy.
17. A method according to claim 1 , wherein controlling the temperature gradient and the solidification velocity of the melt pool comprises controlling at least one of a duration of each laser beam, a pulse energy of each diode laser, a pulse width of each diode laser, an average output power of each diode laser, an energy distribution of each laser beam, power density of each laser beam, a rate of reduction of the power of each laser beam, and/or a distance of ends of the fibers from the powder bed.
18. A method according to claim 1 , wherein controlling the temperature gradient and a solidification velocity of the melt pool comprises emitting laser beams from fibers at least adjacent to the pattern of the layer and heating the powder adjacent to the powder of the layer of the build to control a cooling rate of the melted powder.
19. A method according to claim 18 , wherein heating the powder adjacent to the powder of the layer comprises heating the powder at least one of prior to and/or during and/or after simultaneous melting of the powder of the pattern of the layer.
20. A method according to claim 18 , wherein a power density of the laser beams heating the powder adjacent the pattern is in a range of from about 100 W/cm 2 to about 100,000 W/cm 2 .
21. A method according to claim 1 , wherein a thickness of each layer is between about 1 μm to about 1 mm.
22. A method according to claim 21 , wherein a thickness of each layer is about 100 μm.
23. A method according to claim 22 , wherein a thickness of each layer is about 30 μm-50 μm.
24. A method according to claim 1 , wherein the superalloy article is a turbine component.
25. A method according to claim 14 , wherein the turbine component is an airfoil.
26. A method according to claim 1 , further comprising:
moving the selected fibers and the powder bed relative to each other; and
controlling the diode lasers of the selected fibers during relative movement.
27. A method according to claim 1 , wherein controlling the temperature gradient and the solidification velocity of the melt pool to form the columnar or single crystal microstructure comprises controlling a cooling rate of each layer in two dimensions.
28. A method according to claim 27 , wherein controlling the cooling rate of each layer in two dimensions comprises controlling a cooling rate of a layer that forms a surface layer of the article or repair to have at least one of a predetermined surface roughness and density.