Process for resurfacing a monocrystalline or directionally solidified metallic piece

1. A process for resurfacing a monocrystalline or directionally solidified metallic piece having a length, a width and a thickness (W s ), wherein said thickness, when measured across a side wall of said metallic piece, varies between 0.2 and 2 mm along said width, said process comprising:

applying coaxially a laser beam and a flux of metallic powder to said side wall of the metallic piece and along said width, wherein the metallic powder is of a same nature as that of the metallic piece, to produce at least one layer of metal, monocrystalline or directionally solidified, on said side wall and along said width of the metallic piece,

emitting the laser beam at a power “P” and moving said laser beam along the metallic piece at a speed “v”, and

adapting a P/v ratio as a function of said thickness (Ws) of said metallic piece as said laser beam moves along said side wall of said metallic piece at said speed, wherein said adapting of said P/v ratio is performed as follows:

for a thickness W s between 0.2 and 0.6 mm, maintaining said P/v ratio between two portions of increasing P/v vs Ws curves, one taking values ranging from 0.12 to 0.58 W mm-1 , the other taking values ranging from 0.25 to 0.84 W mm-1 ;

for a thickness W s between 0.6 and 0.8 mm, maintaining said P/v ratio between two portions of increasing P/v vs Ws curves, one taking values ranging from 0.58 to 0.83 W mm-1 , the other taking values ranging from 0.84 to 1.42 W mm-1 ;

for a thickness W s between 0.8 and 1 mm, maintaining said P/v ratio between two portions of increasing P/v vs Ws curves, one taking values ranging from 0.83 to 1.08 W mm-1 , the other taking values ranging from 1.42 to 2.05 W mm-1 ;

for a thickness W s between 1 and 1.2 mm, maintaining said P/v ratio between two portions of increasing P/v vs Ws curves, one taking values ranging from 1.08 to 1.27 W mm-1 , the other taking values ranging from 2.05 to 2.34 W mm-1 ;

for a thickness W s between 1.2 and 1.4 mm, maintaining said P/v ratio between two portions of increasing P/v vs Ws curves, one taking values ranging from 1.27 to 1.33 W mm-1 , the other taking values ranging from 2.34 to 2.48 W mm-1 ;

for a thickness W s between 1.4 and 2 mm, maintaining said P/v ratio between two portions of increasing P/v vs Ws curves, a constant one equal to 1.33 W mm-1 , the other taking values ranging from 2.48 to 2.75 W mm-1 ,

wherein the laser beam and the metallic powder are applied by a projection nozzle, and wherein said adapting of said P/v ratio is performed automatically via a program that includes predetermined information about an evolution of said thickness (W s ) along said side wall and that automatically controls said P/v ratio as a function of a position of said nozzle along said side wall of the metallic piece.

2. The process as claimed in claim 1 , wherein the portions of P/v vs Ws curves are portions of straight lines.

3. The process as claimed in claim 1 , further comprising pre-heating the piece prior to applying the flux of powder.

4. The process as claimed in claim 3 , wherein the pre-heating is carried out by laser beam.

5. The process as claimed in claim 1 , wherein applying the flux of powder is carried out without pre-heating of the piece.

6. The process as claimed in claim 1 , further comprising fabricating successively several layers of metal on top of each other, wherein the energy applied along the metallic piece to all the layers is the same.

7. The process as claimed in claim 6 , wherein a same P/v ratio is maintained for the layers to which the same energy is applied.

8. The process as claimed in claim 1 , further comprising producing successively several layers of metal on top of each other, wherein the energy of a first layer is less than the energy of subsequent layers.

9. The process as claimed in claim 8 , wherein a same P/v ratio is maintained for the layers to which the same energy is applied.

10. The process as claimed in claim 1 , wherein the metallic piece and the metallic powder comprise a monocrystalline alloy known as AM 1 .

11. The process as claimed in claim 1 , wherein the laser beam is a YAG laser beam.

12. The process as claimed in claim 1 , wherein the laser beam and the metallic powder are applied by a projection nozzle, comprising a truncated end portion which comprises a central bore for passage of the laser beam and channels, extending in the generation wall of its truncated end, for supplying the powder.

13. The process as claimed in claim 1 , wherein the metallic piece is a gas turbine motor blade.

14. The process as claimed in claim 1 , wherein said adapting of said P/v ratio is performed as follows:

for a thickness W s between 0.2 and 0.6 mm, maintaining said P/v ratio between two portions of increasing P/v vs Ws curves, one taking values ranging from 0.125 to 0.58 W mm-1 , the other taking values ranging from 0.25 to 0.833 W mm-1 ,

for a thickness W s between 0.6 and 0.8 mm, maintaining said P/v ratio between two portions of increasing P/v vs Ws curves, one taking values ranging from 0.583 to 0.83 W mm-1 , the other taking values ranging from 0.84 to 1.417 W mm-1 ,

for a thickness W s between 0.8 and 1 mm, maintaining said P/v ratio between two portions of increasing P/v vs Ws curves, one taking values ranging from 0.833, to 1.08 W mm-1 , the other taking values ranging from 1.42, to 2.042 W mm-1 ;

for a thickness W s between 1 and 1.2 mm, maintaining said P/v ratio between two portions of increasing P/v vs Ws curves, one taking values ranging from 1.083, to 1.27 W mm-1 , the other taking values ranging from 2.05 to 2.333 W mm-1 ,

for a thickness W s between 1.2 and 1.4 mm, maintaining said P/v ratio between two portions of increasing P/v vs Ws curves, one taking values ranging from 1.271 to 1.33 W mm-1 , the other taking values ranging from 2.34 to 2.479 W mm-1 ,

for a thickness W s between 1.4 and 2 mm, maintaining said P/v ratio between two portions of increasing P/v vs Ws curves, a constant one equal to 1.333 W mm-1 , the other taking values ranging from 2.48 to 2.75 W mm-1 .

15. A process for resurfacing a monocrystalline or directionally solidified metallic piece having a length, a width and a thickness (W s ), wherein said thickness, when measured across a side wall of said metallic piece, varies between 0.2 and 2 mm along said width, said process comprising:

applying coaxially a laser beam and a flux of metallic powder to said side wall of the metallic piece and along said width, wherein the metallic powder is of a same nature as that of the metallic piece, to produce at least one layer of metal, monocrystalline or directionally solidified, on said side wall and along said width of the metallic piece,

emitting the laser beam at a power “P” and moving said laser beam along the metallic piece at a speed “v”, and

adapting a P/v ratio as a function of said thickness (Ws) of said metallic piece as said laser beam moves along said side wall of said metallic piece at said speed, wherein said adapting of said P/v ratio is performed as follows:

for a thickness W s between 0.2 and 0.6 mm, maintaining said P/v ratio between two portions of increasing P/v vs Ws curves, one taking values ranging from 0.12 to 0.58 W mm-1 , the other taking values ranging from 0.25 to 0.84 W mm-1 ;

for a thickness W s between 0.6 and 0.8 mm, maintaining said P/v ratio between two portions of increasing P/v vs Ws curves, one taking values ranging from 0.58 to 0.83 W mm-1 , the other taking values ranging from 0.84 to 1.42 W mm-1 ;

for a thickness W s between 0.8 and 1 mm, maintaining said P/v ratio between two portions of increasing P/v vs Ws curves, one taking values ranging from 0.83 to 1.08 W mm-1 , the other taking values ranging from 1.42 to 2.05 W mm-1 ;

for a thickness W s between 1 and 1.2 mm, maintaining said P/v ratio between two portions of increasing P/v vs Ws curves, one taking values ranging from 1.08 to 1.27 W mm-1 , the other taking values ranging from 2.05 to 2.34 W mm-1 ;

for a thickness W s between 1.2 and 1.4 mm, maintaining said P/v ratio between two portions of increasing P/v vs Ws curves, one taking values ranging from 1.27 to 1.33 W mm-1 , the other taking values ranging from 2.34 to 2.48 W mm-1 ;

for a thickness W s between 1.4 and 2 mm, maintaining said P/v ratio between two portions of increasing P/v vs Ws curves, a constant one equal to 1.33 W mm-1 , the other taking values ranging from 2.48 to 2.75 W mm-1 ,

wherein said adapting of said P/v ratio is performed by an auto-regulator that controls said P/v ratio in real time as a function of data obtained by measuring in real time a property that depends on said thickness (W s ) at any given point along said side wall of said metallic piece.

16. The process as claimed in claim 15 , wherein said property is luminosity and said measuring is performed by a photodiode connected to said auto-regulator.