Method for practicing a feedback controlled laser induced surface modification

• US 6,350,326 B1
• Filed: 10/19/1999
• Issued: 02/26/2002
• Est. Priority Date: 01/15/1996
• Status: Expired due to Term

• Current Assignee: University of Tennessee Research Foundation (University of Tennessee)
• Original Assignee: The University Of Tennessee Research Corporation (University of Tennessee)
• Inventors: Dahotre, Narendra B., McCay, Mary Helen, McCay, T. Dwayne
• Primary Examiner(s): WYSZOMIERSKI, GEORGE P
• Application Number:
  US09/420,675
• Time in Patent Office: 861 Days
• Field of Search: 148/503, 148/511, 148/512, 148/525, 219/121.63, 219/121.64, 219/121.83, 219/121.62, 219/121.8
• US Class Current: 148/503
• CPC Class Codes: B23K 2103/04 Steel or steel alloys
• CPC Class Codes: B23K 2103/08 Non-ferrous metals or alloys
• CPC Class Codes: B23K 2103/50 Inorganic material, e.g. metals, not provided for in B23K2103/02 – B23K2103/26
• CPC Class Codes: B23K 26/034 Observing the temperature of the workpiece
• CPC Class Codes: B23K 26/0626 Energy control of the laser beam B23K26/0622 takes precedence
• CPC Class Codes: B23K 26/064 by means of optical elements, e.g. lenses, mirrors or prisms
• CPC Class Codes: B23K 26/0643 comprising mirrors
• CPC Class Codes: B23K 26/0665 by beam condensation on the workpiece, e.g. for focusing
• CPC Class Codes: B23K 26/32 taking account of the properties of the material involved
• CPC Class Codes: B23K 26/34 Laser welding for purposes other than joining
• CPC Class Codes: B23K 35/0244 Powders, particles or spheres; Preforms made therefrom
• CPC Class Codes: B23K 35/308 with Cr as next major constituent
• CPC Class Codes: C23C 14/16 on metallic substrates or on substrates of boron or silicon
• CPC Class Codes: C23C 14/5813 using lasers
• CPC Class Codes: C23C 24/106 Coating with metal alloys or metal elements only

Abstract

This invention is directed toward a method of calculating the total laser energy needed to produce one or more selected laser induced surface modification reactions in a substrate moving relative to a laser beam. The present invention is further directed to a method for programming a programmable feedback control system with the calculated total laser energy such that the control system may be used to control laser beam power level and beam width in a process for producing a laser induced surface modification.

Claims

1. A method of calculating the total laser energy needed to produce a selected laser induced surface modification reaction in a substrate moving relative to a laser beam, comprising:

a. selecting a reaction to be induced;

b. selecting the temperature, T, at which the selected reaction shall take place;

c. determining the free energy of formation, FEF, of the reaction selected in step (a) at the temperature selected in step (b);

d. selecting the depth of surface modification, D;

e. selecting the volume fraction composition, VF, of the surface modified layer;

f. selecting the translation rate, TR, of the relative movement of the substrate with respect to the laser beam;

g. determining the coating species theoretical density, CSD, based upon the reaction selected in step (a);

h. selecting the laser beam width, BW;

i. calculating the mass of alloying coating species, MAS, needed;

j. calculating the total laser energy, TLE, needed to produce the surface modification having the volume composition selected in step (e); and

k. inputting the total laser energy, TLE, and beam width, BW, into a programmable feedback control system operatively coupled to control the power level and beam width of a laser beam used to induce said surface modification.

2. The method of claim 1, wherein said calculating the mass of alloying coating species needed, MAS, is accomplished by solving the following equation:

3. The method of claim 1, wherein the reaction selected in step (a) is:

4. The method of claim 3, wherein said determining the free energy of formation, FEF, is accomplished using the relationship:

5. The method of claim 1, wherein the reaction selected in step (a) is:

6. The method of claim 5, wherein said determining the free energy of formation, FEF, is accomplished using the relationship:

7. The method of claim 1, wherein the reaction selected in step (a) is:

8. The method of claim 1, wherein the reaction selected in step (a) is:

9. The method of claim 8, wherein said determining the free energy of formation, FEF, is accomplished using the relationship:

10. The method of claim 1, wherein said calculating the total laser energy, TLE, is accomplished by solving the following equation:

11. The method of claim 1, wherein said calculating the total laser energy, TLE, is accomplished by solving the following equation:

12. The method of claim 1, wherein said control system is further operatively coupled to control the speed of a movement system capable of causing relative movement between said substrate and said laser beam, and further comprising inputting the selected translation rate, TR, into said control system.

13. The method of claim 12, wherein said control system is further operatively coupled to a precursor delivery system capable of controlling the rate of delivery of a precursor comprising the selected coating species.

14. The method of claim 1 wherein:

a. said selecting a reaction comprises selecting a multiplicity of reactions;

b. said selecting the temperature is carried out for each selected reaction;

c. said determining the value of FEF is carried out for each selected reaction;

d. said determining the value of CSD is carried out for each selected reaction; and

e. said selecting the value of VF is carried out for each selected reaction.

15. The method of programming a feedback control system used to control the depth and chemistry of a selected laser induced surface modification reaction in a substrate moving relative to a laser beam or a laser beam moving relative to a substrate, comprising:

a. selecting a reaction to be induced;

b. selecting the temperature, T, at which the selected reaction shall take place;

c. determining the free energy of formation, FEF, of the reaction selected in step (a) at the temperature selected in step (b);

d. selecting the depth of surface modification, D;

e. selecting the volume fraction composition, VF, of the surface modified layer;

f. selecting the translation rate, TR, of the relative movement of the substrate with respect to the laser beam;

g. determining the coating species theoretical density, CSD, based upon the reaction selected in step (a);

h. selecting the laser beam width, BW;

i. calculating the mass of alloying coating species, MAS, needed;

j. calculating the total laser energy, TLE, needed to produce the surface modification having the volume composition selected in step (e);

k. inputting the calculated total laser energy and the selected beam width into a programmable feedback control system operatively coupled to control the power level and beam width of a laser beam used to induce said surface modification;

l. coating a substrate having a material composition compatible with the selected reaction to be induced with a precursor comprising the selected coating species;

m. causing relative movement between the coated substrate and a laser beam operatively coupled to be controlled by said control system; and

n. using said control system to control the power level and beam width of the laser beam as it irradiates the substrate.

16. The method of claim 15, further comprising:

a. inputting the translation rate, TR, into said control system; and

b. using said control system to control the translation rate of the relative movement of the substrate with respect to the laser beam.

17. The method of claim 15, wherein said calculating the mass of alloying coating species needed, MAS, is accomplished by solving the following equation:

18. The method of claim 15, wherein said calculating the total laser energy, TLE, is accomplished by solving the following equation: