Method of making ruthenium-based material for spark plug electrode

1. A method of making an electrode material, the method comprising the steps of:

(a) forming a ruthenium-based material into a bar that has a length and a first diameter, the ruthenium-based material having ruthenium (Ru) as the single largest constituent on a weight percentage (wt %) basis;

(b) hot-forming the bar of the ruthenium-based material into an elongated wire that has a second diameter and a fibrous grain structure, the second diameter being smaller than the first diameter; and

(c) intermittently annealing the ruthenium-based material during step (b) to maintain the fibrous grain structure as the ruthenium-based material undergoes diameter reduction from the first diameter of the bar to the second diameter of the elongated wire.

2. The method of claim 1 , wherein step (b) comprises:

hot-drawing the bar of the ruthenium-based material through a heated draw plate at least once to form the elongated wire, and wherein the second diameter of the elongated wire is at least 80% less than the first diameter of the bar.

3. The method of claim 2 , wherein the intermittent annealing step is performed at least once for every 50% reduction in diameter by hot-drawing.

4. The method of claim 2 , further comprising:

hot-swaging the bar of the ruthenium-based material before hot-drawing.

5. The method of claim 1 , wherein the intermittent annealing is performed below the recrystallization temperature of the ruthenium-based material.

6. The method of claim 1 , wherein the ruthenium-based material further comprises at least one of rhodium, iridium, platinum, palladium, gold, or a combination thereof.

7. The method of claim 1 , wherein the ruthenium-based material further comprises at least one of tungsten, rhenium, or a combination of tungsten and rhenium.

8. The method of claim 1 , wherein the ruthenium-based material is selected from the group consisting of Ru-(0.5-5)Re-0.5-5)W, Ru-(1-10)Rh-(0.5-5)Re-0.5-5)W, and Ru-(1-10)Rh-(1-10)Pt-(0.05-5)Re-0.05-5)W, wherein the numerical ranges are provided in wt. %.

9. The method of claim 1 , further comprising:

cutting a segment of the ruthenium-based material from the elongated wire, the segment having a diameter between about 0.3 mm and about 1.5 mm; and

attaching the segment of the ruthenium-based electrode material to a center electrode of a spark plug by way of an intermediate firing tip component.

10. The method of claim 9 , wherein the fibrous grain structure of the segment of the ruthenium-based material includes elongated grains that have axial dimensions aligned generally parallel to a longitudinal axis of the center electrode.

11. A method of making an electrode material, the method comprising the steps of:

(a) providing a ruthenium-based material that comprises ruthenium (Ru) as the single largest constituent on a weight percentage (wt %) basis;

(b) hot-drawing the ruthenium-based material through an opening defined in a heated draw plate along an elongation axis to provide the ruthenium-based material with elongated grains generally parallel to the elongation axis;

(c) annealing the ruthenium-based material at a temperature that maintains the elongated grains; and

(d) repeating steps (b) and (c) to form an elongated wire of the ruthenium-based material.

12. The method of claim 11 , wherein the ruthenium-based material further comprises another precious metal in addition to ruthenium, and further comprises at least one of tungsten, rhenium, or a combination of tungsten and rhenium.

13. The method of claim 11 , further comprising:

hot-swaging the ruthenium-based material, before hot-drawing, at a temperature above the ductile-brittle temperature of the ruthenium-based material.

14. The method of claim 13 , wherein the hot-swaging reduces a diameter of the ruthenium-based material by up to 50%.

15. The method of claim 14 , wherein step (d) is carried out to reduce the diameter of the ruthenium-based material by at least an additional 85% following hot-swaging, and wherein the annealing is performed at least once for every 50% reduction in the diameter of the ruthenium-based material during hot-drawing.

16. The method of claim 11 , further comprising:

cutting a segment of the ruthenium-based material from the elongated wire, the segment including elongated grains that have axial dimensions; and

attaching the segment of the ruthenium-based electrode material to a center electrode or a ground electrode such that a surface of the segment normal to the axial dimensions of the elongated grains constitutes a sparking surface.

17. The method of claim 16 , wherein the segment of the ruthenium-based material is attached to the center electrode by way of an intermediate firing tip component.

18. A spark plug comprising:

a metallic shell having an axial bore;

an insulator being at least partially disposed within the axial bore of the metallic shell, the insulator having an axial bore;

a center electrode being at least partially disposed within the axial bore of the insulator; and

a ground electrode being attached to the metallic shell;

wherein the center electrode, the ground electrode, or both the center and ground electrodes includes a electrode material that has a fibrous grain structure, and wherein the electrode material is a ruthenium-based material having ruthenium (Ru) as the single largest constituent on a weight percentage (wt %) basis.

19. The spark plug of claim 18 , wherein the ruthenium-based material is in the form of a firing tip component that is attached to the center electrode by way of an intermediate firing tip component.

20. The spark plug of claim 19 , wherein the firing tip component includes elongated grains that have axial dimensions aligned generally parallel to a longitudinal axis of the center electrode.