Spark plug electrode with ruthenium-based material

Abstract

A spark plug electrode made of a ruthenium-based material having one or more of the following properties: an equiaxed grain structure, a grain structure having an average grain size of less than or equal to 50 [mu] m, a grain structure having an average porosity of less than or equal to 2%, and / or a grain structure having an average non-uniformity ratio of less than or equal to 6%. In one example, the ruthenium-based material is a binary alloy comprising, by weight, from 1% to 15% of rhodium and the balance ruthenium. In various examples, the ruthenium-based material is a ternary alloy that includes from 1 wt% to 15 wt%, including an end value, rhodium, from 0.5 wt% to 5 wt%, including an end value, rhenium, and a balance of ruthenium. The invention further provides a powder metallurgy method for manufacturing the spark plug electrode.

Description

[0001] This application is a divisional application of Chinese Patent Application No. 202510935546.4, filed on July 8, 2025, entitled “Spark Plug Electrode with Ruthenium-Based Material,” which claims priority to U.S. Patent Application 18 / 794,380, filed on August 5, 2024, the contents of which are incorporated herein by reference. Technical Field

[0002] The present invention relates generally to spark plugs and other ignition devices for internal combustion engines, and more particularly to spark plug electrodes. Background Technology

[0003] Spark plugs are used to ignite combustion in internal combustion engines. Spark plugs typically ignite gases, such as an air / fuel mixture, in an engine cylinder or combustion chamber by generating a spark across a spark gap defined between two or more electrodes. The spark ignites the gases, initiating a combustion reaction in the engine cylinder that causes the engine's power stroke. High temperatures, high voltage, the rapid repetition of the combustion reaction, and the presence of corrosive materials in the combustion gases create the harsh environment in which spark plugs must operate. This harsh environment leads to electrode erosion and corrosion, which, over time, negatively impacts the spark plug's performance and durability, potentially causing misignition or some other undesirable situation.

[0004] Various types of precious metals and their alloys have been used to reduce erosion and corrosion of spark plug electrodes. However, these materials can be expensive. Therefore, spark plug manufacturers often attempt to minimize the amount of such material used in the electrodes by using precious metal materials only at the ignition tip, where the spark jumps across the spark gap. Ignition tips made of platinum and iridium alloys (which have relatively good ductility and can be manufactured using conventional techniques involving drawing and rolling) are already widely used in industry, but are becoming increasingly expensive and economically unfeasible for use in certain applications.

[0005] A cheaper alternative to precious metals is ruthenium. However, ruthenium alloys are relatively brittle, making them difficult to manufacture using conventional techniques. Thermal cracking and intergranular cracking are just some of the undesirable properties that conventional ruthenium-based ignition tips may exhibit when welded or otherwise attached to spark plug electrodes. Figure 11An example of a ruthenium-based ignition tip 510 attached to a nickel-based electrode 512 using a laser-welded portion 514 is shown. Multiple intergranular cracks and / or thermal cracks 520 have formed in the ignition tip 510, particularly near the junction with the laser-welded portion 514. Those skilled in the art will understand that cracks such as intergranular cracks and / or thermal cracks are undesirable, and in some cases, these cracks may even cause the ignition tip 510 to detach from the electrode 512.

[0006] Therefore, it is desirable to provide a spark plug electrode made of a ruthenium-based material, which has robust resistance to erosion and corrosion, as well as enhanced resistance to intergranular cracks and / or thermal cracks. Summary of the Invention

[0007] According to a first embodiment, a spark plug electrode is provided, the spark plug electrode comprising: a ruthenium-based material having ruthenium and rhodium, wherein ruthenium is a single maximum component based on weight %, wherein the ruthenium-based material has an equiaxed grain structure having an average grain size of less than or equal to 50 μm and an average porosity of less than or equal to 2%.

[0008] According to various embodiments, the spark plug electrode of the first embodiment may have one or more of the following features, either alone or in any technically feasible combination: - Rhodium is the second largest component of this ruthenium-based material after ruthenium by weight, and exists in the ruthenium-based material in a range of 0.1% to 35% by weight, including the end value; - The ruthenium-based material is a binary alloy containing 1% to 15% rhodium (including end values) and the balance ruthenium; - At least one of the following metals is the third largest component of this ruthenium-based material by weight percentage, after ruthenium and rhodium: platinum, palladium, iridium, gold, silver, rhenium, tungsten, tantalum, molybdenum, or niobium; - The ruthenium-based material is a ternary alloy containing 1% to 15% rhodium (including the end value), 0.5% to 5% rhenium (including the end value), and the balance ruthenium. - The ruthenium-based material has an average grain size of 5 μm to 40 μm, including the end value; - This ruthenium-based material has an average porosity of less than or equal to 1.5%; - The ruthenium-based material has a grain structure with an average inhomogeneity ratio of less than or equal to 6% with respect to the maximum solute in the ruthenium-based material based on weight %; - The maximum solute, based on weight %, is rhodium; and / or - The spark plug electrode is manufactured using a powder metallurgy method that includes sintering a powder mixture to directly form the spark plug electrode into its near-net-shape.

[0009] According to a second embodiment, a spark plug electrode is provided, comprising: a ruthenium-based material having ruthenium and rhodium, wherein ruthenium is a single maximum component based on weight %; wherein the ruthenium-based material has an equiaxed grain structure having an average grain size of less than or equal to 50 μm and an average non-uniformity ratio of less than or equal to 6% with respect to the maximum solute based on weight % in the ruthenium-based material.

[0010] According to various embodiments, the spark plug electrode of the second embodiment may have one or more of the following features, either alone or in any technically feasible combination: - Rhodium is the second largest component of this ruthenium-based material after ruthenium by weight, and exists in the ruthenium-based material in a range of 0.1% to 35% by weight, including the end value; - The ruthenium-based material is a binary alloy containing 1% to 15% rhodium (including end values) and the balance ruthenium; - At least one of the following metals is the third largest component of this ruthenium-based material by weight percentage, after ruthenium and rhodium: platinum, palladium, iridium, gold, silver, rhenium, tungsten, tantalum, molybdenum, or niobium; - The ruthenium-based material is a ternary alloy containing 1% to 15% rhodium (including the end value), 0.5% to 5% rhenium (including the end value), and the balance ruthenium. - The ruthenium-based material has an average grain size of 5 μm to 40 μm, including the end value; - The largest solute, based on weight percent, is rhodium; - The ruthenium-based material has an average porosity of less than or equal to 2%; and / or - The spark plug electrode is manufactured using a powder metallurgy method that includes sintering a powder mixture to directly form the spark plug electrode into its near-net-shape. Attached Figure Description

[0011] Preferred exemplary embodiments of the invention will now be described in conjunction with the accompanying drawings, wherein like reference numerals denote like elements, and wherein: Figure 1 It is a cross-sectional view of an exemplary spark plug having one or more spark plug electrodes made of ruthenium-based material; Figure 2 yes Figure 1 An enlarged cross-sectional view of the ignition end of a spark plug; Figures 3 to 5It is an enlarged cross-sectional view of the ignition end of another exemplary spark plug having one or more spark plug electrodes made of ruthenium-based material; Figure 6 Spark plug electrodes made of ruthenium-based materials (such as...) Figures 1 to 5 The magnified image shows an example of an equiaxed grain structure of those spark plug electrodes. Figure 7 Spark plug electrodes made of ruthenium-based materials (such as...) Figures 1 to 5 The magnified image shows an example of a grain structure with an average grain size of less than or equal to 50 μm. Figure 8 Spark plug electrodes made of ruthenium-based materials (such as...) Figures 1 to 5 The magnified image shows an example of a grain structure with an average porosity of less than or equal to 2%. Figure 9 Spark plug electrodes made of ruthenium-based materials (such as...) Figures 1 to 5 The magnified image shows an example of a grain structure having an average inhomogeneity ratio of less than or equal to 6% based on the maximum solute in the ruthenium-based material. Figure 10 This is an enlarged image of an exemplary spark plug electrode (in this case, a ruthenium-based ignition tip) attached to the center electrode using a laser-welded portion; and Figure 11 This is an enlarged image of a conventional spark plug electrode (in this case, a ruthenium-based ignition tip) that is attached to the center electrode using a laser-welded part and exhibits multiple intergranular cracks and thermal cracks. Detailed Implementation

[0012] The spark plug electrodes described herein are made of ruthenium-based materials and can be used in a variety of spark plugs and other ignition devices, including automotive spark plugs, industrial plugs, aviation igniters, glow plugs, or any other device for igniting the air / fuel mixture in an engine. This includes, but is certainly not limited to, the exemplary spark plugs shown in the figures and described below.

[0013] refer to Figure 1 and Figure 2An exemplary spark plug 10 is shown, comprising a center electrode 12, an insulator 14, a metal shell 16, and a ground electrode 18. The center electrode or base electrode component 12 is disposed within an axial bore of the insulator 14 and includes an ignition tip 20 protruding beyond a free end 22 of the insulator 14. The ignition tip 20 is a multi-piece rivet comprising a first component 32 made of a rust-resistant and / or corrosion-resistant material (such as ruthenium-based materials as described below) and a second component 34 made of an intermediate material (such as a nickel-based alloy). In this specific embodiment, the first component 32 has a cylindrical shape, and the second component 34 has a stepped shape comprising an enlarged head section and a reduced shank section. The first and second components may be attached to each other via a laser-welded portion, a resistance-welded portion, or some other suitable welded or non-welded joint. The insulator 14 is disposed within an axial bore of the metal shell 16 and is made of a material sufficient to electrically insulate the center electrode 12 from the metal shell 16 (such as a ceramic material). As shown in the figure, the free end 22 of the insulator 14 may protrude beyond the free end 24 of the metal casing 16, or may retract into the metal casing 16. The ground electrode 18 may be constructed according to the conventional J-shaped configuration shown in the figure or according to some other arrangement and may be attached to the free end 24 of the metal casing 16. According to this specific embodiment, the ground electrode 18 includes a side surface 26 opposite to the ignition tip 20 of the center electrode, and has an ignition tip 30 attached to the side surface. The ignition tip 30 is in the form of a flat pad and defines a spark gap G with the ignition tip 20 of the center electrode, such that they provide spark-generating surfaces for electron emission and reception across the spark gap.

[0014] In this specific embodiment, the first component 32 of the center electrode ignition tip 20 and / or the ground electrode ignition tip 30 may be made of the ruthenium-based material described herein; however, these components are not the only application of this material. For example, as Figure 3 As shown, the exemplary center electrode ignition tip 40 and / or ground electrode ignition tip 42 can also be made of ruthenium-based material. In this case, the center electrode ignition tip 40 is a one-piece rivet, and the ground electrode ignition tip 42 is a cylindrical tip that extends a considerable distance away from the side surface 26 of the ground electrode. Ruthenium-based material can also be used to form... Figure 4 The exemplary center electrode ignition tip 50 and / or ground electrode 18 are shown. In this example, the center electrode ignition tip 50 is a cylindrical component located in a recess or blind hole 52 formed in the axial end of the center electrode 12. A spark gap G is formed between the spark-generating surface of the center electrode ignition tip 50 and the side surface 26 of the ground electrode 18, which also serves as a spark-generating surface. Figure 5Another possible application of the ruthenium-based material is shown, in which a cylindrical ignition tip 60 is attached to the axial end of the center electrode 12, and a cylindrical ignition tip 62 is attached to the axial end of the ground electrode 18. The ground electrode ignition tip 62 and the side surface of the center electrode ignition tip 60 form a spark gap G, and are therefore a slightly different ignition tip configuration from other exemplary spark plugs shown in the figure.

[0015] It should be understood that the non-limiting examples described herein represent only some potential embodiments of the spark plug electrode according to this application. As used herein, the term "spark plug electrode" (whether referring to the center electrode, ground electrode, or some other electrode) broadly includes a single base electrode, a single ignition tip, a single component of a multi-piece ignition tip, a single component of some other ignition end, or combinations thereof, to name only a few possibilities. For example, the following are non-limiting examples of potential spark plug electrodes according to this application: center electrode and / or ground electrode, also referred to as base electrode components or base electrodes (e.g., center electrode 12, ground electrode 18); center electrode ignition tip and / or ground electrode ignition tip, also referred to as ignition tip (e.g., center electrode ignition tips 20, 40, 50, 60 and ground electrode ignition tips 30, 42, 62); components of multi-piece center electrode ignition tips and / or multi-piece ground electrode ignition tips (e.g., first component 32 and second component 34 of center electrode ignition tip 20); and ignition end components of pre-combustion chamber spark plugs, such as protrusions of pre-combustion chamber caps or other spark-generating components (not shown). Examples of potential spark plug electrodes may include the following: spark plug electrodes as part of automotive and / or industrial plugs; spark plug electrodes as center electrodes and / or ground electrodes; spark plug electrodes forming axial, radial, air, and / or surface discharge spark gaps; spark plug electrodes directly attached to the base electrode or indirectly attached to the base electrode via one or more intermediate layers, intermediary layers, or stress-relief layers; spark plug electrodes in the shape of rivets, cylinders, bars, pillars, wires, balls, ridges, cones, pads, blocks, discs, rings, sleeves, and / or protrusions; spark plug electrodes located within recesses, embedded in the base electrode, or attached to the surface of the electrode; and / or spark plug electrodes located on side surfaces, axial end surfaces, inner circumferential surfaces, or outer circumferential surfaces (such as sleeves or other annular components). These spark plug electrodes are merely a few possible embodiments of spark plug electrodes having the ruthenium-based material described herein, and other spark plug electrodes exist and are intended to be covered by this application.

[0016] The spark plug electrode of this application is made of a ruthenium-based material having one or more of the following properties: equiaxed grain structure, grain structure with an average grain size of less than or equal to 50 μm, grain structure with an average porosity of less than or equal to 2%, and / or grain structure with an average non-uniformity ratio of less than or equal to 6%. The spark plug electrode described herein exhibits enhanced spark erosion resistance, durability, and solderability, and is ideally suited for a variety of high-performance applications.

[0017] As used herein, the term "ruthenium-based material" broadly includes any alloy or other electrode material in which ruthenium (Ru) is the single largest component based on weight percent. The ruthenium-based material may include materials having more than 50% ruthenium, as well as materials having less than 50% ruthenium, provided that ruthenium is the single largest component. Those skilled in the art will understand that ruthenium has a considerably high melting temperature (2334°C) compared to some noble metals, which can improve the corrosion resistance of the electrode material. However, ruthenium may be more readily oxidized than some noble metals, which may reduce the corrosion resistance of the electrode material. Therefore, the ruthenium-based materials disclosed herein may include ruthenium plus one or more additional components, such as noble metals, such as rhodium (Rh). Rhodium may be the second largest or second most abundant component of the ruthenium-based material based on weight percent, and may be present in the material in amounts from 0.1% to 35% by weight, including the end value, or even more preferably from 1% to 15% by weight, including the end value, or even more preferably from 1% to 10% by weight, including the end value. According to a set of examples, ruthenium-based materials can be binary alloys comprising ruthenium and rhodium (e.g., Ru-(1-15)Rh), ruthenium and palladium (e.g., Ru-(1-15)Pd), ruthenium and platinum (e.g., Ru-(1-15)Pt), ruthenium and iridium (e.g., Ru-(1-15)Ir), ruthenium and gold (e.g., Ru-(1-15)Au), ruthenium and silver (e.g., Ru-(1-15)Ag), etc. A particularly suitable binary alloy is 95Ru-5Rh. In addition to ruthenium and rhodium, ruthenium-based materials may also include one or more additional metals, such as rhenium (Re), platinum (Pt), palladium (Pd), iridium (Ir), gold (Au), silver (Ag), tungsten (W), tantalum (Ta), molybdenum (Mo), and / or niobium (Nb). The combined amount of rhodium and the additional metals preferably includes less than or equal to 35% by weight, even more preferably less than or equal to 15% by weight, and even more preferably less than or equal to 10% by weight. According to some examples, the ruthenium-based material can be a ternary alloy containing ruthenium, rhodium, and one of rhenium (Re), platinum (Pt), palladium (Pd), gold (Au), silver (Ag), or tungsten (W) (e.g., Ru-(1-15)Rh-(0.5-5)Re, Ru-(1-15)Rh-(0.5-5)Ir, Ru-(1-15)Rh-(0.5-5)Pt, or Ru-(1-15)Rh-(0.5-5)Pd). A particularly suitable ternary alloy is 94Ru-5Rh-1Re. In the example above, ruthenium-based materials can be considered as alloys in solid solution form, where ruthenium constitutes the solvent and one or more additional metals constitute the solute (e.g., for 95Ru-5Rh, ruthenium is the solvent and rhodium is the solute; for 94Ru-5Rh-1Re, ruthenium is the solvent and rhodium and rhenium are the solutes, where rhodium is the maximum solute based on weight %).One or more additional elements, compounds and / or other components may be added to the exemplary ruthenium-based materials described above, as the spark plug electrodes described above are not limited to those examples.

[0018] The spark plug electrode and its ruthenium-based material of this application preferably have an equiaxed grain structure. As used herein, the term "equiaxed grain structure" broadly includes a metallic grain structure in which most grains have substantially equal dimensions in all directions when observed in two dimensions (e.g., in a two-dimensional magnified image such as a backscattered electron (BSE) image or a photomicrograph). An equiaxed grain structure differs from an elongated or columnar grain structure in which most grains have significantly larger dimensions in one direction (e.g., the longitudinal direction) than in other directions. Reference Figure 6 A BSE image of an exemplary spark plug electrode 100 made of a ruthenium-based material having an equiaxed grain structure 102 is shown. In this particular example, the ruthenium-based material is a Ru-5Rh-1Re sintered alloy, and the BSE image has been magnified 1000 times to allow for better observation of the shape of the individual grains 104. Figure 6 As illustrated, most of the grains 104 in the ruthenium-based material have approximately equal dimensions in all directions; that is, these grains are not significantly elongated or enlarged in any one direction. This contrasts with spark plug electrodes having a columnar grain structure, in which most grains are larger in one direction than in another (i.e., these grains are elongated). Figure 6 The spark plug electrode samples in the sample have been mounted, ground and polished according to conventional metallurgical sample preparation techniques, followed by an electrolytic etching method applied to the sample to better reveal its grain structure.

[0019] The spark plug electrode also preferably has a grain structure with an average grain size of less than or equal to 50 μm. The grain size can be determined using a suitable measurement method (such as the method outlined in ASTM E112-13 (2021)), wherein the average grain size is determined at one or more samples (e.g., five samples) at the sparking surface of the electrode, away from any welded portion (e.g., measuring the grain size at or near a laser welded portion may produce questionable results, as heat from the welding process can sometimes affect the grain size). For a variety of reasons, it may be desirable to provide a spark plug electrode made of a ruthenium-based material having a grain structure with an average grain size of less than or equal to 50 μm. For example, tests have shown that ruthenium-based materials with an average grain size of less than or equal to 50 μm tend to exhibit fewer intergranular cracks and thermal cracks when the spark plug electrode is subjected to welding or other extreme heat, as described above. Figure 11As described. This, in turn, improves the solderability of the spark plug electrode. Tests also showed that ruthenium-based materials with an average grain size of less than or equal to 50 μm reduced the tendency for stress corrosion cracking in high-temperature environments, such as those typically experienced in internal combustion engines. This improves the durability of the spark plug electrode. Therefore, it is preferred that the spark plug electrode of this application is made of a ruthenium-based material having an average grain size of less than or equal to 50 μm, or even more preferably 5 μm to 40 μm including the end value, or even more preferably 10 μm to 30 μm including the end value. Reference Figure 7 An enlarged image of a spark plug electrode 100 made of a ruthenium-based material with an equiaxed grain structure 102 is shown, wherein the material is a Ru-5Rh sintered alloy, and the image has been magnified 300 times to allow for better observation of the size of the individual grains 104. Figure 7 The spark plug electrode samples in the sample have been mounted, ground and polished according to conventional metallurgical sample preparation techniques, followed by an electrolytic etching method applied to the sample to better reveal its grain structure.

[0020] Additionally, it is preferred that the spark plug electrode has a grain structure with an average porosity of less than or equal to 2%. The porosity of this material can be determined using a suitable image analysis method, such as a combination of the Quantitative Image Analysis (QIA) method outlined in ASTM E562 and the Automated Image Analysis (AIA) method described in ASTM E1245. This suitable image analysis method typically determines the ratio (expressed as a percentage) of the total combined area of ​​pores to the total area of ​​material shown in the image field of view. The average porosity is preferably determined at one or more samples (e.g., five samples) at the sparking surface of the electrode, away from any weld. For a variety of reasons, it may be desirable to provide a spark plug electrode made of a ruthenium-based material having a grain structure in which the average porosity is less than or equal to 2%. For example, testing has shown that ruthenium-based materials with an average porosity of less than or equal to 2% tend to be less susceptible to mass loss that might otherwise occur in high-temperature environments, such as those experienced in a combustion chamber. If the ruthenium-based material has too many pores, oxygen atoms will erode the porous sections of the spark-generating surface and weaken the grain boundaries within the material, which may subsequently lead to quality loss. Providing electrode materials with an average porosity of less than or equal to 2% ruthenium-based materials improves the durability of spark plug electrodes. Therefore, it is preferred that the spark plug electrode of this application is made of a ruthenium-based material having an average porosity of less than or equal to 2%, even more preferably less than or equal to 1.5%, or even more preferably 0.15% to 1.2% including the end value. Reference Figure 8A magnified image of a spark plug electrode 100 made of a ruthenium-based material with an equiaxed grain structure 102 is shown, wherein the material is a Ru-5Rh sintered alloy, and the image has been magnified 100 times to allow for better observation of the relative number and size of the pores 120. The pores or voids 120 are... Figure 8 The spots shown. Figure 8 The spark plug electrode samples in the samples were mounted, ground, and polished according to conventional metallurgical sample preparation techniques, without electrolytic etching, in order to better reveal their porosity.

[0021] The spark plug electrode also preferably has a grain structure with an average inhomogeneity ratio of less than or equal to 6% for the maximum solute in the ruthenium-based material, based on weight % as a percentage. Generally, the inhomogeneity of a ruthenium-based material indicates the degree to which the material or alloy has been sintered; the more complete the sintering process, the lower the inhomogeneity ratio (i.e., a low inhomogeneity ratio corresponds to a fairly homogeneous material). The inhomogeneity ratio of the material can be determined by first identifying solute-rich regions and then using a suitable measurement method to determine the inhomogeneity within those regions. A suitable measurement method involves determining (C... S -C O ) / C O C S This indicates the content of a solute (e.g., rhodium and / or rhenium) in a region or area rich in that particular metal (i.e., a solute-enriched region), and C O This usually indicates the average content of the same solute in ruthenium-based materials. Now turn to Figure 9 A magnified image of a spark plug electrode 100 made of a ruthenium-based material 102 with an equiaxed grain structure 102 is shown, wherein the material is a Ru-5Rh-1Re sintered alloy, and the image has been magnified 1000 times to allow for better observation of the average non-uniformity ratio. In this image, which is a backscattered image (BSE), bright areas or regions have higher contents of heavier metals, such as the solute rhodium, and correspond to solute-rich regions 130 (ruthenium is the lightest metal in ruthenium-based materials in most cases). Once the solute-rich region 130 is identified (in this case, a rhodium-rich region), the solute content C in the solute-rich region 130 can be determined by using any suitable chemical composition analysis, such as by using scanning electron microscopy (SEM) or scanning transmission electrode microscopy (STEM) combined with energy-dispersive spectroscopy (EDS). S This is to determine the elemental content of the sample. Then, the solute content C in the material can typically be determined from one or more non-solute enrichment regions 132. OThis can be done using the same chemical composition analysis. Once the solute content in zones 130 and 132 is determined, the heterogeneity ratio, usually expressed as a percentage, can be determined using the formula described above. Figure 9 In this context, the solutes are rhodium and rhenium, and the solvent is ruthenium, but this is not mandatory as other solutes can be used instead. The average non-uniformity ratio is preferably determined at one or more samples (e.g., five samples) at the sparking surface of the electrode, away from any weld portion. It may be desirable to provide a spark plug electrode made of a ruthenium-based material having a grain structure in which the average non-uniformity ratio is less than or equal to 6%, as this average non-uniformity ratio improves the durability and / or solderability of the ruthenium-based material. Therefore, it is preferred that the spark plug electrode of this application is made of a ruthenium-based material having an average non-uniformity ratio of less than or equal to 6%, even more preferably less than or equal to 5%, or even more preferably less than or equal to 4%. Although it is preferred that all solutes in the material satisfy the average non-uniformity ratio disclosed above, it is only required that the largest or dominant solute in the ruthenium-based material (e.g., Rh in Ru-5Rh-1Re) has an average non-uniformity ratio of less than or equal to 6% to satisfy this requirement. Figure 9 The spark plug electrode sample has been mounted, ground, and polished according to conventional metallurgical sample preparation techniques, and the sample has been subjected to electrolytic etching.

[0022] It should be understood that the characteristics described above for spark plug electrodes are not necessarily independent of each other, but can be related to each other. According to the first example, it is desirable to provide a spark plug electrode made of a ruthenium-based material having ruthenium and rhodium, wherein the ruthenium-based material has an equiaxed grain structure having an average grain size of less than or equal to 50 μm and an average porosity of less than or equal to 2%. In the second example, it is desirable to provide a spark plug electrode made of a ruthenium-based material having ruthenium and rhodium, wherein the ruthenium-based material has an equiaxed grain structure having an average grain size of less than or equal to 50 μm and an average inhomogeneity ratio of less than or equal to 6% with respect to the maximum solute in the ruthenium-based material. According to the third example, it is desirable to provide a spark plug electrode made of a ruthenium-based material having ruthenium and rhodium, wherein the ruthenium-based material has an equiaxed grain structure with an average grain size of less than or equal to 50 μm, an average porosity of less than or equal to 2%, and an average inhomogeneity ratio of less than or equal to 6% for the largest solute in the ruthenium-based material. However, providing such a spark plug electrode can be challenging. To achieve low porosity levels, higher sintering temperatures and longer sintering times are typically required during manufacturing, but these process parameters usually lead to an increase in average grain size. Tests have shown that when the average grain size can be maintained at less than or equal to 50 μm, while the average porosity is maintained at less than or equal to 2% and / or the average inhomogeneity ratio is maintained at less than or equal to 6% for the largest solute in the ruthenium-based material, the synergistic effect of these properties endows the ruthenium-based material with enhanced spark erosion resistance, durability, and solderability. Figure 10 A non-limiting example is shown of a ruthenium-based ignition tip 210 attached to a nickel-based central electrode 212 using a laser welding portion 214. Those skilled in the art will understand that... Figure 11 Compared to the conventional ignition tip 510 shown, the ignition tip 210 exhibits a significant reduction in intergranular cracks and / or hot cracks, particularly in the region of the laser-welded portion 214. The spark plug electrode 210 has undergone engine testing and, in addition to the generally absence of intergranular cracks and / or hot cracks, demonstrates the desired resistance to spark erosion.

[0023] In terms of manufacturing, spark plug electrodes made of ruthenium-based materials and having the optimized grain structure described above can be produced using the following powder metallurgy methods. During the initial steps, each component of the ruthenium-based material can be provided in powder form with a certain powder or particle size. In the example of the binary alloy 95Ru-5Rh, each component of ruthenium and rhodium can be provided in powder form with a particle size of 0.1 μm to 200 μm, including the end value. The component powders are then blended together to form a powder mixture. This step can be performed with or without heat. The blended or mixed powder can then be pressed into the desired shape of the spark plug electrode (the so-called "green state") using a molding press, as understood in the art. The pressed powder or green state component is then sintered to form the spark plug electrode. This sintering step can be performed according to any number of different embodiments, including: sintering in a vacuum or some type of protected environment; sintering at approximately 0.5-0.8T of the matrix alloy. melt Sintering can be carried out at various temperatures (as used herein, "matrix alloy" means an alloy formed from all components, such as 95Ru-5Rh or 94Ru-5Rh-1Re); under pressure or without pressure; and / or sintering to create or prevent a compositional gradient (e.g., a compositional gradient from grain boundary regions to the lattice or matrix); to name just a few possibilities. Sintering the powder mixture directly forms the spark plug electrode because a significant number of post-sintering processing steps are typically not required before the electrode is welded into place. This differs from conventional manufacturing processes, where a sintering step is used to produce a raw part, which is then subsequently stretched or otherwise metallized into its final shape. In this process, the sintering step directly forms the spark plug electrode to its "near-net-shape," unlike the conventional manufacturing processes mentioned above, where the electrode is shaped as close as possible to its final shape. Of course, minor post-sintering processing steps, such as pressing, polishing, or other surface preparation steps, can be used on the near-net-shape electrode prior to welding.

[0024] It should be understood that the spark plug electrodes and / or ruthenium-based materials of this application are not limited to those manufactured according to the powder metallurgy method described above. Other methods and techniques may be used alternatively. For example, the initial steps may be modified such that an atomization process is used to pre-alloy the components and form them as powder before mixing and / or sintering.

[0025] It should be understood that the foregoing description is of one or more preferred exemplary embodiments of the present invention. The invention is not limited to the specific embodiments disclosed herein, but is defined only by the appended claims. Furthermore, the statements contained in the foregoing description relate to specific embodiments and should not be construed as limiting the scope of the invention or the definition of terms used in the claims, unless the terms or phrases are expressly defined above. Various other embodiments, as well as various changes and modifications to the disclosed embodiments, will become apparent to those skilled in the art. All such other embodiments, changes, and modifications are intended to fall within the scope of the appended claims.

[0026] As used in this specification and claims, the terms “for example,” “such as,” and “like,” as well as the verbs “comprising,” “having,” “including,” and other verb forms thereof, when used in conjunction with a list of one or more parts or other items, shall each be interpreted as open-ended, meaning that the list shall not be considered to exclude other, additional parts or items. Other terms shall be interpreted using their broadest reasonable meaning unless they are used in a context that requires a different interpretation.

Claims

1. A spark plug electrode (12, 18, 32, 30), said spark plug electrode comprising: Ruthenium-based materials containing ruthenium and rhodium, where ruthenium is the single largest component based on weight percent. The ruthenium-based material has an equiaxed grain structure (102) having an average grain size of less than or equal to 50 μm and an average porosity of less than or equal to 2%.

2. The spark plug electrode (12, 18, 32, 30) according to claim 1, wherein rhodium is the second largest component of the ruthenium-based material after ruthenium by weight percent, and is present in the ruthenium-based material in an amount of 0.1% to 35% by weight percent, including the end value.

3. The spark plug electrode (12, 18, 32, 30) according to claim 2, wherein the ruthenium-based material is a binary alloy comprising 1% to 15% rhodium (including the end value) and the balance ruthenium.

4. The spark plug electrode (12, 18, 32, 30) according to claim 2, wherein at least one of the following metals is the third largest component of the ruthenium-based material by weight percentage after ruthenium and rhodium: platinum, palladium, iridium, gold, silver, rhenium, tungsten, tantalum, molybdenum or niobium.

5. The spark plug electrode (12, 18, 32, 30) according to claim 4, wherein the ruthenium-based material is a ternary alloy comprising 1% to 15% rhodium (including the end value), 0.5% to 5% rhenium (including the end value), and the balance ruthenium.

6. The spark plug electrode (12, 18, 32, 30) according to any one of claims 1 to 5, wherein the ruthenium-based material has an average porosity of less than or equal to 1.5%.

7. The spark plug electrode (12, 18, 32, 30) according to any one of claims 1 to 5, wherein the ruthenium-based material has a grain structure having an average non-uniformity ratio of less than or equal to 6% with respect to the maximum solute in the ruthenium-based material based on weight % 8. The spark plug electrode (12, 18, 32, 30) according to any one of claims 1 to 5, wherein the spark plug electrode is manufactured using a powder metallurgy method comprising sintering a powder mixture to directly form the spark plug electrode into its near-net-shape.

9. A spark plug electrode (12, 18, 32, 30), said spark plug electrode comprising: Ruthenium-based materials containing ruthenium and rhodium, where ruthenium is the single largest component based on weight percent. The ruthenium-based material has an equiaxed grain structure (102) having an average grain size of less than or equal to 50 μm and an average inhomogeneity ratio of less than or equal to 6% for the maximum solute in the ruthenium-based material based on weight % 10. The spark plug electrode (12, 18, 32, 30) according to claim 9, wherein rhodium is the second largest component of the ruthenium-based material after ruthenium by weight percent, and is present in the ruthenium-based material in an amount of 0.1% to 35% by weight percent, including the end value.

11. The spark plug electrode (12, 18, 32, 30) according to claim 10, wherein the ruthenium-based material is a binary alloy comprising 1% to 15% rhodium, including the end value, and the balance ruthenium.

12. The spark plug electrode (12, 18, 32, 30) according to claim 10, wherein at least one of the following metals is the third largest component of the ruthenium-based material by weight percentage after ruthenium and rhodium: platinum, palladium, iridium, gold, silver, rhenium, tungsten, tantalum, molybdenum or niobium.

13. The spark plug electrode (12, 18, 32, 30) according to claim 12, wherein the ruthenium-based material is a ternary alloy comprising 1% to 15% rhodium including the end value, 0.5% to 5% rhenium including the end value, and the balance being ruthenium.

14. The spark plug electrode (12, 18, 32, 30) according to any one of claims 9 to 13, wherein the ruthenium-based material has an average porosity of less than or equal to 2%.

15. The spark plug electrode (12, 18, 32, 30) according to any one of claims 9 to 13, wherein the spark plug electrode is manufactured using a powder metallurgy method comprising sintering a powder mixture to directly form the spark plug electrode into its near-net-shape.

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