spark plug

Abstract

Spark plug (10), comprising: a first electrode (18) comprising a base material (19) and a discharge element (20), wherein at least a part of the discharge element (20) is connected to the base material (19) with an intermediate diffusion layer (25); and a second electrode (13) which faces the discharge element (20) with an intermediate spark gap (22), wherein the base material (19) contains at least 50 wt% of Ni, at least 8 wt% and at most 40 wt% of Cr, at least 0.01 wt% and at most 2 wt% of Si, at least 0.01 wt% and at most 2 wt% of Al, at least 0.01 wt% and at most 2 wt% of Mn, at least 0.01 wt% and at most 0.1 wt% of C and at least 0.001 wt% and at most 5 wt% of Fe, wherein the discharge element (20) is an alloy which mainly contains Pt and Ni, or is the alloy which furthermore contains at least one of Rh, Ir and Ru, and where, if Pt, Rh, Ir and Ru are referred to as a P group, K (atomic %) is an atomic concentration of the P group in the discharge element (20) where L (atomic %) represents an atomic concentration of the P group in the base material (19), M (atomic %) represents an atomic concentration of Ni in the discharge element (20), and N (atomic %) represents an atomic concentration of Ni in the base material (19), (K+L) / (M+N) ≤ 1.14 is satisfied.

Description

Technical area

[0001] The present invention relates to a spark plug and in particular to a spark plug in which at least a part of a discharge element is connected to a base material with an intermediate diffusion layer. background

[0002] As a result of increased engine performance, improved combustion efficiency, and the like, there is a trend toward high spark plug electrode temperatures under operating conditions. In a spark plug where a first electrode, comprising a discharge element bonded to a base material, faces a second electrode with an intervening spark gap, an increase in the temperature of the first electrode leads to an increase in the thermal stress of a connection section of the discharge element, and therefore concerns arise regarding discharge element detachment. In the technology disclosed in PTL 1, a base material contains at least 0.05 wt% and at most 5 wt% Fe to improve high-temperature strength and high-temperature corrosion resistance, thereby preventing discharge element detachment.In an example in PTL 2, a base material contains 2 wt% of Fe to ensure the high temperature strength of the base material, thereby preventing the detachment of a discharge element.

[0003] The discharge elements in the examples in PTL 1 and PTL 2 are each formed from a Pt-Ir alloy, which consists mainly of Pt and contains Ir. Furthermore, a discharge element is also known that is formed from a Pt-Ni alloy, which consists mainly of Pt and contains Ni. Discharge elements formed from a Pt-Ni alloy are superior to those formed from a Pt-Ir alloy in terms of wear resistance and peel resistance. Citation list of patent literature PTL 1: Unexamined Japanese patent application, publication number JP 2003 - 105 467 A PTL 2: Unexamined Japanese patent application, publication number JP 2007 - 173 116 A Summary of the invention: Technical problem

[0004] As a result of rigorous testing of an electrode in which a Pt-Ni alloy discharge element is bonded to an iron-containing base material, it was discovered that with further temperature increases of the electrode, the wear resistance and delamination resistance of the discharge element might not be sufficiently guaranteed. In other words, because the discharge element contains nickel, iron from the base material readily diffuses into the discharge element under operating conditions. Iron itself has the property of lowering the melting point of a Pt alloy, and therefore there is a possibility that the discharge element will wear down easily.

[0005] Furthermore, if the iron diffusing into the discharge element combines with the platinum of the discharge element and forms an intermetallic bond at a connection point between the discharge element and the base material, the connection point becomes brittle. Moreover, the formation of this intermetallic bond causes a volume change, which increases the stress at the connection point between the discharge element and the base material. Therefore, there is a possibility that the discharge element may detach easily. In particular, compared to an electrode where a discharge element is connected to a base material by an intervening laser-welded fused section, an electrode where at least part of the discharge element is connected to the base material via an intervening diffusion layer exhibits a weak stress-buffering effect caused by the diffusion layer.Therefore, there is a possibility that the discharge element will detach more easily.

[0006] The present invention was made to solve this problem, and its aim is to provide a spark plug which can prevent the detachment and wear of a discharge element connected to a base material. Solution to the problem

[0007] To achieve this objective, a spark plug according to the present invention comprises: a first electrode, which has a base material and a discharge element, wherein at least a portion of the discharge element is connected to the base material with an intervening diffusion layer; and a second electrode, which faces the discharge element with an intervening spark gap. The base material contains at least 50 wt% of Ni, at least 8 wt% and at most 40 wt% of Cr, at least 0.01 wt% and at most 2 wt% of Si, at least 0.01 wt% and at most 2 wt% of Al, at least 0.01 wt% and at most 2 wt% of Mn, at least 0.01 wt% and at most 0.1 wt% of C, and at least 0.001 wt% and at most 5 wt% of Fe. The discharge element is an alloy which mainly contains Pt and which contains Ni, or is the alloy which further contains at least one of Rh, Ir and Ru.If Pt, Rh, Ir and Ru are designated as a P group, K (atomic %) represents an atomic concentration of the P group in the discharge element, L (atomic %) represents an atomic concentration of the P group in the base material, M (atomic %) represents an atomic concentration of Ni in the discharge element and N (atomic %) represents an atomic concentration of Ni in the base material, then (K+L) / (M+N) ≤ 1.14 is satisfied. Advantageous effects of the invention

[0008] According to the spark plug described in claim 1, the base material contains at least 0.001 wt% and at most 5 wt% of Fe and at least 0.01 wt% and at most 2 wt% of Si. Such a composition causes Si diffusing into the discharge element to accelerate the diffusion of Fe into the discharge element. It is therefore possible to ensure that Fe readily reaches the surface of the discharge element. The Fe that reaches the surface of the discharge element oxidizes and is easily removed from the surface of the discharge element, which can prevent an increase in the Fe content in an inner section of the discharge element. It is therefore possible to prevent a decrease in the melting point of the discharge element and to prevent wear of the discharge element.

[0009] The atomic concentration K of the phosphorus group in the discharge element, the atomic concentration L of the phosphorus group in the base material, the atomic concentration M of Ni in the discharge element, and the atomic concentration N of Ni in the base material satisfy (K+L) / (M+N) ≤ 1.14. The relatively high atomic concentration of Ni prevents the Fe diffusing into the discharge element and the phosphorus group atoms contained in the discharge element from readily reacting with each other. This prevents the diffusion layer and the interface between the diffusion layer and the discharge element from becoming brittle, as it prevents the Fe and the phosphorus group atoms in the discharge element from forming an intermetallic compound.It is also possible to prevent thermal stress at the interface between the diffusion layer and the discharge element, which can prevent the discharge element from detaching from the base material.

[0010] According to the spark plug described in claim 2, the base material and the discharge element satisfy (K+L) / (M+N) ≤ 0.82. It is therefore possible to further prevent the discharge element from detaching.

[0011] According to the spark plug described in claims 3 and 4, the X / Y ratio ≥ 0.04 is satisfied when X (wt%) represents a proportion of silicon in the base material and Y (wt%) represents a proportion of iron in the base material. Such a composition causes the silicon diffusing into the discharge element to further accelerate the diffusion of iron into the discharge element. It is therefore possible to make it easier for the iron to reach the surface of the discharge element. In addition to the effect of claim 1 or 2, it is therefore possible to further prevent wear of the discharge element.

[0012] According to the spark plug described in claim 5, X / Y ≥ 0.35 is satisfied if X (mass %) represents a Si content in the base material and Y (mass %) represents an Fe content in the base material. It is therefore possible to further prevent wear of the discharge element.

[0013] According to the spark plug described in claim 6, the base material contains at least 0.001 wt% and at most 2 wt% of Fe. It is therefore possible to reduce the influence of Fe on the reduction of the melting point of the discharge element and on the brittleness of the interface. Therefore, in addition to the effects of claims 1 to 5, it is possible to further prevent the discharge element from detaching.

[0014] According to the spark plug described in claim 7, the base material contains at least 22 wt% and at most 28 wt% of Cr, at least 0.7 wt% and at most 1.3 wt% of Si, at least 0.6 wt% and at most 1.2 wt% of Al, at least 0.1 wt% and at most 1.1 wt% of Mn, at least 0.01 wt% and at most 0.07 wt% of C, and at least 0.001 wt% and at most 2 wt% of Fe. In addition to the effects of claims 1 to 6, it is therefore possible to further prevent simple detachment of the discharge element.

[0015] According to the spark plug described in claim 8, the base material contains a solid solution containing nickel, wherein the solid solution contains a segregation, and wherein, in a cross-section of the base material, the area of ​​the segregation occupying a surface of the base material is at least 0.01% and at most 4%. Accordingly, it is possible to ensure the high-temperature strength of the base material. In addition to the effects of claims 1 to 7, it is therefore possible to further prevent the discharge element from easily detaching. Brief description of the drawings [ Fig. 1] Fig. Figure 1 is a half-section view of a spark plug according to one embodiment. [ Fig. 2] Fig. Figure 2 is a sectional view of a ground electrode. [ Fig. 3] Fig. Figure 3 shows an element distribution in the area of ​​a diffusion layer. [ Fig. 4] Fig. Figure 4 is a sectional view of a base material. [ Fig. 5] Fig. Figure 5 shows an element distribution in the area of ​​a merged section. Description of embodiments

[0016] A preferred embodiment of the present invention is described below with reference to the accompanying drawings. Fig. Figure 1 is a half-section view of a spark plug 10 according to an embodiment with an axis O as the boundary. The lower side in Fig. 1 is referred to as the front of spark plug 10, and the top side in Fig. 1 is referred to as the back of spark plug 10 (the same applies to Fig. 2).

[0017] As in Fig. As shown in Figure 1, the spark plug 10 comprises an insulator 11, a central electrode 13 (second electrode), a metal sleeve 17, and a ground electrode 18 (first electrode). The insulator 11 is an essentially cylindrical element with excellent mechanical and insulating properties at high temperatures and is made of aluminum oxide or the like. The insulator 11 has an axial hole 12 extending along the axis O through it.

[0018] The central electrode 13 is a rod-shaped electrode inserted into the axial hole 12 and held along axis O by the insulator 11. The central electrode 13 comprises a base material 14 and a discharge element 15, which is connected to the front end of the base material 14. A core material with excellent thermal conductivity is embedded in the base material 14. The base material 14 is formed from an alloy consisting mainly of nickel or from a metallic material consisting mainly of nickel. The core material is formed from copper or an alloy containing copper as the main component. It is, of course, possible to omit the core material.The discharge element 15 is, for example, made of a precious metal, such as Pt, Ir, Ru, Rh and the like, or W, whose ignition wear resistance is greater than that of the base material 14, or of an alloy which is mainly made of such a precious metal or W.

[0019] A metal terminal 16 is a rod-shaped element to which a high-voltage cable (not shown) is connected, and the front of the metal terminal 16 is located in the insulator 11. The metal terminal 16 is electrically connected to the central electrode 13 in the axial hole 12.

[0020] The metal sleeve 17 is a substantially cylindrical metal element that is connected to a screw hole (not shown) of an internal combustion engine. The metal sleeve 17 is made of a conductive metallic material (for example, low-carbon steel or the like). The metal sleeve 17 is connected to the outer circumference of the insulator 11. The ground electrode 18 is connected to the front end of the metal sleeve 17.

[0021] The ground electrode 18 comprises a base material 19, which is connected to the metal sleeve 17, and a discharge element 20, which is also connected to the base material 19. A core material with excellent thermal conductivity is embedded in the base material 19. The base material 19 is a metallic material formed from an alloy consisting primarily of nickel. The core material is copper or an alloy containing copper as its main component. It is, of course, possible to omit the core material and form the entire base material 19 from an alloy consisting primarily of nickel. The base material 19 contains nickel, chromium, silicon, aluminum, manganese, carbon, and iron. It should be noted that it may also contain other elements besides these.

[0022] The discharge element 20 is formed from an alloy consisting mainly of platinum and containing nickel. The discharge element 20 may contain at least one of rh, ir, and rubr. A discharge surface 21 of the discharge element 20 faces the central electrode 13 with an intervening spark gap 22. In the present embodiment, the discharge element 20 has a disk shape, with the discharge surface 21 being circular. A discharge element 20 is used in which a height H (see Fig. 2) from the base material 19 to the discharge surface 21 of the discharge element 20 is 0.05 mm to 0.35 mm.

[0023] The spark plug 10 is manufactured, for example, by the following procedure. First, the central electrode 13 is inserted into the axial hole 12 of the insulator 11. After the metal terminal 16 is inserted into the axial hole 12 and conductivity between the metal terminal 16 and the central electrode 13 is ensured, the metal sleeve 17, to which the base material 19 was previously connected, is attached to the outer circumference of the insulator 11. After the discharge element 20 has been connected to the base material 19 by resistance welding, the base material 19 is bent so that the discharge element 20 faces the central electrode 13 in the axial direction, thus forming the spark plug 10. It is possible to subject the base material 19, to which the discharge element 20 has been connected, to a heat treatment after resistance welding.

[0024] Fig. Figure 2 is a sectional view of the ground electrode 18, which includes the straight line 24, parallel to axis O, from the straight lines passing through a center 23 of the discharge surface 21 of the discharge element 20. In the present embodiment, axis O of the spark plug 10 and the straight line 24 coincide. At least a portion of the discharge element 20 is connected to the base material 19 with an intervening diffusion layer 25. The diffusion layer 25 connects the base material 19 and the discharge element 20 by atomic diffusion (interatomic bonding) that occurs between the base material 19 and the discharge element 20. A fused section, where the discharge element 20 and the base material 19 have been fused and solidified, may be formed at a section of the interface between the discharge element 20 and the base material 19.However, the fused section is not included in diffusion layer 25.

[0025] Fig. Figure 3 shows an element distribution in the area of ​​the diffusion layer 25. Fig. Figure 3 shows the proportions of Pt and Ni. The proportions were measured on a polished surface of the ground electrode 18, which encompasses the straight line 24 and is perpendicular to the diffusion layer 25. The measurement was performed from the discharge element 20 to the base material 19 at predetermined intervals (e.g., 1 µm). The horizontal axis of the Fig. Figure 3 represents the percentage by mass of the elements, with the percentages decreasing towards the left. The vertical axis represents the distance (i.e., the position on spark plug 10 in the direction of axis O), and the bottom edge indicates the front of spark plug 10.

[0026] The elemental concentrations contained in the base material 19 and the discharge element 20 are determined by WDS analysis using FE-EPMA (JXA 8500F manufactured by JEOL Ltd.) equipped with a hot cathode field emission electron gun. Following a qualitative WDS analysis, the mass composition is measured by quantitative analysis, determining the concentration percentages (mass %) of the elements within the total mass compositions detected.

[0027] In the present embodiment, the base material 19, which is formed from an alloy consisting mainly of nickel, contains no platinum (Pt). In contrast, the discharge element 20 is composed mainly of platinum and contains nickel. The proportion of nickel in the discharge element 20 is lower than the proportion of nickel in the base material 19. Therefore, if the distribution of Pt and nickel is known, it is possible to determine the position of the diffusion layer 25 between the base material 19 and the discharge element 20, into which atoms diffuse.

[0028] In the diffusion layer 25, the diffusion of atoms is generated by hot-pressure bonding between the discharge element 20 and the base material 19. In the diffusion layer 25, the concentration of a specific element (Pt in the present embodiment) contained in the discharge element 20 decreases continuously from the discharge element 20 towards the base material 19. Similarly, in the diffusion layer 25, the concentration of a specific element (Ni in the present embodiment) contained in the base material 19 decreases continuously from the base material 19 towards the discharge element 20.

[0029] A fused section 26 is described, which is formed by laser welding. Fig. Figure 5 shows an element distribution in the region of the fused section 26 in a sample in which the fused section 26 formed by laser welding is located between the base material 19 and the discharge element 20. Fig. Figure 5 shows the proportions of Pt and Ni. The proportions were measured from the discharge element 20 towards the base material 19 across the fused section 26 at predetermined intervals (e.g., 1 µm). The horizontal axis in Fig. 5 represents the content fractions (mass %), and these fractions decrease towards the left. The vertical axis represents the distance (i.e., the position on the spark plug in the direction of axis O), and the lower side indicates the front of the spark plug. The base material 19 and the discharge element 20, which have been liquefied, flow into the fused section 26 and solidify; and unlike the diffusion layer 25, the elements (Pt and Ni) are thereby mixed with each other without relation to the distance from the discharge element 20 or from the base material 19.

[0030] Referring again to Fig. Section 2 describes a method for measuring the thickness T of the diffusion layer 25. Fig. 2 intersects the straight line 24, which runs through the center 23 of the discharge surface 21 of the discharge element 20, the diffusion layer 25 under perpendicular incidence, and therefore the content fractions of Pt and Ni at measuring points on the straight line 24 from the discharge element 20 in the direction of the base material 19 are measured by a WDS analysis using a FE-EPMA.

[0031] First, a measuring point A, located 10 µm away from the discharge surface 21 of the discharge element 20 in the direction of the base material 19, was defined as the initial measuring point (base point) of the discharge element 20. A quantitative analysis was then performed at five measuring points arranged at 10 µm intervals in the direction of the base material 19. The mean value of the Pt content at the five measuring points is considered to be the Pt content W1 in the discharge element 20.

[0032] Next, a quantitative analysis is performed on measurement points arranged at constant intervals (e.g., 1 µm) along a straight line 24 in the direction of the base material 19, starting from the measurement point of the five measurement points of the discharge element 20 that is closest to the base material 19. From these measurement points, all those are identified where the Pt content W2 is at most W1 and where the Pt content at measurement points closer to the base material 19 than the measurement point itself is at most W2. From all these measurement points, a measurement point B is determined that is closest to the discharge element 20. The position of measurement point B is considered to be the position of the boundary between the discharge element 20 and the diffusion layer 25 for which Pt was measured.

[0033] Next, a measurement point C on the straight line 24, located 100 µm away from measurement point B in the direction away from the discharge element 20, is determined as an initial measurement point (base point) of the base material 19, and a quantitative analysis is performed at five measurement points arranged at 10 µm intervals on the straight line 24 in the direction away from the discharge element 20. The mean value of the Pt content at the five measurement points is considered to be the Pt content W3 in the base material 19.

[0034] Next, a quantitative analysis is performed on measurement points. These five measurement points of the base material 19 are arranged at constant intervals (e.g., 1 µm) along a straight line 24 in the direction of the discharge element 20, starting from measurement point C, which is the closest to the discharge element 20. From these measurement points, all those are identified where the Pt content W4 is at least W3 and where the Pt content at measurement points closer to the discharge element 20 than the measurement point itself is at least W4. From all these measurement points, a measurement point D is determined that is closest to the base material 19. The position of measurement point D is considered to be the position of the boundary between the base material 19 and the diffusion layer 25 for which Pt was measured.A distance in the axial direction between measuring point B and measuring point D is considered to be a thickness T1 of the diffusion layer 25 for which Pt was measured.

[0035] Similarly, measuring point A, located 10 µm away from the discharge surface 21 of the discharge element 20 in the direction of the base material 19, is defined as the initial measuring point (base point) of the discharge element 20, and a quantitative analysis is performed at five measuring points arranged at 10 µm intervals along the straight line 24 in the direction of the base material 19. The mean value of the Ni content at the five measuring points is considered to be the Ni content W5 in the discharge element 20.

[0036] Next, a quantitative analysis is performed on measurement points arranged at constant intervals (e.g., 1 µm) along a straight line 24 in the direction of the base material 19, starting from the measurement point of the five measurement points of the discharge element 20 that is closest to the base material 19. From these measurement points, all those are identified where the Ni content W6 is at least W5 and where the Ni content at measurement points closer to the base material 19 than the measurement point itself is at least W6. From all these measurement points, a measurement point E is determined that is closest to the discharge element 20. The position of measurement point E is considered to be the position of the boundary between the discharge element 20 and the diffusion layer 25 for which Ni was measured.

[0037] Next, a measurement point F on the straight line 24, located 100 µm away from measurement point E in the direction away from the discharge element 20, is determined as an initial measurement point (base point) of the base material 19, and a quantitative analysis is performed at five measurement points arranged at 10 µm intervals on the straight line 24 in the direction away from the discharge element 20. The mean value of the Ni content at the five measurement points is considered to be the Ni content W7 in the base material 19.

[0038] Next, a quantitative analysis is performed on measurement points. These five measurement points of the base material 19 are arranged at constant intervals (e.g., 1 µm) along a straight line 24 in the direction of the discharge element 20, starting from the measurement point F closest to the discharge element 20. From these measurement points, all those are identified where the Ni content W8 is at most W7 and where the Ni content at measurement points closer to the discharge element 20 than the measurement point itself is at most W8. From all these measurement points, a measurement point G is determined that is closest to the base material 19. The position of measurement point G is considered to be the position of the boundary between the base material 19 and the diffusion layer 25 for which Ni was measured.A distance in the axial direction between measuring point E and measuring point G is considered to be a thickness T2 of the diffusion layer 25 for which Ni was measured.

[0039] From the thickness T2 and the thickness T1 of the diffusion layer 25, for which Pt was measured, the greater thickness is considered to be the thickness T of the diffusion layer 25 (see Fig. 3) Taking into account the resistance to detachment of the discharge element 20, the thickness T of the diffusion layer 25 is preferably at least 5 µm, but is usually less than 70 µm.

[0040] A WDS analysis using FE-EPMA to determine the mass compositions of the base material 19 and the discharge element 20 at each set of five measurement points, with measurement points A, C, and F as their respective base points, is performed under conditions of an accelerating voltage of 20 kV and a spot diameter of 10 µm. A WDS analysis to define measurement points B, D, E, and G for determining the thickness of the diffusion layer 25 is performed under conditions of an accelerating voltage of 20 kV and a spot diameter of 1 µm.

[0041] The elements to be analyzed are not limited to Pt and Ni. Two types of elements can be selected as needed from those contained in the base material 19 or the discharge element 20. The thickness of the diffusion layer 25 is considered easy to measure if Ni, the most abundant element in the base material 19, is selected, and an element predominantly contained in the discharge element 20 is selected.

[0042] Depending on the surface shape of the discharge surface 21 of the discharge element 20 or the thickness of the diffusion layer 25, there is a possibility that a concentration gradient exists below the measuring points A, C, and F, or that the measuring points A, C, and F lie within the diffusion layer 25. In such a case, the measured values ​​at the measuring points A, C, and F do not represent the compositions of the discharge element 20 and the base material 19. Therefore, the measurement is carried out with suitably modified positions of the measuring points A, C, and F.In short: Measuring point A can be determined at any section as long as measured values ​​can be obtained that represent the composition of the discharge element 20 before connection, and measuring points C and F can be determined at any section as long as measured values ​​can be obtained that represent the composition of the base material 19 before connection.

[0043] Fig. Figure 4 is a sectional view of the base material 19. If, for example, a segregation 27 of the discharge element 20 or of the base material 19 is present on the straight line 24, if a fused section (not shown) is present next to the diffusion layer 25, or if a cavity (not shown) is present in the base material 19 or in the discharge element 20 on the straight line 24, i.e., if measured values ​​are considered to be influenced by the segregation 27, a cavity, or the like, instead of the measurement points of the measurement, two measurement points that are closest to the measurement points and are not influenced by the segregation 27, the cavity, or the like are selected, and an average of the values ​​measured at the two measurement points is used.

[0044] The base material 19 is a solid solution containing nickel. The segregation 27 has a crystal structure that differs from that of the solid solution of the base material 19. The segregation 27 is, for example, an element that forms the base material 19, or impurities such as carbides, nitrides, oxides, and intermetallic compounds. A suitable amount of the segregation 27 helps to ensure the strength of the base material 19.

[0045] Furthermore, in a spark plug where at least part of a discharge element made of a Pt-Ni alloy is bonded to a base material with an intervening diffusion layer, and the base material contains iron (Fe), a problem arises: the iron can significantly influence the wear and delamination resistance of the discharge element. In other words, when the temperature of a ground electrode rises under the operating conditions of the spark plug, mutual diffusion readily occurs between the discharge element and the base material. The discharge element contains nickel, and the iron in the base material therefore diffuses readily into the discharge element. Iron itself has properties that lower the melting point of a Pt alloy, and thus the discharge element is easily worn.

[0046] Furthermore, if iron diffusing into the discharge element combines with platinum in the discharge element, forming an intermetallic bond at the junction between the discharge element and the base material, this junction becomes brittle. The formation of this intermetallic bond causes a change in volume and therefore increases the stress at the junction between the discharge element and the base material. As a result, the discharge element, which is bonded to the base material via the intervening diffusion layer, detaches easily.

[0047] In contrast, in the spark plug, the discharge element is fused to the base material by the intermediate laser-welded section 26 (see Fig. 5) is connected, a thermal stress generated by a difference in the linear thermal expansion coefficient between the base material and the discharge element is buffered by the fused section 26. The Fe contained in the base material therefore has no significant influence on the detachment of the discharge element.

[0048] According to the present embodiment with the spark plug 10, in which at least a part of the discharge element 20 is connected to the base material 19 with the intermediate diffusion layer 25, the base material 19 contains at least 50 wt% of Ni, at least 8 wt% and at most 40 wt% of Cr, at least 0.01 wt% and at most 2 wt% of Si, at least 0.01 wt% and at most 2 wt% of Al, at least 0.01 wt% and at most 2 wt% of Mn, at least 0.01 wt% and at most 0.1 wt% of C and at least 0.001 wt% and at most 5 wt% of Fe.

[0049] The content fraction (mass-%) of each element of the base material 19 is calculated based on analysis results of the mass composition by WDS analysis using a FE-EPMA at the five measuring points that correspond to measuring point C (see Fig. 2) as the base point. The content fraction (mass %) of each element of the base material 19 can be calculated from the five measuring points, which replace measuring point C with measuring point F (see Fig. 2) as the base point. In short: A measurement can be carried out on any section as long as measured values ​​can be obtained that represent the composition of the base material 19 before joining.

[0050] By containing at least 50 wt% Ni, the base material 19 can ensure heat resistance properties. By containing at least 8 wt% and at most 40 wt% Cr, it is possible to ensure oxidation resistance of the base material 19 by means of a Cr oxide film formed on the surface of the base material 19 and to prevent the formation of segregation 27, for example as Cr nitrides and Cr carbides. By containing at least 0.01 wt% and at most 2 wt% Si, it is possible to ensure oxidation resistance of the base material 19 and to prevent the formation of segregation 27, which is formed from a Si compound. By containing at least 0.01 wt% and at most 2 wt% Al, it is possible to ensure high-temperature strength and high-temperature corrosion resistance.

[0051] By containing at least 0.01 wt% and at most 2 wt% of Mn, the base material 19 can prevent itself from becoming brittle due to desulfurization and can inhibit the formation of segregation 27, for example as Mn sulfides. By containing at least 0.01 wt% and at most 0.1 wt% of C, it is possible to ensure high-temperature strength and to inhibit the formation of segregation 27, for example as Cr carbides. By containing at least 0.001 wt% and at most 5 wt% of Fe, it is possible to inhibit the formation of iron oxide. The proportions of elements of the base material 19 other than Ni, Cr, Si, Al, Mn, C and Fe, and the proportions of elements of unavoidable impurities preferably total at most 1 wt% and further preferably total at most 0.4 wt%.

[0052] The base material 19 contains at least 0.001 wt% and at most 5 wt% of Fe and at least 0.01 wt% and at most 2 wt% of Si. Such a composition causes Si diffusing into the discharge element 20 to accelerate the diffusion of Fe into the discharge element 20. It is therefore possible to ensure that Fe readily reaches the surface of the discharge element 20. Fe that has reached the surface of the discharge element 20 readily detaches from the surface after forming an oxide film. Accordingly, an increase in the Fe content in an inner section of the discharge element 20 can be prevented. Therefore, a decrease in the melting point of the discharge element 20 is prevented, and wear of the discharge element 20 is prevented.

[0053] Spark plug 10 satisfies (K+L) / (M+N) ≤ 1.14, where Pt, Rh, Ir, and Ru are designated as a P-group, K (atomic %) represents the atomic concentration of the P-group in the discharge element 20, L (atomic %) represents the atomic concentration of the P-group in the base material 19, M (atomic %) represents the atomic concentration of Ni in the discharge element 20, and N (atomic %) represents the atomic concentration of Ni in the base material 19. By setting the atomic concentration of Ni to a relatively high level, it is possible to prevent Fe diffusing into the discharge element 20 and the P-group atoms contained in the discharge element 20 from readily reacting with each other.It is possible to prevent the formation of an intermetallic compound by Fe and the phosphorus atoms contained in the discharge element 20, and therefore it is possible to prevent the diffusion layer 25 and the interface between the diffusion layer 25 and the discharge element 20 from becoming brittle. It is also possible to prevent thermal stress at the interface between the diffusion layer 25 and the discharge element 20, and therefore it is possible to prevent the discharge element 20 from detaching from the base material 19. (K+L) / (M+N) ≤ 0.82 is further preferred.

[0054] The atomic concentrations K, L, M and N are calculated based on mass composition analysis results by WDS analysis using FE-EPMA at each set of the five measurement points, which are measurement points A and C (see Fig.2) as their respective base points. The atomic concentration (atomic %) indicates percentages obtained by dividing the content (mass %) of the respective element by the atomic weight of the element. Data listed in the ASM Alloy Phase Diagram Database™ are used for the atomic weights of the elements. In the present embodiment, the atomic concentration L of the P group in the base material 19 is zero (atomic %).

[0055] A ratio of X / Y ≥ 0.04, where X (wt%) represents the Si content in the base material 19 and Y (wt%) represents the Fe content in the base material 19, is preferred. Such a configuration causes Si diffusing into the discharge element 20 to further accelerate the diffusion of Fe diffusing into the discharge element 20. It is therefore possible to further prevent wear of the discharge element 20. A ratio of X / Y ≥ 0.35 is even more preferred.

[0056] The area of ​​the segregation 27, which occupies the area of ​​the base material 19 in a cross-section of the base material 19, is preferably at least 0.01% and at most 4%. This prevents the base material 19 from becoming brittle and ensures its strength. If the area of ​​the segregation 27 is at least 0.01%, the high-temperature strength of the base material 19 is further increased, and therefore the base material 19 is not easily deformed. Accordingly, the oxide film formed on the base material 19 does not detach easily, which prevents oxygen atoms from diffusing into the interface between the diffusion layer 25 and the discharge element 20, into the interface between the diffusion layer 25 and the base material 19, and into an inner section of the diffusion layer 25. As a result, the formation of oxides is further prevented.

[0057] If the area of ​​the segregation 27 is at most 4%, the base material 19 is prevented from becoming brittle. Accordingly, cracks do not readily form in the interface between the diffusion layer 25 and the discharge element 20, in the interface between the diffusion layer 25 and the base material 19, and in the diffusion layer 25 itself, and therefore the discharge element 20 does not detach easily. Therefore, it is preferred that the area of ​​the segregation 27, which occupies the area of ​​the base material 19, is at least 0.01% and at most 4%.

[0058] The segregation 27 can be detected by imaging or analyzing compositional images using an EPMA equipped with a wavelength-dispersive X-ray spectrometer detector (WDX or WDS), a scanning electron microscope (SEM) equipped with an energy-dispersive X-ray spectrometer detector (EDX or EDS), or similar instruments. After photographing a cross-section of the base material 19 with a rectangular field of view measuring 400 µm × 600 µm, the area (%) of the segregation 27 occupying the area of ​​the base material 19 is obtained by image processing. Examples

[0059] The present invention is described in detail with an example. However, the present invention is not limited to this example. (Preparing samples 1 to 63)

[0060] An inspector prepared various types of the base material 19 and the disc-shaped discharge elements 20 with the compositions specified in Table 1 and Table 2. The inspector joined the discharge elements 20 to the base materials 19 by resistance welding, obtaining spark plugs 10 corresponding to samples 1 to 63. In order to perform cross-sectional observations and the like for each sample, in addition to assessing the peel resistance and wear resistance, a large number of samples were prepared under the same conditions. The thickness T of the diffusion layer 25 formed between the base material 19 and the discharge element 20 was less than 70 µm for all samples. The height H of the discharge surface 21 of the discharge element 20 above the base material 19 was 0.25 mm for all samples. The atomic concentration N of Ni contained in the base material 19, the atomic concentration K of the P group contained in the discharge element 20, the atomic concentration M of Ni contained in the discharge element 20, and (K+L) / (M+N) were calculated based on the mass compositions according to the WDS analysis using FE-EPMA and are given in Table 1 and Table 2. The base material 19 contained no P group elements, and the atomic concentration K of the P group contained in the base material 19 is therefore 0.

[0061] Table 1 and Table 2 specify an X / Y ratio, where X (mass %) represents the Si content in the base material and Y (mass %) represents the Fe content in the base material. After photographing a cross-section of the base material 19 in a rectangular field of view measuring 400 µm × 600 µm, the area (%) of the segregation 27 covering the area of ​​the base material 19 was obtained by image processing, and samples where this value was at least 0.01% and at most 4%, and samples where this value was less than 0.01% or greater than 4%, were marked as "good" or "poor" in the segregation column, respectively. (Delamination resistance test)

[0062] The tester conducted a 100-hour test in which each sample was fitted with each cylinder of a four-cylinder, two-liter engine and each sample was repeatedly subjected to a load of 4000 rpm for one minute, followed by a load of idle speed for one minute. The temperature of the discharge element 20 at 4000 rpm was 950 °C. Using a spark plug with a hole extending into the area of ​​the discharge element 20, the temperature of the discharge element 20 was measured before the start of the peel resistance test, with the temperature-measuring portion of a thermocouple positioned on a front section of the base material 19 near the discharge element 20. The amount of energy delivered by an ignition coil to each sample during an ignition discharge was 150 mJ.

[0063] Following the tests, each sample was subjected to an examination of a cross-section of the ground electrode 18 using a scanning electron microscope (SEM). This cross-section included the straight lines 24 passing through the center 23 of the discharge surface 21 of the discharge element 20, the straight line 24 parallel to axis O, and the lengths L1 and L2 of cracks extending from the two ends of the diffusion layer 25 towards its center. A value Q, obtained by dividing the total length of the cracks (L1 + L2) by the length L of the discharge surface 21 (i.e., (L1 + L2) / L), was calculated. Based on this value Q, the samples were classified into five grades from A to E. The criterion was as follows: A: Q < 20%, B: 20% ≤ Q < 30%, C: 30% ≤ Q < 40%, D: 40% ≤ Q < 50%, and E: Q ≥ 50% or the discharge element 20 went off.The results of the peel resistance tests are given in the peel property column in Table 1 and Table 2. (Wear resistance test)

[0064] The tester conducted a test in which each sample was fitted with each cylinder of the same engine as the engine used in the peel resistance test, and the engine was operated according to conditions whereby the temperature of the discharge element was 20 1000 °C to cause an inlet gas valve to assume a fully open state, and the engine was operated continuously for 200 hours.The conditions under which the temperature of the discharge element 20 was 1000 °C were calculated using a spark plug in which a hole had formed extending to the area of ​​the discharge element 20, and by measuring the temperature before the start of the wear resistance test, with the temperature-measuring section of a thermocouple being arranged on a front section of the base material 19 near the discharge element 20, and by checking the relationship between the temperature and the engine's operating conditions. The amount of energy delivered by an ignition coil to each sample during an ignition discharge was 150 mJ.

[0065] After photographing the spark gap 22 of each sample, and after CT scanning in a direction perpendicular to the axis O, the thickness of the thinnest section of the discharge element 20 was calculated as a distance enlargement R using image processing, based on the positions of the discharge surface 21 of the discharge element 20 before and after the test. Based on the distance enlargement R, a classification into five ranks from A to E was performed. The criteria were as follows: A: R < 0.14 mm, B: 0.14 mm ≤ R < 0.16 mm, C: 0.16 mm ≤ R < 0.18 mm, D: 0.18 mm ≤ R < 0.20 mm, and E: R ≥ 0.20 mm or accidental fire occurring during the test. The results of the wear resistance tests are given in Table 1 and Table 2 in the column for wear properties.

[0066] Samples 16, 24, 33, 39, 44, and 54 to 63 were rated E in the peel resistance test. Specifically, samples 55, 56, and 59 to 63 were also rated E in the wear resistance test. In sample 16, the Cr content in the base material 19 was greater than 40 wt%. In sample 24, the Si content in the base material 19 was greater than 2 wt%. In sample 33, the Al content in the base material 19 was greater than 2 wt%. In sample 39, the Mn content in the base material 19 was greater than 2 wt%. In sample 44, the C content in the base material 19 was greater than 0.1 wt%. In samples 54 to 56, the (K+L) / (M+N) ratio > 1.14 was met.

[0067] In sample 57, the Cr content in the base material 19 was less than 8 wt%. In sample 58, the Al content in the base material 19 was greater than 2 wt%. In samples 59 to 61, the Fe content in the base material 19 was greater than 5 wt%. In sample 62, the Si content in the base material 19 was greater than 2 wt%. In sample 63, the Ni content in the base material 19 was less than 50 wt%, the Cr content was greater than 40 wt%, the Si, Al, and Mn contents were each greater than 2 wt%, and the C content was greater than 0.1 wt%.

[0068] Samples 1 to 16 differ from each other mainly in the chromium content of the base material 19. Samples 1 to 16 were rated A in the wear resistance test. Samples 14 and 15 were rated C in the peel resistance test. In sample 14, the area of ​​segregation was not at least 0.01% and at most 4%, and the condition 0.82 < (K+L) / (M+N) ≤ 1.14 was met. In sample 15, the chromium content in the base material 19 was greater than 28 wt% and at most 40 wt%, and the condition 0.82 < (K+L) / (M+N) ≤ 1.14 was met.

[0069] Samples 1 to 7, 12, and 13 were rated B in the peel resistance test. In samples 1 to 4, the Cr content in the base material 19 was at least 8 wt% and less than 22 wt%, the Al content was at least 0.01 wt% and less than 0.6 wt%, and the Mn content was greater than 1.1 wt% and at most 2 wt%. In sample 5, the Cr content in the base material 19 was at least 8 wt% and less than 22 wt%, and the Si content was at least 0.01 wt% and less than 0.7 wt%. In samples 6 and 7, the Cr content in the base material 19 was at least 8 wt% and less than 22 wt%. In samples 12 and 13, the condition 0.82 < (K+L) / (M+N) ≤ 1.14 was met. It was discovered that the Cr content in the base material 19 is preferably at least 8 wt% and at most 40 wt%, and even more preferably at least 22 wt% and at most 28 wt%.

[0070] Samples 17 to 24 differ from each other mainly in the silicon content of the base material 19. Samples 17 to 24 were rated A in the wear resistance test. Samples 17, 22, and 23 were rated C in the peel resistance test. In sample 17, the silicon content in the base material 19 was at least 0.01 wt% and less than 0.7 wt%, and the condition 0.82 < (K+L) / (M+N) ≤ 1.14 was met. In samples 22 and 23, the silicon content in the base material 19 was at least 1.3 wt% and at most 2 wt%, and the condition 0.82 < (K+L) / (M+N) ≤ 1.14 was met. Samples 18, 19, and 21 met the criteria 0.82 < (K+L) / (M+N) ≤ 1.14 and were rated B in the peel resistance test. It was discovered that the silicon content in the base material 19 is preferably at least 0.01 wt% and at most 2 wt%, and more preferably at least 0.7 wt% and at most 1.3 wt%.

[0071] Samples 25 to 33 differ from each other mainly in their aluminum content. Samples 25 to 33 were rated A in the wear resistance test. Samples 25 and 26 were rated C in the peel resistance test. In samples 25 and 26, the aluminum content in the base material 19 was at least 0.01 wt% and less than 0.6 wt%, and the ratio 0.82 < (K+L) / (M+N) ≤ 1.14 was met. Samples 27 to 29, 31, and 32 met the ratio 0.82 < (K+L) / (M+N) ≤ 1.14 and were rated B in the peel resistance test. It was discovered that the Al content in the base material 19 is preferably at least 0.01 wt% and at most 2 wt%, and further preferably at least 0.7 wt% and at most 1.3 wt%.

[0072] Samples 34 to 39 differ from each other mainly in the Mn content of the base material 19. Samples 34 to 39 were rated A in the wear resistance test. Samples 34, 37, and 38 were rated C in the peel resistance test. In sample 34, the Mn content in the base material 19 was at least 0.01 wt% and less than 0.1 wt%, and the condition 0.82 < (K+L) / (M+N) ≤ 1.14 was met. In samples 37 and 38, the Mn content in the base material 19 was greater than 1.1 wt% and less than 2 wt%, and the condition 0.82 < (K+L) / (M+N) ≤ 1.14 was met. Samples 35 and 36 met the criteria 0.82 < (K+L) / (M+N) ≤ 1.14 and were rated B in the peel resistance test. It was discovered that the Mn content in the base material 19 is preferably at least 0.01 wt% and at most 2 wt%, and more preferably at least 0.1 wt% and at most 1.1 wt%.

[0073] Samples 40 to 44 differ from each other mainly in the carbon content of the base material 19. In sample 43, the carbon content of the base material 19 was greater than 0.07 wt% and at most 0.1 wt%, and the area of ​​any segregation was not at least 0.01% and at most 4%. Sample 43 met the criterion 0.82 < (K+L) / (M+N) ≤ 1.14 and was rated as D in the peel resistance test. In sample 42, the area of ​​any segregation was not at least 0.01% and at most 4%. Sample 42 met the criterion 0.82 < (K+L) / (M+N) ≤ 1.14 and was rated as C in the peel resistance test. Sample 41 met the criteria 0.82 < (K+L) / (M+N) ≤ 1.14 and was rated B in the peel resistance test. It was discovered that the content of C in the base material 19 is preferably at least 0.01 wt% and at most 0.1 wt%, and more preferably at least 0.01 wt% and at most 0.07 wt%.

[0074] Samples 45 to 53 differ from each other mainly in their X / Y and (K+L) / (M+N) properties. Samples 45 and 46 were rated D in the wear resistance test and B in the peel resistance test. In sample 45, the Fe content in the base material 19 was at least 2 wt% and at most 5 wt%, and the X / Y value < 0.04 was met. In sample 46, the Mn content in the base material 19 was greater than 1.1 wt% and at most 2 wt%, the Fe content was greater than 2 wt% and at most 5 wt%, and the X / Y value < 0.04 was met.

[0075] Samples 47, 48, and 51 were rated C in the wear resistance test and B in the peel resistance test. In sample 47, the Mn content in the base material 19 was greater than 1.1 wt% and at most 2 wt%, the Fe content was greater than 2 wt% and at most 5 wt%, and the X / Y ratio of 0.04 ≤ 0.35 was met. In samples 48 and 51, the Fe content in the base material 19 was greater than 2 wt% and at most 5 wt%, and the X / Y ratio of 0.04 ≤ 0.35 was met.

[0076] Samples 52 and 53 were rated C in both the wear resistance test and the peel resistance test. In samples 52 and 53, the Fe content in the base material 19 was greater than 2 wt% and at most 5 wt%, the conditions 0.04 ≤ X / Y < 0.35 and 0.82 < (K+L) / (M+N) ≤ 1.14 were met.

[0077] Samples 49 and 50 were rated B in both the wear resistance test and the peel resistance test. In sample 49, the Mn content in the base material 19 was greater than 1.1 wt% and at most 2 wt%, and the condition 0.04 ≤ X / Y < 0.35 was met. In sample 50, the Mn content in the base material 19 was greater than 1.1 wt% and at most 2 wt%, and the Fe content was greater than 2 wt% and at most 5 wt%.

[0078] When comparing samples 45 and 46 with samples 47, 48, and 51, samples 45 and 46, where X / Y < 0.04 was met, were rated as D in the wear resistance test, and samples 47, 48, and 51, where 0.04 ≤ X / Y < 0.35 was met, were rated as C. It was therefore discovered that the wear resistance of the discharge element 20 can be improved by achieving 0.04 ≤ X / Y < 0.35, as in samples 45 to 48 and 51.

[0079] When comparing samples 52 and 53 with samples 47, 48, and 51, samples 52 and 53, where (K+L) / (M+N) ≤ 1.14 was met, were rated as C in the peel resistance test, and samples 47, 48, and 51, where (K+L) / (M+N) ≤ 0.82 was met, were rated as B. It was therefore discovered that the peel resistance of the discharge element 20 can be improved by ensuring (K+L) / (M+N) ≤ 0.82, as in samples 47, 48, and 51 to 53.

[0080] Samples 49 and 50 both met the (K+L) / (M+N) ≤ 0.82 condition and were rated B in both the wear resistance and peel resistance tests. However, in sample 49, the Fe content in the base material 19 was at least 0.001 wt% and at most 2 wt%, and the X / Y <0.35 condition was met. In sample 50, the Fe content in the base material 19 was greater than 2 wt% and at most 5 wt%, and the X / Y ≥ 0.35 condition was met. Therefore, it was discovered that it was possible to ensure the wear resistance and peel resistance of the discharge element 20 by adjusting the Fe content in the base material 19 and the X / Y ratio.

[0081] In samples 8 to 11, 20, 30 and 40, which were rated as A in both the wear resistance test and the peel resistance test, the base material 19 contained at least 22 wt% and at most 28 wt% of Cr, at least 0.7 wt% and at most 1.3 wt% of Si, at least 0.6 wt% and at most 1.2 wt% of Al, at least 0.1 wt% and at most 1.1 wt% of Mn, at least 0.01 wt% and at most 0.07 wt% of C and at least 0.001 wt% and at most 2 wt% of Fe, X / Y ≥ 0.35 was satisfied, the area of ​​segregation was at least 0.01 % and at most 4 % and (K+L) / (M+N) ≤ 0.82 was satisfied.

[0082] According to the example, it was discovered that in the evaluation of the wear resistance test and the peel resistance test, all results A to D could be obtained by ensuring that the base material 19 contained at least 50 wt% of Ni, at least 8 wt% and at most 40 wt% of Cr, at least 0.01 wt% and at most 2 wt% of Si, at least 0.01 wt% and at most 2 wt% of Al, at least 0.01 wt% and at most 2 wt% of Mn, at least 0.01 wt% and at most 0.1 wt% of C, and at least 0.001 wt% and at most 5 wt% of Fe, while (K+L) / (M+N) ≤ 1.14 was satisfied. Furthermore, it was discovered that in the evaluation of the peel resistance test, both A and B could be obtained by ensuring that (K+L) / (M+N) ≤ 0.82 was satisfied.

[0083] The present invention has been described above based on the embodiment described above. However, the present invention is not limited to the aforementioned embodiment and it can readily be assumed that it can be improved or modified in various ways within the spirit of the present invention.

[0084] The embodiment described is one case in which the discharge element 20 has a disc shape; however, the embodiment is not necessarily limited to this, and it is of course possible to use a different shape. Other shapes of the discharge element 20 include, for example, a truncated shape, an elliptical cylindrical shape, and prism shapes, such as a triangular prism and a quadrilateral prism.

[0085] The embodiment described includes a case in which the discharge element 20 is connected to one end section of the base material 19 and in which the other end section of the base material 19 is connected to the metal sleeve 17; however, the embodiment is not necessarily limited to this. It is, of course, possible to insert an intermediate material between one end section of the base material 19 and the discharge element 20. In this case, the intermediate material is a section of the base material 19, and the discharge element 20 is connected to the intermediate material (base material 19) via the intervening diffusion layer 25.

[0086] The embodiment described includes a case in which the P-group elements, consisting of Pt, Rh, Ir, and Ru, are contained in the discharge element 20 and are not contained in the base material 19; however, the embodiment is not necessarily limited to this case. If a concentration gradient of the P-group exists between the base material 19 and the discharge element 20, diffusion of the P-group occurs. It is therefore plausible that, even if the base material 19 contains the P-group elements, it is possible to prevent detachment and wear of the discharge element 20 if the condition described in the embodiment is met. If the base material 19 contains the P-group elements, the atomic concentration L (atomic percent) of the P-group in the base material 19 has a value greater than 0.

[0087] Using the ground electrode 18 as an example of the first electrode, the diffusion layer 25 between the base material 19 of the ground electrode 18 and the discharge element 20 was described in the first embodiment; however, the embodiment is not necessarily limited to this. It is, of course, possible to use the central electrode 13 as the first electrode and the ground electrode 18 as the second electrode. In this case, the base material 14 of the central electrode 13 and the discharge element 15 are connected to each other with the diffusion layer 25 in between. As in the previously mentioned embodiment, it is possible to prevent the discharge element 15 from detaching from the base material 14 by making the composition of the base material 14 of the central electrode 13 similar to the composition of the base material 19 of the ground electrode 18.

[0088] In the embodiment described, a case was formed in which the diffusion layer 25 between the base material 19 and the discharge element 20 is formed by resistance welding; however, the embodiment is not necessarily limited to this. It is of course possible to form the diffusion layer 25 by diffusion of atoms with the base material 19 and the discharge element 20 in close contact with each other to a degree that minimizes plastic deformation, provided that the temperature is at most the melting points of the base material 19 and the discharge element 20, in order to join the base material 19 and the discharge element 20 together (conventionally known as diffusion joining).

[0089] The embodiment described above features a case in which the base material 19 connected to the metal sleeve 17 is bent. However, the present embodiment is not necessarily limited to this. It is, of course, possible to use a straight base material 19 instead of the bent one. In this case, the straight base material is connected to the metal sleeve 17, with the front face of the metal sleeve 17 being extended along the direction of axis O such that the base material faces the central electrode 13.

[0090] In this embodiment, a case is described in which the axis O of the central electrode 13 coincides with the center 23 of the discharge electrode 21 of the discharge element 20, and in which the ground electrode 18 is arranged such that the discharge element 20 faces the central electrode 13 in the axial direction. However, the embodiment is not necessarily limited to this, and the positional relationship between the ground electrode 18 and the central electrode 13 can be adjusted as required. For example, another positional relationship between the ground electrode 18 and the central electrode 13 is an arrangement in which the ground electrode 18 is positioned such that a lateral surface of the central electrode 13 and the discharge element 20 of the ground electrode 18 face each other. Reference symbol list 10 Spark plug 13 central electrode (second electrode) 18 Ground electrode (first electrode) 19 basic materials 20 discharge element 22 spark gap 25 diffusion layer 27 Segregation

Claims

[1] Spark plug (10), comprising: a first electrode (18) comprising a base material (19) and a discharge element (20), wherein at least a part of the discharge element (20) is connected to the base material (19) with an intermediate diffusion layer (25); and a second electrode (13) which faces the discharge element (20) with an intermediate spark gap (22), wherein the base material (19) contains at least 50 wt% of Ni, at least 8 wt% and at most 40 wt% of Cr, at least 0.01 wt% and at most 2 wt% of Si, at least 0.01 wt% and at most 2 wt% of Al, at least 0.01 wt% and at most 2 wt% of Mn, at least 0.01 wt% and at most 0.1 wt% of C and at least 0.001 wt% and at most 5 wt% of Fe, wherein the discharge element (20) is an alloy which mainly contains Pt and Ni, or is the alloy which furthermore contains at least one of Rh, Ir and Ru, and where, if Pt, Rh, Ir and Ru are referred to as a P group, K (atomic %) is an atomic concentration of the P group in the discharge element (20) where L (atomic %) represents an atomic concentration of the P group in the base material (19), M (atomic %) represents an atomic concentration of Ni in the discharge element (20), and N (atomic %) represents an atomic concentration of Ni in the base material (19), (K+L) / (M+N) ≤ 1.14 is satisfied. [2] Spark plug (10) according to claim 1, wherein the base material (19) and the discharge element (20) satisfy (K+L) / (M+N) ≤ 0.

82. [3] Spark plug (10) according to claim 1 or claim 2, wherein if X (mass %) represents a content of Si in the base material (19) and Y (mass %) represents a content of Fe in the base material (19), X / Y ≥ 0.04 is satisfied. [4] Spark plug (10) according to any one of claims 1 to 3, wherein, if X (mass %) represents a content of Si in the base material (19) and Y (mass %) represents a content of Fe in the base material (19), 0.04 ≤ X / Y ≤ 1000 is satisfied. [5] Spark plug (10) according to any one of claims 1 to 4, wherein if X (mass-%) represents a content of Si in the base material (19) and Y (mass-%) represents a content of Fe in the base material (19), X / Y ≥ 0.35 is satisfied. [6] Spark plug (10) according to any one of claims 1 to 5, wherein the base material (19) contains at least 0.001 wt% and at most 2 wt% of Fe. [7] Spark plug (10) according to any one of claims 1 to 6, wherein the base material (19) contains at least 22 wt% and at most 28 wt% of Cr, at least 0.7 wt% and at most 1.3 wt% of Si, at least 0.6 wt% and at most 1.2 wt% of Al, at least 0.1 wt% and at most 1.1 wt% of Mn, at least 0.01 wt% and at most 0.07 wt% of C and at least 0.001 wt% and at most 2 wt% of Fe. [8] Spark plug (10) according to any one of claims 1 to 7, wherein the base material (19) contains a solid solution containing Ni, wherein the solid solution contains a segregation present therein, and wherein in a cross-section of the base material (19) an area of ​​segregation which occupies an area of ​​the base material (19) is at least 0.01% and at most 4%.

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