CN108346975B

CN108346975B - Spark plug

Info

Publication number: CN108346975B
Application number: CN201810001901.0A
Authority: CN
Inventors: 后泽达哉; 鬼海高明; 角力山大典
Original assignee: NGK Spark Plug Co Ltd
Current assignee: Niterra Co Ltd
Priority date: 2017-01-23
Filing date: 2018-01-02
Publication date: 2020-05-19
Anticipated expiration: 2038-01-02
Also published as: CN108346975A; JP6557267B2; JP2018120651A; DE102018200211A1

Abstract

[ problem ] to provide a spark plug capable of suppressing interfacial separation between a relaxation layer and a discharge layer. [ solution ] A1 st electrode of a spark plug comprises: the chip is bonded with a discharge layer mainly composed of Pt and a relaxation layer mainly composed of Pt, and an electrode base material formed by an alloy mainly composed of Ni or Ni. The No. 2 electrode and the No. 1 electrode are opposed to each other with a spark gap interposed therebetween. The relaxation layer is formed of an alloy containing Ni as the 2 nd component and having a thickness of 0.05mm or more, and is welded to the electrode base material. The discharge layer is formed of an alloy containing Rh as the 2 nd component. The average crystal grain diameter of the discharge layer and the average crystal grain diameter of the relaxation layer are different from each other for the structure of the discharge layer and the relaxation layer of the chip after being welded to the electrode base material.

Description

Spark plug

Technical Field

The present invention relates to a spark plug, and more particularly to a spark plug having an electrode provided with a chip mainly made of Pt.

Background

In order to improve the spark erosion resistance of the electrode, there are known: a spark plug is formed by opposing a 1 st electrode and a 2 nd electrode, each of which is formed by bonding a chip mainly composed of Pt to an electrode base material. Patent document 1 discloses a technique of using a chip in which a discharge layer made of a Pt — Ir alloy is bonded to a relaxation layer made of a Pt — Ni alloy in order to relax a thermal stress resulting from a difference in thermal expansion between the chip and an electrode base material.

Documents of the prior art

Patent document

Patent document 1: japanese laid-open patent publication No. 6-60959

Disclosure of Invention

Problems to be solved by the invention

However, in the above-described conventional techniques, the interfacial peeling between the electrode base material and the relaxation layer and the interfacial peeling between the relaxation layer and the discharge layer, which are caused by thermal stress due to thermal shock or the like, become problems.

The present invention has been made to solve the above problems, and an object of the present invention is to provide: a spark plug capable of suppressing the interfacial separation between a relaxation layer and a discharge layer.

Means for solving the problems

In order to achieve the object, a first electrode 1 of a spark plug according to the present invention includes: a chip bonded with a discharge layer mainly composed of Pt and a relaxation layer mainly composed of Pt; and an electrode base material formed of an alloy mainly composed of Ni or Ni. The No. 2 electrode and the No. 1 electrode are opposed to each other with a spark gap interposed therebetween. The relaxation layer is formed of an alloy containing Ni as the 2 nd component and having a thickness of 0.05mm or more, and is welded to the electrode base material. The discharge layer is formed of an alloy containing Rh as the 2 nd component. The average crystal grain diameter of the discharge layer and the average crystal grain diameter of the relaxation layer are different from each other for the structure of the discharge layer and the relaxation layer of the chip after being welded to the electrode base material.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the spark plug of claim 1, since the relaxation layer mainly composed of Pt is formed of an alloy containing Ni as the 2 nd component and having a thickness of 0.05mm or more, thermal stress derived from a difference in thermal expansion between the electrode base material formed of an alloy mainly composed of Ni or Ni and the discharge layer formed of an alloy mainly composed of Pt and containing Rh as the 2 nd component is relaxed.

Further, in the structure of the discharge layer and the relaxation layer after the chip is welded to the electrode base material, the average crystal grain diameter of the discharge layer and the average crystal grain diameter of the relaxation layer are different from each other, and therefore, cracks are generated in the grain boundaries of the discharge layer and the relaxation layer, and the thermal stress can be relaxed. As a result, the interfacial separation between the electrode base material and the relaxation layer and the interfacial separation between the relaxation layer and the discharge layer can be suppressed.

According to the spark plug of claim 2, since the average crystal grain size of the discharge layer is larger than the average crystal grain size of the relaxation layer with respect to the structure of the discharge layer and the relaxation layer after the chip is welded to the electrode base material, cracks are generated in the grain boundary of the discharge layer by the thermal stress, and the thermal stress can be relaxed. This has an effect of further suppressing the interface peeling in addition to the effect of claim 1.

According to the spark plug of claim 3, a value obtained by dividing the thickness of the discharge layer after the chip is welded to the electrode base material by the thickness of the relaxation layer after the chip is welded to the electrode base material is less than 3. As a result, in addition to the effect of claim 2, the discharge layer can be easily deformed by the thermal stress, and the thermal stress relaxation effect can be ensured.

According to the spark plug of claim 4, since the average crystal grain size of the electric discharge layer is smaller than the average crystal grain size of the relaxation layer with respect to the structure of the electric discharge layer and the relaxation layer after the chip is welded to the electrode base material, cracks can easily occur in the grain boundary of the relaxation layer by the thermal stress. As a result, in addition to the effect of claim 1, there is an effect that thermal stress is relaxed by relaxing cracks in the grain boundary of the layer, and interface peeling can be suppressed.

According to the spark plug of claim 5, since the relaxation layer contains Ni in an amount of more than 3 mass%, the linear expansion coefficient of the relaxation layer can be made close to the intermediate between the linear expansion coefficient of the discharge layer and the linear expansion coefficient of the electrode base material. As a result, in addition to the effect of claim 4, there is an effect that the interface peeling can be further suppressed.

According to the spark plug of claim 6, the composition of the discharge layer and the relaxation layer is set so that the average crystal grain diameter of the discharge layer is larger than the average crystal grain diameter of the relaxation layer in the structure of the discharge layer and the relaxation layer after the chip is heated at 1200 ℃ for 33 hours. Therefore, in addition to the effects of any of claims 1 to 5, in the environment where the 1 st electrode is heated to about 1000 ℃ in the combustion chamber, fine cracks can easily occur in the grain boundary of the discharge layer, and there is an effect that thermal stress can be relaxed.

According to the spark plug of claim 7, the composition of the discharge layer and the relaxation layer is set so that the average crystal grain diameter of the discharge layer is smaller than the average crystal grain diameter of the relaxation layer in the structure of the discharge layer and the relaxation layer after the chip is heated at 1200 ℃ for 33 hours. Therefore, in addition to the effects of any of claims 1 to 5, in the environment where the 1 st electrode is heated to about 1000 ℃ in the combustion chamber, cracks are likely to occur in the grain boundaries of the relaxation layer, and there is an effect that thermal stress can be relaxed.

According to the spark plug of claim 8, since the spark discharge layer contains 85 mass% or more of Pt and Rh, the spark wear resistance can be improved in addition to the effects of any one of claims 1 to 7.

Drawings

Fig. 1 is a cross-sectional view of a spark plug according to an embodiment of the present invention.

Fig. 2 is a cross-sectional view of the center electrode and the ground electrode.

Description of the reference numerals

10 spark plug

13 center electrode (No. 2 electrode)

18 ground electrode (No. 1 electrode)

19 electrode base material

20 chip

21 buffer layer

22 discharge layer

Detailed Description

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. Fig. 1 is a sectional view of a spark plug 10 according to an embodiment of the present invention, and fig. 2 is a sectional view of a center electrode 13 and a ground electrode 18. In fig. 1 and 2, the lower side of the paper surface is referred to as the front end side of the spark plug 10, and the upper side of the paper surface is referred to as the rear end side of the spark plug 10.

As shown in fig. 1, the spark plug 10 includes: an insulator 11, a center electrode 13 (2 nd electrode), a body shell 17, and a ground electrode 18 (1 st electrode). The insulator 11 is a substantially cylindrical member formed of alumina or the like having excellent mechanical properties and insulation properties at high temperatures. The insulator 11 passes through the shaft hole 12 along the axis O.

The center electrode 13 is a rod-shaped electrode inserted into the axial hole 12 and held by the insulator 11 along the axis O. The center electrode 13 includes: an electrode base material 14; and a chip 15 bonded to the tip of the electrode base member 14. A core member having excellent thermal conductivity is embedded in the electrode base member 14. The electrode base material 14 is formed of a metal material made of an alloy mainly containing Ni or a metal material made of Ni, and the core material is formed of copper or an alloy mainly containing copper. The chip 15 is formed of a noble metal such as platinum, iridium, ruthenium, or rhodium or an alloy mainly containing a noble metal, which has higher spark wear resistance than the electrode base material 14.

The terminal fitting 16 is a rod-shaped member to which a high-voltage cable (not shown) is connected, and the tip end side thereof is disposed in the insulator 11. The terminal fitting 16 is electrically connected to the center electrode 13 in the axial hole 12. The main body case 17 is a substantially cylindrical metal member fixed to a screw hole (not shown) of the internal combustion engine. The main body case 17 is fixed to the outer periphery of the insulator 11.

The ground electrode 18 includes: an electrode base material 19 joined to the main body case 17; and a chip 20 bonded to the electrode base material 19. A core material having excellent thermal conductivity is embedded in the electrode base material 19. The electrode base material 19 is formed of a metal material made of an alloy mainly containing Ni or Ni, and the core material is formed of copper or an alloy mainly containing copper. It is needless to say that the core material may be omitted, and the entire electrode base material 19 may be formed of a metal material made of an alloy mainly containing Ni or Ni. The electrode base material 19 is bent toward the center electrode 13, and the chip 20 faces the center electrode 13 with a spark gap G (see fig. 2) therebetween.

The spark plug 10 is manufactured by, for example, the following method. First, the center electrode 13 is inserted into the axial hole 12 of the insulator 11. The center electrode 13 is disposed so that the tip end is exposed to the outside from the shaft hole 12. After the terminal fitting 16 is inserted into the axial hole 12 and the terminal fitting 16 and the center electrode 13 are electrically connected to each other, the main body case 17 to which the electrode base material 19 is joined in advance is assembled to the outer periphery of the insulator 11. After the electrode base member 19 is joined to the chip 20, the electrode base member 19 is bent so that the chip 20 and the center electrode 13 face each other in the axis O direction, and the spark plug 10 is obtained.

As shown in fig. 2, the chip 20 is a covering material including a relaxation layer 21 and a discharge layer 22 laminated on the relaxation layer 21, and is formed in a disk shape. The discharge layer 22 is metallically joined to the relaxation layer 21 by various methods such as a rolling method, an explosion welding method, a diffusion method, and an explosion welding rolling method. The chip 20 is joined to the electrode base material 19 by resistance welding or the like with the relaxation layer 21.

The discharge layer 22 is an alloy mainly composed of Pt and containing Rh as the 2 nd component. The discharge layer 22 contains Pt and Rh, thereby ensuring oxidation resistance and spark erosion resistance. The phrase "mainly containing Pt" means that the content of Pt in the discharge layer 22 is 50 mass% or more. The discharge layer 22 may contain the 3 rd component such as Ni, Cr, Ti, Si, Y, Sr, etc. in addition to Pt and Rh. The discharge layer 22 desirably contains 85 mass% or more of Pt and Rh. This is because the spark wear resistance is improved.

The relaxation layer 21 is an alloy mainly composed of Pt and containing Ni as the 2 nd component and having a thickness of 0.05mm or more. The relaxation layer 21 is interposed between the electrode base material 19 and the discharge layer 22, and relaxes a thermal stress derived from a difference in thermal expansion between the electrode base material 19 and the discharge layer 22. Note that "mainly contains Pt" means that the content of Pt in the relaxation layer 21 is 50 mass% or more. The relaxation layer 21 desirably contains Ni more than 3 mass%. This is because the thermal stress relaxation effect by the relaxation layer 21 is ensured.

Since the thickness of the relaxation layer 21 is 0.05mm or more, weldability between the electrode base material 19 and the relaxation layer 21 can be ensured. On the other hand, when the thickness of the relaxation layer 21 is 0.05mm or more, the interface between the electrode base material 19 and the relaxation layer 21 and the interface between the relaxation layer 21 and the discharge layer 22 are likely to be peeled off due to the thermal stress resulting from the difference in thermal expansion between the electrode base material 19 and the discharge layer 22. If the interface separation occurs, the discharge layer 22 and the chip 20 float, and thus the spark gap G becomes small, and the ignitability of the spark plug 10 is impaired. Further, when the interface peeling progresses and the discharge layer 22 and the chip 20 are peeled off, the spark gap G becomes large, and the ignitability of the spark plug 10 is still impaired. These interfacial separations are likely to occur by thermal shock at temperatures up to about 600 to 1000 ℃.

The average crystal grain diameters of the relaxation layer 21 and the discharge layer 22 are controlled in order to suppress the interfacial peeling. When the crystal grain size is large, the range (length) of accumulated phase transformation becomes large, and the accumulated phase transformation also becomes large. As a result, stress concentration can be easily caused, and cracks can easily occur in the grain boundary. That is, by making the average crystal grain size of the relaxation layer 21 different from the average crystal grain size of the discharge layer 22, cracks are generated in the grain boundary of the layer having a larger average crystal grain size of the relaxation layer 21 and the discharge layer 22, so that the thermal stress is relaxed and the interface peeling is suppressed. The grain size of the relaxation layer 21 and the discharge layer 22 can be adjusted by controlling the processing conditions and the composition of the relaxation layer 21 and the discharge layer 22.

Since the structure of the relaxation layer 21 made of PtNi alloy and the structure of the discharge layer 22 made of PtRh alloy are not substantially changed at a temperature of about 600 ℃, the structures of the relaxation layer 21 and the discharge layer 22 welded to the electrode base material 19 greatly affect relaxation of thermal stress due to thermal shock at a maximum temperature of about 600 ℃. The structure of the relaxation layer 21 and the electric discharge layer 22 welded to the electrode base material 19 can be controlled according to the processing conditions of the relaxation layer 21 and the electric discharge layer 22.

On the other hand, when the relaxation layer 21 and the electric discharge layer 22 are heated to about 1000 ℃, the structure changes with time, and the average crystal grain size changes. The structure of the relaxation layer 21 and the discharge layer 22 in this case can be controlled according to the composition of the relaxation layer 21 and the discharge layer 22. The structure of the relaxation layer 21 and the discharge layer 22 controlled by the composition of the relaxation layer 21 and the discharge layer 22 greatly affects the relaxation of the thermal stress due to thermal shock at a maximum temperature of about 1000 ℃.

The average crystal grain diameters of the relaxation layer 21 and the electric discharge layer 22 were determined in accordance with "evaluation by cutting method" of attachment C of JIS G0551 (2013) based on ISO643(2003 edition). The average grain size is an average segment length per 1 crystal grain of a test line crossing inside the crystal grain appearing on a flat cross section of a test piece ground for microscopic observation. In the present embodiment, the average crystal grain diameter is determined by drawing 1 or more test lines of straight lines parallel to the axis O, test lines of straight lines orthogonal to the axis O, and test lines of straight lines intersecting the axis O at 45 ° on a cross section including the axis O. The average segment length per 1 crystal grain of the test line crossing the inside of the crystal grain was determined from the average number of captured crystal grains per 1mm of the test line or the average number of intersections per 1mm of the test line. The number of trapped grains is the number of crystals passed or trapped by the test line, and the number of intersections is the number of intersections between the grain boundaries and the test line.

In the structure of the electric discharge layer 22 and the relaxation layer 21 welded to the electrode base material 19, when the average crystal grain size of the relaxation layer 21 is the same as the average crystal grain size of the electric discharge layer 22, there is a problem that interface peeling between the electrode base material 19 and the relaxation layer 21 and interface peeling between the relaxation layer 21 and the electric discharge layer 22 are likely to occur due to thermal shock at a maximum reaching temperature of about 600 ℃.

On the other hand, in the structure of the discharge layer 22 and the relaxation layer 21 welded to the electrode base material 19, if the average crystal grain size of the discharge layer 22 is larger than the average crystal grain size of the relaxation layer 21, cracks are generated in the grain boundary of the discharge layer 22 by thermal shock at a maximum temperature of about 600 ℃. As a result, the thermal stress is relaxed by the cracks in the grain boundaries of the discharge layer 22 and the deformation of the discharge layer 22 (chip 20), and the interface peeling can be suppressed.

When cracks in the grain boundaries of the discharge layer 22 progress and the crystal grains fall off, the ignitability of the spark plug 10 may be impaired. However, the extent of cracking of the grain boundaries can be reduced by deforming the discharge layer 22 (chip 20), and therefore, the cracking of the grain boundaries of the discharge layer 22 cannot adversely affect the ignitability of the spark plug 10.

In the structure of the electric discharge layer 22 and the relaxation layer 21 welded to the electrode base material 19, if the average crystal grain size of the electric discharge layer 22 is smaller than the average crystal grain size of the relaxation layer 21, cracks are generated in the grain boundary of the relaxation layer 21 by thermal shock at a maximum reaching temperature of about 600 ℃. As a result, the thermal stress is relaxed by the cracks in the grain boundaries of the relaxation layer 21, and the interface peeling can be suppressed. Since the relaxation layer 21 is not a portion that bears the performance such as discharge, even if a crack is generated in the grain boundary of the relaxation layer 21, the ignitability of the spark plug 10 is not adversely affected.

Further, regarding the composition of the discharge layer 22 and the relaxation layer 21, when the average crystal grain diameter of the discharge layer 22 is set to be larger than the average crystal grain diameter of the relaxation layer 21 in the structure of the discharge layer 22 and the relaxation layer 21 after the chip 20 is heated at 1200 ℃ for 33 hours, cracks are likely to be generated in the grain boundary of the discharge layer 22 by thermal shock at a maximum reaching temperature of about 1000 ℃. As a result, the thermal stress is relaxed, and the interface peeling can be suppressed.

In addition, regarding the compositions of the discharge layer 22 and the relaxation layer 21, when the average grain size of the discharge layer 22 is set to be smaller than the average grain size of the relaxation layer 21 in the structures of the discharge layer 22 and the relaxation layer 21 after the chip 20 is heated at 1200 ℃ for 33 hours, cracks are likely to occur in the grain boundary of the relaxation layer 21 due to thermal shock at a maximum reaching temperature of about 1000 ℃. As a result, the thermal stress is relaxed, and the interface peeling can be suppressed.

The thicknesses of the discharge layer 22 and the relaxation layer 21 are preferably set to a value of less than 3, which is obtained by dividing the thickness of the discharge layer 22 after the chip 20 is welded to the electrode base material 19 by the thickness of the relaxation layer 21 after the chip 20 is welded to the electrode base material 19. This is because, by setting the thickness of the discharge layer 22 to be less than 3 with respect to the thickness of the relaxation layer 21, the discharge layer 22 is easily deformed by the thermal stress, and the relaxation effect of the thermal stress is ensured. The thicknesses of the discharge layer 22 and the relaxation layer 21 are thicknesses of the centers of the discharge layer 22 and the relaxation layer 21 in a cross section including the axis O.

[ examples ]

The present invention will be further described in detail with reference to examples, but the present invention is not limited to these examples.

< preparation of sample >

The tester produces various chips 20 having different shapes, compositions of the discharge layer 22 and the relaxation layer 21, average crystal grain diameters, and thicknesses by solid-phase diffusion bonding of the discharge layer 22 and the relaxation layer 21. The discharge layer 22 was joined to the electrode base material 19 made of NFC600 by resistance welding to prepare a sample of the spark plug 10 having various chips 20 provided on the ground electrode 18. The prepared samples are listed in table 1. Since a plurality of evaluations were performed for each sample, a plurality of samples were prepared.

[ Table 1]

In samples 1 to 56, the chip 20 having the discharge layer 22 and the relaxation layer 21 formed of the coating material was provided on the ground electrode 18. In samples 57 to 62, a chip not divided into the discharge layer 22 and the relaxation layer 21 was provided on the ground electrode 18. The numerical values in the columns of "discharge layer" and "relaxation layer" of the chip in table 1 represent the mass% of the element.

The tester performed 2 kinds of tests (test 1 and test 2) for evaluating the spark wear resistance and 2 kinds of cold and hot repetition tests (cold and hot test 1 and cold and hot test 2) in which the ground electrode 18 was heated by a burner and left to cool, respectively, for each sample.

Unlike these tests, the tester embeds the pre-test chip 20 welded to the electrode base material 19 in a resin, polishes the resin, and obtains the average segment length (average crystal grain diameter) per 1 crystal grain of a test line (1 or more straight lines each parallel to, orthogonal to, and crossing at 45 °) crossing the inside of a crystal grain appearing on a cross section including the axis O by observing the test line with a microscope. The average crystal grain size of the discharge layer 22 divided by the average crystal grain size of the relaxation layer 21 is shown in the column "crystal grain size" in table 1. Simultaneously with this, a value obtained by dividing the thickness of the discharge layer 22 appearing on the cross section including the axis O by the thickness of the relaxation layer 21 is obtained. This value is shown in the column "thickness" in table 1.

Unlike these tests, the tester cuts the electrode base material 19 to which the chip 20 is bonded before the test. The cut electrode base material 19 and the chip 20 were heated at 1200 ℃ for 33 hours, and then the electrode base material 19 and the chip 20 embedded in the resin were polished to determine the average segment length (average crystal grain diameter) per 1 crystal grain of a test line (1 or more straight lines each parallel to, orthogonal to, and crossing at 45 °) across the inside of a crystal grain appearing on a cross section including the axis O. The average crystal grain size of the discharge layer 22 divided by the average crystal grain size of the relaxation layer 21 is shown in the column of "crystal grain size" in table 1.

< test method and evaluation method of spark erosion resistance test 1 >

The tester mounts each sample of the ignition plug 10 on a 4-cylinder direct injection engine having an exhaust gas amount of 2.0 liters with an exhaust turbo type supercharging device, and operates the engine. The spark gap (the distance between the discharge layer 22 and the center electrode 13) of each sample was set to 0.75 mm. The operating conditions of the engine were as follows: the number of revolutions was 4000rpm, the air-fuel ratio was 12.0, the load was 190kPa of Indicated Mean Effective Pressure (IMEP), and the engine operation time was continuously 200 hours.

The tester measures the spark gap of each sample after the test with a needle gauge, and determines the amount of increase (consumption) in the spark gap due to the test. The evaluation was as follows: an increase of less than 0.15mm is referred to as "A", an increase of 0.15mm or more and less than 0.20mm is referred to as "B", and an increase of 0.20mm or more is referred to as "C".

< test method and evaluation method of spark erosion resistance test 2 >

The engine of each sample to which the spark plug 10 was attached was operated in the same manner as in test 1 except that the spark gap of each sample was set to 1.05 mm.

The tester measures the spark gap of each sample after the test with a needle gauge, and determines the amount of increase (consumption) in the spark gap due to the test. The evaluation was as follows: an increase of less than 0.15mm is referred to as "S", an increase of 0.15mm or more and less than 0.20mm is referred to as "A", an increase of 0.20mm or more and less than 0.30mm is referred to as "B", and an increase of 0.30mm or more is referred to as "C".

< test method of Cold Heat test 1 >

The tester heats the electrode base material 19 with a burner for 2 minutes so that the temperature of the tip (the portion farthest from the main body case 17) of the electrode base material 19 becomes 600 ℃, and then stands still for 1 minute to cool the electrode base material, and applies 1000 cycles to the electrode base material 19 as 1 cycle.

< test method of Cold Heat test 2 >

The tester heats the electrode base material 19 with a burner for 2 minutes so that the temperature of the tip of the electrode base material 19 becomes 1000 ℃, and then stands still for 1 minute to cool it, and applies 1000 cycles to the electrode base material 19 as 1 cycle.

< evaluation method of interfacial delamination >

The tester embeds the ground electrode 18 after the test in resin and polishes the ground electrode so as to expose a cross section including the center of the chip 20. By microscopic observation, the ratio of interfacial peeling, i.e., X ═ a)/a (%), and Y ═ a (%), were determined using a length of the chip 20 (dimension along the interface between the chip 20 and the electrode base material 19), a length of the portion where interfacial peeling did not occur and the relaxation layer 21 was bonded to the electrode base material 19, and b. The evaluation was as follows: x, Y the larger value is expressed as "S" when the percentage is less than 10%, as "A" when the percentage is not less than 10% and less than 40%, as "B" when the percentage is not less than 40% and less than 50%, and as "C" when the percentage is not less than 50%.

< evaluation method of grain boundary cracking >

In the cross section (including the center of the chip 20 exposed by embedding the ground electrode 18 after the test in resin and polishing) in which the above-described interfacial peeling was evaluated, the tester separately obtained the ratio (%) of the area of the portion missing due to grain boundary cracking with respect to the respective cross-sectional areas of the discharge layer 22 and the relaxation layer 21. The evaluation was as follows: less than 1% is referred to as "A", 1% or more and less than 10% is referred to as "B", and 10% or more is referred to as "C".

< method for evaluating distortion >

The amount of protrusion of the chip 20 from the electrode base material 19 measured by a micrometer before the cold-heat test was subtracted from the amount of protrusion of the chip 20 from the electrode base material 19 measured by a micrometer after the cold-heat test, and the obtained value was used as the amount of deformation (μm) of the chip 20.

< method of comprehensive evaluation >

Each evaluation was given a score of 3 for "S", a score of 2 for "a", a score of 1 for "B" and a score of 0 for C, and the evaluations were quantified to obtain a total score. The overall evaluation was as follows: the total score is 18 points or more and is marked as "S", 15 points to 17 points and is marked as "A", 11 points to 14 points and is marked as "B", and 0 points to 10 points and is marked as "C". In the case where "C" is present in one of the evaluations, the overall evaluation is referred to as "C" regardless of the total score.

< results >

As shown in the column of "chip" and "composition" in table 1, samples 1 to 52 were samples in which the discharge layer was formed of a PtRh alloy and the relaxation layer was formed of a PtNi alloy. Samples 53 and 54 were samples in which the relaxation layer was formed of PtNi alloy, but the discharge layer was formed of metal other than PtRh alloy. Samples 55 and 56 are samples in which the discharge layer is formed of a PtRh alloy, but the relaxation layer is formed of a metal other than a PtNi alloy. Samples 57 to 62 are samples using a chip which is not a clad material.

In the evaluation of the interfacial separation in the cold-hot test 1, the samples 53 to 56, 57, 59, 60, and 62 were evaluated as C, and the samples 1 to 14, 17 to 52, 58, and 61 were evaluated as S to B. Of the samples 1 to 14, 17 to 52, 58 and 61, the evaluation of the spark erosion resistance test 1 of the samples 1 to 14 and 17 to 52 other than the samples 58 and 61 was A or B.

In samples 1 to 52, as shown in the columns of "grain size" and "front" in table 1, the average grain size of the electric discharge layer 22 after welding to the electrode base material 19 was the same as the average grain size of the relaxation layer 21 for

samples

15 and 16. Samples 1 to 14, 17 to 52 are samples in which the average crystal grain size of the discharge layer 22 welded to the electrode base material 19 is different from the average crystal grain size of the relaxation layer 21. In the samples in which the discharge layer was formed of the PtRh alloy and the relaxation layer was formed of the PtNi alloy as in samples 1 to 14 and 17 to 52, it was confirmed that the interface peeling was suppressed in the cold and hot test 1 in which the maximum temperature reached 600 ℃.

Of samples 1 to 14 and 17 to 52, samples 1 to 14 were samples in which the average crystal grain size of the discharge layer 22 after welding to the electrode base material 19 was smaller than the average crystal grain size of the relaxation layer 21. Samples 17 to 52 are samples in which the average crystal grain size of the discharge layer 22 welded to the electrode base material 19 is larger than the average crystal grain size of the relaxation layer 21. It is understood that in the cold and hot test 1, the area of the grain boundary cracks of the relaxation layer 21 is larger than that of the discharge layer 22 in the samples 1 to 14. On the other hand, in samples 17 to 52, it is found that the area of the grain boundary cracks of the electric discharge layer 22 is larger than the area of the grain boundary cracks of the relaxation layer 21 in the cold and hot test 1.

From these results, it is presumed that: the thermal stress generated in the thermal shock of the cold and hot test 1 was relaxed by the grain boundary cracks generated in the layer having a large average crystal grain diameter of the discharge layer 22 and the relaxation layer 21, and the interface peeling could be suppressed.

In the evaluation of the interface peeling in the cold-hot test 1, if the samples 8, 9, 17 to 20, 34, 35 are compared, the sample 17 to 20, 34, 35 having the Ni content of the relaxation layer 21 of 3 mass% or less is evaluated as B. However, samples 8 and 9 in which the relaxation layer 21 contained more than 3 mass% (5 mass%) of Ni were evaluated as S. From this result, it is presumed that: in the relaxation layer 21 containing Ni in an amount of more than 3 mass%, the linear expansion coefficient of the relaxation layer 21 is close to the middle between the linear expansion coefficient of the electric discharge layer 22 and the linear expansion coefficient of the electrode base material 19, and thus interface peeling can be suppressed.

In the evaluation of the interface peeling in the cold and hot test 1, if samples 31 to 33 are compared, the samples 32 and 33 in which the thickness of the discharge layer 22 after welding to the electrode base material 19 is divided by the thickness of the relaxation layer 21 and the value is 3 or more are evaluated as B. However, samples 29 to 31 in which the value obtained by dividing the thickness of the discharge layer 22 by the thickness of the relaxation layer 21 is less than 3 were evaluated as S. From this result, it is presumed that: by reducing the thickness of the discharge layer 22, the discharge layer 22 can be easily deformed by thermal stress, and the effect of relaxing thermal stress can be improved.

In the evaluation of the spark erosion resistance test 2, if

samples

6, 7, 13, and 14 are compared, sample 14 in which the discharge layer 22 contains 80 mass% of Pt and Rh is evaluated as C. However, samples 6, 7, and 13 in which the discharge layer 22 contained 85 mass% or more of Pt and Rh were evaluated as a or B. Similarly, in the evaluation of the spark erosion resistance test 1, if

samples

6, 7, 13, and 14 are compared, sample 14 in which the discharge layer 22 contains 80 mass% of Pt and Rh is evaluated as B. However, samples 6, 7, and 13 in which the discharge layer 22 contained 85 mass% or more of Pt and Rh were evaluated as a. From the results, it is understood that the spark erosion resistance can be improved by the discharge layer 22 containing not less than 85 mass% of Pt and Rh.

In the evaluation of the interface peeling and the grain boundary cracking in the cold-hot test 2, samples 8 to 12 were compared with

samples

13 and 14, samples 17 to 24 were compared with samples 25 to 33, and samples 34 to 36 were compared with samples 37 to 44. Samples 8 to 12, 17 to 24, and 34 to 36 are samples in which the average crystal grain diameter of the relaxation layer 21 is larger than the average crystal grain diameter of the discharge layer 22 after the electrode base material 19 and the chip 20 are heated at 1200 ℃ for 33 hours.

Samples

13, 14, 25 to 33, and 37 to 44 are samples in which the average crystal grain size of the discharge layer 22 is larger than the average crystal grain size of the relaxation layer 21 after heating the electrode base material 19 and the chip 20 at 1200 ℃ for 33 hours.

Comparing them, the results confirmed that: samples 8 to 12, 17 to 24, and 34 to 36 have larger missing portions of the relaxation layer 21 due to grain boundary cracks than

samples

13, 14, 25 to 33, and 37 to 44, respectively. As in samples 8 to 12, 17 to 24, and 34 to 36, it is found that grain boundary cracks can easily occur in the relaxation layer 21 in the cold and hot test 2 in which the maximum temperature is 1000 ℃ by adjusting the compositions of the relaxation layer 21 and the discharge layer 22 so that the average crystal grain diameter of the relaxation layer 21 after heating at 1200 ℃ for 33 hours is larger than the average crystal grain diameter of the discharge layer 22. As a result, the thermal stress is relaxed, and the interfacial peeling of the chip 20 can be suppressed.

In

samples

13, 14, 25 to 33, and 37 to 44, the loss of the relaxation layer 21 due to grain boundary cracking was smaller than in samples 8 to 12, 17 to 24, and 34 to 36. As in

samples

13, 14, 25 to 33, and 37 to 44, it is found that by adjusting the compositions of the relaxation layer 21 and the discharge layer 22 so that the average crystal grain diameter of the discharge layer 22 after heating at 1200 ℃ for 33 hours is larger than the average crystal grain diameter of the relaxation layer 21, grain boundary cracks in the relaxation layer 21 can be suppressed and fine grain boundary cracks can easily occur in the discharge layer 22 in the cold and hot test 2 at a maximum temperature of 1000 ℃. As a result, the thermal stress is relaxed, and the interfacial peeling of the chip 20 can be suppressed.

In the amount of deformation in the cold-hot test 2, when samples 17 to 24 and 34 to 36 were compared, it was confirmed that the amount of deformation of samples 23, 24 and 36 in which the discharge layer 22 contained the 3 rd component was smaller than that of the other samples 17 to 22, 34 and 35.

In the present example, various evaluations were performed on samples 1 to 62 in which the chip 20 having a disk or prism shape was provided on the ground electrode 18. From samples 1 to 62, it was confirmed that the evaluation results were not affected by the shape of the chip 20.

The present invention has been described above based on the embodiments, but the present invention is not limited to the above embodiments at all, and it is easily estimated that various modifications and variations can be made within the scope not departing from the gist of the present invention.

In the above embodiment, the case where the chip 20 has a disk shape or a prism shape has been described, but the shape is not necessarily limited thereto, and it is needless to say that other shapes may be adopted. Examples of other shapes of the chip 20 include a truncated cone shape and an elliptic cylinder shape.

In the above embodiment, the case where the chip 20 is joined to the electrode base material 19 by resistance welding has been described, but the present invention is not necessarily limited thereto, and it is needless to say that the chip 20 may be joined to the electrode base material 19 by other means. As another means, laser welding may be mentioned.

In the above embodiment, the case where the chip 20 (the relaxation layer 21 and the discharge layer 22) is provided in the ground electrode 18 has been described, but the present invention is not necessarily limited thereto. Of course, the electrode base material 14 for bonding the chip 20 to the center electrode 13 may be used instead of the chip 15 provided in the center electrode 13. In the above case, the same operational effects as those described in the above embodiment can be achieved.

In the above embodiment, the case where the electrode base material 19 joined to the main body case 17 is bent has been described. But is not necessarily limited thereto. It is needless to say that a linear electrode base material may be used instead of the bent electrode base material 19. In this case, the distal end side of the main body case 17 is extended in the axis O direction, and the linear electrode base material is joined to the main body case 17 so that the electrode base material faces the center electrode 13.

In the above embodiment, the case where the ground electrode 18 is disposed so that the axis O of the center electrode 13 coincides with the chip 20 and the center electrode 13 face each other in the direction of the axis O has been described. However, the positional relationship between the ground electrode 18 and the center electrode 13 may be appropriately set. As another positional relationship between the ground electrode 18 and the center electrode 13, for example, the ground electrode 18 is disposed so that a side surface of the center electrode 13 faces the ground electrode 18.

Claims

1. A spark plug is characterized by comprising:

a 1 st electrode having a chip to which a discharge layer mainly composed of Pt and a relaxation layer mainly composed of Pt are bonded, and an electrode base material formed of an alloy mainly composed of Ni or Ni and to which the relaxation layer is welded; and a 2 nd electrode facing the discharge layer with a spark gap therebetween,

the discharge layer is formed of an alloy containing Rh as the 2 nd component,

the relaxation layer is formed of an alloy containing Ni as a 2 nd component and having a thickness of 0.05mm or more,

the average crystal grain diameter of the discharge layer and the average crystal grain diameter of the relaxation layer are different from each other with respect to the structure of the discharge layer and the relaxation layer after the chip is welded to the electrode base material.

2. The spark plug according to claim 1, wherein the average crystal grain diameter of the discharge layer is larger than the average crystal grain diameter of the relaxation layer with respect to the structure of the discharge layer and the relaxation layer after the chip is welded to the electrode base material.

3. The spark plug according to claim 2, wherein a value obtained by dividing a thickness of the discharge layer after the chip is welded to the electrode base material by a thickness of the relaxation layer after the chip is welded to the electrode base material is less than 3.

4. The spark plug according to claim 1, wherein the average crystal grain diameter of the discharge layer is smaller than the average crystal grain diameter of the relaxation layer with respect to the structure of the discharge layer and the relaxation layer after the chip is welded to the electrode base material.

5. The spark plug of claim 4 wherein said moderating layer contains more than 3 mass% of Ni.

6. The spark plug according to any one of claims 1 to 5, wherein the composition of the discharge layer and the relaxation layer is set so that the average crystal grain diameter of the discharge layer is larger than the average crystal grain diameter of the relaxation layer in the structure of the discharge layer and the relaxation layer after the chip is heated at 1200 ℃ for 33 hours.

7. The spark plug according to any one of claims 1 to 5, wherein the composition of the discharge layer and the relaxation layer is set so that the average crystal grain diameter of the discharge layer is smaller than the average crystal grain diameter of the relaxation layer in the structure of the discharge layer and the relaxation layer after the chip is heated at 1200 ℃ for 33 hours.

8. The spark plug according to any one of claims 1 to 5, wherein the discharge layer contains 85 mass% or more of Pt and Rh.

9. The spark plug of claim 6 wherein said discharge layer contains 85 mass% or more of Pt and Rh.

10. The spark plug of claim 7 wherein said discharge layer contains 85 mass% or more of Pt and Rh.