JP5794890B2 - Materials for spark plug electrodes - Google Patents

Description

  The present invention relates to a material constituting a center electrode and a ground electrode of a spark plug, and more particularly, to an iridium alloy having excellent durability, particularly high-temperature oxidation characteristics and spark wear resistance, and good workability.

  An ignition plug for an internal combustion engine is required to have excellent wear resistance so that it can be used for a long time even in a harsh environment in a combustion chamber. In order to satisfy such required characteristics, materials made of Ir, Pt, Ni, and alloys thereof are used as constituent materials of the central electrode and the ground electrode, which are the main members (Patent Document 1). These materials are known as excellent plug electrode materials that have a high melting point and are not easily oxidized and consumed even in a combustion chamber in a high-temperature and high-oxidation atmosphere.

  In the examination on the durability of the plug electrode material, more particularly, high temperature oxidation characteristics and spark wear resistance are emphasized. That is, the development of a material that is less consumed by oxidation even under a highly oxidized atmosphere and a material that is less consumed by sparks caused by sparks constantly generated during plug use has been emphasized.

JP 2009-295427 A

  By the way, in recent years, many automobile engines aimed at improving fuel efficiency have been developed, and the compression ratio and precise electronic control for improving the combustion efficiency are in progress. It is more severe than the engine. Therefore, improvement of high-temperature oxidation characteristics and spark wear resistance more than ever is expected for plug electrode materials.

  Accordingly, an object of the present invention is to provide a material for a plug electrode having excellent high-temperature oxidation characteristics and spark wear resistance even under such a severe environment.

  The present invention for solving the above-mentioned problems is a material for a plug electrode made of an Ir alloy to which Co and W, which are essential additive elements for Ir, are added, and the Ir alloy contains 10% by mass to 30% by mass of Co, It is a plug electrode material consisting of 5 mass% to 10 mass% W and the balance Ir.

  The plug electrode material according to the present invention is an alloy based on Ir (iridium), and is an alloy in which Co (cobalt) and W (tungsten) are added at predetermined concentrations as essential additive elements. The Ir-based alloy is applied because Ir is basically excellent in spark wear resistance. On the other hand, Ir has a somewhat inferior high-temperature oxidation characteristic, and it can be said that conventional plug materials made of an Ir alloy cannot sufficiently meet future demands. In the present invention, Co and W are simultaneously added as additive elements that complement the high-temperature oxidation characteristics and further improve the spark wear resistance.

  Hereinafter, the structure of the Ir alloy according to the present invention will be described in more detail. As described above, Co and W are essential additive elements. Co is added for the purpose of improving the high temperature oxidation characteristics of the alloy. The amount of Co added is 10 to 30% by mass. If it is less than 10% by mass, the effect of improving the high-temperature oxidation characteristics is not observed, and Ir inherent high-temperature oxidation consumption tends to occur. On the other hand, if it exceeds 30% by mass, the consumption of sparks tends to increase. On the other hand, W has an effect of improving the spark resistance of the alloy. W addition amount shall be 5-10 mass%. If the amount is less than 5% by mass, the effect of improving the wear resistance of the sparks is not observed. In the present invention, there is the above limitation in the range of the addition amount of each additive element of Co and W. According to the present invention, if the addition amount of each metal is outside the proper range, the high temperature oxidation characteristics and the spark consumption are deteriorated. That is, in order to optimize the balance of the characteristics, it is necessary to limit the amount of each alloy metal added as described above.

  In addition, the plug electrode material made of an Ir alloy according to the present invention can further improve the high-temperature oxidation characteristics and the spark wear resistance, and further improve other characteristics by appropriately adding additional elements. . Another complementary property is improved workability, which is important for materials that require microfabrication, such as plug electrode materials.

  As an additive element for improving workability, either B (boron) or C (carbon) is applied. It is preferable to add at least one of these in an amount of 0.005 to 0.1% by mass. If it is less than 0.005% by mass, there is no effect, and if it exceeds 0.1% by mass, borides and carbides are formed, and workability is deteriorated.

  Further, as an additive element for improving workability, Re (rhenium) or Rh (rhodium) may be added. About Re or Rh, it is preferable to add at least 0.02 to 0.1% by mass of any of these. If it is less than 0.02% by mass, the effect of improving workability is not observed. As for Re or Rh, the workability becomes better as it is added. However, the workability required for the plug electrode material can be secured by addition of 0.1% by mass. Will be pushed up.

  The Ir alloy according to the present invention exhibits high high temperature oxidation characteristics by alloying a predetermined amount of Co and W into Ir, but the high temperature oxidation characteristics can be further improved by a small amount of additive elements. Examples of the additive element for further improving the high-temperature oxidation characteristics include Si (silicon) or Ge (germanium), and it is preferable to add at least one of these in an amount of 0.003 to 0.02 mass%. If it is less than 0.003 mass%, there is no effect, and if it exceeds 0.02 mass%, the workability is deteriorated without significantly improving the high-temperature oxidation characteristics.

  In addition, as an additive element, there is an element that forms an oxide film on the surface of a material to improve high-temperature oxidation characteristics. Specifically, Al (aluminum), V (vanadium), Nb (niobium), Ta (tantalum), Hf (hafnium), Zr (zirconium), Ti (titanium), La (lanthanum), Ce (cerium), Y (yttrium) is mentioned.

  Of these, it is preferable to add at least one of Al, V, Nb, Ta, Hf, Zr, and Ti in an amount of 0.005 to 1.0 mass%. If it is less than 0.005% by mass, there is no effect, and if it exceeds 1.0% by mass, the oxide film tends to be peeled off, and material consumption tends to progress. This is because intermetallic compounds (γ ′ phase) appear therein, and the workability deteriorates.

  La, Ce, and Y also form an oxide film on the alloy surface to improve high-temperature oxidation characteristics, but it is preferable to add a trace amount of at least one of 0.003 to 0.2 mass%. This is because if the amount is less than 0.003% by mass, there is no effect, but if a large amount is added, the workability deteriorates.

  The Ir alloy according to the present invention described above can be manufactured by mixing constituent metals, melting and casting, and using the obtained Ir alloy as a plate or wire, then cutting it to a desired length. It can be processed into a noble metal tip by a method or the like and used as a spark plug. In the Ir—Co—W alloy according to the present invention, depending on the additive element (particularly Al), an intermetallic compound (γ ′ phase) may precipitate when heated at a high temperature for a long time. Since this intermetallic compound deteriorates workability, the alloy according to the present invention avoids the formation of a γ 'phase. Therefore, in the above manufacturing process and processing process, high-temperature heating for a short time in hot processing is allowed, but long-time heating is avoided so that a γ 'phase is not generated.

  The Ir—Co—W alloy of the present invention is a plug material having both high-temperature oxidation resistance and spark consumption resistance. Moreover, this alloy can improve workability, further improve high-temperature oxidation characteristics, and the like by adding an appropriate additive element.

The photograph of the material cross section after the high-temperature oxidation test of Example 1 and Comparative Example 8.

  Hereinafter, preferred embodiments of the present invention will be described. In this embodiment, Ir alloys having various compositions based on an Ir—Co—W alloy were manufactured and their characteristics were evaluated. The production of the Ir alloy was adjusted to have a predetermined alloy composition by an arc melting furnace to produce an alloy ingot (50 to 150 g). And the processing test about this ingot was performed. In this processing test, forging was performed while heating the melting ingot to a temperature just below the melting point, and the workability was evaluated based on the appearance of the ingot and the occurrence of cracks in the cross section.

  Next, each ingot was processed into a wire (diameter 1 mm). For wire processing, a 1.0 mmφ × 20 mmL rod was cut out from the ingot used in the above processing test, and the sample was cut into φ1.0 × 5 mmL to evaluate high-temperature oxidation characteristics and spark consumption. did.

[Evaluation of high temperature oxidation characteristics]
The manufactured alloy wire was evaluated for high temperature oxidation wear resistance. In the evaluation method, heating was performed at 1200 ° C. in the atmosphere for 50 hours, and the residual ratio was calculated by measuring the weight before and after the test.

[Evaluation of spark wear resistance]
A plug having an alloy wire as a center electrode and a ground electrode is manufactured (gap between electrodes: 1.0 mm), discharged for 140 hours with air pressurization (6 atm), and the consumption length (ΔL) after discharge is measured. And evaluated. The results of the above evaluation tests are shown in Tables 1 and 2.

  From Table 1, it can be seen that the Ir—Co—W alloys (Examples 1 to 5) which are the basic composition of the present invention have excellent high-temperature oxidation characteristics and spark consumption characteristics. In this regard, the Ir—Co binary alloy (Comparative Example 1) mainly lacks spark consumption, and the Ir—W binary alloy (Comparative Example 2) has poor high-temperature oxidation resistance. On the other hand, the Ir alloys (Examples 1 to 5) into which Co and W are added at the same optimum amounts can satisfy both characteristics sufficiently. Moreover, when the addition amount of both Co and W elements is outside the preferred range (Comparative Examples 3 to 7), at least one of the high-temperature oxidation characteristics and the spark consumption is inferior.

  Moreover, when the effect of an additive element is seen from Table 2, the effect of workability improvement is seen by addition of 0.005 mass% or more for B or C (Examples 1 and 6 to 10). Re and Rh also have a workability improving effect (Examples 1, 11 to 14).

  Furthermore, as an additive element having an improvement in the high-temperature oxidation characteristics of the plug material, the effect of improving the high-temperature oxidation characteristics can be seen by adding an appropriate amount of Si or Ge (Examples 1, 15 to 20). Al also has an effect of improving the high-temperature oxidation characteristics (Examples 21 to 22), but addition over 1% tends to increase spark consumption and is slightly inferior in workability (Example 23). Furthermore, each additive element of V, Nb, Ta, Hf, Zr, Ti, La, Ce, and Y also exhibits an effect of improving high-temperature oxidation characteristics (Examples 1, 24 to 35).

  FIG. 1 shows a photograph of a cross-section of the material of Example 1 (Ir-11 mass% Co-9 mass% W) and Comparative Example 8 (Ir-10 mass% Rh) after a high temperature oxidation test. From FIG. 1, the conventional plug electrode material of Comparative Example 8 has many sites (black portions on the photograph) due to the progress of oxidation, whereas the Ir—Co—W alloy of Example 2 There is no progress of oxidation, and the oxidation depletion rate is considered to be small.

  The present invention is a plug electrode material that has high wear resistance due to high-temperature oxidation and spark consumption and can be used for a long period of time. The present invention can be applied to a plug that is applied to an automobile engine that is in a harsher environment with the aim of improving fuel consumption.

Claims (6)

A plug electrode material made of an Ir alloy to which Co and W, which are essential additive elements for Ir, are added,
The Ir alloy is a plug electrode material composed of 10 mass% to 30 mass% of Co, 5 mass% to 10 mass% of W, and the balance Ir. The plug electrode material according to claim 1, wherein the Ir alloy is an Ir alloy containing 0.005 to 0.1 mass% in total of at least one of B and C. The plug electrode material according to claim 1 or 2, wherein the Ir alloy is an Ir alloy containing 0.02 to 0.1 mass% in total of at least one of Re and Rh. The plug electrode material according to any one of claims 1 to 3, wherein the Ir alloy is an Ir alloy containing 0.003 to 0.02 mass% in total of at least one of Si and Ge. The Ir alloy is an Ir alloy containing 0.005 to 1.0 mass% in total of at least one of Al, V, Nb, Ta, Hf, Zr, and Ti. Plug electrode material. The plug electrode material according to any one of claims 1 to 5 , wherein the Ir alloy is an Ir alloy containing 0.003 to 0.2 mass% in total of at least one of La, Ce, and Y.