JPH0548598B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a spark plug that is used in internal combustion engines such as automobiles and has excellent wear resistance. (Prior art) Pt alloys, such as Pt-Ir and Pt, have traditionally been used for the spark discharge part of the center electrode and ground electrode of spark plugs.
It is known to extend the life of a spark plug by joining thin plates (chips) or precious metal blocks made of precious metal materials such as -Rh, Pt-Ni, Pt-Pd, Pt-Ru, etc. by electric welding or the like. Among these, Pt-Ni alloys have linear expansion coefficients close to those of Ni-based alloys and base metals, and thermal stress caused by repeated heating and cooling of combustion gas can cause platinum chips and platinum ingots to peel off from the base metal. This material is suitable for platinum electrodes for spark plugs. (Problem to be solved by the invention) However, this Pt-Ni alloy has a working temperature of 1000
If the temperature is extremely high, above ℃, coarsening of crystal grains will easily occur, and thermal strain caused by repeated cooling and heating cycles will cause embrittlement and cracking of grain boundaries, leading to erosion. This kind of metal parts may melt or fall off due to overheating.
It is necessary to improve the high temperature strength of Pt alloys and suppress grain coarsening. (Means for Solving the Problems) The present invention aims to solve the problem of intergranular cracking by improving the strength of Pt-Ni alloys at high temperatures, suppressing grain coarsening, and maintaining grain refinement. It is used as a spark discharge part of an electrode whose base metal is a Ni-based alloy or as an intermediate layer to be bonded to the base metal.
Pt-Ni alloy contains 5 to 40% Ni by weight, Ca, Ba, Nb,
At least one type of oxide of the element Mg 0.05 to 1.0
By using an alloy material consisting of % by weight and the balance being Pt, the present invention aims to provide a spark plug that is highly durable and has a long service life. (Example) The present invention will be specifically described in detail below. 1 and 2 are sectional views of main parts of the ignition part of a typical spark plug of the present invention, in which 1 is a metal shell equipped with an engine mounting screw, and 2 is a metal shell 1 and a lumen inside the metal shell 1. An insulator made of high alumina porcelain or the like is sealed and fixed in the shaft hole of the insulator 2, and 3 is a Ni-based alloy, such as Ni-Si, with a Cu core arranged inside the insulator 2, which is sealed and protrudes from the tip surface of the shaft hole of the insulator 2. -Cr-Al alloy, Ni
- A center electrode made of a base metal such as Cr-Fe alloy (Inconel); 4 is the tip 3a of the center electrode 3;
The spark discharge part is made of Pt-Ni alloy material. Reference numeral 5 denotes a ground electrode made of a Ni-based alloy base metal similar to the center electrode base material, which protrudes from the end surface 1a of the metal shell 1. Reference numeral 6 denotes a spark discharge portion of the ground electrode 5, which is also made of Pt-Ni. The spark discharge part 6 is a spark plug in which a spark gap 7 is formed between the center electrode 3 and the spark discharge part 4. The present invention also provides a central electrode 3 as shown in FIG.
And the spark discharge parts 8 and 9 of the ground electrode 5 are made of Pt-Ir (20% Ir) and Pt-Pd (30% Ir), which have excellent wear resistance.
The spar plug is made of Pd) or the like, and the intermediate layers 10 and 11, which are bonded to the respective base materials, are made of a Pt-Ni alloy material. In these examples, the precious metal material is formed on both the center electrode and the ground electrode, but depending on the characteristics of the engine, the electrode temperature, and the power supply polarity, the precious metal material may be formed on only one of them, or Pt may be formed on either one of them. -Ni alloy material and Pt alloy material with excellent wear resistance can be used in combination. The Pt-Ni alloy material of the present invention used for the spark discharge parts 4, 6 of the base metal electrode or the intermediate layers 10, 11 which are the joint surfaces with the base metal includes 5 to 40% by weight of Ni,
By using an oxide-dispersed alloy consisting of 0.05 to 1.0% by weight of at least one of the oxides of elements consisting of Ca, Ba, Nb, and Mg, and the balance being Pt, coarsening of crystal grains at high temperatures can be suppressed. It was discovered that this method is effective in preventing boundary cracking. In the present invention, the amount of Ni added to the Pt-Ni alloy is limited to 5 to 40% by weight.
Large thermal expansion difference with Ni-based alloy base material, 40% by weight
This is because, although the difference in thermal expansion is small and the adhesion is good in the case above, the oxidation resistance of the alloy itself is significantly deteriorated due to the increase in Ni. In addition, at least one of the oxides of the elements Ca, Ba, Nb, and Mg was specified at 0.05 to 1.0% by weight to suppress crystal grain coarsening.
If it is less than 1.0% by weight, a sufficient grain refining effect cannot be obtained, and if it is more than 1.0% by weight, workability (wire drawability, rollability) will deteriorate significantly, making it impossible to obtain a stable product. . Example 1 As shown in Table 1, Ca, Ba,
CaO, BaO, which are oxides of the elements Nb and Mg,
An alloy material with Nb ₂ O ₅ and MgO added and dispersed was used, and this was inserted into the concave tip of a Ni-based alloy (Inconel 600) base material electrode with a diameter of 1 mmφ, respectively.
×Thickness 0.4 mm Samples No. 1 to No. 15 were joined by resistance welding and the performance was compared. In addition, as a performance evaluation, the crystal grain size (based on austenite grain size) after heat treatment at 1100℃ x 10 hours in the air and the burner
1100℃ x 1 minute heating and cooling 1 minute (up to about 200℃) x
Comparison was made by intergranular cracking after 3000 cycles.

[Table] The test results are as shown in Table 1.
No. 1 easily coarsens the crystal grains at high temperatures;
A large crack appeared due to intergranular cracking after 3000 cycles. On the other hand, in the Pt-Ni alloy of the present invention, CaO,
No. 2 to which oxides of BaO, Nb ₂ O ₅ and MgO were added
All of the No. 15 samples had less coarsening and finer grains, and microcracks were observed in the No. 2 sample even after 3000 cycles of cold and hot cycles, but no abnormalities were observed in the other samples. It was in good condition. In addition, in the spark plug of the present invention, the form of the noble metal material in the spark discharge part of the electrode is not limited to the thin plate embodiments shown in FIGS. 1 and 2. 3 or a spark plug in which precious metal lumps 14, 16 (rod-shaped pieces) are fixed to the tip of the ground electrode 5, or a spark plug in which a precious metal material is arranged on the tip periphery side 17 or the tip periphery of the center electrode 3 as shown in FIG. The present invention can be applied to spark plugs with various electrode shapes, such as spark plugs or semi-climbing spark plugs in which a ground electrode 5 is provided facing the tip periphery side or between the tip periphery. (Effects of the Invention) As described above, the spark plug of the present invention contains at least oxides of the elements Ca, Ba, Nb, and Mg as a third additive in the Pt-Ni alloy used for the spark discharge part or the intermediate layer with the base electrode. By using an alloy material in which 0.05 to 1.0% by weight of 1 type is added and dispersed, it maintains good adhesion to the conventional Ni-based alloy base material electrode and has a remarkable effect of suppressing crystal grain coarsening at high temperatures. Therefore, it is possible to provide a long-life plug with excellent durability and stable quality even in cold and hot cycles.

[Brief explanation of the drawing]

1 to 4 are enlarged sectional views of main parts of the ignition part of a spark plug showing an embodiment of the present invention. 3... Center electrode, 5... Ground electrode, 4, 6,
8, 9, 14, 16, 17...Spark discharge section, 1
0,11...middle class.

Claims (1)

[Claims] 1 Pt as the spark discharge part of at least one of the center electrode and the ground electrode whose base metal is Ni-based alloy.
- Use a Pt alloy with excellent wear resistance as the spark plug fixed with Ni-based alloy or the spark discharge part, and also use Pt alloy between this Pt alloy and the base metal.
- In a spark plug with an intermediate layer made of a Ni-based alloy, Ni5 to 40 is used as the Pt-Ni-based alloy.
1. A spark plug characterized by using an alloy material consisting of 0.05 to 1.0% by weight of at least one oxide of the elements Ca, Ba, Nb, and Mg and the balance being Pt.