| 摘要 |
A spark plug has stress reduction layers (61, 62) with intermediate expansion coefficient and low elasticity modulus values compared with those of its iridium alloy contacts (51, 52) and associated nickel alloy electrode sections (3a, 4a). A spark plug has a stress reduction layer (61, 62) between each iridium alloy contact tip (51, 52) and the associated nickel alloy tip attachment section (3a, 4a) of the earth or center electrode. The novelty is that: (a) the stress reduction layer has a linear expansion coefficient between those of the Ir alloy and the Ni alloy and an elasticity modulus smaller than those of the Ir alloy and the Ni alloy; (b) the stress reduction layer has a linear expansion coefficient between those of the Ir alloy and the Ni alloy and the resistance welded joint interface between the tip and its associated stress reduction layer is in the form of a curved surface; or (c) each tip comprises several discs, each of which is resistance welded to the associated stress reduction layer. An Independent claim is also included for processes for producing the above spark plugs having curved resistance welded joint interfaces between the tips and the associated stress reduction layers. Preferred Features: Each stress reduction layer consists of a Pt-Ir-Ni alloy layer of composition 65-89 wt.% Pt, 10-30 wt.% Ir and 1-5 wt.% Ni or consists of a tip-side Pt-Ir alloy layer and an attachment section-side Pt-Ni alloy layer.
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