Spark plug having iridum alloy tip, iron-based alloy tip bonding portion and stress relieving layer therebetween

摘要

A spark plug having a tip composed of an iridium alloy essentially consisting of iridium is resistance welded through a relieving layer to a front end of a center electrode having an iron-based alloy and a facing portion of a ground electrode and wherein the material of the relieving layer has a coefficient of linear expansion between the iridium alloy and the iron-based alloy and has a Young's modulus of elasticity smaller than that of the two alloys.