Complex Oxide Layer at a Nickel/Steel Interface Bonded under a Moderate Vacuum Condition

Abstract

Microstructures of a nickel/austenitic-steel (AISI304) interface, which has been bonded through in-situ cold-rolling of clean surfaces (pre-sputtered by argon ion) within a vacuum apparatus (~10 -3 Pa), then followed by an annealing at 500°C, are investigated by transmission electron microscopy. We frequently find significant traces of thin oxide layers of 5-10 nm in thickness, which commonly reveal complex microstructures composed of bi-layers of different types of oxides. Origin of such interface oxides is presumably due to a slight oxygen contamination of the sputtered-surface in the present moderate vacuum condition, and the oxide precipitation at the bonded-interface has been promoted during annealing. Concerning that the strength of the present Ni/steel cold-rolled interface remarkably increases during an early stage of the annealing at 500°C, it is concluded that their strong interface bonding is supported both by nanometeric oxide-layers as well as direct metal/metal contacts. KEY WORDS: interface structure; surface activated bonding (SAB); scanning transmission electron microscopy; diffusion bonding.