Interface nanochemistry effects on stainless steel diffusion bonding

Abstract

The diffusion-bonding behavior of single-phase austenitic stainless steel depends strongly on the chemistry of the surfaces to be bonded. We found that very smooth (0.5 nm root-mean-square (RMS) roughness), mechanically polished and lapped substrates would bond completely in ultrahigh vacuum (UHV) in 1 hour at 1000 ЊC under 3.5 MPa uniaxial pressure, if the native oxide on the substrates was removed by ion-beam cleaning, as shown by in-situ Auger analysis. No voids were observed in these bonded interfaces by transmission electron microscopy (TEM), and the strength was equal to that of the unbonded bare material. No bond formed between the substrates if in-situ ion cleaning was not used. The rougher cleaned substrates partially bonded, indicating that roughness, as well as native oxides, reduced the bonding kinetics.

Effect of Surface Asperity on Diffusion Bonding

“…1,2) Ion beam bombardment removes the oxide film on the faying surface, thus lowering the bonding temperature. [1][2][3] Using Ar-beam surface treatment, some joints can be made even at room temperature, e.g. Al foils and Si wafaers.…”

Creep Behavior of Diffusion-Welded Alloy 617

“…The discrete Al-rich oxides along the interface restricted grain-boundary movement, leaving a planar grain boundary. Some researchers have emphasized that the evolution of stable surface oxides (film or discrete type) is a governing factor limiting metal-to-metal joining [34,36,38,39,[50][51][52][53][54].…”

Low temperature diffusion bonding of stainless steel

“…Solid state bonding evolved an alternate technique to join materials for special purposes where conventional welding is not applicable. Recently, many attempts have been made to join stainless steel (SS) by diffusion bonding technique [1][2][3][4][5]. Micro-duplex stainless steel has been joined by transient liquid phase bonding technique using Ni-Cu-B or Fe-B-Si ternary alloys as insert [1].…”

“…Ridley et al [3] have employed isostatic diffusion bonding in the lower temperature range of 1200 to 1320 K using a pressure of 2.8 MPa for 10 h to join micro-duplex stainless steel. Cox et al [2] employed solid state diffusion bonding technique to join stainless steel at a still lower temperature range (723 -1273 K). They concluded Keywords: diffusion bonding; stainless steel; interlayer; nanoindentation that good joint between stainless steel is obtained at 1273 K, with a pressure of 3.5 MPa and with extremely good surface finish of the steel faces.…”

“…Such elaborate surface preparation is expensive and limits the use of this technique. It is true that in solid state bonding techniques the properties of the joints get inferior with decrease in the bonding temperature [2,3] as diffusion is favored at higher temperatures. But, in special situations where high heat input cannot be accepted and for joints which do not demand superior mechanical properties, a lower temperature of bonding may prove advantageous.…”