Thermal stress-based diffusion bonding method: The case of oxygen free copper to 316L stainless steel

Abstract

Fixture composed of 304 stainless steel (SUS304) and 440C stainless steel (SUS440C) was employed for inducing the thermal stress to 316L stainless steel and oxygen free copper (SUS316L/OFC) cylinders to achieve diffusion bonding. For comparison, the same combination was bonded using the conventional diffusion bonding method, i.e. heating in vacuum under constant pressure. Although the thermal stress-based diffusion bonding is conducted in charcoal-reformed air, the bonding starts from 673 K. This temperature is relatively low as compared with the conventional method (873 K). Furthermore, the joint fabricated using the thermal stress-based method exhibits higher joint efficiency than one prepared using the conventional method. The highest tensile strength is attained at 1073K and comparable to one of OFC. The bonding deformation of the thermal stress-based method is smaller than with the conventional method, since the fixture does not apply excess pressure to the diffusion couple. Thus the thermal stress-based diffusion bonding method is a promising and may be superior to the conventional method from view points of simplicity and bondability.