Evaluation of diffusion-bonded joints of austenitic alloys exposed to S-CO 2 environment

Abstract

Diffusion bonding is the key joining method of the micro-channel type heat exchangers for high temperature supercritical-CO 2 (S-CO 2 ) systems. In this study, diffusion-bonded joints of various 300-series austenitic stainless steels and Ni-base alloys were prepared. The tensile properties of diffusion-bonded specimens were evaluated from room temperature to 650 o C. Compared to base metals, loss of strength and ductility was greater for heat resistance alloys, especially for Alloy 800HT, which failed at the bond line at all test temperatures. For other alloys, diffusion-bonded specimens performed better at lower temperature. When the diffusion-bonded specimens were exposed to high temperature S-CO 2 up to 3,000 h, most austenitic stainless steels failed at the bond-line during tensile test. The microstructure near diffusion-bond line and fracture surface were examined before and after S-CO 2 exposure, and the results were compared with the observed tensile properties.