Effects of metallurgical and environmental variables on the performance of alloy 718 for heat exchanger applications.

摘要

Austenitic Alloy 718 was extensively investigated, evaluating its tensile properties, crack-growth-rate (CGR), impact resistance, and resistance to stress-corrosion-cracking (SCC) and localized corrosion. The tensile data enabled a development of mechanisms on dynamic strain aging (DSA) and yield strength anomaly (YSA). The magnitudes of dislocation density, activation energy and work-hardening index, related to the DSA phenomenon, were estimated using different analytical approaches. The occurrence of YSA was verified based on transmission electron microscopic evaluations. The steady state CGR followed the Paris equation, showing a linear relationship. Alloy 718 exhibited a respectable impact resistance irrespective of the testing temperature. The SCC susceptibility of this alloy was enhanced in the 90°C acidic solution, showing reduced ductility and true failure stress. The corrosion potential, measured by polarization technique, became more active with increasing temperature. The failure morphologies of all tested specimens were characterized by scanning electron microscopy.