Tóm tắt

The influence of ageing heat treatment on alloy A-286 microstructure and stress corrosion cracking behaviour in simulated Pressurized Water Reactor (PWR) primary water has been investigated. A-286 microstructure was characterized byrntransmission electron microscopy for ageing heat treatments at 670 u0002C and 720 u0002C for durations ranging from 5 h to 100 h.rnSpherical c0 phase with mean diameters ranging from 4.6 to 9.6 nm and densities ranging from 8.5 · 1022 mu00023 torn2 · 1023 mu00023 were measured. Results suggest that both the c0 phase mean diameter and density quickly saturate with timernfor ageing heat treatment at 720 u0002C while the c0 mean diameter increases significantly up to 100 h for ageing heat treatmentrnat 670 u0002C. Grain boundary g phase precipitates were systematically observed for ageing heat treatment at 720 u0002C even forrnshort ageing periods. In contrast, no grain boundary g phase precipitates were observed for ageing heat treatments atrn670 u0002C except after 100 h. Hardening by c0 precipitation was well described by the dispersed barrier hardening model withrna c0 barrier strength of 0.23. Stress corrosion cracking behaviour of A-286 was investigated by means of constant elongation rate tensile tests at 1.5 · 10u00027 su00021 in simulated PWR primary water at 320 u0002C and 360 u0002C. In all cases, initiation wasrntransgranular while propagation was intergranular. Grain boundary g phase precipitates were found to have no significantrneffect on stress corrosion cracking. In contrast, yield strength and to a lesser extent temperature were found to havernsignificant influences on A-286 susceptibility to stress corrosion cracking.