Role of TiN inclusion on corrosion fatigue behavior of Alloy 690 steam generator tubes in borated and lithiated high temperature water

• Boat-shaped sample was used to study LCF behavior of Alloy 690 SG tubes.
• TiN and Al2O3/MgO inclusions were found in Alloy 690 SG tubes.
• Broken TiN and TiN clusters facilitated CF crack initiation and propagation.
• Inclusion-involved fatigue cracking mechanisms for Alloy 690 SG tubes were proposed.

Influence of TiN inclusion on corrosion fatigue behavior of three types of as-received Alloy 690 steam generator tubes (J, C1 and C2) in borated and lithiated high temperature water was investigated. The volume fraction of inclusions in tube J, C1 and C2 were about 0.0894%, 0.0384% and 0.1843%. The fatigue life of tube C2 was slightly shorter than that of tube J and C1. Large broken TiN inclusions and TiN-inclusion clusters played a significant role on fatigue crack initiation and propagation for tube C2 in high temperature water. The inclusion-involved fatigue cracking mechanisms are discussed.