Creep behaviour of alloy 690 in the temperature range 800–1000 °C

Abstract

The creep behaviour of Ni-base superalloy 690 has been studied in the temperature range of 800–1000 °C, and stress range of 25–105 MPa under constant load creep conditions. The alloy follows a power-law creep behaviour in the tested conditions and obeys a Monkman-Grant relationship. All the creep data points lay within a ±5% scatter band of the Larson-Miller parameter vs. log stress plot. The alloy spent more than 50% of its life in the tertiary regime and failed predominantly by cavitation. Creep parameters, like apparent activation energy and stress exponent, were relatively high (∼363–498 kJ/mol and 5.5–7, respectively). A high value of the apparent activation energy has been attributed to the resistance of fine carbide particles that form during creep. The microstructural sub-structure of creep deformed samples shows subgrains separated by low angle grain boundaries and randomly oriented dislocations suggesting dislocation climb as the rate-controlling creep mechanism.

Keywords

• Alloy 690
• Creep behaviour
• Activation energy
• Stress exponent
• Creep deformation mechanism map
• Creep fracture