Lee Hsun Lecture Series    

Topic: Damage mechanisms and durability in very high cycle fatigue of Ni-based SX superalloys 

Speaker: Dr. Jonathan Cormier 

Associate Professor (HDR) at ISAE-ENSMA 

Editor of Metallurgical and Materials Transactions A 

Institut Pprime - Physics and Mechanics of Materials Department

Time: 10:00-12:00, (Tue.) Feb. 27th, 2024  

Venue: Room 403，Shi Changxu Building, IMR CAS  

Abstract 

Ni-based single crystal (SX) superalloys and now commonly used in the hot sections of aero-engines for blades and vanes. To reduce CO2 emissions and improve overall efficiency, new aero-engine designs require lighter components, higher spinning rate and hotter temperature leading to the use of Ni-based SX superalloys up to the low pressure turbine section for airfoils. Before being use, each new engine architecture has to be certified by airworthiness authorities. If the creep and low-cycle fatigue properties of Ni-based SX superalloys have been widely studied, there is no strict requirement in terms of LCF/creep failure from a certification point of view. However, it is mandatory to demonstrate that airfoils, whatever their thermo-mechanical history, will survive more than 10^7 cycles in fatigue, i.e. there is a certification requirement on (very) high cycle fatigue at their vibration frequency. Within this context, two ultrasonic fatigue machines have been developed at Institut Pprime/ISAE-ENSMA and an extensive database of more than 500 results has been generated, allowing to better understand failure mechanisms in VHCF and to develop lifing methodologies for a large variety of Ni-based SX superalloys (more than 10 alloys studied). In this presentation, failure mechanisms in fully-reversed conditions and under positive stress ratio at high temperature will be reviewed and fatigue life modeling will be detailed. The question of the fatigue limit in excess of 10^10 cycles will be discussed and some perspectives regarding the impact of environment/improved processing routes and stress concentrations will be proposed.