Effect of interdiffusion on mechanical and thermal expansion properties at high temperature of a MCrAlY coated Ni-based superalloy

Free-standingmicrotensile specimens were extracted fromthe substrate and the interdiffusion zone of a MCrAlY coated nickel-based single-crystal superalloy. Testing of these specimens was conducted at elevated temperatures, up to 1100 °C under controlled atmosphere, to assess the tensile and thermal expansion properties of the interdiffusion zone materials. These properties were measured and found to lie between the properties of the substrate and those of the coating. The poor mechanical strength of the interdiffusion zone evidenced its non-load bearing contribution to the system for uniaxial creep loading at high temperature representative of service conditions. It was also shown that the fabrication process of MCrAlY coated nickel-based superalloy affects the mechanical properties of the system due to the presence of voids and non-adherent grit-blasting particles within the interdiffusion zone

Creep behaviour of a nickel-based single crystal superalloy at the dendritic scale using micro-tensile specimen

International audienceBecause of their resistance to high temperature creep and fatigue, single crystal superalloys are the most suitable materials for the design of high performance turbine blades. Processing of these alloys induces macroscopic heterogeneities, such as dendrites, whose size is comparable to the thickness of the thinnest blades walls. Mechanical behaviour of “bulk” commercial single crystal superalloys has been widely investigated. However, local high temperature creep behaviour hasn’t been characterised at the scale of microstructural and chemical heterogeneities until now. In the present study, differences in the g/g’ microstructure have been observed and correlated with chemical variation from dendritic cores to interdendritic regions. Furthermore, microtensile specimens, thinner than the size of dendritic motifs, were prepared and will be tested at 1100°C

Creep behaviour of a nickel-based single crystal superalloy at the dendritic scale using micro-tensile specimen

International audienceBecause of their resistance to high temperature creep and fatigue, single crystal superalloys are the most suitable materials for the design of high performance turbine blades. Processing of these alloys induces macroscopic heterogeneities, such as dendrites, whose size is comparable to the thickness of the thinnest blades walls. Mechanical behaviour of “bulk” commercial single crystal superalloys has been widely investigated. However, local high temperature creep behaviour hasn’t been characterised at the scale of microstructural and chemical heterogeneities until now. In the present study, differences in the g/g’ microstructure have been observed and correlated with chemical variation from dendritic cores to interdendritic regions. Furthermore, microtensile specimens, thinner than the size of dendritic motifs, were prepared and will be tested at 1100°C

Impact of microstructural evolutions during thermal aging of Alloy 625 on its monotonic mechanical properties

Alloy 625 is widely used for petrochemical, marine and aerospace applications owing to its outstanding corrosion and mechanical properties at high temperatures. However, this alloy is prone to complex microstructure evolutions above 500 ∘C that may impact its mechanical properties. In this study, the impact of its microstructure evolutions occurring upon thermal aging on the monotonic mechanical properties has been studied. Thermal exposures of up to ∼2000 hours in the 550 ∘C – 900 ∘C temperature range have been investigated. TTT diagrams of the δ and γ′′ phases were established based on high resolution scanning electron microscopy observations. The evolutions of secondary carbides distributions were also followed. It has been observed a steep increase of the room temperature micro-hardness after overagings performed at 650 ∘C and 700 ∘C due to the precipitation of the γ′′ phase. Moreover, it is clearly demonstrated a strengthening effect of the δ phase observed after long term thermal exposures at temperatures in excess of 700 ∘C. Finally, the impact of a thermal aging in the γ′′ precipitation domain on the tensile properties was evaluated from room temperature up to 800 ∘C. It is shown that the loss of high temperature ductility is not correlated to the precipitation of grain boundary secondary carbides

High temperature low cycle fatigue properties of alloy 625

International audienceThe impact of a thermal overaging at 650 °C on Alloy 625 high temperature low cycle fatigue (LCF) and tensile properties was investigated. This prior thermal aging in the γ“ precipitation domain improve both the tensile properties in the 20–750 °C temperature range (Tensile resistance and Yield stress) and the LCF lifetime at 650 °C. The improvements in monotonic and LCF properties compared to the samples without any prior aging are provided by the γ” structural hardening which limits the cyclic ratcheting during LCF tests. In addition, using a combination of strain-controlled LCF experiments, interrupted stress-controlled LCF experiments followed by a tensile tests and microstructure inspections, it is shown that the microstructure of Alloy 625 without any prior aging is unstable during LCF solicitation and that the γ″ precipitation as well as the γ″→δ transformation are occurring during mechanical cycling, affecting the mechanical behavior of the alloy

Development and use of a new burner rig facility to mimic service loading conditions of Ni-based single crystal superalloys

Performing representative experiments of in-service operating conditions of Ni-based superalloys used as high pressure turbine blades in aeroengines is a challenging issue due to the complex environmental, mechanical and thermal solicitations encountered by those components. A new burner rig test facility called MAATRE (French acronym for Mechanics and Aerothermics of Cooled Turbine Blades) has been developed at ENSMA – Pprime Institute to mimic as close as possible those operating conditions. This new test bench has been used to perform complex non-isothermal creep tests representative of thermomechanical solicitations seen by some sections of HP turbine blades during engine certification procedure

Development and use of a new burner rig facility to mimic service loading conditions of Ni-based single crystal superalloys

Performing representative experiments of in-service operating conditions of Ni-based superalloys used as high pressure turbine blades in aeroengines is a challenging issue due to the complex environmental, mechanical and thermal solicitations encountered by those components. A new burner rig test facility called MAATRE (French acronym for Mechanics and Aerothermics of Cooled Turbine Blades) has been developed at ENSMA – Pprime Institute to mimic as close as possible those operating conditions. This new test bench has been used to perform complex non-isothermal creep tests representative of thermomechanical solicitations seen by some sections of HP turbine blades during engine certification procedure