Study on Microstructure and Fatigue Properties of FGH96 Nickel-Based Superalloy

Abstract

In this study, using synchrotron radiation X-ray imaging, the microstructure, tensile properties, and fatigue properties of FGH96 nickel-based superalloy were tested, and the fatigue damage mechanism was analyzed. An analysis of the experimental results shows that the alloy structure is dense without voids or other defects. It was observed that the primary γ′ phase is distributed on the grain boundary in a chain shape, and the secondary γ′ phase is found inside the crystal grains. The X-ray diffraction (XRD) pattern indicates that no other phases were seen except for the γ and γ′ phases. The tensile strength of the alloy is 1570 MPa and the elongation is 12.1%. Using data fitting and calculation, it was found that the fatigue strength of the alloy under the condition of 5 × 106 cycles is 620.33 MPa. A fatigue fracture has the characteristics of secondary crack, cleavage step, fatigue stripe, tire indentation, and dimple. The fracture is a mix of cleavage fracture and ductile fracture. Through a three-dimensional reconstruction of the alloy synchrotron radiation imaging area, it was found that the internal defects are small and mostly distributed at the edge of the sample. The dimple morphology is formed by cavity aggregation and cavity germination resulting from defects in the material itself, fracture of the second-phase particles, and separation of the second-phase particles from the matrix interface. By analyzing the damage mechanism of fatigue fractures, it is concluded that the cleavage step is formed by the intersection of cleavage planes formed by branch cracks, with the main crack of the confluence extending forward to form a cleavage fracture. The crack propagation path was also analyzed, and under the action of cyclic load and tip passivation, the crack shows Z-shaped propagation.

Fatigue Behavior of the FGH96 Superalloy under High-Temperature Cyclic Loading

“…Shi et al [13,14] artificially introduced defects on smooth samples of FGH96 superalloy and studied the effect of surface defects on the fatigue life of the FGH96 superalloy. Bai et al [3] used synchrotron radiation X-ray imaging technology to test the fatigue performance of the FGH96 superalloy turbine disks to determine their fatigue life limit. However, most of the aforementioned literature focuses on macroscopic qualitative research on the FGH96 superalloy or the LCF life, lacking studies on the cyclic soft/hardening law under cyclic strain loading conditions and the ratcheting strain behaviors of the CFI under typical asymmetric stress loading conditions.…”

“…With the continuous improvement of aero-engine performances, the turbine inlet temperature, speed, and engine thrust continue to increase, and the load conditions of the turbine system become increasingly harsh, which puts higher requirements on the mechanical properties of the key hot end parts of the aero-engine [1][2][3]. Due to its unique formation process, uniform structure, lack of macro segregation, high yield and tensile strengths, good creep resistance, and fatigue resistance, the powder metallurgy superalloy has become the material of choice for aero-engine turbine systems [4].…”

“…With its excellent high-temperature mechanical properties, the FGH96 superalloy has been widely used in key hot-end components, such as aero-engine high-pressure turbine disks [5,6]. Aero-engine high-pressure turbine disks are subjected to a large number of high-temperature cyclic loads when they are used [3], and the resulting high-temperature low-cycle fatigue (LCF) damage and creep-fatigue interaction (CFI) damage are the main damage forms that limit their longevity and reliability.…”

“…Shi et al [13,14] artificially introduced defects on smooth samples of FGH96 superalloy and studied the effect of surface defects on the fatigue life of the FGH96 superalloy. Bai et al [3] used synchrotron radiation X-ray imaging technology to test the fatigue performance of the FGH96 superalloy turbine disks to determine their fatigue life limit.…”

Study on High-Temperature Low-Cycle Fatigue Behavior of the FGH96 Superalloy Based on Internal Stress Division

“…With the rapid development of aviation technology, the requirements for the thrustto-weight ratio, turbine speed, and other performance of aero-engines are constantly increasing. As a result, key components of aero-engines, such as turbine disks, are subjected to more severe and complex load conditions [1,2]. In order to meet the increasingly complex working conditions of aero-engine turbine disks and other core components, powder metallurgy superalloy materials have risen to the occasion.…”