The effect of porosity size on the high cycle fatigue life of nickel-based single crystal superalloy at 980 °C

In the present study, a superalloy round tube specimen prepared by directional precision casting without mechanical turning is experimentally investigated under the thermomechanical fatigue conditions of the in-phase and out-ofphase thermomechanical angels from 500 C to 1000 C. The deformation behavior and damage mechanism of the round tube specimens under TMF load are discussed. It was confirmed that the tension-compression asymmetry under TMF cycling is affected by temperature-load phasing and mechanical strain range. Moreover, the damage to round tube specimens includes creep, fatigue and oxidation. Due to the concentrated stress, the rough surface of the specimen provides suitable locations for crack initiation. A novel life prediction approach that combines the Neu-Sehitoglu model and modified Manson-Coffin model was proposed in response to the traditional life model's insufficient prediction performance. This method may explain the TMF life of precision cast specimens.

Section: Resultsmentioning

confidence: 96%

Section: Microstructuresmentioning

confidence: 99%

Thermomechanical fatigue of round tube specimens manufactured by precision directional solidification casting method

Song

Shen

Teng

et al. 2022

“…The test material was the second-generation nickel-base single-crystal superalloy DD5 made in China. 43 Compared to the first generation, the high-temperature resistance of DD5 has been further enhanced thanks to the introduction of refractory element Re (3%). The nominal composition of the alloy is given in Table 1.…”

Section: Materials and Specimenmentioning

confidence: 99%

“…Murakami's theory has laid the foundations for the research on the fatigue behavior of metallic materials that contain small defects and non-metallic inclusions. 39 Based on the available knowledge, [40][41][42][43] this paper focuses on the S-N curve dispersion of NBSX DD5 caused by pore size distribution. A porosity-distribution-related life prediction model is proposed, and the test results are used for validation.…”

Section: Introductionmentioning

confidence: 99%

The porosity distribution of nickel‐base single‐crystal superalloy DD5 and its fatigue life property

Susmel

Jiang³

et al. 2023

Self Cite

The porosity of nickel-base single crystals (NBSXs) is still an unavoidable casting problem that has a significant influence on the fatigue life of NBSXs. In order to quantify the porosity effect, a porosity-distribution-related life prediction method is proposed in this paper. The porosity size in a NBSX was measured, and the size distribution was regressed. The results show that the porosity size that is characterized by Feret's diameter follows a modified logarithmic normal distribution. The relation among the applied stress, porosity size, and lifetime is expressed by using the proposed method. The disperse band of S-N curve is investigated based on the probability distribution of the porosity size. The results show that the predicted S-N curve agrees well with the experimental data.

“…30 Jiang et al found the pore defect size is the dominant parameter controlling fatigue life of nickel-based single crystal superalloys. 35 Kevinsanny et al investigated the effect of different defects on the fatigue limit of Inconel 718. 36 Besides, the microstructure has a strong influence on the fatigue crack growth behavior, causing the fatigue crack growth rate to fluctuate in the initial stage.…”

Section: Introductionmentioning

confidence: 99%

Effect of texture evolution and defect on the crack initiation of a Ni‐based superalloy electron beam welded joint

Wen,

Liu,

Jiang

et al. 2023

Electron beam welding (EBW), a high‐quality and precise joining process, is widely used in aerospace manufacturing. In this study, through in situ scanning electron microscope (SEM) fatigue experiments and X‐ray computed tomography (CT) scanning technology, we revealed the fatigue crack initiation and propagation mechanism in GH4169 superalloy EBW joints under different post‐welding heat treatment conditions. The welded pores have a decisive effect on the fatigue properties of direct aging treatment welded joints. Fatigue cracks initiate from pore defects on the surface or in the subsurface. Due to the heterogeneous microstructure in weld seam, fatigue cracks tend to grow along the primary dendrite axis and secondary dendrite arms. Besides, in homogenization and aging treatment specimen, intergranular fatigue cracks tend to nucleate in the slip zone of large grains and twin boundaries. Although homogenization treatment can eliminate segregation, it also results in significant grain growth in both weld seam and base material.