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. 2019 Nov 30;12(23):3979.
doi: 10.3390/ma12233979.

Effects of the γ″-Ni3Nb Phase on Fatigue Behavior of Nickel-Based 718 Superalloys with Different Heat Treatments

Li-Shi-Bao Ling  1 , Zheng Yin  1   2 , Zhi Hu  2 , Jun Wang  1 , Bao-De Sun  1
Affiliations

Effects of the γ″-Ni3Nb Phase on Fatigue Behavior of Nickel-Based 718 Superalloys with Different Heat Treatments

Li-Shi-Bao Ling et al. Materials (Basel). .

Abstract

The effects of the γ″-Ni3Nb phase on fatigue behavior of nickel-based 718 superalloys with standard heat treatment, hot isostatic pressing + solution treatment + aging, and hot isostatic pressing + direct aging were investigated by scanning electron microscope, transmission electron microscopy, and fatigue experiments. The standard heat treatment, hot isostatic pressing + solution treatment + aging, and hot isostatic pressing + direct aging resulted in the formation of more and smaller γ″ phases in the matrix in the nickel-based 718 superalloys. However, the grain boundaries of the hot isostatic pressing + direct aging sample showed many relatively coarse disk-like γ″ phases with major axes of ~80 nm and minor axes of ~40 nm. The hot isostatic pressing + direct aging sample with a stress amplitude of 380 MPa showed the longest high cycle fatigue life of 5.16 × 105 cycles. Laves phases and carbide inclusions were observed in the crack initiation zone, and the cracks propagated along the acicular δ phases in the nickel-based 718 superalloys. The precipitation of fine γ″ phases in the matrix and relatively coarse γ″ phases in the grain boundaries of the hot isostatic pressing + direct aging sample can hinder the movement of dislocation.

Keywords: fatigue behavior; heat treatment; hot isostatic pressing; nickel-based 718 superalloy; γ″-Ni3Nb.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Schematic geometry of fatigue testing specimens: (a) high cycle fatigue (ASTM E466); (b) low cycle fatigue (ASTM E606).
Figure 2
Figure 2
X-ray diffraction patterns of the nickel-based 718 superalloys after different heat treatments.
Figure 3
Figure 3
Optical microstructures of nickel-based 718 superalloys after different heat treatments: (a) as-cast, (b) standard heat treatment (SHT), (c) hot isostatic pressing + solution treatment + aging (HIP + STA), (d) hot isostatic pressing + direct aging (HIP + DA).
Figure 4
Figure 4
SEM images of the HIP + DA nickel-based 718 superalloy: (a) γ″ phases in the interdendritic, (b) γ″ phases in the grain boundaries.
Figure 5
Figure 5
TEM bright field images and selected area electron diffraction patterns of the nickel-based 718 superalloys: (a) acicular δ phase, (b) angular carbide particle.
Figure 6
Figure 6
TEM images of the γ″ phase in samples using the (010) and (1/210) reflections in {001} orientation: (a) dark field (DF) image of SHT sample; (b) DF image of HIP + STA sample; (c) DF image of HIP + STA sample; (d) SAED pattern of γ″ phase.
Figure 7
Figure 7
The high cycle fatigue life of the SHT, HIP + STA, and HIP + DA nickel-based 718 superalloys under different stress levels.
Figure 8
Figure 8
The low cycle fatigue life of the SHT, HIP + STA, and HIP + DA nickel-based 718 superalloys: (a) the fatigue life; (b) the stress amplitude.
Figure 9
Figure 9
Fatigue crack initiation zone of the nickel-based 718 superalloys after a fatigue test of 380MPa: (a) SHT; (b) HIP + STA; (c) HIP + DA.
Figure 10
Figure 10
The fatigue crack propagation zone of the nickel-based 718 superalloys after a fatigue test of 380 MPa: (a) SHT; (b) HIP + STA; (c) HIP + DA.
Figure 11
Figure 11
The final fracture zone of the nickel-based 718 superalloys after fatigue test of 380 MPa: (a) SHT; (b) HIP + STA; (c) HIP + DA.
Figure 12
Figure 12
TEM dark field images of the HIP + DA nickel-based 718 superalloy after a fatigue test of 380 MPa: (a) small γ″ phases in the matrix, (b) relatively coarse γ″ phases.
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