Microstructure and Mechanical Properties of Inconel 718 Powder Alloy Prepared by Hot Isostatic Pressing
XU Lei1(), TIAN Xiaosheng1,2, WU Jie1, LU Zhengguan1, YANG Rui1
1Shi -changxu Innovation Center for Advanced Materials, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China 2School of Materials Science and Engineering, University of Science and Technology of China, Shenyang 110016, China
Cite this article:
XU Lei, TIAN Xiaosheng, WU Jie, LU Zhengguan, YANG Rui. Microstructure and Mechanical Properties of Inconel 718 Powder Alloy Prepared by Hot Isostatic Pressing. Acta Metall Sin, 2023, 59(5): 693-702.
Inconel 718 alloy, with outstanding high-temperature resistance and mechanical properties, has been widely used in aviation fields. However, large and complex structural components are difficult to produce by traditional processes, which may lead to segregation, micropores, and Laves phases. Net-shape hot isostatic pressing (HIP) is a powder metallurgy processing technology that produces near-shape or net-shape components with the desired microstructures, properties, and cost effectiveness. In this study, Inconel 718 pre-alloyed powder was prepared using the electrode induction melting gas atomization technique, and then the pre-alloyed powder was characterized. Powder compacts were prepared by the HIP of the pre-alloyed powder, and their mechanical properties were tested. Although clean, high-quality powder can be obtained from Inconel 718 alloy due to its lower chemical reactivity compared to titanium alloys, carbide-forming elements diffuse to the powder surface during HIP. These form a hard film with the original oxide particles as nuclei, consisting of Ni3Nb and carbides of Ti and Nb. These films become prior particle boundaries (PPBs) in the obtained powder metallurgy Inconel 718 alloy, resulting in lower ductility, toughness, and stress rupture life than those of the wrought version of the alloy. Suppressing the formation of the PPBs during HIP or eliminating them via subsequent processing significantly improves the comprehensive mechanical properties of the material.
Fund: National Science and Technology Major Project of China(J2019-VII-0005-0145);Strategic Priority Research Program of the Chinese Academy of Sciences(XDA22010102);CAS Project for Yo-ung Scientists in Basic Research(YSBR-025)
Fig.1 Geometric dimensions of special-shaped cylindrical capsule (unit: mm)
Fig.2 Differential size distributions of Inconel 718 pre-alloyed powders (D10, D50, and D90 indicate 10%, 50%, and 90% cumulative particle sizes, respectively)
Fig.3 XRD spectrum of Inconel 718 pre-alloyed powders
Fig.4 SEM images of Inconel 718 pre-alloyed powders in full view (a) and high-magnification of Fig.4a (b)
Fig.5 Powder metallurgical (PM) Inconel 718 component partial photo (a) and room temperature tensile fracture (Inset shows the magnified image) (b)
Sample
Temperature
Tensile property
Impact property
Stress rupture life
UTS / MPa
YS / MPa
El / %
Z / %
J
h
Wrought[19]
RT
1275-1400
1030-1167
12-21
15.0
30
-
Component
RT
1273
1086
4.5
4.0
8
-
Test bar
RT
1321
1044
15.0
13.0
35
-
Wrought[19]
650oC
1000-1200
860-1000
12-19
15.0
-
≥ 25
Component
650oC
1164
927
4.0
4.0
-
26
Test bar
650oC
1180
997
13.0
19.0
-
37
Table 1 Mechanical properties of PM Inconel 718 component and test bars
Fig.6 Simulation results of relative density of Inconel 718 powder alloy at different locations of special-shaped cylindrical capsule
Fig.7 Tensile properties of PM Inconel 718 alloys at room temperature (a) and 650oC (b)
Fig.8 Industrial computerized tomography (CT) (a) and Micro-CT (b) analyses of PM Inconel 718 alloys
Fig.9 Microstructures of Inconel 718 component (White dotted circles represent prior particle boundaries (PPBs)) (a), and test bars (b) and high magnification morphology of PPBs (c), and the EDS analyses of PPBs (d, e)
Point
Phase
C
Al
Ti
Cr
Fe
Ni
Nb
O
1
MC
14.27
0.10
11.11
6.18
5.06
12.29
50.99
-
2
δ
6.67
0.88
10.33
16.14
14.21
35.81
14.97
0.99
Table 2 EDS results at the prior particle boundaries of Inconel 718 parts
Fig.10 SEM fractographs of component (a) and SEM image of longitudinal sections near the fractures of tensile samples (b)
Fig.11 Relationships between the proportion of PPBs area and the mechanical properties of the alloys from various PM Inconel 718 powders
Fig.12 Microstructures of PM Inconel 718 alloys with particle sizes of fine (a) and coarse (b) (Insets show the particle size distributions of the powder used)
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