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Frontiers of Mechanical Engineering

Front. Mech. Eng.    2018, Vol. 13 Issue (2) : 243-250     https://doi.org/10.1007/s11465-018-0479-9
RESEARCH ARTICLE
Experimental study of surface integrity and fatigue life in the face milling of Inconel 718
Xiangyu WANG1,2, Chuanzhen HUANG1,2(), Bin ZOU1,2, Guoliang LIU1,2, Hongtao ZHU1,2, Jun WANG1,2,3
1. Centre for Advanced Jet Engineering Technologies (CaJET), School of Mechanical Engineering, Shandong University, Jinan 250061, China
2. Key Laboratory of High-efficiency and Clean Mechanical Manufacture (Shandong University), Ministry of Education, Jinan 250061, China
3. School of Mechanical and Manufacturing Engineering, UNSW Australia, Sydney, NSW 2052, Australia
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Abstract

The Inconel 718 alloy is widely used in the aerospace and power industries. The machining-induced surface integrity and fatigue life of this material are important factors for consideration due to high reliability and safety requirements. In this work, the milling of Inconel 718 was conducted at different cutting speeds and feed rates. Surface integrity and fatigue life were measured directly. The effects of cutting speed and feed rate on surface integrity and their further influences on fatigue life were analyzed. Within the chosen parameter range, the cutting speed barely affected the surface roughness, whereas the feed rate increased the surface roughness through the ideal residual height. The surface hardness increased as the cutting speed and feed rate increased. Tensile residual stress was observed on the machined surface, which showed improvement with the increasing feed rate. The cutting speed was not an influencing factor on fatigue life, but the feed rate affected fatigue life through the surface roughness. The high surface roughness resulting from the high feed rate could result in a high stress concentration factor and lead to a low fatigue life.

Keywords roughness      hardness      residual stress      microstructure      fatigue life     
Corresponding Author(s): Chuanzhen HUANG   
Just Accepted Date: 24 November 2017   Online First Date: 29 December 2017    Issue Date: 16 March 2018
 Cite this article:   
Xiangyu WANG,Chuanzhen HUANG,Bin ZOU, et al. Experimental study of surface integrity and fatigue life in the face milling of Inconel 718[J]. Front. Mech. Eng., 2018, 13(2): 243-250.
 URL:  
http://journal.hep.com.cn/fme/EN/10.1007/s11465-018-0479-9
http://journal.hep.com.cn/fme/EN/Y2018/V13/I2/243
Material grades Yield strength
s0.2/MPa
Tensile strength
sb/MPa
Elongation/% Hardness/HRC Average grain size (grade)
Inconel 718 1093 1295 14 42 8
Tab.1  Mechanical properties of the workpiece
No. v/(m•min–1) fz/(mm•tooth–1) ap/mm ae/mm
1 30 0.10 0.3 55
2 45 0.10 0.3 55
3 60 0.10 0.3 55
4 75 0.10 0.3 55
5 90 0.10 0.3 55
6 45 0.15 0.3 55
7 45 0.20 0.3 55
8 45 0.25 0.3 55
Tab.2  Cutting parameters for the face milling experiments
Fig.1  Schematic diagram of the three-point bending fatigue life test
Fig.2  3D morphologies and surface roughness profiles of the workpiece surface when machined at different cutting speeds. The unit of the values is μm. (a) v=45 m/min, fz=0.1 mm/tooth; (b) v=90 m/min, fz=0.1 mm/tooth
v/(m•min?1) Rp/mm Rv/mm Rz/mm Ra/mm Rc/mm Rsk Rku
30 0.74 0.72 1.46 0.19 0.97 0.05 2.84
45 0.63 0.58 1.32 0.16 0.85 0.08 2.69
60 0.49 0.63 1.11 0.16 0.83 −0.07 2.71
75 0.60 0.65 1.25 0.16 0.93 −0.34 2.94
90 0.58 0.80 1.38 0.17 0.97 −0.44 3.47
Tab.3  Surface roughness at different cutting speeds
fz/(mm•tooth?1) Rp/mm Rv/mm Rz/mm Ra/mm Rc/mm Rsk Rku
0.1 0.63 0.58 1.32 0.16 0.86 0.08 2.69
0.15 0.85 0.85 1.69 0.28 1.35 0.00 2.22
0.2 0.97 1.09 2.06 0.40 1.70 −0.17 1.98
0.25 1.19 1.31 2.50 0.51 2.02 −0.11 2.05
Tab.4  Surface roughness at different feed rates
Fig.3  Surface hardness of workpiece when machined at different cutting parameters
Fig.4  Cross-section microstructures at different cutting speeds. (a) 30 m/min; (b) 60 m/min; (c) 90 m/min (no white layer); (d) 90 m/min (with white layer)
Fig.5  Cross-section microstructures at different feed rates. (a) 0.1 mm/tooth; (b) 0.2 mm/tooth
Fig.6  Surface residual stress at different cutting speeds (fz=0.1 mm/tooth)
Fig.7  Surface residual stress at different feed rates (v=45 m/min)
Fig.8  Macro morphology of the fracture after fatigue life experiment
Fig.9  Micromorphologies of the fractures after the fatigue life experiment. (a) Crack initiation zone; (b) slow crack propagation zone
Fig.10  Fatigue life of the workpiece machined at different cutting speeds
Fig.11  Fatigue life of the workpiece machined at different feed rates
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