Effect of Pre-Oxidation on Microstructure and Wear Resistance of Titanium Alloy by Low Temperature Plasma Oxynitriding
WANG Haifeng1,2, ZHANG Zhiming1, NIU Yunsong2(), YANG Yange2(), DONG Zhihong2, ZHU Shenglong2, YU Liangmin1, WANG Fuhui3
1.Frontiers Science Center for Deep Ocean Multispheres and Earth System, and Key Laboratory of Marine Chemistry Theory and Technology, Ministry of Education, Ocean University of China, Qingdao 266100, China 2.Shi -changxu Innovation Center for Advanced Materials, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China 3.Shenyang National Key Laboratory for Materials Science, Northeastern University, Shenyang 110819, China
Cite this article:
WANG Haifeng, ZHANG Zhiming, NIU Yunsong, YANG Yange, DONG Zhihong, ZHU Shenglong, YU Liangmin, WANG Fuhui. Effect of Pre-Oxidation on Microstructure and Wear Resistance of Titanium Alloy by Low Temperature Plasma Oxynitriding. Acta Metall Sin, 2023, 59(10): 1355-1364.
Titanium alloys are used in the aerospace industries, chemical industries, biomedicine, marine ships and other fields because of their high strength-to-weight ratio, good corrosion resistance, and biocompatibility. However, titanium alloys have low hardness and poor wear resistance, which limit their applications, especially under sliding contact. Plasma nitriding (PN) is an effective method for improving titanium alloy's tribological properties. PN can produce a composite layer composed of TiN and Ti2N to improve the friction and wear properties of titanium alloy. However, the high temperature in the nitriding treatment results in a brittle “α-stabilized layer” (a continuous layer of α phase titanium enriched with interstitial nitrogen atoms) and unfavorable phase transformations in the substrate that can impair the fracture toughness, ductility, and fatigue properties. In this study, a low-temperature plasma-composite treatment, consisting of plasma oxidizing and oxynitriding, has been developed to improve the hardness and wear resistance of Ti-6Al-4V alloy. The effect of the preoxidation process on the surface microstructure, phase composition, and wear performance of titanium alloy was studied. The microstructure and phase composition of the plasma-composite layer were observed using SEM, TEM, XRD, and other methods. The results showed that the composite layer of titanium alloy treated using plasma-composite-treatment is composed of compound and diffusion layers, and the phase is TiO2 (rutile) and TiN0.26. Microhardness and wear-resistance properties of the composite layer were characterized using microhardness tester, nanoindentation, and reciprocating-friction tester. The plasma-composite treatment can increase infiltration depth of the diffusion layer, surface hardness, elastic modulus, and wear resistance of the titanium alloy more than the traditional nitriding process.
Fund: National Key Research and Development Program of China(2019YFC0312100);National Natural Science Foundation of China(51701223);Civil Aircraft Special Scientific Research Project(MJ-2017-J-99)
Corresponding Authors:
NIU Yunsong, senior engineer, Tel: (024)23992860, E-mail: ysniu@imr.ac.cn; YANG Yange, associate professor, Tel: (024)23881473, E-mail: ygyang@imr.ac.cn
Fig.2 Cross-sectional morphologies of coatings obta-ined by different processes (a) PN 3h (b) PO+PN 3h (c) PO+PN 4h
Fig.3 XRD spectra of coating obtained by different processes
Fig.4 TEM image (a) and selected area electron diffraction patterns (b-d) of different regions of sample PO+PN 4h
Fig.5 Hardness (a) and elastic modulus (b) vs depth for the different processes
Sample
H / GPa
E / GPa
H / E
H 3 / E2
Untreated TC4
4.57
127.5
0.036
5.87 × 10-3
PN 3h
5.60
132.6
0.042
1.0 × 10-2
Matrix (PN 3h)
4.77
116.6
0.041
7.98 × 10-3
PO+PN 3h
8.54
149.1
0.057
2.8 × 10-2
Matrix (PO+PN 3h)
4.92
115.4
0.043
8.94 × 10-3
PO+PN 4h
11.22
208.3
0.054
3.25 × 10-2
Matrix (PO+PN 4h)
4.73
120.7
0.039
7.25 × 10-3
Table 2 Mechanical properties of titanium alloy matrix and heat-treated samples
Fig.6 Microhardness distributions of coatings obtained by different plasma heat-treated processes
Fig.7 Friction coefficient as a function of time for the coating obtained by different plasma heat-treated processes
Fig.8 Wear rates of coatings and the corresponding grinding balls
Fig.9 3D morphologies (a-c) and cross-section traces (d-f) of wear scar for the coating obtained by different processes (a, d) PN 3h (b, e) PO+PN 3h (c, f) PO+PN 4h
Fig.10 Low (a-c) and high (d-f) magnified wear trace morphologies of coatings obtained by different processes (a, d) PN 3h (b, e) PO+PN 3h (c, f) PO+PN 4h
Fig.11 Enlarged images of the areas in Figs.10a-c and the corresponding EDS results (a) PN 3h (b) PO+PN 3h (c) PO+PN 4h
Fig.12 Surface morphologies of grinding ball corresponding to samples obtained by different processes after the friction experiment (a) PN 3h (b) PO+PN 3h (c) PO+PN 4h
Fig.13 Schematics of wear mechanisms for the oxynitriding layer (FN—positive pressure, v—velocity) (a-d) PN sample (e-h) PN+PO sample
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