EFFECT OF Mo CONTENT ON THE MICROSTRUC-TURE AND PROPERTIES OF CrMoN COMPOSITE COATINGS
QI Dongli, LEI Hao, FAN Di, PEI Zhiliang, GONG Jun(), SUN Chao
Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016
Cite this article:
QI Dongli, LEI Hao, FAN Di, PEI Zhiliang, GONG Jun, SUN Chao. EFFECT OF Mo CONTENT ON THE MICROSTRUC-TURE AND PROPERTIES OF CrMoN COMPOSITE COATINGS. Acta Metall Sin, 2015, 51(3): 371-377.
Ceramic coatings are usually used as protective coatings to improve performance and durability of tools and components now. Compared with conventional TiN based hard coating, CrN based coating like Cr-X-N (X=Ti, Al, Si, C, B, Ta, Nb, Ni) is a more interesting choice because of low friction coefficient, superior oxidation resistance and excellent corrosion resistance under severe environment conditions. The CrMoN is among these coatings and attractive since self-lubricating phase MoO3 may be formed in tribological process. However the effect of Mo content on structure and tribological properties of CrMoN coatings is not still clear. In the present study, CrMoN composite coatings with different Mo content were deposited on M2 high speed steel (HSS) substrates by DC reactive magnetron sputtering. The effect of Mo content on the microstructure and properties was investigated systematically, including the chemical composition, phase structure, chemical valence, cross-section morphologies, microhardness and tribological properties. The results showed that the phase transformation of the as-deposited coatings occurred with the increase of Mo content. The phase structure changed to (Cr, Mo)N substitutional solid solution based on CrN-type firstly, and then to mixed phase with g-Mo2N as main phase, and a small amount of elemental bcc-Mo phase appeared when the Mo content is 69.3%. The microhardness of the CrMoN composite coatings always increased until the highest hardness when the Mo content reached to 45.4%, and then decreased; a relatively low friction coefficient was obtained compared with that of the CrN coating when more than 45.4%Mo content was doped. The reason is that the more MoO3 lubricant phase could be formed in tribological process.
Fund: Supported by National Basic Research Program of China (No.2012CB625100), National Natural Science Foundation of China (No.51171197) and Natural Science Foundation of Liaoning Province ( Nos.2013020132 and 2013010442-401)
Table 1 Deposition conditions for CrMoN composite coatings
Sample No.
Atomic fraction / %
Thickness μm
Deposition rate (nm·s-1)
Grain size nm
Hardness HV
Cr
Mo
1
100.0
0.0
1.58
0.44
19.0
1802
2
79.6
20.4
1.66
0.23
16.3
1910
3
68.7
31.3
1.70
0.24
15.2
1993
4
61.6
45.4
1.80
0.25
12.5
2714
5
45.8
54.2
1.57
0.22
14.5
2235
6
30.7
69.3
1.52
0.20
18.0
2206
Table 2 Atomic fraction of the metal elements, thickness, deposition rate, grain size and hardness of CrMoN composite coatings with different Mo content
Fig.2 XRD spectra of CrMoN composite coatings with different Mo content
Fig.3 Influence of Mo content on the lattice constant of fcc structure
Fig.4 Cross-section SEM images of CrMoN composite coatings of samples No.1 (a), No.2 (b), No.3 (c), No.4 (d), No.5 (e) and No.6 (f)
Fig.5 XPS spectra of CrMoN composite coatings of samples No.2 and No.6
Fig.6 Friction coefficient and wear rate of CrMoN composite coatings with different Mo content
Fig.7 Wear track depth profiles of CrMoN composite coatings with different Mo content
Fig.8 Surface SEM images of wear tracks of CrMoN composite coatings of samples No.1 (a), No.2 (b), No.3 (c), No.4 (d), No.5 (e) and No.6 (f)
