1 Key Laboratory for Material Modification by Laser, Ion and Electron Beams, Ministry of Education, Dalian University of Technology, Dalian 116024, China 2 Institute of Metals Research, Chinese Academy of Sciences, Shenyang 110016, China
Cite this article:
Kechang HAN,Yiqi LIU,Guoqiang LIN,Chuang DONG,Kaiping TAI,Xin JIANG. STUDY ON ATOMIC-SCALE STRENGTHENING MECHANISM OF TRANSITION-METAL NITRIDE MNx (M=Ti, Zr, Hf) FILMS WITHIN WIDE COMPOSITION RANGES. Acta Metall Sin, 2016, 52(12): 1601-1609.
Transition-metal nitrides have long attracted considerable attention among researchers and ubiquitous applications in various fields due to their renowned mechanical properties. However almost all the discussions of the strengthening mechanism were on conventional meso scale. For further understanding on the atomic scale strengthening mechanism of transition-metal nitrides, three groups of MNx (M=Ti, Zr, Hf) films with different nitrogen contents were synthesized on the Si substrates by magnetic filtering arc ion plating. The morphologies and thickness of the as-deposited films were characterized by FESEM, the microstructures and the residual stresses were characterized by XRD, the XPS and Nano Indenter were used to measure the chemical states and hardness (also the elastic modulus) of as-deposited films, respectively. The results show that all three groups MNx films perform the B1-NaCl single-phase structure within the large composition ranges. The preferred orientation, thickness, grain size and residual stress of the MNx films with different nitrogen contents were not changed so much. While the nanohardness and elastic modulus of MNx both first increased and then decreased with the rise of nitrogen content, and the peak values all existed when x near to 0.82. The strengthening mechanism was discussed and the decisive factor of composition dependent hardness enhancement was found from the atomic-scale chemical bonding states and electronic structure in this work, rather than the conventional meso-scale factors, such as preferred orientation, grain size and residual stress.
Fig.1 Schematic of enhanced magnetic filtering arc ion plating apparatus
Film
Sample
N2 flow rate / (Lmin-1)
TiNx
T-1
0.03
T-2
0.06
T-3
0.09
T-4
0.12
T-5
0.18
T-6
0.24
T-7
0.27
T-8
0.30
ZrNx
Z-1
0.06
Z-2
0.09
Z-3
0.12
Z-4
0.15
Z-5
0.18
Z-6
0.21
Z-7
0.24
Z-8
0.27
HfNx
H-1
0.03
H-2
0.06
H-3
0.12
H-4
0.18
Table 1 N2 flow rates of MNx films deposited by arc ion plating
Fig.2 Representative surface (a, c, e) and cross-section (b, d, f) SEM images of TiNx (a, b), ZrNx (c, d) and HfNx (e, f)
Fig.3 XRD spectra of TiNx (a), ZrNx (b) and HfNx (c) films deposited at different N2 flow rates
Fig.4 Lattice parameters of MNx films deposited at different N2 flow rates
Fig.5 Grain sizes of MNx films deposited at different N2 flow rates
Fig.6 Typical XPS spectra of TiNx film
Fig.7 High resolution XPS spectra of the MNx films(a) Ti2p in TiNx film (b) N1s in TiNx film (c) Zr3d in ZrNx film(d) N1s in ZrNx film (e) Hf4f in HfNx film (f) N1s in HfNx film
Film
Sample
Atomic fraction / %
x
Ti(Zr, Hf)
N
O
TiNx
T-1
55.5
41.8
2.7
0.75
T-2
55.1
42.6
2.3
0.77
T-3
53.5
44.1
2.4
0.82
T-4
51.3
46.4
2.3
0.91
T-5
50.5
47.4
2.1
0.94
T-6
49.7
48.1
2.2
0.97
T-7
49.4
48.4
2.2
0.98
T-8
49.1
48.8
2.1
0.99
ZrNx
Z-1
55.7
41.6
2.7
0.74
Z-2
55.2
42.2
2.6
0.76
Z-3
53.7
43.3
2.8
0.81
Z-4
53.2
44.4
2.4
0.84
Z-5
52.1
45.3
2.6
0.87
Z-6
51.4
45.7
2.9
0.89
Z-7
50.7
46.5
2.8
0.92
Z-8
49.8
47.3
2.9
0.95
HfNx
H-1
58.4
39.1
2.5
0.67
H-2
54.8
42.5
2.7
0.78
H-3
53.7
43.9
2.4
0.82
H-4
52.0
46.0
2.0
0.89
Table 2 Compositions of the MNx films by XPS
Fig.8 Residual stress of the MNx films vs N content x
Fig.9 Hardness-displacement curve of T-3 sample
Fig.10 Hardness and elastic modulus of the TiNx (a), ZrNx (b) and HfNx (c) films vs x
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