Elsevier

Ceramics International

Volume 41, Issue 9, Part A, November 2015, Pages 11013-11023
Ceramics International

Effect of codeposition parameters on the hardness and adhesion of TiVN coatings

https://doi.org/10.1016/j.ceramint.2015.05.046Get rights and content

Abstract

A systematic study of the effect of PVD cathodic arc deposition parameters on TiVN coating performance was carried out to analyze the structure, surface morphology, chemical composition, hardness and adhesion of these coatings. The effects of four factors including operation pressure, substrate bias voltage, and the currents applied to the Ti target and to the V target were evaluated. The investigated coatings were analyzed by X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy, adhesion tests (i.e., scratch tests) and Vickers microhardness tests. The results of this study showed that the current applied to the V target was the factor having the greatest effect on TiVN coating hardness, while the bias voltage applied to the substrate had the greatest effect on adhesion strength. The obtained TiVN coatings were shown to have good hardness values near 15 GPa and high adhesion critical loads near 113 N.

Introduction

Ternary nitrides such as TiVN have gained attention as substitutes for the binary nitride TiN in many applications, including cutting tools, wear protection and machinery components [1]. Reports in the literature have shown that adding V to TiN leads to an improvement in mechanical and tribological properties [2], [3], [4]. The ternary TiVN system is formed due to the total miscibility of the Ti–V system [5], which creates a solid solution while preserving the crystalline structure B1 of TiN. Such miscibility can be attributed to the small difference between the atomic radii of Ti (1.36 Å) and V (1.25 Å) [6]. The vanadium content of the TiVN coatings influences the hardness of the coating [7] and reduces its friction coefficient [8], [2]. Thus, combining B1 transition metal nitrides such as TiN and more ductile bcc metals such as V can yield increased plasticity rates while retaining hardness characteristics [9]. This behavior is associated with a pronounced electronic arrangement on the metal stacking that allows a selective response to strain and shear deformations of the crystal [9]. Such a charge distribution is induced in the crystal by the substitution of Ti with V atoms and by the effect of weaker V–N bonds. Ternary TiVN exhibits hardness values comparable to those of TiN as well as enhanced ductile characteristics [9]. These properties increase life and reduce wear [5], making these coatings attractive for industrial applications and particularly for cutting tools.

Most studies of the effects of deposition parameters on TiVN coating properties investigate one or two parameters and kept the rest fixed. For instance, Knotek et al. [6] modified the coating composition of the TiVN magnetron-sputtered thin films, by altering the TiV target composition (Ti87V13, Ti71V29, Ti48V52), and the partial nitrogen pressure PN2/PAr (1.5–9%), while the bias voltage was kept fixed at −60 V. The results showed the highest hardness (3100 HV) for the coatings at 52 at% V and PN2/PAr ~3%, and the best adhesive strength, 100 N at 29 at% V and PN2/PAr ~5%. Deeleard et al. [10] tailored the coating composition of the TiVN magnetron co-sputtered thin films altering the V sputtering current IV: 0.4,0.6,0.8 and 1.0 A, keeping the Ti sputtering current (ITi) constant at 0.6 A without biasing. The results showed that the lattice parameter decreased, while the crystallite size and RMS roughness increased by increasing the V sputtering current. Ouyang et al. [2] investigated the TiVN cathodic arc ion plating thin films deposited with a Ti target and a V target alternately at fixed currents of 67 and 133 A respectively and nitrogen pressures of 1–3 Pa, while the bias voltage was kept fixed at −10 V. The results showed that the friction coefficient varied between 0.53 and 1.08 depending on the thermal oxidation temperature. It was 0.81 at room temperature, and increased to 1.01, 1.08 and 1.06, with the increase in temperature at 200, 300 and 400 °C, respectively, while, at 500, 600 and 650 °C decreased to 0.68, 0.55 and 0.53 respectively. The low friction coefficient exhibited at 650 °C was attributed to the formation of aV2O5 and TiO2 oxide layer on the surface. At 700 °C, the friction coefficient increased to 0.61 due to the surface melting phenomenon. Yeung et al. [11] modified the grain size and roughness of the TiVN magnetron co-sputtered thin films using different partial nitrogen pressures, PN2: 0.053–0.128 Pa. The results showed that by decreasing the nitrogen deposition pressure, the grain diameter of the coatings decreased, which led to higher hardness. The coatings hardness was 13.6–18.6 GPa. Ichimiya et al. [7] tailored the composition of the TiVN cathodic arc ion plating thin films using targets with different V/(Ti+V) atomic ratios from 0 to 1 with a nitrogen atmosphere pressure in the range of 2–5 Pa and a fixed bias voltage of −50 V. The results showed that the best coating hardness was 2600 HV, at around V/(Ti+V)=0.25−0.50, and the best friction coefficient was of 0.51 at 600 °C. Ouyang et al. [12] modified the composition of the TiVN cathodic arc ion plating thin films adjusting the Ti target and the V target alternately with a total arc current power applied of 200 A. The pressure and the bias voltage were kept fixed at 0.67 Pa and −10 V respectively. The results showed friction coefficients between 0.68 and 1.08 at room temperature, depending on load and frequency. The friction coefficient gradually decreased from 0.81 to 0.68, with the load increasing from 20 to 70 N, and gradually increased from 0.73 to 1.08 with the frequency increasing from 6 to 50 Hz. Hasegawa et al. [1] studied TiVN cathodic arc ion plating thin films deposited with Ti–V alloy cathodes at a fixed current of 100 A, PN2 of 3.3 Pa and bias voltage of −20 V. The results showed hardness of 2400 HV.

It must be pointed out that the simultaneous variation of all variables (operation pressure, substrate bias voltage and currents applied to targets of Ti and V) has not been studied completely. These parameters as a whole modify the erosion rate of the cathodes, the mean free path of the eroded species and their kinetic energy consequently playing roles that jointly have a great effect on TiVN coatings properties. In this study, TiVN coatings were deposited on AISI D2 steel by PVD arc, and the effect of these different deposition variables, such as operating pressure (Po), bias voltage applied to the substrate (Vb), current applied to the Ti target (ITi) and that applied to the V target (IV) on the TiVN coatings structure, composition, deposition rate (Vt), hardness (Hf) and adhesion critical load (Fc) were studied. A Taguchi orthogonal array (TOA) experimental design was proposed to perform this study because of each experiment׳s extended duration requirements.

Section snippets

Experimental details

The TiVN coatings were produced using the PVD cathodic arc deposition method with two different metal targets: titanium and vanadium. The effects of four deposition parameters including operation pressure (Po), substrate bias voltage (Vb), and the currents applied to the cathodes of titanium and vanadium (ITi and IV, respectively) were studied. The parameters values were selected within an interval in which optimal conditions were reported and were recorded at three levels (e.g., 1, 2 and 3)

Substrate chemical composition

The analyzed chemical composition of AISI D2 steel substrates was 1.57 wt% C, 0.286 wt% Si, 0.256 wt% Mn, 0.0067 wt% S, 11.040 wt% Cr, 0.755 wt% Mo, 0.149 wt% Ni, 0.710 wt% V, 0.026 wt% W and 85.19 wt% Fe. The analyzed elemental chemical composition of carbide WC–TiC–Co (i.e., WC–Co) substrates was 64.16 wt% W, 18.53 wt% C, 15.64 wt% Ti, and 1.67 wt% Co.

Orthogonal arrangement of deposition parameters

A Taguchi orthogonal arrangement (TOA) L934 design was used. For the experimental design, all four parameters (e.g., A-Po, B-Vb, C-ITi, D-IV) at their three

Discussion

The statistical analysis of the XRD results show a large effect of IV on a, which is clearly illustrated for the I1 and I3 coatings, for which a decreases from 4.22 Å to 4.11 Å when IV increases from level 1 to 3, respectively, regardless of the remaining operation parameters levels. Values below 4.14 Å indicate that more V ions occupy Ti ions sites, and because V ions are smaller in size than those of Ti, the lattice parameter decreases. These results are consistent with those reported in the

Conclusions

TiVN coatings were deposited on AISI D2 steel substrates by PVD cathodic arc erosion at conditions in accordance with a Taguchi orthogonal design of experiments. The results showed that TiVN coatings have a cubic B1 structure over the entire range of experimental conditions. The obtained TiVN coatings were shown to have a good hardness near 15 GPa, and high adhesion critical loads of 113 N.

The experimental design showed the effect of operational parameters such as reactive gas pressure (Po), bias

Acknowledgments

The authors would like to acknowledge the National Science and Technology Council of Mexico, CONACYT for supporting this research under Grant no. 38467U. And also are very grateful to M.Sc. M. Santisteban Abad for his valuable contribution to this research.

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