Investigation of the hard films deposited by PVD-magnetron sputtering on the cutting tools.

Vlasceanu, Daniel ; Cotrut, Cosmin ; Tarcolea, Mihai 等

1. INTRODUCTION

Generally, coatings have a major influence on the performance of cutting tools. The insufficient adhesion is still one of the most important aspects in the development of new coating technologies for hard metal cutting tools. Particularly, the principal purpose was to find coatings that could be deposit at lower temperatures, in order to allow to sharper edges tools to be coat without any embrittlement effect (Brookes, 2001).

The solution was PVD (physical vapor deposition), where deposition temperature normally can be kept about 500[degrees]C.

A particular aspect of PVD technology it is linked to the coating thickness; one can say that this quantity is strongly dependent on the loading of the reactor and the supporting device. The main purpose of PVD is to obtain a straight line of deposition (Wissmann, 1972).

For hard metal cutting tools, thickness control is one of the key factors in order to optimize the properties and to facilitate the PVD coating techniques, with a well-defined processing way, the fully control of charges offering a clear competitive advantage. The cutting tools are obtained from hard metals (made from WC powders), coated with TiN through PVD-magnetron sputtering technology (Ruset et al., 2007).

The PVD methods have been preferred for a wide range of materials and applications due to their relative simplicity, versatility, and the general high quality of the resultant coatings (Kelly, et al., 1993).

Physical vapor deposition is a generic term for a number of processes, which are use to deposit solid coatings, or films, from the vapor phase. Processes currently included in this definition are vacuum evaporation, ion plating and sputtering (Mateescu, G., 1998). The most widely used material for wear resistant coatings is titanium nitride (TiN).

2. EXPERIMENTAL PVD-MAGNETRON SPUTTERING DEPOSITION

In TiN deposition process, Ti layer is deposit on the surface of the wafer by creating a high partial pressure of N near the wafer surface and by creating a high partial pressure of Ar at or near the target. This minimizes nitrogen concentrations at or near the target, thus minimizing any nitriding of the target. To accomplish this, the Ar gas is introduced through gas inlet located near the target and the N gas is introduced using a lower gas inlet located at or near the wafer surface or otherwise located near the bottom of the chamber.

In order to investigate the effect of the angle between magnetron axis and sample surface, the depositions at two different inclinations (15[degrees] and 45[degrees]) was made.

3. INVESTIGATIONS AND RESULTS

The hardness-testing machine was loaded with a force of 1 N. Several tests have been made on three different samples (Table 1), having different thicknesses on the deposited layer.

Although the principal parameters of deposition process have been the same, the microhardness it is influenced by the sample geometry.

One of the principal factors taken into account is the angle between the plane area and the treatment chamber axis.

This angle depends in a direct manner on the incidence of ions energy of the substratum area.

The microhardness obtained is superior by respect to the microhardness obtained by usual deposition techniques (CVD, mechanical deposition).

A possible explanation for large values of microhardness obtained through PVD--magnetron-sputtering method is due to the big compressible tensions induced between the substratum and plasma.

3.2 Layer growth

After preparation of the specimen for metallographic analysis, the following aspects have been taken into account:

* thickness determination after the deposition;

* thickness determination, where there is possible, of the titanium intermediate layer;

* deposition inspection on the cutting edges;

* interface inspection between deposited layer and substratum.

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3.5 Adherence to the substratum

The layer adherence to the substratum--beside the microhardness--represents one of most important feature, which determinates the efficient coatings used for wear resistant growth.

By the "scratch test" was realized the adherence determination, one of the most adequate methods in order to estimate adherence of hard layers applied on the cutting tools.

The results of these analyses are indicated in Table 3.

The method is accomplished by pressing a pyramidal or conic penetrator, made from diamond or ruby, with a progressive load from 0 to 100 N, on the surface area of a cutting tool having a displacement rate of 10 mm min-1.

The normally critical force is then determined; this one represents the pressing force which produces the layer damage by apparition of some breaches to the layer-substrate interface.

The method presented above utilizes a ruby conic penetrator with a radius of 0.2 mm.

With a microscope, in order to establish the values of the normally critical force (FNC), were examined the scratch stamps.

4. CONCLUSIONS

The results obtained have shown a superiority of the procedure presented in the paper in comparison with the conventional techniques, having in view the following points of view:

* The hardness of some TiN layers obtained by this new technique is about 3000 HV004, in comparison with the usual hardness (of about 1000-1500 HV004) obtained by the classical methods;

* It is possible to obtain layer thicknesses up to 15 [micro]m, with a good adherence to the substratum. Usually, by application of classical methods there are obtained layers with a 2-5 [micro]m thickness;

* The interface between the layer and the substratum could be of about 5-6 [micro]m, in comparison with the standard thickness of 1 [micro]m;

* The investigated coatings exhibited a high microhardness having good adhesion on the substrate (> 50 N).

5. REFERENCES

Kelly, P.J., Arnell, R.D., Ahmed, W., (1993), Some recent applications of materials deposited by unbalanced magnetron sputtering, Surface Engineering, Volume 9, Number 4, pp 287-291.

Brookes, K.J.A., (2001), Annapolis shows the cutting edge of hard metals technology, Metal Powder Report, Volume 56, Number 4, pp. 8-14.

Mateescu, G., (1998), Advanced technologies--Vacuum deposition thin films, Ed. Dorotea, Bucharest, Romania.

Wissmann, P., (1972), The effect of gas adsorption on the conductivity of thin metal films, Thin Solid Films, Volume 13, pp189.

Holmberg, K., Matthews, A., (1994), Coatings Tribology: Properties, Techniques and Applications in Surface Engineering, Tribology Series, Volume 28, Elsevier, Amsterdam, The Netherlands.

Ruset, C., Grigore, E., Maier, H., Neu, R., Li, X., Dong, H., Mitteau, R., and Courtois, X., (2007), Tungsten coatings deposited on CFC tiles by the combined magnetron sputtering and ion implantation technique, Physica Scripta, Volume T128, pp. 171-174.

Tab. 1. Micro hardness values

Code Conditions of deposition [HV.sub.0.1]

P1 Inclined to 45[degrees]/2 hours 2587
P2 Inclined to 15[degrees]/3 hours 2587
P3 Inclined to 15[degrees]/5 hours 2850

Tab. 2. Layer growth of the cutting tools

Code Conditions of Thickness
 deposition ([micro]m)

 P1 Inclined to 9
 45[degrees]/2 hours

 P2 Inclined to 15
 15[degrees]/3 hours

 P3 Inclined to 21
 15[degrees]/5 hours

Tab. 3. Scratch test values

Code Growth, [F.sub.nc], Observation
 ([micro]m) (N)

P1 9 50 Detach marginally
P2 15 55 Detach marginally
P3 21 57 --