Surface and Coatings Technology, 49(1991) 311-315 311 Morphology and thickness distribution of sputtered W—C—Co films deposited on differently shaped substrates A. Cavaleiro and M. T. Vieira Departainento de Engenkaria Mecdnica, Universidade de Coimbra, Largo D. Dinis, 3000 Coimbra (Portugal) Abstract The performance of a coated cutting tool depends on the correct coverage of all of the sample. Previous work on sputtered W—C—Co films showed the excellent wear behaviour of these films if suitable deposition conditions, particularly the substrate bias, were selected. In this work we have studied the influence of the rake face angle of a cutting insert and of the substrate bias on the morphology and on the thickness distribution of sputtered W—C—Co films. When the deposition was carried out just by one side, the best thickness distribution in the lateral face was achieved for unbiased films and large rake face angles or for biased films and small angles. The substrate bias led to worse uniformity of the thickness in the plane face and to a greater difference between thickness values in the plane and lateral faces. For the inserts coated on both sides, the lateral faces showed a uniform coverage irrespective of the rake face angle and the substrate bias used in the deposition. The morphology of the plane faces was always featureless while, in the lateral faces, less dense morphologies were obtained; the compactness degree on these faces depended on the substrate bias. 1. Introduction The substrates were high speed steel M2 (AISI) heat treated (quenched and tempered) with a Vickers hard- The effectiveness of the coating on cutting tools is not ness of 850 HV 30. only dependent on the cutting characteristics of the Figure 1 shows the shape of the substrates; the angle coating—substrate assembly; it also depends on the x was varied in the range 0—20°. All the faces of the geometry adjustment that must be carried out whenever inserts were polished with diamond paste of particle a cutting tool is to be coated. The sputtering technique size down to 0.25 l.tm. can induce a film thickness variation depending on the tool geometry, which can give rise to a change in the 2.2. Deposition technique wear characteristics of the film. This problem can be The films were r.f. sputtered deposited in magnetron one of the causes of tool failure if the variation in mode in a basic ESM100 Edwards unit which permits thickness is localized in critical zones of the tool. For the application of an r.f. bias to the substrate. The W—C—Co films, we have shown earlier how different sputtering chamber was evacuated down to 10 ~ Pa by process parameters affect the characteristics of the a turbomolecular pump provided with a liquid-nitrogen films, particularly the deposition rate and the morphol- cold trap. ogy [1, 2]. This research study was carried out on plane The deposition parameters were as follows: diameter substrates and several considerations were made in of the chamber, 30 cm; diameter of the cathode, 10 cm; order to justify the differences found in the deposited anode-to-cathode distance, 6 cm; discharge power, coatings. 6.25 W cm 2 deposition pressure, 0.3 Pa. The negative The aim of this study is to evaluate the influence of substrate bias was varied in the range 0—350 V. the substrate bias and the substrate shape on the thick- Firstly, the inserts were coated with face A in front of ness distribution and on the morphology of the films. the target (mode 1). Afterwards the chamber was We have used as substrate a normalized cutting tip for opened and half of the inserts were rotated and placed a lathe machine where the rake face angle was varied, in the substrate holder with face C in front of the target for posterior coating (mode 2); the other half of the inserts were taken out of the chamber. 2. Experimental details The coated inserts were observed by scanning elec- tron microscopy (SEM) in order to quantify the thick- 2.1. Materials ness and to identify the morphology of the films. For The target used for the depositions was sintered WC the first operation the inserts were sawed and the with 6 wt.% Co addition. section carefully polished. To observe the morphologies Elsevier Sequoia, Lausanne