Structural Investigation of Ti-N Films
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using a Philips x-ray powder diffractometer and CuKa-radiation. Diffraction peak positions were evaluated by applying a computer program [2] where the diffraction intensity profile is described with a modified Lorentzian function [3]. Silicon powder was employed as an internal standard for confirming the exact angular positions of the reflections. The stability of the phases was tested by heat treating samples in evacuated quartz tubes at 773 K for 20 h and at 1173 K for 2 h. After annealing, x-ray diffraction measurements were carried out to check for possible changes in the structure of the films. The hardness of the Ti-N coatings was determined with a microhardness tester applying 15,25 and 50 g loads and a Knoop indenter. It may be noted that the coating thickness critically affects the hardness. It has been suggested [4] that for hardness measurements the TiN-film should be five times thicker than the indentation depth. Another factor affecting the hardness is the strong load dependence of the Knoop microhardness values, which generally tend to increase at lower loads. Therefore, loads as high as possible were chosen for this investigation. Since N/Ti-ratio varied somewhat in the through thickness direction, nitrogen content at a depth of I pm was taken as a representative value when the hardness values of the films were compared. RESULTS AND DISCUSSION In series of experiments Ti-N films containing a-Ti, c-TiN and 6-TiN phases in-various proportions were produced. The nitrogen content of the films varied from about 16 to 53 at. %. In the sample A (Fig. 1) with the nitrogen content of 26 - 30 at. % a-Ti and e-Ti 2 N phases can be found by x-ray diffraction. The a-Ti phase is oriented strongly along the (002) direction. Fig. 2 shows the structure of TiN-coating in the sample B with 32 - 43 at. % N. Here the first peaks corresponding to cubic 6-TiN are seen in addition to a-Ti and c-Ti 2 N. The structure of the film in the sample C (Fig. 3) with 43 - 53 at. % N consists dominantly of the 6-TiN phase. e-Ti 2 N and a-Ti are only minor constituents, the latter being represented only by a trace of the a-Ti (002) reflection. With increasing nitrogen content up to about 25 at. % N the interplanar spacings (d-values) corresponding to a-Ti (002), (011) and ý0
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Fig. 1. X-ray diffraction curve of the sample A. Ti-N film deposited on the austenitic stainless steel,
nitrogen content 26 - 30 at. %.
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X-ray diffraction curve of the sample B. Ti-N film deposited on the austenitic stainless steel, nitrogen content 32 - 43 at. %.
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