Tribological behaviour of hard wear resistant layers at high temperatures

Transcription

1 Tribological behaviour of hard wear resistant layers at high temperatures Ing. Jiří Hájek Dr. Ing. Antonín Kříž Ing. Petr Beneš WBU Plzeň, Univerzitní 22, Plzeň, ČR, WBU Plzeň, Univerzitní 22, Plzeň, ČR, WBU Plzeň, Univerzitní 22, Plzeň, ČR,

2 Tribological analysis PIN-on-DISC PIN-on-DISC Equipment parameters: Load 1N - 60N. Rotation speed from 10 to 500 revolutions/min. Temperature range 20 C 1000 C. Data processing with the use of PC. PIN-on-DISC test is provided on CSEM Instruments tribometer. During the test tightly griped PIN (shape of ball) is loaded onto the test sample ( DISC ) with a constant force (chosen radius). The sample rotates with a constant speed. 1/18

3 Experimental materials On substrate from high-speed steel X82WMoCrV654 were deposited three various types of PVD layers. These are AlTiN, TiAlSiN, CrAlSiN. Thin wear resistant layers were deposited on substrates by the PVD low- voltage arc evaporating in vacuum. Deposition temperature did not exceed 500 C, so the substrate was not thermally influenced. 2/18

4 Wear resistance at room temperature Friction coefficients, PIN -Al 2, F = 10N, r = 8mm, T = 20 C, n = cycles Against hard Al 2 ball - most wear resistant layer is CrAlSiN. This resistance is evident for example from course of friction coefficient, which does not show strong deviation of friction coefficient values. By AlTiN and TiAlSiN layers is wear of "PIN" ball covered by transfer layer. 3/18

5 T ransfer layer This layer inhibits contact of "PIN" ball with surface of thin layer. These layers are strongly adhesively connected with the ball surface. By CrAlSiN layer this phenomenon did not arise. Depends on the type of thin layer and on conditions load /frictional speed. Layer sticks (adheres) on ceramics during friction and forms on it a transfer film influences the results. AlTiN TiAlSiN Most important factors: adhesion and friction between surfaces (important is toughness of the layer). Adhesion is influenced by presence of impurities. CrAlSiN 4/18

6 koeficient tření 0,9 0,8 0,7 0,6 0,5 0,4 0,3 0,2 0,1 0 0,79 0,80 0,78 Comparison of friction coefficient 0,73 0,60 TiN TiAlN AlTiN TiAlSiN CrAlSiN with other layers koeficient tř 1 0,9 0,8 0,7 0,6 0,5 0,4 0,3 0,2 0,1 0 0,86 0,83 0,82 0,75 0,67 TiN TiAlN AlTiN TiAlSiN CrAlSiN Friction coefficients PIN-Al 2,T=20 C, cycles Friction coefficients PIN-Si3N4,T=20 C, cycles PIN ball material H it Measured values We[%] Al 2 30,83 ± 0,70 57,41 Si 3 N 4 27,60 ± 1,84 65,38 5/18

7 Resistance of system thin layer - substrate at thermal influence Temperatures were chosen according to steady thermal field during the machining process. Distribution of steady thermal field during the machining process. Chosen parameters were constant for AlTiN, CrAlSiN, TiAlSiN layers. F [N] r [mm] v [cm/s] Temperature [ C] n [number of cycles] "PIN" ball Si 3 N 4 Si 3 N 4 6/18

8 Layer AlTiN At 500 C there are evident two increases of friction coefficient values. Friction coefficient at 700 C is stationary. Higher friction coefficient at 500 C is probably caused by adhesive wear. During this test the oxidation of wear debris creates compact unit - glaze. It is probable that the time to the glaze creation is connected with increasing friction coefficient. After its creation only slight wear appears. This claim confirms the fact, that the wear of "PIN" ball is very low. At 700 C is friction coefficient influenced by thick oxidised film, whose plasticity at 700 C is lower than at 500 C, which may result in decrease of friction coefficient. 7/18 T= 500 C, 700 C, F= 2N, cycles

9 Layer AlTiN a) T= 500 C with marked area of plastic flow of the layer b) T= 700 C At 500 C there was no exposure of the substrate, while at 700 C there was complete damage of the layer. At 500 C only very small wear of PIN ball appeared. Spot, which was created on the PIN ball at 700 C, had irregular shape. At its margin of the spot is caught small debris from the layer. Wear of PIN ball: a) T= 500 C, b) T= 700 8/18

10 Layer TiAlSi AlSiN Friction coefficient also in this case was higher at 500 C than at 700 C. At 500 C happens similar phenomenon as in the case of layers AlTiN (creation of "glaze"), but in case of TiAlSiN there is no such a high ploughing of PIN ball in the thin layer. This documents the SEM analysis. It is possible to think, that even microhardness of thin layer TiAlSiN is at these temperatures higher than microhardness of AlTiN layer. At thermal stress of 700 C there is frequent failure of oxidised film, thereby PIN ball gets in the contact with thin layer and marked deviation of friction coefficient follows. Courses of friction coefficients, T= 500 C, 700 C, F= 2N 9/18

11 Layer TiAlSi AlSiN Wear tracks from SEM: a) T= 500 C, b) T= 700 C At temperature 500 C is wear track covered by oxidised layer throughout whole perimeter. Track is created by debris from damaged thin layer and from oxidised film. This oxidised film is very fast adhesively connected with TiAlSiN layer. 10/18

12 Layer TiAlSi AlSiN Wear track T= 500 C Wt [%] Point N O Al Si Ti Fe Σ [%] 1 0,48 4,11 8,37 1,26 70,49 15, ,07 0,90 7,43 0,79 63,00 26, /18

13 Layer CrAlSiN Courses of friction coefficients, T= 500 C, 700 C, F= 2N Friction coefficient is at temperature 700 C lower than at 500 C. However differences between friction coefficients are smaller than by other layers. During thermal exposition of CrAlSiN layer creates on its surface highly efficient oxidised protective layer Cr-Al-O, which prevents further oxidation of the layer. 12/18

14 Layer CrAlSiN Wear tracks from SEM: a) T= 500 C, b) T=700 C Wear depth is by both tracks minimal. Resulting from calottes, there was no substrate exposure at any temperature. Wear spots of PIN balls have almost circular shape and their surface is plane without any noticeable abrasive ploughing. 13/18

15 Formation of glaze 14/18

16 Tribological measurements after the thermal load Thermal load PIN-on-DISC Parameters are the same like by test at room temperature PIN -Al 2, F = 10N, r = 8mm, T = 20 C, n = cycles 15/18

17 Tribological measurements after the thermal load Load Layer PIN AlTiN TiAlSiN CrAlSiN F= 10N Al 2 X/2 N/2 N/1 Si 3 N 4 r=4mm N/1 N/1 N/1 F= 2N Si 3 N 4 r=2mm N/1 N/1 N/1 Load Layer PIN AlTiN TiAlSiN CrAlSiN F= 10N Al 2 X/3 X/3 X/3 F= 2N Si 3 N 4 r=4mm Si 3 N 4 r=2mm N/2 N/2 N/2 N/2 N/1-2 N/1-2 Detection of the substrate/damage area of the layer: X detection occures, N detection doesn t occure 3 - extensive wear, 2 - middle-sized wear, 1 - slight wear 16/18

18 Tribological measurements after the thermal load Wear track - layer AlTiN, PIN Al 2 Detail of wear track - layer AlTiN, PIN Al 2 Wear track - layer TiAlSiN, PIN Al 2 Wear track - layer CrAlSiN, PIN Al 2 17/18

19 Conclusion Obtained results show significant influence of silicium on tribological properties, but above all, replacement of titanium by chromium seems to be really revolutionary, because layer CrAlSiN proves several times higher wear resistance. Also generation of oxidised barrier Cr-Al-O at these layers is highly efficient. In cases of TiAlSiN and AlTiN generated thermal barrier was not so effective. Part of the experiment was also the comparison of tribological properties at normal temperatures where the samples were before the tribological test thermally loaded. Results show that at temperatures above 500 C thin layer loses markedly its adhesion to substrate. Up to which certain point it is, will be the subject of further research. Text of this contribution and the presentation will be available at website This contribution was solved under the support of PhD. grant. 921/2005/G1 and post-phd. grant 106/03/P /18

20 Thank you for your attention Contact: WBU Plzeň, Univerzitní 22, Plzeň, ČR, WBU Plzeň, Univerzitní 22, Plzeň, ČR, WBU Plzeň, Univerzitní 22, Plzeň, ČR,