EFFECT OF MATERIAL AND CONDITIONS OF MODIFICATION ON TRIBOLOGICAL BEHAVIOUR OF ION-MIXED LAYERS

Size: px

Start display at page:

Download "EFFECT OF MATERIAL AND CONDITIONS OF MODIFICATION ON TRIBOLOGICAL BEHAVIOUR OF ION-MIXED LAYERS"

Corey Griffith
6 years ago
Views:

1 EFFECT OF MATERIAL AND CONDITIONS OF MODIFICATION ON TRIBOLOGICAL BEHAVIOUR OF ION-MIXED LAYERS Z. RYMUZA Warsaw University of Technology, Chodkiewicza 8, Warsaw, POLAND; A. PIATKOWSKA, J. JAGIELSKI Institute of Technology of Electronic Materials, Wolczynska 133, Warsaw, POLAND SUMMARY The effect of material and conditions of modification on the tribological behaviour of ion-mixed layers deposited on high-speed steel were studied. Various materials for sputtering ultrathin films, Kr ions doses and energies of ion-mixing were applied. The results of the tribological investigations are presented and discussed in this paper. Keywords: ion-beam mixing, ion implantation, ultrathin films, friction, wear 1 INTRODUCTION Ion implantation is an interesting method to control surface properties of materials. Ion implantation is a doping process in which a beam of accelerated ions is directed towards the sample surface [1, 2]. The process is carried out at low temperatures, in general, from room temperature up to about 150 ºC. The temperature is an independent parameter; the sample can be cooled down or additionally heated during the process. Subsequent implantation of different elements can be easily performed, in order to obtain a multi-elemental doping. The other process used to modify interface properties of materials in which a beam of accelerated is used is Ion- Beam Mixing (IBM). In the IBM technique, a thin layer composed of impurity material is first deposited on the sample surface. The layer is then bombarded with energetic inert ions. The incoming ions colliding with layer atoms transfer them part of their kinetic energy ensuring the penetration of the layer thus a less expensive atoms into the underlaying substrate. Contrary to ion implantation, in the IBM process, the ion-beam serves only the purpose of energy carrier. During the mixing process the bombarded target is exposed to heavy radiation damage leading to the formation of a layer characterised by a metastable, often amorphous phase structure. The main advantages of IBM with respect to ion implantation are almost no impurity concentration limitations and simple ion implanters without mass separation could be used. The IBM process is thus a less expensive and more reliable method for metallic impurity doping than classical ion implantation. We have studied the effect of material and conditions of modification on tribological behaviour of ion-mixed layers. 2 EXPERIMENTAL Ultrathin films (40-50 nm thick) of Mo, Si, Al and W were sputtered on high-speed steel substrate and then ion-mixed using Kr ions with various fluences. The energy of ions were chosen so that the penetration depths slightly exceeded the thickness of the deposited layer. The materials used for layers, ion doses and energies used in ion-mixing process are presented in Table. Disk specimen were made from high speed steel of composition 0.88 %C, 4.2 %Cr, 6.5 %W, 5.0 %Mo, 1.9 %V. The diameter of the disks was 14 mm and the thickness about 2 mm. All samples were thermally treated to about 64 HRC and polished to Ra about 5 nm. The ultrathin films of Al, Si, Mo and W were deposited on such substrates by the RF-sputtering technique. The energies of ions were chosen so that the penetration depths slightly exceeded the thickness of the deposited layer. Some samples used for comparison were 100 kev nitrogen ions ( cm -2 ) or 100 kev titanium ions and 50 kev carbon ions ( cm cm -2 ) implanted. The modified layer of material after ion implantation or IBM processes is relatively thin (up to several hundreds nanometers). Hysitron`s Triboscope nanoindentation device was used to measure hardness and elasticity modulus of nanometer thick layers. Tribological tests were performed using ball-on-flat tribotester. Two bearing steel balls were used: 6.5 and 14.3 mm. A constant force of 20 N was used, the stroke was equal 4 mm and the average sliding speed 3.34 mm/s. During the tests the tangential force was recorded, allowing the analyses of friction coefficient changes. The wear extent was measured via 3D profilometric analysis of the wear tracks. Numerical analyses of removed and built-up volumes were performed in about 1 mm long track area.

2 Sample description Method Deposited layer material Layer thickness Ion dose Energy (kev) 3Mo45 Ion-beam mixing Molybdenum 45 nm 3x10 16 Kr/cm Mo45 Ion-beam mixing Molybdenium 45 nm 5x10 16 Kr/cm Mo25 Ion-beam mixing Molybdenum 25 nm 3x10 16 Kr/cm Mo25 Ion-beam mixing Molybdenium 25 nm 5x10 16 Kr/cm Si47 Ion-beam mixing Silicium 47 nm 3x10 16 Kr/cm Si47 Ion-beam mixing Silicium 47 nm 5x10 16 Kr/cm Si29 Ion-beam mixing Silicium 29 nm 3x10 16 Kr/cm Si47 Ion-beam mixing Silicium 29 nm 5x10 16 Kr/cm W41 Ion-beam mixing Tungsten 41 nm 3x10 16 Kr/cm W41 Ion-beam mixing Tungsten 41 nm 5x10 16 Kr/cm W24 Ion-beam mixing Tungsten 24 nm 3x10 16 Kr/cm W24 Ion-beam mixing Tungsten 24 nm 5x10 16 Kr/cm Al49 Ion-beam mixing Aluminium 49 nm 3x10 16 Kr/cm Al49 Ion-beam mixing Aluminium 49 nm 5x10 16 Kr/cm Al25 Ion-beam mixing Aluminium 25 nm 3x10 16 Kr/cm Al25 Ion-beam mixing Aluminium 25 nm 5x10 16 Kr/cm NRT Ion implantation x10 17 N 2 /cm Ti1C Ion implantation Ion implantation Titanium Carbon x10 17 Ti/cm x10 17 C/cm 2 80 Table 1: Materials used for sputtering ultrathin films and conditions of ion-mixing/implantation

3 100 untreated sample - speed steel SW7M 3x10 16 Kr + /cm 2 5x10 16 Kr + /cm 2 a b Concentration [at.%] Al Si c d Mo W Depth [A] Fig. 1: Rutherford Backscattering Spectroscopy (RBS) depth profiles for materials used to sputtered ultrathin films: a) Al, b) Si, c) Mo, d) W after irradiation using two different doses of Kr ions during ion-mixing.

4 0,80 Friction coefficient 0,70 0,60 0,50 0,40 0,30 untreated 3Mo45 5Mo45 3Si47 5Si47 3Al49 5Al49 3W41 5W41 NRT 4Ti1C 0,20 0,10 0, Number of cycles Fig. 2. Friction coefficient vs. number of cycles for different materials (see Table) used for sputtering ultrathin films and then ion-mixed and for untreated high speed steel and ion-implanted high speed steel. Diameter of ball 6.5 mm. Fig. 3. Friction coefficient vs. number of cycles for different materials (see Table) used for sputtering ultrathin films on high speed steel and then ion-mixed as compared with untreated high speed steel and high speed steel implanted with Ti+ C or N ions. Diameter of ball 14.3 mm. Podloze= substrate.

5 1,50 1,25 untreated 1,00 0,75 3Al49 Wear [µm] 0,50 0,25 0,00 NRT 4Ti1C 3Si47 5Si47 5Al49 3W41 5W41-0,25-0,50-0,75 Fig. 4. Wear depth of scratches and height of pile-ups after rubbing (100 cycles) of steel 6.5 mm ball against various materials (see Table1). 3 RESULTS AND DISCUSSION The Rutherford Backscattering Spectroscopy ( RBS) depth profiles are presented in Fig.1. On the graph it is possible to observe the level of the sample surface (substrate) - points (0, 0) and the thickness of the deposited film. In every case it was found some material on the top of the substrate after ion-mixing. The thickness of this film was between 5 nm for W (5W24) up to 40 nm in the case of Al (3Al25). The concentration of the material is clearly dependent on the dose of Kr ions. For smaller dose the concentration is about 65% and is independent on the material of the film; at higher dose the concentration is higher (85-90 %). The depth of penetration of the mixed material is strongly dependent on the dose of ions. For Al, Mo and W however it is approximately the same. Only in the case of Si the maximum depth of penetration is two times smaller. The frictional behaviour of the tested samples are presented in Figs.2 and 3 for 6.5 mm and 14.3 mm balls used counter face respectively. It is possible to observe the significant effect of the material used and the technique of modification on the frictional behaviour of the tested samples. The lowest friction coefficient was found for tungsten (3W41) and for the samples implanted with Ti+C ions. The higher dose of Kr ions was more effected in the decrease of the friction coefficient as compared with the friction coefficient of the untreated high speed steel. The wear was observed by profilometric cross-sections studies. The surface of the samples was changed both by some scratches and pile-ups (Fig.4 ). The smallest destructions of the surface was observed for the ion-mixed tungsten films and for Ti+C ions implanted high-speed steel. The comparison of the depth of scratches and the height of the pile-ups for two different diameters of the ball makes possible to state that the depths of the scratches are similar however the pile-ups are significantly higher in the case of higher diameter of the ball. The width of the wear tracks is higher for the ball with diameter of 14.3 mm ( mm). The width of the wear tracks in the case of 6.5 mm are mostly mm but in the case of

tungsten films and Ti+C ions implantation are of 0.1 mm. The surface of the wear tracks of W ionmixed films and Ti+C ions implanted high-speed steel are relatively smooth (Fig. 5).

6 tungsten films and Ti+C ions implantation are of 0.1 mm. The surface of the wear tracks of W ionmixed films and Ti+C ions implanted high-speed steel are relatively smooth (Fig. 5). The distinct oxidation of the materials on the wear tracks was observed by EDX method. The most intensive oxidation was observed for untreated high speed steel (the poorest tribological behaviour). The series of tests of the tribological behaviour as a function of the sliding cycles revealed that during the friction and wear processes of the tested samples the effect of the wear debris. The agglomeration of the wear particles and the changes of the chemical compositions (revealed by EDX X-ray microprobe analysis) showed that profound physicochemical modifications of the rubbing surfaces effects on the observed frictional and wear performance of the tested materials. The results of the tests shown that the profound mechanical and physicochemical modifications of the surfaces after ion-mixing or ion-implantation influence on the tribological behaviour of the tested samples. The material and the conditions of modification (does of ions, their energy) are very important. Better ion-mixing of the material of the sputtered film with the substrate effects in better wear resistance and frictional performance. 4 CONCLUSIONS Ion-mixing is effective way to improve tribological behaviour of materials. The comparison of various ionmixed materials revealed that the best behaviour can be expected using tungsten as compared with Al, Si and Mo. The ions dose and their energy are important for ion-mixing. Complex mechanical and physicochemical changes of surface layers of material after ion-mixing and during the friction process effect on the ultimate tribological behaviour. The agglomeration of the wear particles play important role. 5 ACKNOWLEDGEMENTS Thanks are due for the help of M. Misiak by performing nanomechanical tests of some samples and Hysitron Inc. for possibility to realize such tests. We thank also D. Treheux from Ecole Centrale de Lyon for making accessible the test instrument. Fig.5. SEM image of wear scars of various materials (see Table) after 100 cycles of rubbing against steel 6.5 mm ball. The mechanical properties of the modified layers play also very important role. The results of nanomechanical testing of the showed that the higher wear resistance of the sample is correlated with better mechanical properties of the surface layer. The general rule is such that the surfaces which demonstrate higher nanohardness on the depth of several nanometers characterize by the lowest coefficient of friction (until the surface layer was not destroyed). The financial support from Polish State Committee for Research under grant No. 7T08C is greatly acknowledged. 6 REFERENCES [1] T. Burakowski and T. Wierzchon: Surface Engineering of Metals. CRC Press, Boca Raton 1999 [2] Ion Beam Modification of Materials. Conference Proceedings, last volume published in Nuclear Instruments and Methods in Physics Research B127/128 (1997).

WEAR PROPERTIES OF PLASMA NITRIDED INCONEL 718 SUPERALLOY

WEAR PROPERTIES OF PLASMA NITRIDED INCONEL 718 SUPERALLOY Halim Kovacı 1, Hojjat Ghahramanzadeh ASL 1, Çiğdem Albayrak 2, Akgün Alsaran 1 1 Ataturk University, Erzurum, Turkey 2 Erzincan University, Erzincan,