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Reduction of pull-off force with nanometer scale forming using magnetic fluid and magnetic field
Journal of Magnetism and Magnetic Materials 201 (1999) 372}375
Reduction of pull-o! force with nanometer scale forming using magnetic #uid and magnetic "eld Noritsugu Umehara*, Kazuaki Suzuki Department of Mechatronics and Precision Engineering, Graduate School of Engineering, Tohoku University, Aoba-ku, Sendai, Miyagi 980-8579, Japan Received 20 May 1998; received in revised form 24 August 1998
Abstract In order to make well-arranged asperities on Al-alloy substrates of magnetic rigid disk as a texturing process, a new nanometer scale indentation method using magnetic #uid and magnetic "eld was developed. These asperities made by this method could decrease the pull-o! force against the Si N ball in humid air. A large applied load and coil current of the electric magnet in the indentation process provided a smaller pull-o! force. Peak radius of indentation marks is a governing parameter of the pull-o! force. 1999 Elsevier Science B.V. All rights reserved. Keywords: Pull-o! force; Nanometer scale indentation; Magnetic #uids; Magnetic "eld
1. Introduction In order to reduce the pull-o! force between two contact parts in the "eld of magnetic storage system or MEMS, it can be considered that mating surfaces should have an ideal surface pro"le. The surface should consist of micro-asperity arrays whose heights are uniform for avoidance of wear. We tried to make a nanometer scale indentation mark using a magnetic #uid and a magnetic "eld, and evaluate the pull-o! force of patterned surface and ball in this paper. Skjeltorp [1] and Fujita et al. [2] showed that two non-magnetic particles in a magnetized magnetic #uid are subject to an attractive force when
* Corresponding author. Tel.: #81-22-217-6956; fax: #8122-217-6955. E-mail address: [email protected] (N. Umehara)
aligned along magnetic "eld lines, and a repulsive force when aligned perpendicular to magnetic "led lines. On the basis of their researches, the authors tried to control the distribution and the number of non-magnetic abrasives on a workpiece, and also showed that the control of distribution and arrangement of non-magnetic abrasives improved surface roughness and removal rate well [3]. Also, the authors tried to make nm scale indentation marks by applying extra normal load as shown in Fig. 1 [4]. Typical indentation marks are shown in Fig. 2. The diameter, depth and the edge height of an observed indentation mark was about 2 lm, 200 and 100 nm, respectively. In the present paper, the e!ect of textured surface by this method on pull-o! force is investigated. Especially, e!ects of coil current of the electric magnet, resting time, load and peak radius of the indentation mark on pull-o! force of
0304-8853/99/$ - see front matter 1999 Elsevier Science B.V. All rights reserved. PII: S 0 3 0 4 - 8 8 5 3 ( 9 9 ) 0 0 0 5 9 - 1
N. Umehara, K. Suzuki / Journal of Magnetism and Magnetic Materials 201 (1999) 372}375
373
Fig. 1. Principles of nanometer scale indentation forming using magnetic #uid and magnetic "eld.
an Si N ball against a patterned surface were investigated.
2. Experimental procedure for the measurement of the pull-o4 force of a nanoscale patterned specimen After an Si N ball ( 1 2) was pressed on the specimen in 1 mN of contact load during a certain resting time, the pull-o! force of the ball against the specimen was obtained by the strain of leaf springs which was measured by a laser displacement meter. The whole equipment was in a chamber, whose atmosphere was controlled with constant humidity (88% RH) and temperature (133C).
Fig. 2. AFM images of indentation marks.
3. Experimental results and discussion 3.1. Ewect of coil current of the electric magnet during the indentation process on the pull-ow force Fig. 3 shows the variation of the pull-o! force with resting time under di!erent coil currents of the electric magnet during the indentation process. Without the indentation process, the pull-o! force rapidly increased with resting time, and reached a certain value, which is consistent with the theory on meniscus force [5]. From this "gure, it is seen that a larger coil current decreases the pull-o! force. The e!ect of coil current of the electric magnet on the pull-o! force can be considered as follows: by applying a large normal magnetic "eld to the specimen, distances between particles became larger, and the number density of indentation marks become large. It can be considered that a large number of asperities casued enough gap
Fig. 3. E!ect of coil current of the electric magnet during the indentation process on the pull-o! force.
between the ball and the specimen to prevent making su$cient meniscus by capillary condensation of water vapor. Therefore, the specimen with a large
374
N. Umehara, K. Suzuki / Journal of Magnetism and Magnetic Materials 201 (1999) 372}375
Fig. 6. E!ect of peak radius of the indentation mark on the pull-o! force. Fig. 4. E!ect of the applied load during the indentation process on the pull-o! force.
this "gure, it can be seen that, when the load was less than 56.8 N, we could not "nd the e!ect of patterning for reduction of the pull-o! force. On the other hand, when the load was more than 76.4 N, we could not measure pull-o! force. Therefore a su$ciently large load which is more than 76.4 N during the indention process is necessary for decreasing the pull-o! force. 3.3. Ewect of peak height of the indentation mark on the pull-ow force Fig. 5 shows the e!ect of mean peak height of the indentation mark on the pull-o! force. From this "gure, it can be seen that larger peak height provides smaller pull-o! force. Fig. 5. E!ect of peak height of the indentation mark on the pull-o! force.
coil current needed a long period to reach the saturated condition by "lling water vapor in the gap between the ball and the specimen. This result, shows that the magnetic "eld can control the pull-o! force in this method. 3.2. Ewect of an applied load during the indentation process on the pull-ow force Fig. 4 shows the e!ect of an applied load during the indentation process on the pull-o! force. From
3.4. Ewect of peak radius of the indentation mark on the pull-ow force On the basis of the theory of meniscus force, meniscus force F is proportional to asperity radius R as shown by the following equation [5]: F "2pR c(cos h #cos h ), (1) where c is the surface energy of the liquid, h the contact angle of the upper surface, and h the con tact angle of the lower surface. Therefore, the relationship between peak radius of the indentation mark R and the pull-o! force is shown in Fig. 6. Peak radius is the mean value
N. Umehara, K. Suzuki / Journal of Magnetism and Magnetic Materials 201 (1999) 372}375
which was calculated from the AFM images of ten indentation marks in each indentation condition. The applied load and coil current during the indentation process changed the peak radius. From this "gure, it can be seen that the peak radius is the exact governing surface parameter for controlling the pull-o! force. A small radius of indentation marks was generated under a large load.
375
(2) The pull-o! force decreased with increasing peak height. The pull-o! force is controlled by the peak radius of indentation marks.
Acknowledgements We thank Taiho Industrial Co. Ltd. for supplying the magnetic #uid, and Mr. Kanemi Fukurai for his suggestions on the experiments.
4. Conclusions A nanoscale indentation method and a principle of the method were proposed, and its reduction properties in pull-o! force against Si N ball were investigated. The important results obtained are as follows: (1) The pull-o! force was decreased by nanometer scale indentation. Larger electric current and load during the indentation process provided larger decreasing of the pull-o! force.
References [1] A.T. Skjeltorp, J. Magn. Magn. Mater. 55 (1983) 195. [2] T. Fujita, M. Mamiya, J. Magn. Magn. Mater. 65 (1987) 207. [3] N. Umehara, K. Kato, T. Hayashi, J. Magn. Magn. Mater. 149 (1995) 181. [4] N. Umehara, K. Kato, K. Suzuki, Ann. CIRP 46 (1) (1997) 155. [5] F.S. McFarlane, D. Tabor, Proc. Roy. Soc. London A 202 (1950) 224.
Reduction of pull-o! force with nanometer scale forming using magnetic #uid and magnetic "eld Noritsugu Umehara*, Kazuaki Suzuki Department of Mechatronics and Precision Engineering, Graduate School of Engineering, Tohoku University, Aoba-ku, Sendai, Miyagi 980-8579, Japan Received 20 May 1998; received in revised form 24 August 1998
Abstract In order to make well-arranged asperities on Al-alloy substrates of magnetic rigid disk as a texturing process, a new nanometer scale indentation method using magnetic #uid and magnetic "eld was developed. These asperities made by this method could decrease the pull-o! force against the Si N ball in humid air. A large applied load and coil current of the electric magnet in the indentation process provided a smaller pull-o! force. Peak radius of indentation marks is a governing parameter of the pull-o! force. 1999 Elsevier Science B.V. All rights reserved. Keywords: Pull-o! force; Nanometer scale indentation; Magnetic #uids; Magnetic "eld
1. Introduction In order to reduce the pull-o! force between two contact parts in the "eld of magnetic storage system or MEMS, it can be considered that mating surfaces should have an ideal surface pro"le. The surface should consist of micro-asperity arrays whose heights are uniform for avoidance of wear. We tried to make a nanometer scale indentation mark using a magnetic #uid and a magnetic "eld, and evaluate the pull-o! force of patterned surface and ball in this paper. Skjeltorp [1] and Fujita et al. [2] showed that two non-magnetic particles in a magnetized magnetic #uid are subject to an attractive force when
* Corresponding author. Tel.: #81-22-217-6956; fax: #8122-217-6955. E-mail address: [email protected] (N. Umehara)
aligned along magnetic "eld lines, and a repulsive force when aligned perpendicular to magnetic "led lines. On the basis of their researches, the authors tried to control the distribution and the number of non-magnetic abrasives on a workpiece, and also showed that the control of distribution and arrangement of non-magnetic abrasives improved surface roughness and removal rate well [3]. Also, the authors tried to make nm scale indentation marks by applying extra normal load as shown in Fig. 1 [4]. Typical indentation marks are shown in Fig. 2. The diameter, depth and the edge height of an observed indentation mark was about 2 lm, 200 and 100 nm, respectively. In the present paper, the e!ect of textured surface by this method on pull-o! force is investigated. Especially, e!ects of coil current of the electric magnet, resting time, load and peak radius of the indentation mark on pull-o! force of
0304-8853/99/$ - see front matter 1999 Elsevier Science B.V. All rights reserved. PII: S 0 3 0 4 - 8 8 5 3 ( 9 9 ) 0 0 0 5 9 - 1
N. Umehara, K. Suzuki / Journal of Magnetism and Magnetic Materials 201 (1999) 372}375
373
Fig. 1. Principles of nanometer scale indentation forming using magnetic #uid and magnetic "eld.
an Si N ball against a patterned surface were investigated.
2. Experimental procedure for the measurement of the pull-o4 force of a nanoscale patterned specimen After an Si N ball ( 1 2) was pressed on the specimen in 1 mN of contact load during a certain resting time, the pull-o! force of the ball against the specimen was obtained by the strain of leaf springs which was measured by a laser displacement meter. The whole equipment was in a chamber, whose atmosphere was controlled with constant humidity (88% RH) and temperature (133C).
Fig. 2. AFM images of indentation marks.
3. Experimental results and discussion 3.1. Ewect of coil current of the electric magnet during the indentation process on the pull-ow force Fig. 3 shows the variation of the pull-o! force with resting time under di!erent coil currents of the electric magnet during the indentation process. Without the indentation process, the pull-o! force rapidly increased with resting time, and reached a certain value, which is consistent with the theory on meniscus force [5]. From this "gure, it is seen that a larger coil current decreases the pull-o! force. The e!ect of coil current of the electric magnet on the pull-o! force can be considered as follows: by applying a large normal magnetic "eld to the specimen, distances between particles became larger, and the number density of indentation marks become large. It can be considered that a large number of asperities casued enough gap
Fig. 3. E!ect of coil current of the electric magnet during the indentation process on the pull-o! force.
between the ball and the specimen to prevent making su$cient meniscus by capillary condensation of water vapor. Therefore, the specimen with a large
374
N. Umehara, K. Suzuki / Journal of Magnetism and Magnetic Materials 201 (1999) 372}375
Fig. 6. E!ect of peak radius of the indentation mark on the pull-o! force. Fig. 4. E!ect of the applied load during the indentation process on the pull-o! force.
this "gure, it can be seen that, when the load was less than 56.8 N, we could not "nd the e!ect of patterning for reduction of the pull-o! force. On the other hand, when the load was more than 76.4 N, we could not measure pull-o! force. Therefore a su$ciently large load which is more than 76.4 N during the indention process is necessary for decreasing the pull-o! force. 3.3. Ewect of peak height of the indentation mark on the pull-ow force Fig. 5 shows the e!ect of mean peak height of the indentation mark on the pull-o! force. From this "gure, it can be seen that larger peak height provides smaller pull-o! force. Fig. 5. E!ect of peak height of the indentation mark on the pull-o! force.
coil current needed a long period to reach the saturated condition by "lling water vapor in the gap between the ball and the specimen. This result, shows that the magnetic "eld can control the pull-o! force in this method. 3.2. Ewect of an applied load during the indentation process on the pull-ow force Fig. 4 shows the e!ect of an applied load during the indentation process on the pull-o! force. From
3.4. Ewect of peak radius of the indentation mark on the pull-ow force On the basis of the theory of meniscus force, meniscus force F is proportional to asperity radius R as shown by the following equation [5]: F "2pR c(cos h #cos h ), (1) where c is the surface energy of the liquid, h the contact angle of the upper surface, and h the con tact angle of the lower surface. Therefore, the relationship between peak radius of the indentation mark R and the pull-o! force is shown in Fig. 6. Peak radius is the mean value
N. Umehara, K. Suzuki / Journal of Magnetism and Magnetic Materials 201 (1999) 372}375
which was calculated from the AFM images of ten indentation marks in each indentation condition. The applied load and coil current during the indentation process changed the peak radius. From this "gure, it can be seen that the peak radius is the exact governing surface parameter for controlling the pull-o! force. A small radius of indentation marks was generated under a large load.
375
(2) The pull-o! force decreased with increasing peak height. The pull-o! force is controlled by the peak radius of indentation marks.
Acknowledgements We thank Taiho Industrial Co. Ltd. for supplying the magnetic #uid, and Mr. Kanemi Fukurai for his suggestions on the experiments.
4. Conclusions A nanoscale indentation method and a principle of the method were proposed, and its reduction properties in pull-o! force against Si N ball were investigated. The important results obtained are as follows: (1) The pull-o! force was decreased by nanometer scale indentation. Larger electric current and load during the indentation process provided larger decreasing of the pull-o! force.
References [1] A.T. Skjeltorp, J. Magn. Magn. Mater. 55 (1983) 195. [2] T. Fujita, M. Mamiya, J. Magn. Magn. Mater. 65 (1987) 207. [3] N. Umehara, K. Kato, T. Hayashi, J. Magn. Magn. Mater. 149 (1995) 181. [4] N. Umehara, K. Kato, K. Suzuki, Ann. CIRP 46 (1) (1997) 155. [5] F.S. McFarlane, D. Tabor, Proc. Roy. Soc. London A 202 (1950) 224.