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Research Papers: Magnetic Storage

The Effect of Diamondlike Carbon Overcoat on the Tribological Performance of the Dimple/Gimbal Interface in Hard Disk Drives1

[+] Author and Article Information
Youyi Fu

Center for Memory and Recording Research,
University of California, San Diego,
9500 Gilman Drive,
La Jolla, CA 92093-0401
e-mail: yof001@ucsd.edu

Vlado A. Lubarda

Department of NanoEngineering,
University of California, San Diego,
9500 Gilman Drive,
La Jolla, CA 92093-0448
e-mail: vlubarda@ucsd.edu

Frank E. Talke

Fellow ASME
Center for Memory and Recording Research,
University of California, San Diego,
9500 Gilman Drive,
La Jolla, CA 92093-0401
e-mail: ftalke@ucsd.edu

2Corresponding author.

Contributed by the Tribology Division of ASME for publication in the JOURNAL OF TRIBOLOGY. Manuscript received June 15, 2015; final manuscript received August 25, 2015; published online July 8, 2016. Assoc. Editor: Min Zou.

J. Tribol 138(4), 041901 (Jul 08, 2016) (12 pages) Paper No: TRIB-15-1197; doi: 10.1115/1.4032797 History: Received June 15, 2015; Revised August 25, 2015

Fretting wear at the dimple/gimbal interface of a hard disk drive suspension was investigated for stainless steel dimples in contact with stainless steel gimbals coated with diamondlike carbon (DLC) of different thicknesses and different elastic moduli. Scanning electron microscopy (SEM) was used to evaluate the size and characteristics of the wear scar of both the dimple and the gimbal. Fretting wear and fatigue-type cracks were found predominantly on the dimple. For different dimple/gimbal combinations tested in this study, the least amount of wear was obtained for the case of a 690 nm thick DLC overcoat. Numerical simulations were performed to calculate the maximum principal stress in the dimple and the gimbal with the goal of correlating wear and the maximum principal stress. The maximum principal stress in both the dimple and the gimbal was found to increase with an increase of the elastic modulus of the DLC overcoat on the gimbal. On comparing the experimental and simulation results, we conclude that wear and fatigue crack formation can be explained by the different level of the maximum principal stress in both the dimple and the gimbal.

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Figures

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Fig. 1

Schematic of the head/disk interface: (a) pitch motion and (b) roll motion of slider

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Fig. 2

Schematic of the fretting wear tester

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Fig. 3

Typical friction hysteresis loop

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Fig. 4

Schematic of the dimple/gimbal interface coated with a thin layer of DLC. The radius of the spherical dimple is 200 μm. The thickness of the stainless steel substrate of the gimbal tsu is 40 μm. The thickness of the DLC overcoat tco is 15 nm, 70 nm, 250 nm, and 690 nm, respectively.

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Fig. 5

Coefficient of friction versus number of fretting wear cycles for (a) 15 nm DLC-coated gimbal, (b) 70 nm DLC-coated gimbal, (c) 250 nm DLC-coated gimbal, (d) 690 nm DLC-coated gimbal, and (e) uncoated gimbal

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Fig. 6

Mean coefficient of friction for different dimple/gimbal combinations

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Fig. 7

SEM images of the typical wear scars on stainless steel dimples after 3.45×106 fretting wear cycles against (a) 15 nm DLC-coated gimbal, (b) 70 nm DLC-coated gimbal, (c) 250 nm DLC-coated gimbal, (d) 690 nm DLC-coated gimbal, and (e) uncoated gimbal

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Fig. 8

SEM images of the typical gimbal wear scars on (a) 15 nm DLC-coated gimbal, (b) 70 nm DLC-coated gimbal, (c) 250 nm DLC-coated gimbal, (d) 690 nm DLC-coated gimbal, and (e) uncoated gimbal, after 3.45×106 fretting wear cycles

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Fig. 9

(a) sp3 fraction, (b) elastic modulus, and (c) hardness of 15 nm, 70 nm, 250 nm, and 690 nm DLC overcoats

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Fig. 10

Finite element model for contact between dimple and gimbal

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Fig. 11

Distribution of the maximum principal stress around the contact area of the dimple when the gimbal coated with 690 nm DLC slides in (a) positive x direction and (b) negative x direction

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Fig. 12

Distribution of the maximum principal stress around the contact area of the dimple contacting (a) 15 nm DLC-coated gimbal, (b) 70 nm DLC-coated gimbal, (c) 250 nm DLC-coated gimbal, (d) 690 nm DLC-coated gimbal, and (e) uncoated gimbal when gimbals move in the positive x direction

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Fig. 13

Distribution of the von Mises stress around the contact area of the dimple contacting (a) 15 nm DLC-coated gimbal, (b) 70 nm DLC-coated gimbal, (c) 250 nm DLC-coated gimbal, (d) 690 nm DLC-coated gimbal, and (e) uncoated gimbal when gimbals move in the positive x direction

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Fig. 14

Distribution of the von Mises stress around the contact area of the dimple when the gimbal coated with 690 nm DLC slides in (a) positive x direction and (b) negative x direction

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Fig. 15

Distribution of the maximum principal stress around the contact area of the gimbal when the gimbal coated with 690 nm DLC slides in (a) positive x direction and then in (b) negative x direction

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Fig. 16

Distribution of the maximum principal stress around the contact area of (a) 15 nm DLC-coated gimbal, (b) 70 nm DLC-coated gimbal, (c) 250 nm DLC-coated gimbal, (d) 690 nm DLC-coated gimbal, and (e) uncoated gimbal sliding in the positive x direction against dimples

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Fig. 17

The largest maximum principal tensile stress in the dimple contacting a gimbal coated with 70 nm and 690 nm DLC of different elastic moduli, assuming the friction coefficient is constant

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Fig. 18

The largest maximum principal tensile stress in the dimple contacting a gimbal coated with stiff and compliant DLC overcoat of different thickness, assuming the friction coefficient is constant

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