Lubricant Transfer Behavior In The Head Disk Interface Based On Molecular Dynamics And Its Experimental Study

As mainstream removable storage device, the read/write process of the hard disk drive is complicated by the read/write element embedded in the trailing edge of the slider. The decrease of the read/write element to disk spacing is to satisfy the requirement of the increase of hard disk drive storage capacity. However, with the reduction of the slider flying height, the lubricant transfer between slider and disk is becoming one of the promising problems to influence the slider flying height and increase the areal density of the disks. Nevertheless, the head/disk interface will face a serial of tribological issues with a decrease of the slider flying height and slider flying stability. Currently, the smallest flying height of the slider has been decreased to less than2nm. In this case, the lubricant is likely to transfer to the slider even in the absence of slider to disk contacts. Therefore, investigating the lubricant transfer without the slider to disk contacts is helpful to improve slider flying stability, decrease the chance of slider to disk contacts to occur, and then increase the life time of the hard disk drive.In this study, the transfer mechanism between the slider and the disk in the absence of slider to disk contacts was investigated, and the effect of its affecting factors on the lubricant transfer process was studied by using the molecular dynamics simulation from microcosmic point of view. The parameters, including the slider tilt angle, dynamic pitch and roll angles of disk, and etc., which may influence the lubricant transfer process between the slider and the disk, as well as the lubricant distribution on slider surface, were studied experimentally. The characteristics of transferred lubricant motion on slider surface were analyzed.According to the interactions between diamond-like-carbon (DLC) layer and the lubricant molecules, the improved coarse grained bead spring model was established using molecular dynamics theory. With consideration of the air bearing pressure change and disk velocity, the lubricant transfer model was established based on the improved coarse grained bead spring model. The lubricant transfer process was analyzed using the lubricant transfer model from the microcosmic point of view. The effect of chamfer angle of the pads on the slider air bearing surface was studied. Moreover, the effect of functional bead number on the DLC layer, the roughness of DLC layer, the protrusion on the disk surface on the lubricant transfer and lubricant distribution were investigated.With consideration of some factors which are likely to affect the amount of lubricant transfer, such as lubricant film thickness on the disk surface, local temperature increase caused by the development of HAMR slider, the change of air bearing pressure difference induced by slider flying posture change or the air bearing surface variation, the degradation of lubricant molecules, the effect of lubricant film thickness, different kind of lubricant molecules, local temperature difference, local air bearing pressure change, slider to disk spacing, lubricant fragments on lubricant transfer between the slider and the disk were investigated based on the established molecular dynamics model.The effect of slider pitch static angle and roll static angle on lubricant transfer and on lubricant distribution were studied. The lubricant distribution on the slider surface was analyzed by the Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS), while the lubricant distribution on the disk surface was analyzed by the optical surface analyzer. The effect of slider flying pitch and roll angles on lubricant were studied by the flying height tester. The slider flying height was measured using the disk coated with3lubricant during the experiment. A charge-couple device (CCD) camera was used to observe transferred lubricant motion on the disk surface. The effects of slider flying pitch and roll angles on lubricant transfer between the slider and the disk were investigated using the disk coated with12lubricant. The experimental results indicated that the slider roll static angle has more effect on lubricant transfer and lubricant distribution on the disk surface than the slider pitch angle. The effect of slider flying roll angle on lubricant transfer is severer than the slider flying pitch angle. The transferred lubricant flows to the slider inner trailing edge when the slider is flying on the outer of the disk; while the transferred lubricant goes to the slider outer trailing edge when the slider flies on the inner of the disk.