Search

The electrochemical corrosion behavior of laser aided additive manufactured (LAAMed) CoCrNi medium entropy alloys (MEAs) with different oxide inclusion level was investigated in 3.5 wt.% NaCl solution. Different from the 316 L stainless steel, no pitting appeared on the LAAMed CoCrNi within the test regime used in this study. The LAAMed sample with a higher oxide inclusion level demonstrated lower corrosion current density and higher charge transfer resistance, implying a more compact passive film. After holding in the solution at 0.2 VSCE for 30 mins, the passive films formed on the LAAMed CoCrNi MEAs have similar thickness and dominant constituent (i.e. Cr2O3 and Cr(OH)3). More oxides in the LAAMed CoCrNi MEA could facilitate the formation of a compact passive film, which leads to superior corrosion resistance.

Heat-assisted magnetic recording (HAMR) is a technique for overcoming the superparamagnetic limit and enabling large increases in the storage density of hard disk drives. A tiny area of the magnetic recording media has to be heated up to a high temperature with a laser to lower the coercivity temporarily before information can be written on the area. The possible degradation of the ultrathin media carbon overcoat induced by the laser heating is a concern. In this paper, the laser heating-induced degradation of ultrathin a-C:Nx, a-C:Hx, and a-C overcoats on HAMR media is studied. Surface topography changes induced by the laser heating are evaluated with atomic force microscopy and structure changes with the visible Raman spectrum and X-ray photoelectron spectroscopy (XPS). Laser heating areas are analyzed with time-of-flight secondary ion mass spectrometry and XPS to reveal the underlying mechanism of the degradations. It is found that at a proper HAMR writing temperature and for a total laser heating duration corresponding to a five-year drive life, the surface topography, structure, and composition of the a-C:Nx overcoat are changed by the laser heating. However, the surface topographies of the a-C:Hx and a-C overcoats are not changed. The structure and composition of the a-C:Hx and a-C overcoats are also not changed much. Interlayer diffusion between the carbon overcoat and the underlying magnetic layer is confirmed in the laser heating area for all the three overcoats.

Lube-surfing recording combined with thermal fly-height control (TFC) technology is considered as a promising head-disk interface (HDI) scheme for further increasing magnetic areal density to 5–10 Tbits/in2. To realize this alternative technology, however, a lot of tricky issues are required to be solved. Among them, how to characterize the flying of slider in the lubricant or light lube-contact by the slider is probably one of the tough but inevitable challenges. In this study, the slider/lubricant/disk contact induced tribo-current is investigated with a modified media-tester in which the TFC slider is electrically isolated with the rest of the tester. The measured tribo-currents versus the heater voltages or the powers to the slider’s heater clearly indicate three different intensity regions of tribo-current, by which the three different contact types, namely, non-contact, lube-contact and solid-contact can be differentiated clearly. This method provides a promising way for accurately studying of lube-surfing recording.

In this study, a new type of femto slider (Panda IV) with improved force arrangement and higher air pressure/higher stiffness at trailing edge of the slider was evaluated and compared experimentally with our previous type of femto sliders (Panda II and III). The evaluations were conducted on the Candela 5100 Optical Surface Analyzer (OSA) with the VENA CSS/load–unload system attached. Disks coated with a layer of 1.2 nm lubricant were specially prepared with a lubricant step for the comparison tests. Flying height (FH) of each slider was calibrated by bump disk with 3.5 nm bump height for maintaining the consistent FH during the tests. The relative amount of lubricant redistribution was analyzed with an OSA immediately after each slider is flown on-track for a period of time. It is found that the amount of lubricant transferred or the slider–lubricant interaction are minimized by reducing the size of slider’s central trailing pad. Finally, possible explanations on the lubricant transfer are discussed.

Reducing the spacing between the magnetic head and the magnetic disk media is of crucial importance in enabling further increased recording density of the magnetic disk drives. The head-disk interface technology explored up to now can be classified into the following two categories: in-fly recording and in-contact recording. Pushing the areal density towards 10 Tb/in2 requires the magnetic spacing down to 3 nm level, which it is difficult for the conventional in-fly or in-contact schemes to achieve so small a magnetic spacing. This paper reports the authors' exploration of lube-surfing recording mechanism-majority of slider surface flying over the disk surface and only the tiny protruded read/write head area surfing on the lubricant surface of the disk. The key factors for achieving such a mechanism include technology to sense slider-lubricant contact, nano-actuator and active contact depth control, advanced slider air-bearing design to make the slider well follow up the disk surface waviness and secure the contact depth, super-smooth slider and disk surfaces, and so on. Results presented in this work suggest that the read head can be a promising transducer for slider-lubricant contact detection. Results also suggest that contact depth control is important for this scheme and it is possible to have stable slider surfing on the lubricant, if the contact depth is within a certain range.

Reducing the spacing between the magnetic head and the magnetic media is of crucial importance in enabling future high-density magnetic data storage. The magnetic spacing has been reduced to a level that we have to explore new schemes for the further reduction of the spacing. This paper reports authors’ efforts towards fly- and lubricant-contact recording scheme. The targeted objective is to minimize the mean-plane spacing between the slider and disk surfaces and to allow the further reduction of the overcoat thickness. The slider will still fly over the disk surface. The read/write head part of the slider will be protruded to contact lubricant—to minimize the mean-plane mechanical spacing. The key factors for achieving such a mechanism include super-smooth slider and disk surfaces, advanced slider air-bearing design to significantly reduce flying height modulation caused by disk waviness and flatness, nano-actuator design, position feedback control scheme to control the contact depth, and so on. The preliminary experimental data confirm the feasibility of such a lubricant-contact scheme. The slider air-bearing design presented in this work also indicates the feasibility of high-performance slider design, which can well follow the disk waviness. A parameter, anti-modulation factor, is introduced for the evaluation of slider's performance in reducing flying height modulation caused by disk waviness.

In order to design the flying height of a burnishing slider accurately, the contact force between the burnishing slider and the disk needs to be well evaluated. This paper studies the contact force of a burnishing slider by both experiment and simulation. The experiment is conducted by measuring the acoustic emission signals of the contact force avalanche, and the simulation is based on the self-developed air bearing surface simulation code applying the probability model for the contact force calculation. The influence of contact force on the burnishing effect is discussed. It is observed that the simulation results are well correlated with the experimental measurements. It is believed that the simulation code is capable to design burnishing sliders with reasonable accuracy.

To achieve rigorous glide performance for ultra-low flying height, disk media with asperities that exceed the flying height of the magnetic head must be eliminated. Burnishing process is one of the critical ways to remove such asperities from the disk surface. A successful burnishing process demonstrating improved disk yields and less disk damages depends on an effective burnish head that is designed by the understanding of asperities to be burnished. However, optimization of sputtering process is the most essential to avoid those asperities on the disk surface and strongly relies on the formation mechanism understanding of the asperities. It was attempted to trace and characterize the asperities on specially prepared disks in this work. Experimental studies after aggressive burnishing processes on the disks categorized the asperities and indicated their possible formation mechanisms.

With the increase in recording density, any accumulation on slider surface can cause serious problems, such as high fly–stiction and extensive slider–disk interaction. Therefore, how to mitigate the accumulation on slider surface and thus, improve the stability and reliability of head–disk interface is becoming an important issue. In this work, a nanothin fluoropolymer overcoat with very good oleophobic and hydrophobic properties was applied on slider surface with a dipping process. Tribological performance, such as fly–stiction, normal stiction, and takeoff and landing processes, of the coated sliders was studied. Test results show that although normal stiction is not lowered, normal stiction modulation is reduced obviously by the overcoat. Fly–stiction and its modulation of coated sliders are much smaller than those of uncoated sliders. Coated sliders show much better takeoff and landing performance during contact start stop tests. After tests, the surfaces of tested sliders and disks were examined with an optical microscope, surface reflectance analyzer, and TOF–SIMS to interpret the tribological performance of the coated sliders. It can be concluded that the fluoropolymer overcoat reduces the amount of accumulation on slider surface and thus, improves the tribological performance of the coated sliders.

The thermal energy generated during slider-disk interaction is another factor which leads to the decay of recorded magnetic signal on disk media. As technology moves to sub-10 nm spaced head-disk systems, high spindle speed, ramp load/unload mechanism, and high seeking speed, the likelihood of such thermal energy generation increases and so is the intensity of such interaction. Experimental results presented in this work indicate that signal can be decayed by slider disk contact in load/unload operation, even when the contact cannot be detected easily by AE sensor attached at the end of the suspension arm. A special disk is proposed and used for the visualization of potential tribological decay. The disk uses a layer of magneto-optical material with low Curie temperature to replace the magnetic layer used in magnetic media and record the traces left by potential sources of tribologically induced decay. The method and corresponding setup were used successfully in the study of the effectiveness of anti-particulate designs and the identification of the worst case among loading and unloading operations at high longitudinal load/unload speed.

Reactive ion etching processes for texture fabrication on air bearing surface is investigated to improve the etching selectivity between Al2O3 and TiC. Etching parameters, such as gas flow rate, pressure, ICP power, and RF power, are optimized. The high selectivity etching between Al2O3 and TiC is achievable by the ICP reactive ion etching with CF4. The selectivity between Al2O3 and TiC can be larger than 6, it means that the Al2O3 is only etched 1 nm to fabricate texture with more than 5-nm height. The experimental results show that the textured sliders fabricated with the developed process can prevent sharp increase of friction force and reduce contact vibration

Tribocurrent phenomenon is one of important effects associated with intermittent slider disk interaction. By simulating the interaction with a conductive AFM probe and measuring the induced current simultaneously using a conductive AFM (c-AFM), some critical points, which divide the probe sample interaction into probe-disk, probe-lubricant and non-contact, can be observed. Similar phenomena were also observed when flying a TFC slider over a specially prepared disk. This proposed technique might be applied to ascertain the dynamic interaction exactly between the slider and the lubricant, which would be the critical issue for accurately studying of “fly- and lubricant-contact recording” approaches in which the slider will be in continuous contact with the lubricant.

A novel visualization technique was used to study slider-disk interactions during loading and unloading operations. The outcomes of the study prove that the technique is a very convenient, effective and promising method to study slider-disk interactions. The design of a loading/unloading system can be evaluated effectively in a very short period of time. Many details of loading and unloading processes invisible before are now observable and have been revealed in this study.

A novel methodology has been introduced to map slider-disk interactions and, thus, study the potential of magnetic decay caused by such interactions. Investigations are focused on the visualization of such interactions. The methodology is based on a specially prepared disk which is of the same structure as a conventional magnetic disk except a magnetooptical (MO) layer is used, which is of low Curie temperature, to replace the magnetic layer of the magnetic disk media. Interactions that generate a temperature above the Curie temperature of the MO material are recorded, visualized and analyzed by optical and magnetic tools. It is noticed that the signatures of the interactions recorded are mainly line-like. Results also indicate that slider-disk contact during the interaction process is also a contact vibration process and the vibration frequency is not a constant. Results presented in this work also show the unique advantage of the proposed method in visualizing severe slider-disk interaction which cannot be revealed by either atomic force microscopy (AFM) or high-resolution observation of carbon wear or lubricant degradation with optical surface analyzers.

This work reports a novel method for the visualization of slider-disk or slider-particle-disk interactions. The method is based on a special testing disk which is same as the conventional magnetic disk media except using a layer of magneto-optical (MO) material to replace the magnetic layer of the magnetic disk media. The magnetization in the MO layer will be switched by a small external field applied if the temperature generated by the interactions is higher than the Curie temperature of the MO material. The proposed method and corresponding setup were used successfully in the experimental study of slider-disk and slider-particle-disk interactions.