The Influence of Ultraviolet Irradiation on the Surface Chemistry of Ztetraol Magnetic Hard Disk Lubricant: a Combined Temperature Programed Desorption and X-Ray Photoelectron Spectroscopic Study

Magnetic hard disks coated with ztetraol lubricant were characterized with temperature programed desorption (TPD) and X-ray photoelectron spectroscopy (XPS). Ztetraol was found to have two adsorbed states, with desorption temperatures of ~650 and ~950 K. The complete removal of the low temperature state by solvent extraction identified it as due to the mobile lubricant. Desorption of the CF₃ mass fragment was observed only at high temperature, indicating that lubricant in this state was in contact with the surface, which allowed the assignment of this high temperature state to the bonded lubricant. UV irradiation was found not to alter the TPD of the unextracted lubricant film. In contrast, the TPD of the UV-bonded layer remaining after extraction was observed to have only one desorption state, stabilized at ~40 K higher temperature as compared with the naturally bonded layer. XPS of the mobile layer was accomplished using spectral subtraction of the C1s carbon overcoat peak (284.8 eV BE), and the perfluoroethylene and perfluoromethylene lubricant peaks (293.5 and 295.0 eV BE, respectively), as a function of UV exposure. No change in the mobile lubricant layer was found with increasing UV exposure. C1s XPS of the UV-bonded layer identified five surface species and assigned XPS peaks to each: the carbon overcoat peak at 284.8 eV BE, ether peak at 286.4 eV BE, organic acid peak at 288.7 eV BE, perfluoroethylene peak at 293.5 eV BE, and the perfluoromethylene peak at 295.0 eV BE. Changes in the relative intensity of the assigned peaks with increasing UV irradiation exposure time were observed. The integration of the assigned XPS peaks from the UV-bonded layer with increasing UV exposure was used to identify UV dependent changes in the bonded layer. A significant relative decrease in the perfluoromethylene lubricant component was observed with increasing exposure, with a simultaneous increase of both the ether and organic acid surface concentrations. Quantum chemical calculations using small molecular models of the ztetraol were used to elucidate the XPS and TPD observations. The calculations revealed that the lubricant is fragmented with irradiation, forming reactive end groups, a volatile CF₂O, and a hydrolyzeable CFO terminated fragment all consistent with the XPS results. The mechanistic implications and the possible surface chemistry are discussed.     

Probing the role of C+ ion energy,thickness and graded structure on the functional and microstructural characteristics of ultrathin carbon films (<2 nm)

We report a comprehensive study on the protective, functional and microstructural properties of filtered cathodic vacuum arc (FCVA) deposited ultrathin carbon overcoats (COCs), which are being considered as potential candidates for future media recording technology such as heat-assisted magnetic recording (HAMR). Specifically, the influence of the C⁺ ion energy (50–345 eV) and the film thickness (0.5–3.2 nm) on these properties were investigated and supported with Raman and X-ray photoelectron spectroscopy (XPS). Finally, an optimized deposition recipe has been proposed to develop an ultrathin (≤2.0 nm) yet continuous COC with improved wear and corrosion resistance compared to thicker conventional COCs (~2.7 nm).     

Investigation into the wear behaviour of Stellite 6 during rotation as an unlubricated bearing at 600 °C

The wear behaviour of Stellite 6 was studied during rotational sliding in a bespoke bearing rig at 600 °C for times between 2 min and 12 h. Six stages of wear were identified: (i) formation of a mixed oxide ‘glaze’, (ii) cobalt and chromium elemental diffusion to the ‘glaze’ surface forming chromium- and cobalt-dominated oxide layers, (iii) oxygen diffusion into the ‘glaze’ leading to a chromium-dominated oxide layer at the ‘glaze’/substrate interface, (iv) spallation of the ‘glaze’ through chemical failure, (v) re-formation of the ‘glaze’ and (vi) elemental diffusion within the ‘glaze’, again resulting in discrete oxide layer formation.     

Wear behavior of AA1060 reinforced with alumina under different loads

The wear behavior of samples of AA1060 aluminum matrix reinforced with 15 vol% of alumina particles in a range of loads between 4.9 and 91.2 N was determined using a pin-on-ring machine at a velocity of 2.7 m/s. The counterface was a carbon steel ring of 272 HB in hardness. Optical and electronic microscopy, X-ray energy analysis and hardness measurement were performed in order to characterize the worn samples. A mild wear mechanism is present for loads lower than 80 N and at larger loads the mechanisms change to a severe mode. In the mild wear regime a mechanically mixed layer (MML), with iron from the counterface and material of the composite, was formed. This MML was responsible of the wear resistance of the composite. Two mechanisms were observed as a way to increase the resistance of the MML; first hardening by mechanical alloying and strain hardening, and then an increase in thickness. At a larger load the conditions produced large instabilities which prevented the formation of a protective mechanically mixed layer.     

A Study of Friction and Wear Behavior of Nitrided Layer on 2cr13 Steel in Vacuum

Tribological characteristics and wear mechanisms of gas-nitrided layer on a 2Cr13 steel in vacuum were investigated using a pin-on-disk type tribometer under self-mating dry sliding conditions with various normal loads and sliding velocities. The wear mechanisms involved were investigated by microscopic observations of the worn surfaces, the wear debris, and the corresponding cross sections. Experimental results show that for both sliding velocities of 0.2 and 1.6 m s⁻¹, friction forces are relatively stable in the case of lower loads (≤50 N), whereas become unstable and show high fluctuations under higher loads (>50 N). Wear mechanisms of the nitrided layer in vacuum are different for the lower and the higher sliding velocities. In the former case, mild abrasive wear dominates. In the latter case, a transition takes place from mild adhesive wear to severe adhesive or even delamination wear, with increasing normal load from 10 to 90 N.     

Torsional fretting wear of a biomedical Ti6Al7Nb alloy for nitrogen ion implantation in bovine serum

Ti6Al7Nb is a high-strength titanium alloy used in replacement hip joints that possesses the excellent biocompatibility necessary for surgical implants. Ti6Al7Nb treated with nitrogen gas (N₂) plasma immersion ion implantation–deposition (PIII–D) was investigated. Torsional fretting wear tests of untreated and nitrogen-ion-implanted Ti6Al7Nb alloys against a Zr₂O ball (diameter 25.2 mm) were carried out under simulated physiological conditions (serum solution) in a torsional fretting wear test rig. Based on the analyses of the frictional kinetics behavior, the observation of 3D profiles, SEM morphologies and surface composition analyses, the damage characteristics of the surface modification layer and its substrate are discussed in detail. The influence of nitrogen ion density on the implantation and torsional angular displacement amplitudes were investigated. The results indicated that ion implantation layering can improve resistance to torsional fretting wear and thus has wide potential application for the prevention of torsional fretting damage in artificial implants. The damage mechanism prevented by the ion implantation layer on the Ti6Al7Nb alloy is a combination of oxidative wear, delamination and abrasive wear. An increase in ion implantation concentration inhibited detachment by delamination.     

Development of a ta-C Wear Resistant Coating with Composite Interlayer for Recording Heads of Magnetic Tape Drives

The effect of two different surface modification methods on the wear life of the coating of magnetic tape drive heads has been studied. In this research, the heads were coated with 10 nm tetrahedral amorphous carbon (ta-C) film using filtered cathodic vacuum arc (FCVA) technique. The surface of the heads was pretreated by bombarding with energetic carbon ions or by developing a Si–Al–C composite interlayer before deposition of the coating. The coated heads were tested at a real head/tape interface of a tape drive. Surface characterization and tribological behavior of the head coatings with and without surface modification has been studied by transmission electron microscopy (TEM), Auger electron spectroscopy (AES), and scanning electron microscopy (SEM). The results reveal that the ta-C coating without any surface modification is not durable and the coating fails due to delamination. Pre-treating the head surface with energetic carbon ions improves the durability of the coating, especially on the head read/write elements; however, the coating of the head ceramic substrate is still partially delaminated. The application of a Si–Al–C composite interlayer is shown to be able to solve the delamination problem effectively and increase the wear life of the coating up to six times in comparison with the sample pretreated with carbon ions. The formation of strong chemical bonds between the head surface and the overcoat is found to be an important factor in improving the durability of the ta-C head coating.     

Critical load for wear particle generation in carbon nitride coatings by single sliding against a spherical diamond

The ‘critical load' for wear particle generation of carbon nitride coatings sliding against a spherical diamond under a linearly increasing load has been examined in situ in relation to different nitrogen incorporation conditions, i.e. assisted N ion acceleration energy and N ion beam current density, and different coating thickness. An environmental scanning electron microscope (E-SEM), in which a pin-on-disk tribotester was installed, has provided direct evidence in situ of when, how and where wear particle generation occurs during the sliding of carbon nitride coatings against a spherical diamond. The in-situ examination of non-conductive carbon nitride coatings are available in E-SEM free from surface charging with controllable relative humidity. The sliding tests under linearly increasing load up to 300 mN at a sliding speed of 10 μm/s have been carried out with the purpose of measuring the ‘critical load' for wear particle generation in a similar way to the traditional macro scratch testing. However, instead of the ‘critical load', the critical maximum Hertzian contact pressure P_max will also be used in the following for better understanding. Based on the systematic study of seven combinations of nitrogen incorporation parameters and five kinds of thickness (0, 10, 50, 100 and 200 nm), the applicable range of P_max for wear particle generation can be increased from 1.6Y to 1.831.92Y or to 1.801.89Y, where Y is defined as the yield strength of silicon of 7 GPa, by coating carbon nitride onto silicon with changing nitrogen incorporation conditions of ion acceleration energy and ion current density, or varing coating thickness from 10 to 200 nm. It also appears that the observed wear particle generation of carbon nitride coatings was associated with a failure initiated in the silicon substrate rather than within the carbon nitride coating or at the coating–substrate interface in the light of both the empirical identification and the theoretical discussion.     

Effect of disk roughness and carbon impact energy on corrosion protection of magnetic recording films

Hard disks with different roughness levels have been coated with hydrogenated and/or nitrogenated carbon using magnetron sputtering and plasma beam based carbon guns. The plasma beam is generated by means of the self bias effect of an asymmetric, magnetically enhanced rf glow discharge. Acetylene is used in the sub-μbar pressure range. The ion impact energy was approx. 190 eV/carbon atom, as opposed to typically <10 eV for the sputtered atoms. Hard disks have been coated with 2–10 nm a-C:H. They were subjected to a hot–wet environment for 4 days. The corrosion was measured by the cobalt extraction test. For either mode of deposition it was confirmed that disk surface roughness considerably affects the corrosion protection achieved by the respective carbon top coat. Plasma beam deposition yielded a better corrosion protection than sputtering.     

Improvement of the tribological properties of Al6061–T6 alloy under dry sliding conditions

The tribological properties of ultrasonic nanocrystalline surface modification (UNSM) treated Al6061–T6 alloy were investigated at various normal loads under dry sliding conditions. Electron backscattering diffraction (EBSD) analysis revealed a microstructure alteration of about 70 μm in thickness generated by the UNSM technique. The friction test results showed that the friction coefficient and wear rate of the UNSM-treated specimen reduced by about 25 and 20% compared to that of the UNSM-free specimen, respectively. X-ray photoelectron spectroscopy (XPS) results showed that the oxide percentage on the worn surface increased, but that of carbon percentage decreased after the UNSM treatment.     

Wear behavior of AISI D2 steel by enhanced ion nitriding with atomic attrition

An experimental study was performed to investigate the effect of atomic attrition on wear behavior of AISI D2 steel. Wear tests were conducted under three different loads (5, 10, and 20 N) and sliding speeds (100, 200, and 500 rpm), using ball-on-disk type tester and SiC ball. After wear test, the specimen nitrided with ion bombardment showed superior wear behavior. The enhanced hardness by ion bombardment could have a beneficial effect on increased wear resistance. In addition, a wider and more adhesive oxide layer formed on the worn surface of ion-bombarded specimen, because of the rougher structure on the surface by ion bombardment, could lead the surface to withstand wear for longer duration time, acting as a protective layer.     

The effect of nitrogen on the scratch resistance of austenitic stainless steels

High nitrogen stainless steels (HNSS) are being considered a new promising class of engineering materials. When nitrogen is added to austenitic steels it can simultaneously improve fatigue life, strength and wear and localized corrosion resistance. In this work, a single pass pendulum scratch test was used to study the effect of nitrogen on the scratch resistance of an UNS S30403 austenitic stainless steel. Samples with increasing nitrogen contents at the surface were obtained through high temperature gas nitriding. The thermochemical treatments were performed at 1473 K in (N₂+Ar) gas atmospheres for 36.0 ks, obtaining fully austenitic cases (surface nitrogen contents up to 0.5 wt%) ca. 1.5 mm in depth. The scratch tests were performed in a single-pass pendulum, equipped with strain gages to measure normal and tangential forces during scratching. The specific absorbed energy was calculated as the ratio between the measured absorbed energy and the amount of mass removed from the specimen. An increase of the specific absorbed energy with increasing nitrogen content was observed. The results of the scratch tests were analyzed taking into account the stress–strain behavior during depth sensing indentation tests and the energy absorbed during Charpy impact tests. The improvement in scratch resistance due to nitrogen alloying was attributed to the strong hardening effect of nitrogen in solid solution, which does not affect significantly work hardening and toughness. A comparison between the scratch resistance and the cavitation-erosion resistance, measured in previous work, was made too.     

Friction and wear behaviors of nanocrystalline surface layer of pure copper

Surface mechanical attrition treatment (SMAT) was employed to fabricate a nanocrystalline surface layer on a pure copper plate. The grain size is about 10 nm in the top layer and increases with an increasing depth from the treated surface. The tribological behavior of the nanocrystalline surface layer was investigated under dry conditions. Experimental results show that the load-bearing ability is markedly enhanced with the nanocrystalline surface layer relative to the coarse-grained form. The friction coefficient of the nanocrystalline layer is lower than that of the coarse-grained copper when the applied load is below 20 N. With increase of the load, the difference in wear resistance between the SMAT and the conventional Cu decreases. When the load exceeds 40 N, for the SMAT Cu, there occurs a transition of wear regime from local damage to delamination of a mechanical mixed layer. There is an abrupt increase of the wear volume, which corresponds to the wearing away of the nanocrystalline layer. The enhanced wear properties of the nanocrystalline surface layer are correlated with the stability of the mechanical mixed layer and the high hardness of the nanocrystalline structure.     

Temperature-Dependent Atomic Scale Friction and Wear on PbS(100)

Friction and wear on PbS(100) surfaces have been investigated on the atomic scale as a function of temperature with atomic force microscopy. At room temperature and above, the PbS(100) surface exhibited low friction (μ < 0.05) in contact with a silicon nitride probe tip, provided that interfacial wear was not encountered. In the absence of wear, friction increased exponentially with decreasing temperature, transitioning to an athermal behavior near 200 K. An Arrhenius analysis of the temperature dependence of friction yielded an activation energy ∆E = 0.32 ± 0.02 eV for the sliding contact of a silicon nitride tip on PbS(100).     

RB-SiC基底反射镜表面改性工艺的改进

为了满足空间用大口径、复杂轻量化结构RB-SiC基底反射镜对高性能表面质量的需求,针对RB-SiC基底的特性,提出了改进表面改性工艺的方法.采用高能量考夫曼离子源辅助,预先对基底进行碳化和加镀C缓冲层,并制备Si改性涂层的方法对RB-SiC基底进行了表面改性.测试结果表明:与单纯霍尔离子源辅助方法相比,该工艺方法制备的Si改性涂层生长得更加致密、均匀,抛光特性良好;改性抛光后表面粗糙度(rms)降低到0.635 nm,达到了S-SiC基底的水平;改性后RB-SiC基底的反射率明显提高,达到了抛光良好的微晶玻璃的水平.结果表明,该工艺方法是提高RB-SiC基底表面改性效果的一种合理有效的方法.     

Fretting wear behavior of nitrogen ion implanted titanium alloys in bovine serum lubrication

Nitrogen ion implantation was performed on biomedical titanium alloys by using of the PBII technology to improve the surface mechanical properties for the application of artificial joints. The titanium nitride phase was characterized with X-ray photoelectron spectroscopy (XPS). The nanohardness of the titanium alloys and implanted samples were measured by using of in-situ nano-mechanical testing system (TriboIndenter). Then, the fretting wear of nitrogen ion implanted titanium alloys was done on the universal multifunctional tester (UMT) with ball-on-flat fretting style in bovine serum lubrication. The fretting wear mechanism was investigated with scanning electron microscopy (SEM) and 3D surface profiler. The XPS analysis results indicate that nitrogen diffuses into the titanium alloy and forms a hard TiN layer on the Ti6Al4V alloys. The nanohardness increases from 6.40 to 7.7 GPa at the normal load of 2 mN, which reveals that nitrogen ion implantation is an effective way to enhance the surface hardness of Ti6Al4V. The coefficients of friction for Ti6Al4V alloy in bovine serum are obviously lower than that in dry friction, but the coefficients of friction for nitrogen ion implanted Ti6Al4V alloy in bovine serum are higher than that in dry friction. Fatigue wear controls the fretting failure mechanism of nitrogen ion implanted Ti6Al4V alloy fretting in bovine serum. The testing results in this paper prove that nitrogen ion implantation can effectively increase the fretting wear resistance for Ti6Al4V alloy in dry friction, and has a considerable improvement for Ti6Al4V alloy in bovine serum lubrication.     

Conformation and Fundamental Properties of Novel Lubricant TA-30 for Near Contact Magnetic Recording

A novel perfluoropolyether (PFPE) lubricant called TA-30 has been developed recently. We investigate the conformation of TA-30 on diamond-like carbon (DLC) thin films, by attempting the direct observation of a lubricant film by atomic force microscopy (AFM) using a fluoride probe. We investigate the fundamental properties of a TA-30 lubricant film, such as its spreading characteristics, and the film thickness dependence of surface energy. Considering these experimental results, we conclude that the conformation of TA-30 is considerably different from that of conventional Z-tetraol2000 whose molecular height is 1.7 nm and which was adsorbed on the DLC surface with the random coil. The TA-30 molecules are adsorbed rigidly to the DLC surface with double layers. The thickness of the first TA-30 layer is ~0.9 nm (similar to diameter of the PFPE backbone) and that of the second layer from the DLC surface is 1.4 nm. Since TA-30 has a lower film thickness than Z-tetraol2000 on the DLC surface, it can have two layers, even if the film thickness is approximately of the order of 1 nm, whereas Z-tetraol2000 does not cover the DLC surface and does not form the complete first layer. In addition, we conduct slider touchdown and takeoff hysteresis tests by using TA-30 and Z-tetraol2000. It is confirmed that the use of TA-30 can improve the head–disk interface (HDI) reliability at low-fly-height conditions.     

钛合金铣削加工中的刀具扩散磨损的研究

本文针对在较高切削速度下使用硬质合金刀具铣削钛合金时的刀具扩散磨损的作用机理进行了研究。通过对刀刃剖面的元素浓度的分布进行电子探针的波谱分析和俄歇能谱分析,发现在钛合金高速铣削时刀具的扩散磨损是由于刀具材料中的粘结相钴和硬质相中的碳元素作用的结果。并发现了硬质相中的碳元素扩散的新规律,碳元素的扩散在刀具和工件的界面处形成富碳层,而不是通常所认为的缺碳层,而在刀具的次表面才形成脱碳层。这样更加完善地解释了刀具表面层弱化以及其次表面层的脆化的联合作用而形成刀具的扩散磨损的作用机理。同时也对刀具材料中的钨元素以及工件材料中的钛元素的扩散进行了探讨。     

Binder extrusion in sliding wear of WC-Co alloys

It has previously been proposed that preferential removal of the cobalt binder is an important mechanism in the abrasive wear of cemented carbides in the WC-Co family. It is here demonstrated that binder extrusion occurs also in metal-to-metal sliding wear contacts. The wear scar generated by sliding a hardened steel ball repeatedly over a polished WC-Co surface was studied by scanning electron microscopy. The extruded cobalt fragments accumulate at surface defects, such as cracks caused by the sliding loaded ball, and gradual microfragmentation of the carbide grains follows. The energy required to extrude the cobalt and to cause the gradual change in surface layer microstructure is provided by the frictional forces.